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Microbial population biology is the application of the principles of population biology to microorganisms .
Microbial population biology, in practice, is the application of population ecology and population genetics toward understanding the ecology and evolution of bacteria , archaebacteria , microscopic fungi (such as yeasts ), additional microscopic eukaryotes (e.g., " protozoa " and algae ), and viruses .
Microbial population biology also encompasses the evolution and ecology of community interactions ( community ecology ) between microorganisms, including microbial coevolution and predator-prey interactions . In addition, microbial population biology considers microbial interactions with more macroscopic organisms (e.g., host - parasite interactions), though strictly this should be more from the perspective of the microscopic rather than the macroscopic organism. A good deal of microbial population biology may be described also as microbial evolutionary ecology . On the other hand, typically microbial population biologists (unlike microbial ecologists ) are less concerned with questions of the role of microorganisms in ecosystem ecology , which is the study of nutrient cycling and energy movement between biotic as well as abiotic components of ecosystems.
Microbial population biology can include aspects of molecular evolution or phylogenetics . Strictly, however, these emphases should be employed toward understanding issues of microbial evolution and ecology rather than as a means of understanding more universal truths applicable to both microscopic and macroscopic organisms. The microorganisms in such endeavors consequently should be recognized as organisms rather than simply as molecular or evolutionary reductionist model systems. Thus, the study of RNA in vitro evolution is not microbial population biology and nor is the in silico generation of phylogenies of otherwise non-microbial sequences, even if aspects of either may in some (especially unintentional) manner be analogous to evolution in actual microbial populations.
Microbial population biology can (and often does) involve the testing of more-general ecological and evolutionary hypotheses. Again, it is important to retain some emphasis on the microbe since at some point this "question-driven" microbial population biology becomes instead population biology using microorganisms. Because the point of departure of these potentially disparate emphases can be somewhat arbitrary, there exist vague and not universally accepted delimits around what the discipline of microbial population biology does and does not constitute.
A Microbial Population Biology Gordon Research Conference is held every odd year, to date in New England (and usually in New Hampshire). The 2007 conference web page introduces the meetings as:
Microbial Population Biology covers a diverse range of cutting edge issues in the microbial sciences and beyond. Firmly founded in evolutionary biology and with a strongly integrative approach, past meetings have covered topics ranging from the dynamics and genetics of adaptation to the evolution of mutation rate, community ecology, evolutionary genomics, altruism, and epidemiology.
This meeting is never dull: some of the most significant and contentious issues in biology have been thrashed out here.
A history of the meeting can be found here .
The next Microbial Population Biology Gordon conference is scheduled for 2025. Information on past (and future) meetings is summarized as follows: | https://en.wikipedia.org/wiki/Microbial_population_biology |
Microbial synergy is a phenomenon in which aerobic and anaerobic microbes support each other's growth and proliferation. In this process aerobes invade and destroy host tissues, reduce tissue oxygen concentration and redox potential , thus creating favorable conditions for anaerobic growth and proliferation. Anaerobes grow and produce short chain fatty acids such as butyric acid , propionic acid . These short chain fatty acids inhibit phagocytosis of aerobes. Thus aerobes grow, proliferate and destroy more tissues. Microbial synergy complicates and delays the healing of surgical and other chronic wounds or ulcers such as diabetic foot ulcers , venous ulcers , pressure ulcers [ 1 ] [ 2 ] etc. Microbial synergy also helps with eliminating oxygen redox. This allows the growth of organisms without the effects of oxygen reacting negatively. As a result, Microbial growth increases because other organisms can grow in the absence of Oxygen redox.
Rotstein, O. D., T. L. Pruett, and R. L. Simmons. "Mechanisms of Microbial Synergy in Polymicrobial Surgical Infections." Reviews of Infectious Diseases. U.S. National Library of Medicine, n.d. Web. 19 Apr. 2017.
This microbiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microbial_synergy |
Microbial toxins are toxins produced by micro-organisms , including bacteria , fungi , protozoa , dinoflagellates , and viruses . Many microbial toxins promote infection and disease by directly damaging host tissues and by disabling the immune system. Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria. The botulinum toxin , which is primarily produced by Clostridium botulinum and less frequently by other Clostridium species, is the most toxic substance known in the world. [ 1 ] However, microbial toxins also have important uses in medical science and research. Currently, new methods of detecting bacterial toxins are being developed to better isolate and understand these toxins. Potential applications of toxin research include combating microbial virulence, the development of novel anticancer drugs and other medicines, and the use of toxins as tools in neurobiology and cellular biology . [ 2 ]
Bacteria toxins which can be classified as either exotoxins or endotoxins . Exotoxins are generated and actively secreted; endotoxins remain part of the bacteria. Usually, an endotoxin is part of the bacterial outer membrane , and it is not released until the bacterium is killed by the immune system . The body's response to an endotoxin can involve severe inflammation . In general, the inflammation process is usually considered beneficial to the infected host, but if the reaction is severe enough, it can lead to sepsis . Exotoxins are typically proteins with enzymatic activity that interfere with host cells triggering the symptoms associated with the disease. Exotoxins are also relatively specific to the bacteria that produce it; for example, diphtheria toxin is only produced by Corynebacterium diphtheriae bacteria and is required for the diphtheria disease. [ 3 ] Some bacterial toxins can be used in the treatment of tumors . [ 4 ] Endotoxins most commonly refer to the lipopolysaccharide (LPS) or lipooligosaccharide (LOS) that are in the outer plasma membrane of Gram-negative bacteria. Not all strains of a bacteria species are virulent; there are some strains of Corynebacterium diphtheriae that do not produce diphtheria toxin and are considered nonvirulent and nontoxigenic. Additional classifications used to describe toxins include enterotoxin , neurotoxin , leukocidin or hemolysin which indicate where in the host's body the toxin targets. Enterotoxins target the intestines, neurotoxins target neurons, leukocidin target leukocytes (white blood cells), and hemolysins target red blood cells. Exotoxin activity can be separated into specific cytotoxic activity or broad cytotoxic activity based on whether the toxin targets specific cell types or various cell types and tissues, respectively. Lethal toxins refers to the group of toxins that are the obvious agents responsible for death associated with the infection.
Toxinosis is pathogenesis caused by the bacterial toxin alone, not necessarily involving bacterial infection (e.g. when the bacteria have died, but have already produced toxin, which are ingested). It can be caused by Staphylococcus aureus toxins, for example. [ 5 ]
There are over 200 Clostridium species in the world that live in mundane places such as soil, water, dust, and even our digestive tracts. Some of these species produce harmful toxins such as botulinum toxin and tetanus toxin among others. Most Clostridium species that do have toxins typically have binary toxins with the first unit involved in getting the toxin into the cell and the second unit cause cellular stress or deformation. [ 6 ] Clostridial toxins are widespread and aid in the production of many diseases in humans and other organisms. Clostridial toxins are known to aid in gastrointestinal diseases and there is a wide range of mechanisms that clostridial toxins take to invade or enter the cell of the host. Pore forming bacterial toxins are common and have a very interesting way of entering or invading the host's cell. The mechanism that clostridial toxins follow includes clostridia forming pores and then the pores inserting themselves into the cell membrane of cells. Clostridial toxins have the ability to damage or alter the cell membrane damaging the extracellular matrix of the organism.
Toxin A and toxin B are two toxins produced by Clostridioides difficile . Toxin A and toxin B are glycosyltransferases that cause the antibiotic-associated pseudomembranous colitis and severe diarrhea that characterize disease presentation of C. diff infections . [ 7 ]
Botulinum neurotoxins (BoNTs) are the causative agents of the deadly food poisoning disease botulism, and could pose a major biological warfare threat due to their extreme toxicity and ease of production. They also serve as powerful tools to treat an ever expanding list of medical conditions that benefit from its paralytic properties, an example drug with BoNTs as the active ingredient is Botox. [ 2 ] TBotulinum neurotoxins (BoNTs) are protein neurotoxins that are produced by the bacteria Clostridium . BoNTs are now largely being studied due to their ability to aid in chronic inflammatory diseases such as acne, multiple sclerosis, and for cosmetic purposes.
Clostridium tetani produces tetanus toxin (TeNT protein), which leads to a fatal condition known as tetanus in many vertebrates (including humans) and invertebrates. While tetanus toxin is produced from Clostridium tetani , a spore forming bacteria found in soil, Tetanus is a paralytic disease that is global and commonly affects newborns as well as non-immunized individuals. Tetanus enters the body of organisms through wounds or skin breaks and can be found in manure, soil, and dust. Tetanus mechanism includes tetanus preventing the transmission of glycine and γ-aminobutyric acid from inhibitory interneurons in the spinal cord, leading to spastic paralysis. Glycine is an important amino acid that is essential for adequate nervous system function aiding in cell communication throughout the body. When tetanus toxin enters the body it is taken up by cholinergic nerve endings traveling axonally into the brain and spinal cord, disrupting motor function in individuals. Although tetanus is a damaging toxin that has a multitude of symptoms it can be prevented through vaccination.
Clostridium perfringens is an anaerobic , gram-positive bacteria that is often found in the large and small intestines of humans and other animals. Clostridium perfringens has the ability to reproduce quickly producing toxins relating to the cause of diseases. The pore-forming toxin perfringolysin has the ability to cause gangrene in calves with the presence of alpha toxin.
Immune evasion proteins from Staphylococcus aureus have a significant conservation of protein structures and a range of activities that are all directed at the two key elements of host immunity, complement and neutrophils . These secreted virulence factors assist the bacterium in surviving immune response mechanisms. [ 2 ]
Examples of toxins produced by strains of S. aureus include enterotoxins that cause food-poisoning, exfoliative toxins that cause scalded skin syndrome , and toxic-shock syndrome toxin (TSST) that underlies toxic shock syndrome . [ 7 ] These toxin examples are classified as superantigens . [ 7 ]
Multi-drug resistant S. aureus strains also produce alpha toxin, classified as a pore-forming toxin , which can cause abscesses . [ 7 ]
Shiga toxins (Stxs), responsible for foodborne illnesses, are a classification of toxins produced by Shiga toxin-producing Escherichia coli (STEC) and Shigella dysenteriae serotype 1. Stx was first identified in S. dysenteriae and was later found to be produced by certain strains of E. coli . [ 8 ] Stxs act through inhibiting protein synthesis of infected cells and can be divided into two antigenically different groups: Stx/Stx1 and Stx2. [ 7 ] Stx1 is immunologically equivalent to Stx; however, it received a separate name to indicate that it is produced by STEC and not S. dysenteriae . Stx2 is produced only by STEC and is antigenically different from Stx/Stx1. The term shiga-like toxins was previously used to further distinguish the shiga toxins produced by E. coli, but nowadays, they are collectively referred to as shiga toxins. [ 8 ] Within the STEC strains, a subgroup classified as enterohemorrhagic E. coli (EHEC) represent a class of pathogens with more severe virulence factors in addition to the ability to produce Stxs. EHEC infections result in more severe diseases of hemorrhagic colitis and hemolytic uremic syndrome . [ 7 ] There are around 200 strains of STEC, and the wide range of diversity and virulence between them can be partly attributed to phage-mediated horizontal transfer of genetic material. [ 9 ]
Anthrax disease in humans results from infection with toxin producing Bacillus anthracis strains that can be inhaled, ingested in contaminated food or drink, or obtained through breaks in the skin like cuts or scrapes. [ 10 ] Domestic and wild animals can also be infected via inhalation or ingestion. Depending on the route of entry, disease can present initially as inhalation anthrax, cutaneous anthrax, or gastrointestinal anthrax, but eventually will spread throughout the body, resulting in death, if not treated with antibiotics. [ 10 ] Anthrax toxin is composed of three domains: protective antigen (PA), edema factor (EF), and lethal factor (LF). EF is an adenylate cyclase that targets ATP. LF enzyme is a metalloprotease that confers the lethal phenotype associated with anthrax disease. [ 7 ] As LF is the agent responsible for the death of infected hosts, it is classified in the group of lethal toxins. [ 3 ]
Diphtheria toxin is produced by virulent Corynebacterium diphtheriae that infect the mucosal membranes of the throat and nasal cavity causing a gray, thickened lining of the throat, sore throat, weakness, mild fever, swollen glands of the neck, and difficulty breathing. [ 11 ] Diphtheria toxin is an ADP-ribosyltransferase that inhibits protein synthesis which causes the symptoms associated with the disease. [ 7 ] Diphtheria used to be a leading cause of childhood death until the creation of a vaccine. [ 11 ] The diphtheria vaccine contains a diphtheria toxoid, antigenically identical yet inactivated and non-toxic. When the toxoid is introduced to the body in a vaccine, an immune response is mounted without sequelae associated with the toxigenicity. [ 3 ]
Pertussis toxin is produced by virulent Bordetella pertussis and is responsible for the disease of whooping cough, a respiratory disease that can be fatal for infants. The severe, uncontrollable coughing makes it difficult to breathe causing the "whooping" sound that occurs with inhalation. [ 12 ] Bordetella pertussis targets cilia of the upper respiratory tract which are damaged by the pertussis toxin, an ADP-ribosyltransferase that targets G-proteins. [ 7 ]
Cholera , characterized by copious watery diarrhea, is a potentially life-threatening illness transmitted through the fecal–oral route via food or water contaminated with toxigenic Vibrio cholerae . [ 13 ] V. cholerae targets the intestines and secretes cholera toxin , an exotoxin and potent enterotoxin that acts as an ADP-ribosyltransferase targeting G-proteins . [ 7 ] This causes an increase in intracellular cAMP and forces intestinal cells to expel significant amounts of water and electrolytes into the lumen. [ 14 ]
Listeriolysin O toxin is an exotoxin produced by Listeria monocytogenes and is associated with foodborne systemic illness and meningitis . [ 7 ] Listeriolysin O toxin is classified as a pore-forming toxin that targets host cholesterol cells, inserting a pore into the host cell plasma membrane and permanently disabling cellular functioning. [ 3 ]
Lipopolysaccharides (LPS) produced by gram-negative bacteria are an example of endotoxins. LSP are structural components of the bacteria's outer membrane that only become toxic to the host as a result of the immune system's destruction of the bacteria cell membrane. [ 3 ]
β-Methylamino- L -alanine (BMAA) is a neurotoxin produced by cyanobacteria that live in the roots of cycads . BMAA may be present in starch made from the stems and/or seeds of cycads (such as Florida arrowroot flour) that has not been sufficiently washed, or in meat from animals that have eaten cycads. [ 15 ]
The most prominent natural toxin groups that exist in aquatic environments are mycotoxins , algal toxins , bacterial toxins, and plant toxins (8). These marine biotoxins are dangerous to human health and have been widely studied due to their high potential to bioaccumulate in edible parts of seafood. [ 16 ]
Autotrophic bacteria and algae are unrelated organisms; however, in aquatic environments, they are both primary producers . [ 17 ] Cyanobacteria are an important autotrophic bacteria in the water food web. Explosions of cyanobacteria known as algal blooms can produce cyanotoxins harmful to both the ecosystem and human health. These harmful algal blooms are more likely to be produced at a dangerous amount when there is an excess of nutrients , the temperature is 20 °C, there is more light, and calmer waters. [ 17 ] Eutrophication and other contamination can lead to an environment that promotes cyanobacteria blooms . [ 17 ] Processes that promote an excess of nutrients, and human activities, such as agricultural runoff and sewage overflows , are primarily responsible. [ 16 ] Other factors include algal species and grazers being in higher concentrations, allowing for an abundance of cyanobacterial organisms that are associated with the production of toxins. [ 16 ] Detection of the extent of an algal bloom begins by taking samples of water at various depths and locations in the bloom. [ 16 ]
SPATT was introduced in 2004 as a method of monitoring aquatic toxins. This tool is able to adsorb toxins generated by microalgae or cyanobacteria, known as cyanotoxins . [ 18 ] The adsorption is passive, and the biotoxins adhere to porous, resin filled sachets, or SPATT bags where they are then physically removed and examined. [ 19 ]
SPATT is a useful tool in tracking algal blooms as it is reliable, sensitive, and inexpensive. It has the ability to quickly alert the existence of aquatic toxins which prevents it from bioaccumulating in marine life. [ 19 ] One of the downsides is that it does not give very good results for water-soluble toxins as compared to hydrophobic compounds. This tool is mainly used to determine intercellular concentrations of toxins but the cyanobacteria can also be lysed to determine the total toxin amount in a sample. [ 16 ] Other drawbacks, such as a lack in calibration and the ability to only monitor dissolved toxins, make it difficult for this tool to be implemented in a more widespread manner. [ 18 ] However, SPATT devices are able to detect many lipophilic and hydrophilic toxins that are linked to harmful algal bloom. [ 18 ]
PCR is a molecular tool that allows for analysis of genetic information. PCR is used to amplify the amount of certain DNA within a sample which are usually specific genes within a sample. Genetic targets for cyanobacteria in PCR include the 16S ribosomal RNA gene, phycocyanin operon, internal transcribed spacer region, and the RNA polymerase β subunit gene. PCR is effective when the gene of a known enzyme for producing the microbial toxin or the microbial toxin itself is known. [ 16 ] One type of PCR is real time PCR also called quantitative PCR. [ 20 ] This type of PCR uses fluorescence and then does an analysis by measuring the amount of fluorescence that reflects the DNA sample more specifically nucleic acids at specific times. [ 20 ] Another type of PCR is digital PCR that looks at nucleic acid quantifications. Digital PCR uses dilutions and samples from microlitre reactions to achieve a more accurate quantification of nucleic acids. This type offers a more linear analysis by looking at the positive and negative reactions. [ 21 ] Both PCR's are beneficial but there are advantages and disadvantages for both. The digital PCR has several advantages over real time PCR which includes no standard curve, more precise, less affected by simple inhibitors. [ 22 ] Digital also has disadvantages to real time which is limited reaction mixture time, more complex and high risk of contamination. [ 22 ]
There are many diverse ways of monitoring enzyme levels through the use of enzyme inhibition. The general principle in many of these is the use the knowledge that many enzymes are driven by phosphate-releasing compounds such as adenosine triphosphate . Using radiolabelled 32 P phosphate a fluorometric analysis can be used. Or unique polymers can be used to immobilize enzymes and act in an electrochemical biosensor. Overall, the benefits include a fast response time and little sample preparation. Some of the downsides include a lack of specificity in terms of being able to get readings of very small amounts of toxin and the rigidity of the assays in apply certain procedures to different toxins. [ 16 ]
This detection method uses mammalian antibodies to bind to microbial toxins which can then be processed in a variety of different ways. Of the commercial ways of using immunochemical detection would be enzyme-linked immunosorbent assays (ELISA). This assay has the advantage of being able to screen for a broad range of toxins but could have issues with specificity depending on the antibody used. [ 16 ] A more exotic setup involves the use of CdS quantum dots which are used in an electro-chemiluminescent immunosensor. [ 23 ] A major aspect of immunochemical methods being tested in laboratories are uses of nanowires and other nanomaterials to detect microbial toxins. [ 16 ]
These toxins are produced by Vibrio species of bacteria and like to accumulate in marine life such as the pufferfish. These toxins are produced when Vibrio bacteria are stressed by changes in temperature and salinity of environment which leads towards production of toxins. The main hazard towards humans is during consumption of contaminated seafood. Tetrodotoxin poisoning is becoming common in more northern and typically colder marine waters as higher precipitation and warmer waters from climate change triggers Vibrio bacteria to produce toxins. [ 7 ] Most of the marine life that produce this toxin are typically found in warm water, for example the Red Sea and the Mediterranean Sea. [ 24 ] For example, pufferfish do produce this toxin, some pufferfish, such as Takifugu V., produce tetrodotoxin in their skin glands. [ 25 ] Another organism that releases the tetrodotoxin from their skin are blue-ringed octopuses ( Hapalochlaena fasciata ). The Natica lineata snails produce the tetrodotoxin and store it in the muscle. The snail releases the toxin by absorbing water into the muscle cavity and it is released when the snail is attacked. [ 26 ] Once a human consumes the toxin, the individual could experience mild symptoms such as paresthesias of the lips or tongue, vomiting and headaches. The individual could also experience severe symptoms such as respiratory or heart failure. At this time there is no treatment for tetrodotoxin poisoning other than respiratory support. [ 27 ]
There is only one viral toxin that has been described so far: NSP4 from rotavirus . It inhibits the microtubule -mediated secretory pathway and alters cytoskeleton organization in polarized epithelial cells . It has been identified as the viral enterotoxin based on the observation that the protein caused diarrhea when administered intraperitoneally or intra-ileally in infant mice in an age-dependent manner. [ 28 ] NSP4 can induce aqueous secretion in the gastrointestinal tract of neonatal mice through activation of an age- and Ca 2+ -dependent plasma membrane anion permeability. [ 29 ]
Several bacteriophages contain toxin genes that become incorporated into the host bacteria genome through infection and render the bacteria toxic. [ 9 ] Many well known bacterial toxins are produced from specific strains of the bacteria species that have obtained toxigenicity through lysogenic conversion, pseudolysogeny, or horizontal gene transfer . [ 9 ] Although these are not viral toxins, researchers remain extremely interested in the role phages play bacterial toxins due to their contribution to pathogenesis (toxigenesis), virulence, transmissibility and general evolution of bacteria. [ 9 ] Examples of toxins encoded by phage genes:
Some mycoviruses also contain toxin genes expressed by host fungal species upon viral infection. [ 34 ] While these toxins are classified as mycotoxins, the role of mycoviruses is also of interest to researchers in terms of fungal virulence. [ 34 ] Examples include the mycoviruses ScV-M1, ScV-M2, and ScV-M28 in the Totiviridae family that contain " killer toxin " genes K1, K2, and K3, respectively. [ 34 ] These "killer toxins" are produced by yeast, namely of the Saccharomyces cerevisiae species, that destroy neighboring yeast cells. [ 34 ] Recently, researchers discovered that it is only the yeasts infected with either ScV-M1, ScV-M2, or ScV-M28 mycoviruses that have the ability to produce a "killer toxin". [ 34 ]
Mycotoxins are secondary metabolites that are constructed by microfungi . [ 35 ] Mycotoxins can be harmful because they can cause disease and death in humans and animals. [ 35 ] They are found in many pharmaceuticals like antibiotics and growth developments. [ 35 ] Mycotoxins can also play a role in chemical warfare agents (CWA), which are chemicals that contain toxins that are used to cause death, harm, or injuries to individuals that are considered enemies by the military during warfare. [ 36 ]
Mycotoxins are synthesized by different types of moulds and are built by a wide group of toxins. [ 37 ] Mycotoxins have a low molecular weight compound that is usually less than 1000 grams per mol. [ 37 ] There are roughly 400 toxic mycotoxins that are constructed by 100 different fungi species that have been researched. [ 37 ] Mycotoxins gain access into the body of a human or animal by food, they can contaminate many different types of agriculture during cultivation, harvesting, storage, and areas with high humidity. [ 37 ] The Food and Agriculture Organization reported that about 25% of products produced by agriculture contain mycotoxins and this can lead to economic losses in the agricultural community. [ 37 ] Levels of mycotoxin secretion can rely on varying temperatures, the ideal temperature for mycotoxins to grow is from 20 degrees Celsius to 37 degrees Celsius. [ 37 ] Mycotoxin production also relies heavily on water activity, the ideal range would be from 0.83 to 0.9 aw and higher. [ 37 ] Humidity plays a key in the production of mycotoxins as well. [ 37 ] Higher levels of humidity (between 70% and 90%) and moisture (between 20% and 25%) allow mycotoxins to grow more rapidly. [ 37 ] Foods that mycotoxins are found in cereal, spices, and seeds. [ 37 ] They can also be found in eggs, milk, and meat from animals that have been contaminated during their feeding process. [ 37 ] Since they are resistant to high temperatures and physical and chemical reception, it is considered unavoidable while cooking at high temperatures. [ 37 ]
Trichothecene is a mycotoxin that is produced from the fungi species Fusarium graminearum . [ 38 ] The T-2 toxin , Type A, and DON, Type B, are major mycotoxins that are responsible for toxicity in humans and animals. [ 38 ] These two types come from an epoxide at the C12 and C13 positions in the trichothecenes. [ 38 ] The T-2 toxin was found after civilians ate wheat that was contaminated by the Fusarium fungi during WWII from a biological weapon. The T-2 toxin was an outbreak and made humans develop symptoms like food poisoning , chills, nausea, dizziness, etc. [ 38 ] The trichothecenes mycotoxin affects animals by decreasing plasma glucose, red blood cell and leukocyte counts. [ 38 ] Pathological changes in the liver and stomach, as well as weight loss has been accounted for. [ 38 ]
Zearalenone is a mycotoxin that is produced from Fusarium graminearum and Fusarium culmorum that are found in different types of foods and feeds. [ 38 ] Zearalenone is a non-steroidal estrogenic mycotoxin that is found in farm animal's reproductive disorders and in humans it causes hypoestrogenic syndrome. [ 38 ] Effects that come from zearalenone include enlarged uterus , improperly running reproductive tract, decreasing the fertility in women, and causes progesterone and estradiol levels to become abnormal. [ 38 ] If zearalenone is consumed during pregnancy, it can cause reduced fetal weight and decrease the chance of survival for the embryo. [ 38 ]
Fumonisins , Fusarium verticillioides , are found in nature where fumonisin B1 has largely contaminated the area. [ 38 ] These mycotoxins are hydrophilic compounds. Studies have shown that esophageal cancer can be related back to corn grain that contains fumonisins. [ 38 ] Other effects from fumonisins are birth defects of the brain, spine, and spinal cord. [ 38 ] In animals, problems with the pulmonary edema and hydrothorax swines have been proven to have association with fumonisins. [ 38 ]
Ochratoxin is a mycotoxin that is produced by Aspergillus species and Penicillium species. [ 38 ] The most researched ochratoxin is the ochratoxin A (OTA), which is a fungal toxin. [ 38 ] This mycotoxin targets the OTA of kidneys and causes kidney disease in humans. [ 38 ] Ochratoxin A is an immunosuppressive compound. [ 38 ] Ochratoxin is a renal carcinogen, which has been found by animals containing OTA. [ 38 ]
Aflatoxin is a mycotoxin that is produced from Aspergillus flavus and Aspergillus parasiticus . [ 38 ] A type of aflatoxin, AFB1 , is the most common mycotoxin that is found in human food and animal feed. [ 38 ] AFB1 targets the liver of both humans and animals. [ 38 ] Acute aflatoxicosis can make humans and animals have symptoms like abdominal pain, vomiting, and even death. [ 38 ] | https://en.wikipedia.org/wiki/Microbial_toxin |
A microbiological culture , or microbial culture , is a method of multiplying microbial organisms by letting them reproduce in predetermined culture medium under controlled laboratory conditions. Microbial cultures are foundational and basic diagnostic methods used as research tools in molecular biology .
The term culture can also refer to the microorganisms being grown.
Microbial cultures are used to determine the type of organism, its abundance in the sample being tested, or both. It is one of the primary diagnostic methods of microbiology and used as a tool to determine the cause of infectious disease by letting the agent multiply in a predetermined medium. For example, a throat culture is taken by scraping the lining of tissue in the back of the throat and blotting the sample into a medium to be able to screen for harmful microorganisms, such as Streptococcus pyogenes , the causative agent of strep throat. [ 1 ] Furthermore, the term culture is more generally used informally to refer to "selectively growing" a specific kind of microorganism in the lab.
It is often essential to isolate a pure culture of microorganisms. A pure (or axenic ) culture is a population of cells or multicellular organisms growing in the absence of other species or types. A pure culture may originate from a single cell or single organism, in which case the cells are genetic clones of one another. For the purpose of gelling the microbial culture, the medium of agarose gel ( agar ) is used. Agar is a gelatinous substance derived from seaweed . A cheap substitute for agar is guar gum , which can be used for the isolation and maintenance of thermophiles .
The first culture media was liquid media, designed by Louis Pasteur in 1860. [ 2 ] This was used in the laboratory until Robert Koch's development of solid media in 1881. [ 3 ] Koch's method of using a flat plate for his solid media was replaced by Julius Richard Petri's round box in 1887. [ 2 ] Since these foundational inventions, a diverse array of media and methods have evolved to help scientists grow, identify, and purify cultures of microorganisms.
The culturing of prokaryotes typically involves bacteria, since archaea are difficult to culture in a laboratory setting. [ 4 ] To obtain a pure prokaryotic culture, one must start the culture from a single cell or a single colony of the organism. [ 5 ] Since a prokaryotic colony is the asexual offspring of a single cell, all of the cells are genetically identical and will result in a pure culture.
Virus and phage cultures require host cells in which the virus or phage multiply. For bacteriophages, cultures are grown by infecting bacterial cells. The phage can then be isolated from the resulting plaques in a lawn of bacteria on a plate. Viral cultures are obtained from their appropriate eukaryotic host cells. The streak plate method is a way to physically separate the microbial population, and is done by spreading the inoculate back and forth with an inoculating loop over the solid agar plate. Upon incubation , colonies will arise and single cells will have been isolated from the biomass . Once a microorganism has been isolated in pure culture, it is necessary to preserve it in a viable state for further study and use in cultures called stock cultures. These cultures have to be maintained, such that there is no loss of their biological, immunological and cultural characters.
Eukaryotic cell cultures provide a controlled environment for studying eukaryotic organisms . Single-celled eukaryotes - such as yeast, algae, and protozoans - can be cultured in similar ways to prokaryotic cultures. The same is true for multicellular microscopic eukaryotes, such as C. elegans .
Although macroscopic eukaryotic organisms are too large to culture in a laboratory, cells taken from these organisms can be cultured. This allows researchers to study specific parts and processes of a macroscopic eukaryote in vitro .
One method of microbiological culture is liquid culture, in which the desired organisms are suspended in a liquid nutrient medium, such as Luria broth , in an upright flask. This allows a scientist to grow up large amounts of bacteria or other microorganisms for a variety of downstream applications.
Liquid cultures are ideal for preparation of an antimicrobial assay in which the liquid broth is inoculated with bacteria and let to grow overnight (a ‘shaker’ may be used to mechanically mix the broth, to encourage uniform growth). Subsequently, aliquots of the sample are taken to test for the antimicrobial activity of a specific drug or protein ( antimicrobial peptides ).
Static liquid cultures may be used as an alternative. These cultures are not shaken, and they provide the microbes with an oxygen gradient. [ 6 ]
Microbiological cultures can be grown in petri dishes of differing sizes that have a thin layer of agar-based growth medium. Once the growth medium in the petri dish is inoculated with the desired bacteria, the plates are incubated at the optimal temperature for the growing of the selected bacteria (for example, usually at 37 degrees Celsius, or the human body temperature , for cultures from humans or animals, or lower for environmental cultures). After the desired level of growth is achieved, agar plates can be stored upside down in a refrigerator for an extended period of time to keep bacteria for future experiments.
There are a variety of additives that can be added to agar before it is poured into a plate and allowed to solidify. Some types of bacteria can only grow in the presence of certain additives. This can also be used when creating engineered strains of bacteria that contain an antibiotic-resistance gene . When the selected antibiotic is added to the agar, only bacterial cells containing the gene insert conferring resistance will be able to grow. This allows the researcher to select only the colonies that were successfully transformed.
Miniaturized version of agar plates implemented to dipstick formats, e.g. Dip Slide, Digital Dipstick [ 7 ] show potential to be used at the point-of-care for diagnosis purposes. They have advantages over agar plates since they are cost effective and their operation does not require expertise or laboratory environment, which enable them to be used at the point-of-care.
Selective and differential media reveal characteristics about the microorganisms being cultured on them. This kind of media can be selective, differential, or both selective and differential. Growing a culture on multiple kinds of selective and differential media can purify mixed cultures and reveal to scientists the characteristics needed to identify unknown cultures.
Selective media is used to distinguish organisms by allowing for a specific kind of organism to grow on it while inhibiting the growth of others. For example, eosin methylene blue (EMB) may be used to select against Gram-positive bacteria, most of which have hindered growth on EMB, and select for Gram-negative bacteria, whose growth is not inhibited on EMB. [ 8 ]
Scientists use differential media when culturing microorganisms to reveal certain biochemical characteristics about the organisms. These revealed traits can then be compared to attributes of known microorganisms in an effort to identify unknown cultures. An example of this is MacConkey agar (MAC), which reveals lactose-fermenting bacteria through a pH indicator that changes color when acids are produced from fermentation. [ 9 ]
On multitarget panels, bacteria isolated from a previously grown colony are distributed into each well, each of which contains growth medium as well as the ingredients for a biochemical test, which will change the absorbance of the well depending on the bacterial property for the tested target. The panel will be incubated in a machine, which subsequently analyses each well with a light-based method such as colorimetry, turbidimetry, or fluorometry. [ 10 ] The combined results will be automatically compared to a database of known results for various bacterial species, in order to generate a diagnosis of what bacterial species is present in the current panel. Simultaneously, it performs antibiotic susceptibility testing .
Stab cultures are similar to agar plates, but are formed by solid agar in a test tube. Bacteria is introduced via an inoculation needle or a pipette tip being stabbed into the center of the agar. Bacteria grow in the punctured area. [ 11 ] Stab cultures are most commonly used for short-term storage or shipment of cultures. Additionally, stab cultures can reveal characteristics about cultured microorganisms such as motility or oxygen requirements.
For solid plate cultures of thermophilic microorganisms such as Bacillus acidocaldarius, Bacillus stearothermophilus, Thermus aquaticus and Thermus thermophilus etc. growing at temperatures of 50 to 70 degrees C, low acyl clarified gellan gum has been proven to be the preferred gelling agent comparing to agar for the counting or isolation or both of the above thermophilic bacteria. [ 12 ]
Microbial culture collections focus on the acquisition, authentication, production, preservation, cataloguing and distribution of viable cultures of standard reference microorganisms , cell lines and other materials for research in microbial systematics . [ 13 ] [ 14 ] Culture collection are also repositories of type strains . | https://en.wikipedia.org/wiki/Microbiological_culture |
A microbiologist (from Greek μῑκρος ) is a scientist who studies microscopic life forms and processes. This includes study of the growth, interactions and characteristics of microscopic organisms such as bacteria , algae , fungi , and some types of parasites and their vectors. [ 1 ] Most microbiologists work in offices and/or research facilities, both in private biotechnology companies and in academia . Most microbiologists specialize in a given topic within microbiology such as bacteriology , parasitology , virology , or immunology .
Microbiologists generally work in some way to increase scientific knowledge or to utilise that knowledge in a way that improves outcomes in medicine or some industry. For many microbiologists, this work includes planning and conducting experimental research projects in some kind of laboratory setting. [ 1 ] Others may have a more administrative role, supervising scientists and evaluating their results. Microbiologists working in the medical field, such as clinical microbiologists , may see patients or patient samples and do various tests to detect disease-causing organisms . [ 1 ]
For microbiologists working in academia, duties include performing research in an academic laboratory, writing grant proposals to fund research, as well as some amount of teaching and designing courses. [ 2 ] Microbiologists in industry roles may have similar duties except research is performed in industrial labs in order to develop or improve commercial products and processes. Industry jobs may also not include some degree of sales and marketing work, as well as regulatory compliance duties. Microbiologists working in government may have a variety of duties, including laboratory research, writing and advising, developing and reviewing regulatory processes, and overseeing grants offered to outside institutions. [ 2 ] Some microbiologists work in the field of patent law , either with national patent offices or private law practices. Her duties include research and navigation of intellectual property regulations. [ 2 ] Clinical microbiologists tend to work in government or hospital laboratories where their duties include analyzing clinical specimens to detect microorganisms responsible for the disease. Some microbiologists instead work in the field of science outreach , where they develop programs and materials to educate students and non-scientists and encourage interest in the field of microbiology for the younger generation
. [ 2 ]
Entry-level microbiology jobs generally require at least a bachelor's degree in microbiology or a related field. [ 3 ] These degree programs frequently include courses in chemistry , physics , statistics , biochemistry , and genetics , followed by more specialized courses in sub-fields of interest. Many of these courses have laboratory components to teach trainees basic and specialized laboratory skills. [ 3 ]
Higher-level and independent jobs like a clinical/Medical Microbiologist in a hospital or medical research centre generally require a Masters in Microbiology along with PhD in any of the life-sciences ( Biochem , Micro, Biotech, Genetics, etc) as well as several years experience as a microbiologist. This often includes time spent as a postdoctoral researcher wherein one leads research projects and prepares to transition to an independent career. Postdoctoral researchers are often evaluated largely based on their record of published academic papers , as well as recommendations from their supervisors and colleagues. [ 3 ]
In certain sub-fields of microbiology, licenses or certifications are available or required in order to qualify for certain positions. This is true for clinical microbiologists, as well as those involved in food safety and some aspects of pharmaceutical/medical device development. [ 3 ]
Microbiologists are expected to be needed to help pharmaceutical and biotechnology companies develop new drugs that are produced with the aid of microorganisms. In addition, demand for biofuels production is expected to increase the need for microbiologists to conduct advanced research and development in these areas. [ 4 ]
In the United States , the Bureau of Labor Statistics predicts that employment of microbiologists will grow 5 percent from 2022 (20,900 employed) to 2032 (22,000 employed). This represents slower growth than the average occupation, as well as slower growth than life scientists as a whole (7 percent projected). [ 4 ] | https://en.wikipedia.org/wiki/Microbiologist |
Microbiology (from Ancient Greek μῑκρος ( mīkros ) ' small ' βίος ( bíos ) ' life ' and -λογία ( -logía ) ' study of ' ) is the scientific study of microorganisms , those being of unicellular (single-celled), multicellular (consisting of complex cells), or acellular (lacking cells). [ 1 ] [ 2 ] Microbiology encompasses numerous sub-disciplines including virology , bacteriology , protistology , mycology , immunology , and parasitology .
The organisms that constitute the microbial world are characterized as either prokaryotes or eukaryotes; Eukaryotic microorganisms possess membrane-bound organelles and include fungi and protists , whereas prokaryotic organisms are conventionally classified as lacking membrane-bound organelles and include Bacteria and Archaea . [ 3 ] [ 4 ] Microbiologists traditionally relied on culture, staining, and microscopy for the isolation and identification of microorganisms. However, less than 1% of the microorganisms present in common environments can be cultured in isolation using current means. [ 5 ] With the emergence of biotechnology , Microbiologists currently rely on molecular biology tools such as DNA sequence-based identification, for example, the 16S rRNA gene sequence used for bacterial identification.
Viruses have been variably classified as organisms [ 6 ] because they have been considered either very simple microorganisms or very complex molecules. Prions , never considered microorganisms, have been investigated by virologists; however, as the clinical effects traced to them were originally presumed due to chronic viral infections, virologists took a search—discovering "infectious proteins".
The existence of microorganisms was predicted many centuries before they were first observed, for example by the Jains in India and by Marcus Terentius Varro in ancient Rome. The first recorded microscope observation was of the fruiting bodies of moulds, by Robert Hooke in 1666, but the Jesuit priest Athanasius Kircher was likely the first to see microbes, which he mentioned observing in milk and putrid material in 1658. Antonie van Leeuwenhoek is considered a father of microbiology as he observed and experimented with microscopic organisms in the 1670s, using simple microscopes of his design. Scientific microbiology developed in the 19th century through the work of Louis Pasteur and in medical microbiology Robert Koch .
The existence of microorganisms was hypothesized for many centuries before their actual discovery. The existence of unseen microbiological life was postulated by Jainism which is based on Mahavira 's teachings as early as 6th century BCE (599 BC - 527 BC). [ 7 ] : 24 Paul Dundas notes that Mahavira asserted the existence of unseen microbiological creatures living in earth, water, air and fire. [ 7 ] : 88 Jain scriptures describe nigodas which are sub-microscopic creatures living in large clusters and having a very short life, said to pervade every part of the universe, even in tissues of plants and flesh of animals. [ 8 ] The Roman Marcus Terentius Varro made references to microbes when he warned against locating a homestead in the vicinity of swamps "because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and thereby cause serious diseases." [ 9 ]
Persian scientists hypothesized the existence of microorganisms, such as Avicenna in his book The Canon of Medicine , Ibn Zuhr (also known as Avenzoar) who discovered scabies mites, and Al-Razi who gave the earliest known description of smallpox in his book The Virtuous Life (al-Hawi). [ 10 ] The tenth-century Taoist Baoshengjing describes "countless micro organic worms" which resemble vegetable seeds , which prompted Dutch sinologist Kristofer Schipper to claim that "the existence of harmful bacteria was known to the Chinese of the time." [ 11 ]
In 1546, Girolamo Fracastoro proposed that epidemic diseases were caused by transferable seedlike entities that could transmit infection by direct or indirect contact, or vehicle transmission. [ 12 ]
In 1676, Antonie van Leeuwenhoek , who lived most of his life in Delft , Netherlands, observed bacteria and other microorganisms using a single-lens microscope of his own design . [ 14 ] [ 2 ] He is considered a father of microbiology as he used simple single-lensed microscopes of his own design. [ 14 ] While Van Leeuwenhoek is often cited as the first to observe microbes, Robert Hooke made his first recorded microscopic observation, of the fruiting bodies of moulds , in 1665. [ 15 ] It has, however, been suggested that a Jesuit priest called Athanasius Kircher was the first to observe microorganisms. [ 16 ]
Kircher was among the first to design magic lanterns for projection purposes, and so he was well acquainted with the properties of lenses. [ 16 ] He wrote "Concerning the wonderful structure of things in nature, investigated by Microscope" in 1646, stating "who would believe that vinegar and milk abound with an innumerable multitude of worms." He also noted that putrid material is full of innumerable creeping animalcules. He published his Scrutinium Pestis (Examination of the Plague) in 1658, stating correctly that the disease was caused by microbes, though what he saw was most likely red or white blood cells rather than the plague agent itself. [ 16 ]
The field of bacteriology (later a subdiscipline of microbiology) was founded in the 19th century by Ferdinand Cohn , a botanist whose studies on algae and photosynthetic bacteria led him to describe several bacteria including Bacillus and Beggiatoa . Cohn was also the first to formulate a scheme for the taxonomic classification of bacteria, and to discover endospores . [ 17 ] Louis Pasteur and Robert Koch were contemporaries of Cohn, and are often considered to be the fathers of modern microbiology [ 16 ] and medical microbiology , respectively. [ 18 ] Pasteur is most famous for his series of experiments designed to disprove the then widely held theory of spontaneous generation , thereby solidifying microbiology's identity as a biological science. [ 19 ] One of his students, Adrien Certes, is considered the founder of marine microbiology. [ 20 ] Pasteur also designed methods for food preservation ( pasteurization ) and vaccines against several diseases such as anthrax , fowl cholera and rabies . [ 2 ] Koch is best known for his contributions to the germ theory of disease , proving that specific diseases were caused by specific pathogenic microorganisms. He developed a series of criteria that have become known as the Koch's postulates . Koch was one of the first scientists to focus on the isolation of bacteria in pure culture resulting in his description of several novel bacteria including Mycobacterium tuberculosis , the causative agent of tuberculosis . [ 2 ]
While Pasteur and Koch are often considered the founders of microbiology, their work did not accurately reflect the true diversity of the microbial world because of their exclusive focus on microorganisms having direct medical relevance. It was not until the late 19th century and the work of Martinus Beijerinck and Sergei Winogradsky that the true breadth of microbiology was revealed. [ 2 ] Beijerinck made two major contributions to microbiology: the discovery of viruses and the development of enrichment culture techniques. [ 21 ] While his work on the tobacco mosaic virus established the basic principles of virology, it was his development of enrichment culturing that had the most immediate impact on microbiology by allowing for the cultivation of a wide range of microbes with wildly different physiologies. Winogradsky was the first to develop the concept of chemolithotrophy and to thereby reveal the essential role played by microorganisms in geochemical processes. [ 22 ] He was responsible for the first isolation and description of both nitrifying and nitrogen-fixing bacteria . [ 2 ] French-Canadian microbiologist Felix d'Herelle co-discovered bacteriophages in 1917 and was one of the earliest applied microbiologists. [ 23 ]
Joseph Lister was the first to use phenol disinfectant on the open wounds of patients. [ 24 ]
The branches of microbiology can be classified into applied sciences, or divided according to taxonomy, as is the case with bacteriology , mycology , protozoology , virology , phycology , and microbial ecology . There is considerable overlap between the specific branches of microbiology with each other and with other disciplines, and certain aspects of these branches can extend beyond the traditional scope of microbiology. [ 25 ] [ 26 ] A pure research branch of microbiology is termed cellular microbiology .
While some people have fear of microbes due to the association of some microbes with various human diseases, many microbes are also responsible for numerous beneficial processes such as industrial fermentation (e.g. the production of alcohol , vinegar and dairy products ), antibiotic production can act as molecular vehicles to transfer DNA to complex organisms such as plants and animals. Scientists have also exploited their knowledge of microbes to produce biotechnologically important enzymes such as Taq polymerase , [ 27 ] reporter genes for use in other genetic systems and novel molecular biology techniques such as the yeast two-hybrid system . [ 28 ]
Bacteria can be used for the industrial production of amino acids . organic acids , vitamin , proteins , antibiotics and other commercially used metabolites which are produced by microorganisms. Corynebacterium glutamicum is one of the most important bacterial species with an annual production of more than two million tons of amino acids, mainly L-glutamate and L-lysine. [ 29 ] Since some bacteria have the ability to synthesize antibiotics, they are used for medicinal purposes, such as Streptomyces to make aminoglycoside antibiotics . [ 30 ]
A variety of biopolymers , such as polysaccharides , polyesters , and polyamides , are produced by microorganisms. Microorganisms are used for the biotechnological production of biopolymers with tailored properties suitable for high-value medical application such as tissue engineering and drug delivery. Microorganisms are for example used for the biosynthesis of xanthan , alginate , cellulose , cyanophycin , poly(gamma-glutamic acid), levan , hyaluronic acid , organic acids, oligosaccharides polysaccharide and polyhydroxyalkanoates. [ 31 ]
Microorganisms are beneficial for microbial biodegradation or bioremediation of domestic, agricultural and industrial wastes and subsurface pollution in soils, sediments and marine environments. The ability of each microorganism to degrade toxic waste depends on the nature of each contaminant . Since sites typically have multiple pollutant types, the most effective approach to microbial biodegradation is to use a mixture of bacterial and fungal species and strains, each specific to the biodegradation of one or more types of contaminants. [ 32 ]
Symbiotic microbial communities confer benefits to their human and animal hosts health including aiding digestion, producing beneficial vitamins and amino acids, and suppressing pathogenic microbes. Some benefit may be conferred by eating fermented foods, probiotics (bacteria potentially beneficial to the digestive system) or prebiotics (substances consumed to promote the growth of probiotic microorganisms). [ 33 ] [ 34 ] The ways the microbiome influences human and animal health, as well as methods to influence the microbiome are active areas of research. [ 35 ]
Research has suggested that microorganisms could be useful in the treatment of cancer . Various strains of non-pathogenic clostridia can infiltrate and replicate within solid tumors . Clostridial vectors can be safely administered and their potential to deliver therapeutic proteins has been demonstrated in a variety of preclinical models. [ 36 ]
Some bacteria are used to study fundamental mechanisms. An example of model bacteria used to study motility [ 37 ] or the production of polysaccharides and development is Myxococcus xanthus . [ 38 ] | https://en.wikipedia.org/wiki/Microbiology |
Microbiology of decomposition is the study of all microorganisms involved in decomposition , the chemical and physical processes during which organic matter is broken down and reduced to its original elements.
Decomposition microbiology can be divided into two fields of interest, namely the decomposition of plant materials and the decomposition of cadavers and carcasses.
The decomposition of plant materials is commonly studied in order to understand the cycling of carbon within a given environment and to understand the subsequent impacts on soil quality . Plant material decomposition is also often referred to as composting. The decomposition of cadavers and carcasses has become an important field of study within forensic taphonomy .
The breakdown of vegetation is highly dependent on oxygen and moisture levels. During decomposition, microorganisms require oxygen for their respiration. If anaerobic conditions dominate the decomposition environment, microbial activity will be slow and thus decomposition will be slow. Appropriate moisture levels are required for microorganisms to proliferate and to actively decompose organic matter. In arid environments, bacteria and fungi dry out and are unable to take part in decomposition. In wet environments, anaerobic conditions will develop and decomposition can also be considerably slowed down. Decomposing microorganisms also require the appropriate plant substrates in order to achieve good levels of decomposition. This usually translates to having appropriate carbon to nitrogen ratios (C:N). The ideal composting carbon-to-nitrogen ratio is thought to be approximately 30:1. As in any microbial process, the decomposition of plant litter by microorganisms will also be dependent on temperature. For example, leaves on the ground will not undergo decomposition during the winter months where snow cover occurs as temperatures are too low to sustain microbial activities. [ 1 ]
The decomposition processes of cadavers and carcasses are studied within the field of forensic taphonomy in order to:
Decomposition microbiology as applied to forensic taphonomy can be divided into 2 groups of studies:
When considering cadavers and carcasses, putrefaction is the proliferation of microorganisms within the body following death and also encompasses the breakdown of tissues brought upon by the growth of bacteria. The first signs of putrefaction are usually the discolorations of the body which can vary between shades of green, blue, red or black depending on 1) where the color changes are observed and 2) how far along within the decomposition process the observation is made. This phenomenon is known as marbling. Discolorations are the results of bile pigments being released following an enzymatic attack of the liver , gallbladder and pancreas and the release of hemoglobin breakdown products. [ 2 ] Proliferation of bacteria throughout the body is accompanied with the production of considerable amounts of gases due to their capacities of fermentation . [ 3 ] As gases accumulate within the bodily cavities the body appears to swell as it enters the bloat stage of decomposition.
As oxygen is present within a body at the beginning of decomposition, aerobic bacteria flourish during the first stages of the process. As the microbial population increases, an accumulation of gases changes the environment into anaerobic conditions which is consequently followed by a change to anaerobic bacteria . [ 4 ] Gastro-intestinal bacteria are thought to be responsible for the majority of the putrefactive processes that occur in cadavers and carcasses. This can be in part attributed to the impressive concentrations of viable gastro-intestinal organisms and the metabolic capacities they possess allowing them to use an array of different nutrient sources. [ 5 ] Gastro-intestinal bacteria are also capable of migrating from the gut to any other region of the body by using the lymphatic system and blood vessels . [ 6 ] Furthermore, we know that coliform varieties of Staphylococcus are important members of the aerobic putrefactive bacteria and that members of the genus Clostridium make up a large part of anaerobic putrefactive bacteria. [ 7 ]
Cadavers and carcasses are usually left to decompose in contact with soil whether through burial in a grave or if left to decompose on the soil surface. This allows microorganisms in the soil and air to come in contact with the body and to take part in the decomposition process. Soil microorganism communities also undergo changes as a result of decomposition fluids leaching in the environment. Cadavers and carcasses often show signs of fungal growth suggesting that fungi use the body as a source of nutrients.
The exact impacts that decomposition may have on surrounding soil microbial communities remains unclear as some studies have shown increases in microbial biomass following decomposition whereas other have seen decreases. It is likely that the survival of microorganisms throughout the decomposition process is highly dependent of a multitude of environmental factors including pH, temperature and moisture.
Decomposition fluids entering the soil represent an important influx of organic matter and can also contain a large microbial load of organisms from the body. [ 8 ] The area where the majority of the decomposition fluid leaches into the soil is often referred to as a cadaver decomposition island (CDI). [ 9 ] It has been observed that decomposition can have a favorable influence on the growth of plants due to increased fertility, a useful tool when trying to locate clandestine graves. [ 10 ] The changes in the concentration of nutrients can have lasting effects that are still seen years after a body or carcass has completely disappeared. [ 11 ] The influence that the surge in nutrients can have on the microorganisms and vegetation of a given site is not well understood but it appears that decomposition initially has an inhibitory effect for an initial stage before entering a second stage of increased growth.
It is well known that fungi are heterotrophic for carbon compounds and almost all other nutrients they require. They must obtain these through saprophytic or parasitic associations with their hosts which implicates them in many decomposition processes.
Two major groups of fungi have been identified as being linked to cadaver decomposition:
Ammonia fungi are broken-down into two groups referred to as "early stage fungi" and "late stage fungi." Such a classification is possible due to the successions that are observed between the types of fungi that fruit in or around a burial environment. The progression between the two groups occurs following the release of nitrogenous products from a body in decomposition. Early stage fungi are described as being ascomycetes , deuteromycetes and saprophytic basidiomycetes whereas late stage fungi consisted of ectomycorrhizal basidiomycetes. [ 12 ]
Considering the number of forensic cases in which significant amounts of mycelia are observed is quite high, investigating cadaver associated mycota may prove valuable to the scientific community as they have much forensic potential.
Only one attempt at using fungi as a PMI marker in a forensic case has been published to date. [ 13 ] The study reported the presence of two types of fungi ( Penicillium and Aspergillus ) on a body found in a well in Japan and stated that they could estimate PMI as being approximately ten days based on the known growth cycles of the fungi in question. | https://en.wikipedia.org/wiki/Microbiology_of_decomposition |
An oxygen minimum zone (OMZ) is characterized as an oxygen-deficient layer in the world's oceans. Typically found between 200 m to 1500 m deep below regions of high productivity, such as the western coasts of continents. [ 1 ] OMZs can be seasonal following the spring-summer upwelling season. Upwelling of nutrient-rich water leads to high productivity and labile organic matter, that is respired by heterotrophs as it sinks down the water column. High respiration rates deplete the oxygen in the water column to concentrations of 2 mg/L or less forming the OMZ. [ 2 ] OMZs are expanding, with increasing ocean deoxygenation . Under these oxygen-starved conditions, energy is diverted from higher trophic levels to microbial communities that have evolved to use other biogeochemical species instead of oxygen, these species include nitrate , nitrite , sulphate etc. [ 3 ] Several Bacteria and Archea have adapted to live in these environments by using these alternate chemical species and thrive. The most abundant phyla in OMZs are Pseudomonadota , Bacteroidota , Actinomycetota , and Planctomycetota . [ 3 ]
In the absence of oxygen, microbes use other chemical species to carry out respiration, in the order of the electrochemical series. [ 4 ] With nitrate and nitrite reduction yielding as much energy as oxygen respiration, followed by manganese and iodate respiration and yielding the least amount of energy at the bottom of the series are the iron and sulfate reducers. The utilization of these chemical species by microbes plays an important role in their biogeochemical cycling in the world's oceans. [ 5 ]
Biological productivity ( photosynthesis ) in marine ecosystems is often limited by the bioavailability of nitrogen. [ 6 ] The amount of bioavailable nitrogen (nitrate (NO 3 − ), nitrite (NO 2 − ), and ammonium (NH 4 + )) depends on the inputs from nitrogen fixation and losses from denitrification and anammox as dinitrogen gas (N 2 ), a compound only accessible to nitrogen-fixing bacteria. [ 7 ] [ 6 ] N 2 production from denitrification and anammox closes the nitrogen cycle by reducing the nitrogen available in organic matter fixed by phytoplankton at the surface ocean. Denitrification in OMZs leads to a significant loss of inorganic nitrogen from the oceans, limiting growth/productivity in many regions around the world. OMZs are known for their role in the global nitrogen cycle. As no oxygen is present to fuel aerobic respiration, anoxic systems are primarily dominated by microbially-mediated nitrogen cycling.
N 2 fixation is performed by diazotrophs (N 2 fixing bacteria and archaea), which convert N 2 gas into ammonia (NH 3 ). The amount of N 2 fixation and the distribution of diazotrophs in the ocean is determined by the availability of oxygen (O 2 ), light, phosphorus (P), iron (Fe), and organic matter, as well as habitat temperature. N 2 fixation has been found in some anoxic systems, generally associated with sulfate reducers or oxidizers. [ 8 ] However, heterotrophic denitrification is a more dominant process under anoxic conditions. Denitrification is the reduction of NO 3 − and NO 2 − to the gaseous form of nitrogen (N 2 ), including the greenhouse gas nitrous oxide (N 2 O). [ 9 ] Heterotrophic denitrification is a multi-step process that uses organic matter to reduce NO 3 − to N 2 in oxygen-depleted environments like OMZs and sediments. [ 6 ] In OMZs, different steps in the denitrification processes are performed by separate groups of bacteria, and these denitrifiers are often found directly on sinking organic matter particles, which are hotspots of microbial activity. [ 10 ] [ 11 ] The first step of denitrification is nitrate reduction where NO 3 − is reduced to NO 2 − by the protein nitrate reductase. Anaerobic ammonia-oxidizing bacteria (anammox) convert NO 2 − and NH 4 + to N 2 using an enzyme called hydrazine oxidoreductase. Genomic studies conducted in these ecosystems reveal a growing abundance of the genes encoding for the proteins responsible for the dissimilatory nitrate reduction to ammonium (DNRA) and anammox at the core of these OMZs. [ 12 ] Such studies provide information to map out the nitrogen cycle and demystify missing links and unexplored pathways in the water column. [ 13 ] Anammox is often coupled to denitrification as a source of NH 4 + in OMZs or to DNRA in sediments. [ 7 ] [ 6 ] DNRA has been found to be the dominant process supplying NH 4 + near the shelf and upper slope of sediments because of the presence of large bacterial mats made up of the giant sulfur-oxidizing bacteria Thioploca spp. and Beggiatoa spp. which reduce NO 3 − and/or NO 2 − to NH 4 + using reduced sulfur. [ 7 ] [ 14 ] Denitrification and anammox account for about 30-50% of the N losses in OMZs, where the total N loss determined by the supply of sinking organic matter available. [ 15 ] [ 16 ] [ 6 ]
Additionally, ammonium and nitrite oxidation are key processes in N cycling in anoxic environments. Ammonium oxidation is the first step in nitrification and ammonia-oxidizing bacteria (AOB) converts NH 3 to NO 2 − . [ 6 ] Followed by nitrite oxidation by nitrite-oxidizing bacteria (NOB), which converts NO 2 − to NO 3 − . [ 6 ] Ammonium and nitrite oxidizers have a high affinity for O 2 and can use nanomolar concentrations of O 2 to oxidize ammonium and nitrite. [ 17 ] These small concentrations of O 2 can be supplied by photosynthesis by Prochlorococcus spp. [ 18 ] or by horizontal mixing by jets and eddies. [ 19 ] In anoxic environments, the competition between ammonium and nitrite oxidization and anammox and denitrification for ammonium and nitrite play an important role in controlling nitrogen loss in OMZs. [ 17 ]
Anaerobic ammonium oxidation with nitrite (anammox) is a major pathway of fixed nitrogen removal in the anoxic zones of the open ocean. [ 20 ] Anammox requires a source of ammonium, which under anoxic conditions could be supplied by the breakdown of sinking organic matter via heterotrophic denitrification. However, at many locations where anammox is observed, denitrification rates are small or undetectable. [ 21 ] Alternative sources of NH 4 + than denitrification, such as the DNRA, the diffusion and advection from sulfate-reducing sediments, or from microaerobic remineralization at the boundaries of anoxic waters, can supply NH 4 + to anammox bacterial communities, [ 22 ] even though it is not yet clear how much they can influence the process. [ 22 ] [ 23 ] Another source of NH 4 + , which plays an important role in the N cycle of OMZs by contributing to the decoupling of anammox and denitrification, is the excretion of NH 4 + by diel vertically migrating animals. To escape predation, diel vertical migration (DVM) of zooplankton and micronekton can reach the anoxic layers of the major OMZs of the open ocean, and because animals excrete reduced N mostly as NH 4 + , they can fuel anammox directly and decouple it from denitrification. The downward export of organic matter by migrating zooplankton and micronekton is generally smaller than that of particles at the base of the euphotic zone. [ 24 ] However, sinking particles are rapidly consumed with depth, and the active transport by migrators can exceed particle remineralization in deeper layers where animals congregate during the daytime. [ 24 ] As a result, inside anoxic waters the excretion of NH 4 + by vertically migrating animals could alter the balance between fixed N removal pathways, decoupling anammox and denitrification and enhancing anammox above the values predicted by typical stoichiometry. [ 24 ]
Methanogenesis is the process by which methanogen microbes form methane (CH 4 ). OMZs are known to contain the largest amount of methane in the open ocean. [ 25 ] Methanogens can also oxidize methane as they have the genes to do so, however this requires oxygen which they obtain from photosynthetic organisms in the upper anoxic zone . [ 25 ] Ciliates may also aid methanogens through symbiosis to help facilitate methanogenesis. [ 26 ] As ciliates have hydrogenosomes , which release hydrogen molecules under low oxygen conditions, they have the ability to host endosymbiotic methanogens. [ 27 ]
Sulfate reduction, which occurs with the help of sulfate-reducing microorganisms , is used in the cryptic sulfur cycle . This cycle is continuous oxidation and reduction of sulfate and uses sulfate as the terminal electron acceptor rather than oxygen . The cycle was purposed to help contribute to the energy flow to anoxic water off the coast of Chile. [ 28 ]
Aerobic organisms require oxygen to survive and as oxygen becomes limited in OMZs bacteria begin to use other molecules to oxidize organic matter such as nitrate. [ 29 ] Aerobic respiration in OMZs helps remineralize organic matter and is a major source of ammonium for most of the upper oxygen minimal zones. [ 30 ] It was also found that bacteria from OMZs use a 1/6 of the oxygen for respiration compared bacteria in normal waters. [ 31 ]
While oxygen minimum zones (OMZs) occur naturally, they can be exacerbated by human impacts like climate change and land-based pollution from agriculture and sewage. The prediction of current climate models and climate change scenarios is that substantial warming and loss of oxygen throughout the majority of the upper ocean will occur. [ 32 ] Global warming increases ocean temperatures, especially in shallow coastal areas. When the water temperature increases, its ability to hold oxygen decreases, leading to oxygen concentrations going down in the water. [ 33 ] This compounds the effects of eutrophication in coastal zones described above.
Open ocean areas with no oxygen have grown more than 1.7 million square miles in the last 50 years, and coastal waters have seen a tenfold increase in low-oxygen areas in the same time. [ 34 ]
Measurement of dissolved oxygen in coastal and open ocean waters for the past 50 years has revealed a marked decline in oxygen content. [ 35 ] [ 36 ] [ 37 ] This decline is associated with expanding spatial extent, expanding vertical extent, and prolonged duration of oxygen-poor conditions in all regions of the global oceans. Examinations of the spatial extent of OMZs in the past through paleoceanographical methods clearly shows that the spatial extent of OMZs has expanded through time, and this expansion is coupled to ocean warming and reduced ventilation of thermocline waters. [ 38 ]
Research has attempted to model potential changes to OMZs as a result of rising global temperatures and human impact. This is challenging due to the many factors that could contribute to changes in OMZs. [ 39 ] The factors used for modeling change in OMZs are numerous, and in some cases hard to measure or quantify. [ 40 ] Some of the processes being studied are changes in oxygen gas solubility as a result of rising ocean temperatures, as well as changes in the amount of respiration and photosynthesis occurring around OMZs. [ 41 ] Many studies have concluded that OMZs are expanding in multiple locations, but fluctuations of modern OMZs are still not fully understood. [ 41 ] [ 40 ] [ 42 ] Existing Earth system models project considerable reductions in oxygen and other physical-chemical variables in the ocean due to climate change , with potential ramifications for ecosystems and humans.
The global decrease in oceanic oxygen content is statistically significant and emerging beyond the envelope of natural fluctuations. [ 35 ] This trend of oxygen loss is accelerating, with widespread and obvious losses occurring after the 1980s. [ 43 ] [ 35 ] The rate and total content of oxygen loss varies by region, with the North Pacific emerging as a particular hotspot of deoxygenation due to the increased amount of time since its deep waters were last ventilated (see thermohaline circulation) and related high apparent oxygen utilization (AOU). [ 35 ] [ 36 ] Estimates of total oxygen loss in the global ocean range from 119 to 680 T mol decade −1 since the 1950s. [ 35 ] [ 36 ] These estimates represent 2% of the global ocean oxygen inventory. [ 37 ] | https://en.wikipedia.org/wiki/Microbiology_of_oxygen_minimum_zones |
The microbiota are the sum of all symbiotic microorganisms ( mutualistic , commensal or pathogenic ) living on or in an organism. The fruit fly Drosophila melanogaster is a model organism and known as one of the most investigated organisms worldwide. The microbiota in flies is less complex than that found in humans. It still has an influence on the fitness of the fly, [ 1 ] and it affects different life-history characteristics such as lifespan ( life expectancy ), resistance against pathogens ( immunity ) and metabolic processes ( digestion ). Considering the comprehensive toolkit available for research in Drosophila , analysis of its microbiome could enhance our understanding of similar processes in other types of host-microbiota interactions, including those involving humans. Microbiota plays key roles in the intestinal immune and metabolic responses via their fermentation product ( short chain fatty acid ), acetate . [ 2 ]
Drosophila melanogaster possesses a comparatively simple gut microbiota, consisting of only few bacterial species, mainly from two bacterial taxonomic groups: Bacillota and Pseudomonadota . [ 3 ] [ 4 ] The most common species belong to the families Lactobacillaceae (abundance of approx. 30%, members of the Bacillota) and Acetobacteraceae (approx. 55%, members of the Proteobacteria). Other less common bacterial species are from the families Leuconostocaceae, Enterococaceae, and Enterobacteriaceae (all with an abundance in between 2–4%). [ 4 ] The most common species include Lactobacillus plantarum , Lactobacillus brevis , Acetobacter pomorum and Enterococcus faecalis , while other species such as Acetobacter aceti , Acetobacter tropicalis and Acetobacter pasteurianus are also often found. [ 3 ]
The particular species of the host fly has a central influence on the composition and quality of the gut microbiota, even if flies are raised under similar conditions. [ 5 ] Nevertheless, the host's diet and nutritional environment also shape the exact composition of the microbiota. For instance the exact pH of the food can kill certain bacterial species. [ 3 ] In general, the type of food used by the fly affects the microbiota composition. [ 6 ] Mushroom feeder species like Drosophila falleni and Microdrosophila harbour many Lactobacillales and generally maintain high bacterial diversity in their guts. The microbiota of flower feeders such as Drosophila elegans and Drosophila flavohirta shows higher abundance of Enterobacteriaceae and to a lesser extent of acido-philic bacteria (such as Acetobacteraceae and Lactobacillaceae) if compared to fruit-eating species such as Drosophila hydei , Drosophila immigrans , Drosophila sulfurigaster , Drosophila melanogaster , Drosophila sechellia or Drosophila takahashii . [ 3 ] The microbial load and bacterial composition also vary with the age of the host fly. [ 3 ]
Feeding is a key determinant of the microbiota composition. Not only the diet influences presence and abundance of the bacteria inside the gut, but the bacteria also need to be taken up continuously from the environment to prevail as members of the intestinal flora. [ 7 ] Feeding on feces seems to play a central role for establishment of the Drosophila microbiota, as it allows the flies to recycle the bacteria within a fly population at a particular time point and also across generations. Flies seed the embryonic eggshell with feces. Upon hatching, young larvae eat their eggshells and thereby pick up the bacteria. The microbiota, which subsequently establishes itself inside the gut of the developing larvae, is similar to that of the larvae's mothers. [ 8 ] This may further be promoted by the particular life history of the flies. Young adult flies, which harbor fewer bacteria than old flies, proliferate in an environment shaped by the feces of the preceding fly generation, thus allowing them to take up additional bacteria. [ 8 ]
In the gut of Drosophila melanogaster the composition and action of the microbiome appears to be tightly regulated within compartments, that is different sections of the intestines. This is indicated by the differential expression of genes, especially with a regulatory function, in the epithelium of different parts of the gut. In detail, the gut is compartmentalized into three parts, the foregut , the midgut , and the hindgut . While foregut and hindgut are lined with a cuticle formed by the ectodermal epithelium, the midgut is of endodermal origin. [ 9 ] In adult flies the midgut is further divided into five smaller regions. [ 10 ] The immune response varies among the gut regions. The immune deficiency (IMD) pathway responds to bacterial infections and is activated by certain receptors (e.g., the peptidoglycan receptor protein PGRP-LC ). These receptors and also other components of the Drosophila immune system such as Toll receptor and dDUOX pathway molecules control immune responses in ectodermal tissue of the anterior gut. Moreover, the anterior midgut is enriched in certain antimicrobial peptides ( AMPs ). This suggests that the immune defence in this area is particularly responsive, possibly because this regions represents the first contact region for newly taken up food, microbiota, and/or intestinal pathogens. In the middle and posterior midgut, other genes such as the receptor PGRP-LB , which down-regulates the IMD immune response, are expressed, possibly in order to minimize expression of immune defence against the microbiota. In addition, the microbiota itself seems to control the expression of several Drosophila metabolic genes within the midgut, possibly to facilitate digestion of food. [ 11 ] Recently, IMD pathway in the anterior midgut region has been proposed to play multi-pronged roles to modulate key metabolic and mechanic functions in the gut. [ 12 ] Taken together, it appears that the interaction between host and microbiota is precisely regulated across different regions within the gut. [ 13 ]
Drosophila microbiota have been implicated in mating success by influencing assortative mating; a phenomenon detected in some studies of Drosophila , [ 14 ] but not others. [ 15 ]
The microbiota seem to affect the lifespan of Drosophila melanogaster . To date, the mechanisms of this effect remain elusive. Fruit flies raised under axenic conditions (i.e., without any bacteria in the environment) or cured of their microbiota with antibiotics had a shorter lifespan than flies raised under normal conditions. The microbiota influence on longevity seems to be particularly strong early in development. [ 16 ] To date, however, the exact mechanisms underlying these effects remain elusive. It is possible that the microbiota-induced proliferation of intestinal stem cells and associated metabolic homeostasis is important in this context. [ 17 ] In contrast, the microbiota seems to have a negative effect on lifespan in older Drosophila melanogaster , because their removal in ageing flies increases longevity. Old flies have a reduced ability to fight infections and this may also relate to the bacterial members of the microbiota. [ 18 ] In aged animals, immune responses may over-shoot, possibly harming the host and favoring colonization with pathogens (e.g. Gluconobacter morbifer ). [ 19 ]
Almost all current approaches for the characterization of Drosophila microbiota rely on destructive approaches, that is flies are killed, their gut is extracted and from these the bacteria are isolated and/or analyzed. For an assessment of microbiota dynamics across the lifespan of an individual fly or across development of a fly population, a non-destructive approach would be favorable. Such an approach was recently developed, focusing on the microbial characterization of fly feces. Fly feces are indeed informative on composition of the gut microbiota, since the diversity of gut bacteria, feces bacteria and bacteria of whole fly of Drosophila melanogaster are all strongly correlated. This new approach could be used to demonstrate the known influence of diets. [ 20 ] | https://en.wikipedia.org/wiki/Microbiome_in_the_Drosophila_gut |
Microbiomes of the built environment [ 1 ] [ 2 ] is a field of inquiry into the communities of microorganisms that live in human constructed environments like houses, cars and water pipes. It is also sometimes referred to as microbiology of the built environment.
A 2016 paper by Brent Stephens [ 7 ] highlights some of the key findings of studies of "microbiomes of the indoor environment". These key findings include those listed below:
The microbiomes of the built environment are being studied for multiple reasons including how they may impact the health of humans and other organisms occupying the built environment but also some non health reasons such as diagnostics of building properties, for forensic application, impact on food production, impact on built environment function, and more.
Extensive research has been conducted on individual microbes found in the built environment. More recently there has been a significant expansion in the number of studies that are examining the communities of microbes found in the built environment. Such studies have covered a range of environments.
Overall the many studies that have been conducted on the microbiomes of the built environment have started to identify some general patterns regarding the microbes are found in various places. Different areas and kinds of buildings are linked to different sorts of microbiota. [ 57 ] Pakpour et al. in 2016 reviewed the patterns relating to the presence of archaea in indoor environments (based on analysis of rRNA gene sequence data). [ 58 ]
Many studies have documented possible human health implications of the microbiomes of the built environment. [ 59 ]
A major component of studies of microbiomes of the built environment involves determining how components of the built environment impact these microbes and microbial communities. Factors that are thought to be important include humidity, pH, chemical exposures, temperature, filtration, surface materials, and air flow. [ 68 ] There has been an effort to develop standards for what built environment "metadata" to collect associated with studies of the microbial communities in the built environment. [ 69 ] A 2014 paper reviews the tools that are available to improve the built environment data that is collected associated with such studies. [ 70 ] Data covered in this review include building characteristics and environmental conditions, HVAC system characteristics and ventilation rates, human occupancy and activity measurements, surface characterizations and air sampling and aerosol dynamics.
Just as the built environment has an impact on the microbiomes found therein, the microbial communities of the built environment can impact the built environment itself. Examples include degradation of building materials, altering fluid and airflow, generating volatiles, and more. [ citation needed ]
The microbiome of the built environment has some potential for being used as a feature for forensic studies. Most of these applications are still in the early research phase. For example, it has been shown that people leave behind a somewhat diagnostic microbial signature when they type on computer keyboards, [ 71 ] use phones [ 72 ] or occupy a room. [ 11 ]
There has been a significant amount of research on the role that microbes play in various odors in the built environment. For example, Diekmann et al. examined the connection between volatile organic emissions in automobile air conditioning units. [ 73 ] They reported that the types of microbes found were correlated to the bad odors found. Park and Kim examined which microbes found in an automobile air conditioner could produce bad smelling volatile compounds and identified candidate taxa producing some such compounds. [ 74 ]
Many methods are used to study microbes in built environment. A review of such methods are some of the challenges in using them was published by NIST. Hoisington et al. in 2014 reviewed methods that could be used by building professionals to study the microbiology of the built environment. [ 75 ] Methods used in the study of microbes in the built environment include culturing (with subsequent studies of the cultured microbes), microscopy , air, water and surface sampling, chemical analyses, and culture independent DNA studies such as ribosomal RNA gene PCR and metagenomics . [ citation needed ]
There are a growing number of research projects and groups focusing directly or indirectly on microbiomes of the built environment. | https://en.wikipedia.org/wiki/Microbiomes_of_the_built_environment |
Microbiota are the range of microorganisms that may be commensal , mutualistic , or pathogenic found in and on all multicellular organisms , including plants . Microbiota include bacteria , archaea , protists , fungi , and viruses , [ 2 ] [ 3 ] and have been found to be crucial for immunologic, hormonal, and metabolic homeostasis of their host.
The term microbiome describes either the collective genomes of the microbes that reside in an ecological niche or else the microbes themselves. [ 4 ] [ 5 ] [ 6 ]
The microbiome and host emerged during evolution as a synergistic unit from epigenetics and genetic characteristics, sometimes collectively referred to as a holobiont . [ 7 ] [ 8 ] The presence of microbiota in human and other metazoan guts has been critical for understanding the co-evolution between metazoans and bacteria. [ 9 ] [ 10 ] Microbiota play key roles in the intestinal immune and metabolic responses via their fermentation product ( short-chain fatty acid ), acetate . [ 11 ]
All plants and animals, from simple life forms to humans, live in close association with microbial organisms. [ 12 ] Several advances have driven the perception of microbiomes, including:
Biologists have come to appreciate that microbes make up an important part of an organism's phenotype , far beyond the occasional symbiotic case study. [ 13 ]
Commensalism , a concept developed by Pierre-Joseph van Beneden (1809–1894), a Belgian professor at the University of Louvain during the nineteenth century [ 14 ] is central to the microbiome, where microbiota colonize a host in a non-harmful coexistence. The relationship with their host is called mutualistic when organisms perform tasks that are known to be useful for the host, [ 15 ] : 700 [ 16 ] parasitic , when disadvantageous to the host. Other authors define a situation as mutualistic where both benefit, and commensal, where the unaffected host benefits the symbiont. [ 17 ] A nutrient exchange may be bidirectional or unidirectional, may be context dependent and may occur in diverse ways. [ 17 ] Microbiota that are expected to be present, and that under normal circumstances do not cause disease, are deemed normal flora or normal microbiota ; [ 15 ] normal flora can not only be harmless, but can be protective of the host. [ 18 ]
The initial acquisition of microbiota in animals from mammalians to marine sponges is at birth, and may even occur through the germ cell line. In plants, the colonizing process can be initiated below ground in the root zone , around the germinating seed, the spermosphere , or originate from the above ground parts, the phyllosphere and the flower zone or anthosphere. [ 19 ] The stability of the rhizosphere microbiota over generations depends upon the plant type but even more on the soil composition, i.e. living and non living environment. [ 20 ] Clinically, new microbiota can be acquired through fecal microbiota transplant to treat infections such as chronic C. difficile infection. [ 21 ]
The human microbiota includes bacteria , fungi , archaea and viruses. Micro-animals which live on the human body are excluded. The human microbiome refers to their collective genomes . [ 15 ]
Humans are colonized by many microorganisms; the traditional estimate was that humans live with ten times more non-human cells than human cells; more recent estimates have lowered this to 3:1 and even to about 1:1 by number (1:350 by mass). [ 22 ] [ 23 ] [ 24 ] [ 25 ] [ 26 ]
In fact, these are so small that there are around 100 trillion microbiota on the human body, [ 27 ] around 39 trillion by revised estimates, with only 0.2 kg of total mass in a "reference" 70 kg human body. [ 26 ]
The Human Microbiome Project sequenced the genome of the human microbiota, focusing particularly on the microbiota that normally inhabit the skin, mouth, nose, digestive tract, and vagina. [ 15 ] It reached a milestone in 2012 when it published initial results. [ 28 ]
The plant microbiome was recently discovered to originate from the seed. [ 46 ] Microorganism which are transmitted via seed migrate into the developing seedling in a specific route in which certain community move to the leaves and others to the roots. [ 46 ] In the diagram on the right, microbiota colonizing the rhizosphere , entering the roots and colonizing the next tuber generation via the stolons , are visualized with a red color. Bacteria present in the mother tuber , passing through the stolons and migrating into the plant as well as into the next generation of tubers are shown in blue. [ 45 ]
Plants are attractive hosts for microorganisms since they provide a variety of nutrients. Microorganisms on plants can be epiphytes (found on the plants) or endophytes (found inside plant tissue). [ 47 ] [ 48 ] Oomycetes and fungi have, through convergent evolution, developed similar morphology and occupy similar ecological niches. They develop hyphae , threadlike structures that penetrate the host cell. In mutualistic situations the plant often exchanges hexose sugars for inorganic phosphate from the fungal symbiont. It is speculated that such very ancient associations have aided plants when they first colonized land. [ 17 ] [ 49 ] Plant-growth promoting bacteria (PGPB) provide the plant with essential services such as nitrogen fixation , solubilization of minerals such as phosphorus, synthesis of plant hormones , direct enhancement of mineral uptake, and protection from pathogens. [ 50 ] [ 51 ] PGPBs may protect plants from pathogens by competing with the pathogen for an ecological niche or a substrate, producing inhibitory allelochemicals , or inducing systemic resistance in host plants to the pathogen [ 19 ]
The symbiotic relationship between a host and its microbiota is under laboratory research for how it may shape the immune system of mammals. [ 52 ] [ 53 ] In many animals, the immune system and microbiota may engage in "cross-talk" by exchanging chemical signals, which may enable the microbiota to influence immune reactivity and targeting. [ 54 ] Bacteria can be transferred from mother to child through direct contact and after birth . [ 55 ] As the infant microbiome is established, commensal bacteria quickly populate the gut, prompting a range of immune responses and "programming" the immune system with long-lasting effects. [ 54 ] The bacteria are able to stimulate lymphoid tissue associated with the gut mucosa, which enables the tissue to produce antibodies for pathogens that may enter the gut. [ 54 ]
The human microbiome may play a role in the activation of toll-like receptors in the intestines, a type of pattern recognition receptor host cells use to recognize dangers and repair damage. Pathogens can influence this coexistence leading to immune dysregulation including and susceptibility to diseases, mechanisms of inflammation , immune tolerance , and autoimmune diseases . [ 56 ] [ 57 ]
Organisms evolve within ecosystems so that the change of one organism affects the change of others. The hologenome theory of evolution proposes that an object of natural selection is not the individual organism, but the organism together with its associated organisms, including its microbial communities.
Coral reefs . The hologenome theory originated in studies on coral reefs. [ 58 ] Coral reefs are the largest structures created by living organisms, and contain abundant and highly complex microbial communities. Over the past several decades, major declines in coral populations have occurred. Climate change , water pollution and over-fishing are three stress factors that have been described as leading to disease susceptibility. Over twenty different coral diseases have been described, but of these, only a handful have had their causative agents isolated and characterized. Coral bleaching is the most serious of these diseases. In the Mediterranean Sea, the bleaching of Oculina patagonica was first described in 1994 and shortly determined to be due to infection by Vibrio shiloi . From 1994 to 2002, bacterial bleaching of O. patagonica occurred every summer in the eastern Mediterranean. Surprisingly, however, after 2003, O. patagonica in the eastern Mediterranean has been resistant to V. shiloi infection, although other diseases still cause bleaching. The surprise stems from the knowledge that corals are long lived, with lifespans on the order of decades, [ 59 ] and do not have adaptive immune systems . [ citation needed ] Their innate immune systems do not produce antibodies, and they should seemingly not be able to respond to new challenges except over evolutionary time scales. [ citation needed ]
The puzzle of how corals managed to acquire resistance to a specific pathogen led to a 2007 proposal, that a dynamic relationship exists between corals and their symbiotic microbial communities. It is thought that by altering its composition, the holobiont can adapt to changing environmental conditions far more rapidly than by genetic mutation and selection alone. Extrapolating this hypothesis to other organisms, including higher plants and animals, led to the proposal of the hologenome theory of evolution. [ 58 ]
As of 2007 [update] the hologenome theory was still being debated. [ 60 ] A major criticism has been the claim that V. shiloi was misidentified as the causative agent of coral bleaching, and that its presence in bleached O. patagonica was simply that of opportunistic colonization. [ 61 ] If this is true, the basic observation leading to the theory would be invalid. The theory has gained significant popularity as a way of explaining rapid changes in adaptation that cannot otherwise be explained by traditional mechanisms of natural selection. Within the hologenome theory, the holobiont has not only become the principal unit of natural selection but also the result of other step of integration that it is also observed at the cell ( symbiogenesis , endosymbiosis ) and genomic levels. [ 7 ]
Targeted amplicon sequencing relies on having some expectations about the composition of the community that is being studied. In target amplicon sequencing a phylogenetically informative marker is targeted for sequencing. Such a marker should be present in ideally all the expected organisms. It should also evolve in such a way that it is conserved enough that primers can target genes from a wide range of organisms while evolving quickly enough to allow for finer resolution at the taxonomic level. A common marker for human microbiome studies is the gene for bacterial 16S rRNA ( i.e. "16S rDNA", the sequence of DNA which encodes the ribosomal RNA molecule). [ 62 ] Since ribosomes are present in all living organisms, using 16S rDNA allows for DNA to be amplified from many more organisms than if another marker were used. The 16S rRNA gene contains both slowly evolving regions and 9 fast evolving regions, also known as hypervariable regions (HVRs); [ 63 ] the former can be used to design broad primers while the latter allow for finer taxonomic distinction. However, species-level resolution is not typically possible using the 16S rDNA. Primer selection is an important step, as anything that cannot be targeted by the primer will not be amplified and thus will not be detected, moreover different sets of primers can be selected to amplify different HVRs in the gene, or pairs of them. The appropriate choice of which HVRs to amplify has to be made according to the taxonomic groups of interest, as different target regions has been shown to influence taxonomical classification. [ 64 ]
Targeted studies of eukaryotic and viral communities are limited [ 65 ] and subject to the challenge of excluding host DNA from amplification and the reduced eukaryotic and viral biomass in the human microbiome. [ 66 ]
After the amplicons are sequenced, molecular phylogenetic methods are used to infer the composition of the microbial community. This can be done through clustering methodologies, by clustering the amplicons into operational taxonomic units (OTUs); or alternatively with denoising methodologies, identifying amplicon sequence variants (ASVs).
Phylogenetic relationships are then inferred between the sequences. Due to the complexity of the data, distance measures such as UniFrac distances are usually defined between microbiome samples, and downstream multivariate methods are carried out on the distance matrices. An important point is that the scale of data is extensive, and further approaches must be taken to identify patterns from the available information. Tools used to analyze the data include VAMPS, [ 67 ] QIIME , [ 68 ] mothur [ 69 ] and DADA2 [ 70 ] or UNOISE3 [ 71 ] for denoising.
Metagenomics is also used extensively for studying microbial communities. [ 72 ] [ 73 ] [ 74 ] In metagenomic sequencing, DNA is recovered directly from environmental samples in an untargeted manner with the goal of obtaining an unbiased sample from all genes of all members of the community. Recent studies use shotgun Sanger sequencing or pyrosequencing to recover the sequences of the reads. [ 75 ] The reads can then be assembled into contigs . To determine the phylogenetic identity of a sequence, it is compared to available full genome sequences using methods such as BLAST . One drawback of this approach is that many members of microbial communities do not have a representative sequenced genome, but this applies to 16S rRNA amplicon sequencing as well and is a fundamental problem. [ 62 ] With shotgun sequencing, it can be resolved by having a high coverage (50–100x) of the unknown genome, effectively doing a de novo genome assembly . As soon as there is a complete genome of an unknown organism available it can be compared phylogenetically and the organism put into its place in the tree of life , by creating new taxa . An emerging approach is to combine shotgun sequencing with proximity-ligation data ( Hi-C ) to assemble complete microbial genomes without culturing. [ 76 ]
Despite the fact that metagenomics is limited by the availability of reference sequences, one significant advantage of metagenomics over targeted amplicon sequencing is that metagenomics data can elucidate the functional potential of the community DNA. [ 77 ] [ 78 ] Targeted gene surveys cannot do this as they only reveal the phylogenetic relationship between the same gene from different organisms. Functional analysis is done by comparing the recovered sequences to databases of metagenomic annotations such as KEGG . The metabolic pathways that these genes are involved in can then be predicted with tools such as MG-RAST, [ 79 ] CAMERA [ 80 ] and IMG/M . [ 81 ]
Metatranscriptomics studies have been performed to study the gene expression of microbial communities through methods such as the pyrosequencing of extracted RNA. [ 82 ] Structure based studies have also identified non-coding RNAs (ncRNAs) such as ribozymes from microbiota. [ 83 ] Metaproteomics is an approach that studies the proteins expressed by microbiota, giving insight into its functional potential. [ 84 ]
The Human Microbiome Project launched in 2008 was a United States National Institutes of Health initiative to identify and characterize microorganisms found in both healthy and diseased humans. [ 85 ] The five-year project, best characterized as a feasibility study with a budget of $115 million, tested how changes in the human microbiome are associated with human health or disease. [ 85 ]
The Earth Microbiome Project (EMP) is an initiative to collect natural samples and analyze the microbial community around the globe. Microbes are highly abundant, diverse and have an important role in the ecological system. Yet as of 2010 [update] , it was estimated that the total global environmental DNA sequencing effort had produced less than 1 percent of the total DNA found in a liter of seawater or a gram of soil, [ 86 ] and the specific interactions between microbes are largely unknown. The EMP aims to process as many as 200,000 samples in different biomes, generating a complete database of microbes on earth to characterize environments and ecosystems by microbial composition and interaction. Using these data, new ecological and evolutionary theories can be proposed and tested. [ 87 ]
The gut microbiota are very important for the host health because they play role in degradation of non-digestible polysaccharides (fermentation of resistant starch, oligosaccharides, inulin) strengthening gut integrity or shaping the intestinal epithelium, harvesting energy, protecting against pathogens, and regulating host immunity. [ 88 ] [ 89 ]
Several studies showed that the gut bacterial composition in diabetic patients became altered with increased levels of Lactobacillus gasseri , Streptococcus mutans and Clostridiales members, with decrease in butyrate-producing bacteria such as Roseburia intestinalis and Faecalibacterium prausnitzii. [ 90 ] [ 91 ] This alteration is due to many factors such as antibiotic abuse, diet, and age .
The decrease in butyrate production is associated with defects in intestinal permeability, which could lead to endotoxemia , which is the increased level of circulating Lipopolysaccharides from gram negative bacterial cells wall. It is found that endotoxemia has association with development of insulin resistance. [ 90 ]
In addition that butyrate production affects serotonin level. [ 90 ] Elevated serotonin level has contribution in obesity, which is known to be a risk factor for development of diabetes.
The human gut microbial composition is modulated by dietary bile acids. [ 92 ] [ 93 ] There appears to be a metabolic link between cancer associated gut microbes and a fat- and meat rich diet. [ 94 ] In rodents, elevated levels of bile acids produced by the gut microbiota in response to a high fat diet are associated with an increased the risk of colorectal cancer. [ 93 ] The secondary bile acid deoxycholic acid , produced from the primary bile acid cholic acid by the gut microbiota, is elevated in the colonic contents of humans in response to a high fat diet. [ 92 ] [ 93 ] In populations that have a high incidence of colorectal cancer fecal concentrations of bile acids, particularly deoxycholic acid produced by the action of gut microbiota, are higher. [ 92 ] [ 93 ]
The colonization of the human gut microbiota may start already before birth. [ 95 ] There are multiple factors in the environment that affects the development of the microbiota with birthmode being one of the most impactful. [ 96 ]
Another factor that has been observed to cause huge changes in the gut microbiota, particularly in children, is the use of antibiotics, associating with health issues such as higher BMI, [ 97 ] [ 98 ] and further an increased risk towards metabolic diseases such as obesity. [ 99 ] In infants it was observed that amoxicillin and macrolides cause significant shifts in the gut microbiota characterized by a change in the bacterial classes Bifidobacteria, Enterobacteria and Clostridia. [ 100 ] A single course of antibiotics in adults causes changes in both the bacterial and fungal microbiota, with even more persistent changes in the fungal communities. [ 101 ] The bacteria and fungi live together in the gut and there is most likely a competition for nutrient sources present. [ 102 ] [ 103 ] Seelbinder et al . found that commensal bacteria in the gut regulate the growth and pathogenicity of Candida albicans by their metabolites, particularly by propionate, acetic acid and 5-dodecenoate. [ 101 ] Candida has previously been associated with IBD [ 104 ] and further it has been observed to be increased in non-responders to a biological drug, infliximab, given to IBD patients with severe IBD. [ 105 ] Propionate and acetic acid are both short-chain fatty acids (SCFAs) that have been observed to be beneficial to gut microbiota health. [ 106 ] [ 107 ] [ 108 ] When antibiotics affect the growth of bacteria in the gut, there might be an overgrowth of certain fungi, which might be pathogenic when not regulated. [ 101 ]
Microbial DNA inhabiting a person's human body can uniquely identify the person. A person's privacy may be compromised if the person anonymously donated microbe DNA data. Their medical condition and identity could be revealed. [ 109 ] [ 110 ] [ 111 ] | https://en.wikipedia.org/wiki/Microbiota |
Microbiota-accessible carbohydrates (MACs) are carbohydrates that are resistant to digestion by a host's metabolism, and are made available for gut microbes , as prebiotics , to ferment or metabolize into beneficial compounds, such as short chain fatty acids . [ 1 ] The term, ‘‘microbiota-accessible carbohydrate’’ contributes to a conceptual framework for investigating and discussing the amount of metabolic activity that a specific food or carbohydrate can contribute to a host's microbiota . [ 1 ]
MACs may come from plants , fungi , animal tissues , or food-borne microbes , and must be metabolized by the microbiome . [ 1 ] A significant quantity of the cellulose humans consume is not metabolized by gut microbes and therefore cannot be considered a MAC. [ 2 ] The amount of dietary MACs found within a food source will differ for each individual, since which carbohydrates are metabolized depends upon the composition of each person's microbiota. For example, many Japanese individuals possess the genes for the consumption of the algal polysaccharide porphyran in their microbiomes, which are rarely found in North American and European individuals. [ 3 ] [ 4 ] For individuals who harbor such a porphyran-degrading strain, porphyran would be a MAC. However, porphyran would not be a MAC for those without a microbiota adaptation to seaweed. In similar fashion, germ-free mice without a microbiota might consume a diet with large quantities of potential MACs, but none of the carbohydrates would be considered MACs, since they would escape the digestive tract without being metabolized by microbes. [ 1 ]
Lack of dietary MACs results in a microbiota reliant upon endogenous host-derived MACs, such as mucin glycans. [ 5 ] Different host genotypes can influence the identity of MACs available to the microbiota in multiple ways. For example, a host's genes may affect the level of mucus structures, such as the absence of alpha-1-2 fucose residues in the mucus of nonsecretor individuals who lack alpha-1-2- fucosyltransferase activity in the intestine. [ 6 ] Similarly, a host may have genes that can determine the efficiency of digestion and absorption of carbohydrates in the small intestine. For example, lactose is accessible to the microbiota in people who are lactose intolerant, and should therefore be considered a MAC for those individuals. For nursing infants, dietary MACs that are naturally found in breast milk are known as human milk oligosaccharides (HMOs) . [ 7 ] [ 8 ] [ 9 ] For formula-fed infants, dietary MACs, such as galacto-oligosaccharides, are artificially added to formula. [ 10 ] Therefore, the research, discussion and quantification of MACs and their impact on a host's microbiota may be critical to determining their impact on human health. [ 1 ]
Diets in developed countries have lost microbiota-accessible carbohydrates which is the cause of a substantial depletion of gut microbiota taxa. This loss of microbiota diversity is likely involved in the increasing propensity for a broad range of inflammatory diseases, such as allergic disease, asthma, inflammatory bowel disease (IBD), obesity, and associated noncommunicable diseases (NCDs). Rural human communities from South America and Africa have a low prevalence of NCDs and this fact has been related with a higher gut microbiota diversity. [ 11 ] Some of these lost taxa belong to the families of Bacteroidales ( Bacteroides fragilis , B. ovatus , B. uniformis , B. distasonis , Parabacteroides gordonii ), Clostridiales ( Ruminococcus gnavus , Blautia producta , Faecalibacterium prausnitzii ) and Verrucomicrobiales ( Akkermansia muciniphila ). [ citation needed ] Introduction of dietary MACs in the diet is insufficient to regain the lost taxa, to restore the gut microbiota to its original state requires the administration of missing taxa, which can be achieved either by administering probiotics (food) or live biotherapeutics (drugs), in combination with dietary MAC consumption. Enriching the food supply with dietary fiber might have an essential role in preventing loss of certain beneficial bacterial species. [ 12 ] | https://en.wikipedia.org/wiki/Microbiota-accessible_carbohydrates |
Microbivory (adj. microbivorous, microbivore [ 1 ] ) is a feeding behavior consisting of eating microbes (especially bacteria ) practiced by animals of the mesofauna , microfauna and meiofauna . [ 2 ] [ 3 ] [ 4 ]
Microbivorous animals include some soil nematodes , [ 5 ] [ 6 ] [ 7 ] springtails or flies such as Drosophila sharpi . A well known example of microbivorous nematodes is the model roundworm Caenorhabditis elegans which is maintained in culture in labs on agar plates, fed with the 'OP50' Escherichia coli strain of bacteria.
In food webs of ecosystems , microbivores can be distinguished from detritivores , generally thought playing the roles of decomposers, as they don't consume decaying dead matter but only living microorganisms.
There is also use of the term 'microbivore' to qualify the concept of robots autonomously finding their energy in the production of bacteria. Robert Freitas has also proposed microbivore robots that would attack pathogens in the manner of white blood cells. [ 8 ]
This zoology –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microbivory |
A microbody (or cytosome ) is a type of organelle that is found in the cells of plants, protozoa, and animals. Organelles in the microbody family include peroxisomes , glyoxysomes , glycosomes and hydrogenosomes . In vertebrates, microbodies are especially prevalent in the liver and kidney . Many membrane bound vesicles called microbodies that contain various enzymes, are present in both plant and animal cells.
Microbodies are different type of bodies present in the cytosol, also known as cytosomes. A microbody is usually a vesicle with a spherical shape, ranging from 0.2-1.5 micrometers in diameter. [ 1 ] Microbodies are found in the cytoplasm of a cell, but they are only visible with the use of an electron microscope . They are surrounded by a single phospholipid bilayer membrane and they contain a matrix of intracellular material including enzymes and other proteins, but they do not seem to contain any genetic material to allow them to self-replicate. [ 1 ]
Microbodies contain enzymes that participate in the preparatory or intermediate stages of biochemical reactions within the cell. This facilitates the breakdown of fats, alcohols and amino acids. Generally microbodies are involved in detoxification of peroxides and in photo respiration in plants. Different types of microbodies have different functions:
A peroxisome is a type of microbody that functions to help the body break down large molecules and detoxify hazardous substances. It contains enzymes like oxidase , react hydrogen peroxide as a byproduct of its enzymatic reactions. Within the peroxisome, hydrogen peroxide can then be converted to water by enzymes like catalase and peroxidase . Discovered and named by Christian de Duve .
Glyoxysomes are specialized peroxisomes found in plants and mold , which help to convert stored lipids into carbohydrates so they can be used for plant growth. In glyoxysomes the fatty acids are hydrolyzed to acetyl-CoA by peroxisomal β-oxidation enzymes. Besides peroxisomal functions, glyoxysomes also possess the key enzymes of the glyoxylate cycle .
Microbodies were first discovered and named in 1954 by Rhodin. [ 2 ] Two years later in 1956, Rouiller and Bernhard presented the first worldwide accepted images of microbodies in liver cells. [ 2 ] Then in 1965, Christian de Duve and coworkers isolated microbodies from the liver of a rat. De Duve also believed that the name microbody was too general and chose the name of peroxisome because of its relationship with hydrogen peroxide. [ 3 ] In 1967, Breidenbach and Beevers were the first to isolate microbodies from plants, which they named glyoxysomes because they were found to contain enzymes of the glyoxylate cycle . | https://en.wikipedia.org/wiki/Microbody |
Microbotics (or microrobotics ) is the field of miniature robotics , in particular mobile robots with characteristic dimensions less than 1 mm. The term can also be used for robots capable of handling micrometer size components.
Microbots were born thanks to the appearance of the microcontroller in the last decade of the 20th century, and the appearance of microelectromechanical systems (MEMS) on silicon, although many microbots do not use silicon for mechanical components other than sensors. The earliest research and conceptual design of such small robots was conducted in the early 1970s in (then) classified research for U.S. intelligence agencies . Applications envisioned at that time included prisoner of war rescue assistance and electronic intercept missions. The underlying miniaturization support technologies were not fully developed at that time, so that progress in prototype development was not immediately forthcoming from this early set of calculations and concept design. [ 1 ] As of 2008, the smallest microrobots use a scratch drive actuator . [ 2 ]
The development of wireless connections, especially Wi-Fi (i.e. in household networks ) has greatly increased the communication capacity of microbots, and consequently their ability to coordinate with other microbots to carry out more complex tasks. Indeed, much recent research has focused on microbot communication, including a 1,024 robot swarm at Harvard University that assembles itself into various shapes; [ 3 ] and manufacturing microbots at SRI International for DARPA's "MicroFactory for Macro Products" program that can build lightweight, high-strength structures. [ 4 ] [ 5 ]
Microbots called xenobots have also been built using biological tissues instead of metal and electronics. [ 6 ] Xenobots avoid some of the technological and environmental complications of traditional microbots as they are self-powered, biodegradable, and biocompatible.
While the "micro" prefix has been used subjectively to mean "small", standardizing on length scales avoids confusion. Thus a nanorobot would have characteristic dimensions at or below 1 micrometer, or manipulate components on the 1 to 1000 nm size range. [ citation needed ] A microrobot would have characteristic dimensions less than 1 millimeter, a millirobot would have dimensions less than a cm, a mini-robot would have dimensions less than 10 cm (4 in), and a small robot would have dimensions less than 100 cm (39 in). [ 7 ]
Many sources also describe robots larger than 1 millimeter as microbots or robots larger than 1 micrometer as nanobots. See also: Category:Micro robots
The way microrobots move around is a function of their purpose and necessary size. At submicron sizes, the physical world demands rather bizarre ways of getting around. The Reynolds number for airborne robots is less than unity; the viscous forces dominate the inertial forces , so “flying” could use the viscosity of air, rather than Bernoulli's principle of lift. Robots moving through fluids may require rotating flagella like the motile form of E. coli . Hopping is stealthy and energy-efficient; it allows the robot to negotiate the surfaces of a variety of terrains. [ 8 ] Pioneering calculations (Solem 1994) examined possible behaviors based on physical realities. [ 9 ]
One of the major challenges in developing a microrobot is to achieve motion using a very limited power supply . The microrobots can use a small lightweight battery source like a coin cell or can scavenge power from the surrounding environment in the form of vibration or light energy. [ 10 ] Microrobots are also now using biological motors as power sources, such as flagellated Serratia marcescens , to draw chemical power from the surrounding fluid to actuate the robotic device. These biorobots can be directly controlled by stimuli such as chemotaxis or galvanotaxis with several control schemes available. A popular alternative to an onboard battery is to power the robots using externally induced power. Examples include the use of electromagnetic fields, [ 11 ] ultrasound and light to activate and control micro robots. [ 12 ]
The 2022 study focused on a photo-biocatalytic approach for the "design of light-driven microrobots with applications in microbiology and biomedicine". [ 13 ] [ 14 ] [ 15 ]
Microrobots employ various locomotion methods to navigate through different environments, from solid surfaces to fluids. These methods are often inspired by biological systems and are designed to be effective at the micro-scale. [ 16 ] Several factors need to be maximized (precision, speed, stability), and others have to be minimized (energy consumption, energy loss) in the design and operation of microrobot locomotion in order to guarantee accurate, effective, and efficient movement. [ 17 ]
When describing the locomotion of microrobots, several key parameters are used to characterize and evaluate their movement, including stride length and transportation costs. A stride refers to a complete cycle of movement that includes all the steps or phases necessary for an organism or robot to move forward by repeating a specific sequence of actions. Stride length (𝞴 s ) is the distance covered by a microrobot in one complete cycle of its locomotion mechanism. Cost of transport (CoT) defines the work required to move a unit of mass of a microrobot a unit of distance [ 17 ]
Microrobots that use surface locomotion can move in a variety of ways, including walking, crawling, rolling, or jumping. These microrobots meet different challenges, such as gravity and friction. One of the parameters describing surface locomotion is the Frounde number, defined as:
F r = v 2 g ∗ λ s {\displaystyle Fr={\frac {v^{2}}{g*\lambda _{s}}}}
Where v is motion speed, g is the gravitational field, and 𝞴s is a stride length. A microrobot demonstrating a low Froude number moves slower and more stable as gravitational forces dominate, while a high Froude number indicates that inertial forces are more significant, allowing faster and potentially less stable movement. [ 17 ]
Crawling is one of the most typical surface locomotion types. The mechanisms employed by microrobots for crawling can differ but usually include the synchronized movement of multiple legs or appendages. The mechanism of the microrobots' movements is often inspired by animals such as insects, reptiles, and small mammals. An example of a crawling microrobot is RoBeetle. The autonomous microrobot weighs 88 milligrams (approximately the weight of three rice grains). The robot is powered by the catalytic combustion of methanol. The design relies on controllable NiTi-Pt–based catalytic artificial micromuscles with a mechanical control mechanism. [ 18 ]
Other options for actuating microrobots' surface locomotion include magnetic, electromagnetic, piezoelectric, electrostatic, and optical actuation.
Swimming microrobots are designed to operate in 3D through fluid environments, like biological fluids or water. To achieve effective movements, locomotion strategies are adopted from small aquatic animals or microorganisms, such as flagellar propulsion, pulling, chemical propulsion, jet propulsion, and tail undulation. Swimming microrobots, in order to move forward, must drive water backward. [ 17 ]
Microrobots move in the low Reynolds number regime due to their small sizes and low operating speeds, as well as high viscosity of the fluids they navigate. At this level, viscous forces dominate over inertial forces. This requires a different approach in the design compared to swimming at the macroscale in order to achieve effective movements. The low Reynolds number also allows for accurate movements, which makes it good application in medicine, micro-manipulation tasks, and environmental monitoring. [ 16 ] [ 17 ]
Dominating viscous ( Stokes ) drag forces T drag on the robot balances the propulsive force F p generated by a swimming mechanism.
T = T ( d r a g ) = b v m {\displaystyle T=T_{(}drag)={\frac {bv}{m}}}
Where b is the viscous drag coefficient, v is motion speed, and m is the body mass. [ 17 ]
One of the examples of a swimming microrobot is a helical magnetic microrobot consisting of a spiral tail and a magnetic head body. This design is inspired by the flagellar motion of bacteria. By applying a magnetic torque to a helical microrobot within a low-intensity rotating magnetic field, the rotation can be transformed into linear motion. This conversion is highly effective in low Reynolds number environments due to the unique helical structure of the microrobot. By altering the external magnetic field, the direction of the spiral microrobot's motion can be easily reversed. [ 19 ]
In the specific instance when microrobots are at the air-fluid interface, they can take advantage of surface tension and forces provided by capillary motion. At the point where air and a liquid, most often water, come together, it is possible to establish an interface capable of supporting the weight of the microrobots through the work of surface tension. Cohesion between molecules of a liquid creates surface tension, which otherwise creates ‘skin’ over the water’s surface, letting the microrobots float instead of sinking. Through such concepts, microrobots could perform specific locomotion functions, including climbing, walking, levitating, floating, and or even jumping, by exploring the characteristics of the air-fluid interface. [ 17 ] [ 20 ]
Due to the surface tension ,σ, the buoyancy force, F b , and the curvature force, F c , play the most important roles, particularly in deciding whether the microrobot will float or sink on the surface of the liquid. This can be expressed as
σ = F b + F c {\displaystyle \sigma =F_{b}+F_{c}}
F b is obtained by integrating the hydrostatic pressure over the area of the body in contact with the water. In contrast, F c is obtained by integrating the curvature pressure over this area or, alternatively, the vertical component of the surface tension, σ sin θ {\displaystyle \sigma \sin \theta } , along the contact perimeter. [ 21 ]
One example of a climbing, walking microrobot that utilizes air-fluid locomotion is the Harvard Ambulatory MicroRobot with Electroadhesion (HAMR-E). [ 22 ] The control system of HAMR-E is developed to allow the robot to function in a flexible and maneuverable manner in a challenging environment. Its features include its ability to move on horizontal, vertical, and inverted planes, which is facilitated by the electro-adhesion system. This uses electric fields to create electrostatic attraction, causing the robot to stick and move on different surfaces. [ 23 ] With four compliant and electro-adhesion footpads, HAMR-E can safely grasp and slide over various substrate types, including glass, wood, and metal. [ 22 ] The robot has a slim body and is fully posable, making it easy to perform complex movements and balance on any surface.
Flying microrobots are miniature robotic systems meticulously engineered to operate in the air by emulating the flight mechanisms of insects and birds. These microrobots have to overcome the issues related to lift, thrust, and movement that are challenging to accomplish at such a small scale where most aerodynamic theories must be modified. Active flight is the most energy-intensive mode of locomotion, as the microrobot must lift its body weight while propelling itself forward. [ 17 ] To achieve this function, these microrobots mimic the movement of insect wings and generate the necessary airflow for producing lift and thrust. Miniaturized wings of the robots are actuated with Piezoelectric materials, which offer better control of wing kinematics and flight dynamics. [ 24 ]
To calculate the necessary aerodynamic power for maintaining a hover with flapping wings, the primary physical equation is expressed as
m g = 2 ∗ ρ ∗ l 2 ∗ ϕ ∗ υ i 2 {\displaystyle mg=2*\rho *l^{2}*\phi *\upsilon _{i}^{2}}
where m is the body mass, L is the wing length, Φ represents the wing flapping amplitude in radians, ρ indicates the air density, and V i corresponds to the induced air speed surrounding the body, a consequence of the wings' flapping and rotation movements. This equation illustrates that a small insect or robotic device must impart sufficient momentum to the surrounding air to counterbalance its own weight. [ 25 ]
One example of a flying microrobot that utilizes flying locomotion is the RoboBee and DelFly Nimble, [ 26 ] [ 27 ] which, regarding flight dynamics, emulate bees and fruit flies, respectively. Harvard University invented the RoboBee, a miniature robot that mimics a bee fly, takes off and lands like one, and moves around confined spaces. It can be used in self-driving pollination and search operations for missing people and things. The DelFly Nimble, developed by the Delft University of Technology, is one of the most agile micro aerial vehicles that can mimic the maneuverability of a fruit fly by doing different tricks due to its minimal weight and advanced control mechanisms. [ 26 ] [ 27 ]
Due to their small size, microbots are potentially very cheap, and could be used in large numbers ( swarm robotics ) to explore environments which are too small or too dangerous for people or larger robots. It is expected that microbots will be useful in applications such as looking for survivors in collapsed buildings after an earthquake or crawling through the digestive tract. What microbots lack in brawn or computational power, they can make up for by using large numbers, as in swarms of microbots. Bioinspired microrobots have emerged as a game-changing tool in the quest for precise drug delivery. [ 28 ] These microscopic robots are designed to navigate the human body with a degree of precision previously unimaginable. [ 28 ]
Potential applications with demonstrated prototypes include:
Biohybrid microswimmers, mainly composed of integrated biological actuators and synthetic cargo carriers, have recently shown promise toward minimally invasive theranostic applications . [ 32 ] [ 33 ] [ 34 ] [ 35 ] Various microorganisms, including bacteria, [ 36 ] [ 37 ] microalgae , [ 38 ] [ 39 ] and spermatozoids , [ 40 ] [ 41 ] have been utilised to fabricate different biohybrid microswimmers with advanced medical functionalities, such as autonomous control with environmental stimuli for targeting, navigation through narrow gaps, and accumulation to necrotic regions of tumor environments. [ 42 ] Steerability of the synthetic cargo carriers with long-range applied external fields, such as acoustic or magnetic fields, [ 43 ] [ 44 ] and intrinsic taxis behaviours of the biological actuators toward various environmental stimuli, such as chemoattractants , [ 45 ] pH , and oxygen, [ 46 ] [ 47 ] make biohybrid microswimmers a promising candidate for a broad range of medical active cargo delivery applications. [ 42 ] [ 29 ]
For example, there are biocompatible microalgae -based microrobots for active drug-delivery in the brain, [ 28 ] lungs and the gastrointestinal tract, [ 48 ] [ 49 ] [ 50 ] and magnetically guided engineered bacterial microbots for 'precision targeting' [ 51 ] for fighting cancer [ 52 ] [ 53 ] that all have been tested with mice. | https://en.wikipedia.org/wiki/Microbotics |
A microcarrier is a support matrix that allows for the growth of adherent cells in bioreactors . Instead of on a flat surface, cells are cultured on the surface of spherical microcarriers so that each particle carries several hundred cells, and therefore expansion capacity can be multiplied several times over. [ 1 ] It provides a straightforward way to scale up culture systems for industrial production of cell or protein-based therapies , or for research purposes. [ 2 ] [ 3 ]
These solid or porous spherical matrices range anywhere between 100-300 um in diameter to allow sufficient surface area while retaining enough cell adhesion and support, and their density is minimally above that of water (1 g/ml) so that they remain in suspension in a stirred tank. [ 1 ] [ 4 ] They can be composed of either synthetic materials such as acrylamide or natural materials such as gelatin. [ 2 ] [ 3 ]
The advantages of microcarrier technology in the biotech industry include (a) ease of scale-up, (b) ability to precisely control cell growth conditions in sophisticated, computer-controlled bioreactors, (c) an overall reduction in the floor space and incubator volume required for a given-sized manufacturing operation, (d) a drastic reduction in technician labor, and (e) a more natural environment for cell culture that promotes differentiation. [ 5 ]
There are several types of microcarriers that can be used, the selection of which is crucial for optimal performance for the application. Early in microcarrier development history, synthetic materials were overwhelmingly used, as they allowed for easy control of mechanical properties and reproducible results for the evaluation of their performance. [ 3 ] These materials include DEAE-dextran, glass, polystyrene plastic, and acrylamide . [ 3 ] In 1967, microcarrier development began when van Wezel found that the material could support the growth of anchorage-dependent cells, and he used diethylaminoethyl–Sephadex microcarriers. [ 3 ] However, synthetic polymers prevent sufficient cell interactions with their environment and stunts their growth. [ 4 ] Cells may not differentiate properly without feedback from their environment, and attachment levels would be low. [ 3 ] Therefore, the second generation of microcarrier development involves use of natural polymers such as gelatin , collagen , chitin and its derivatives, and cellulose . [ 2 ] Not only are these materials easily obtained, but the natural materials provide attachment sites for cells and a similar microenvironment that provides the cell signaling pathways necessary for their proper differentiation. [ 3 ] Furthermore, as these are biocompatible, the resulting suspension can be used for delivery of cell therapies in vivo . [ 1 ]
Although liquid microcarriers have been developed, a large majority of commercially available microcarriers are solid particles, synthesized through suspension polymerization . [ 3 ] However, cells grown on solid microcarriers risk damage from external forces and collisions with other particles and the tank. [ 4 ] Therefore, extra precaution must be taken on determining the stir speed and mechanism, so that the resulting fluid dynamic forces are not strong enough to adversely affect culture. [ 4 ] [ 3 ] The development of porous microcarriers greatly expanded the capabilities of this technology as it further increased the number of cells that the material can hold, but more importantly, it shielded those within the particle from external forces. [ 3 ] These include drag and frictional forces of the suspension fluid, pressure gradients , and shear stresses . [ 1 ] The 1980s were marked with a wave of microcarrier development with the breakthrough of porous particles. [ 4 ]
Microcarriers of the same material can differ in their porosity, specific gravity , optical properties, presence of animal components, and surface chemistries. [ 4 ] Surface chemistries can include extracellular matrix proteins, functional groups , recombinant proteins, peptides , and positively or negatively charged molecules, added through conjugation , co-polymerization , plasma treatment or grafting. [ 3 ] These may serve to provide higher attachment levels of the cells to the particles, provide a controlled release for isolation, or make the particles more thermally and physically resistant, among other reasons. [ 3 ]
Several types of microcarriers are available commercially including alginate -based (GEM, Global Cell Solutions), dextran -based (Cytodex, GE Healthcare ), collagen -based (Cultispher, Percell), and polystyrene -based (SoloHill Engineering) microcarriers. [ 5 ]
A prominent advantage in using microcarrier suspensions for the culture of cells over traditional two-dimensional plates is its capacity to hold more cells in smaller volumes. [ 1 ] [ 6 ] A hallmark of regular cell culture lab protocol is continual passaging as the cells reach confluence on plates fairly quickly, a bottleneck in biologics production. [ 1 ] Multilayer vessels, stacked plates, hollow fibers , and packed bed reactors were other technologies developed to combat this capacity limit in plate cell culture. [ 1 ] [ 2 ] Although they were an improvement, cell numbers produced through these methods still did not reach the threshold for clinical applications. [ 2 ] Microcarrier cell culture, however, was the breakthrough required for cell culture to reach industrial and clinical significance. [ 2 ] Studies have shown that microcarrier suspensions, compared to multi-layer vessel culture, improve cell yield by 80-fold at only ten percent of Good Manufacturing Practice space, and only sixty percent of the original cost. [ 4 ] Without the need for continual passaging, there is less risk of bacterial contamination and labor costs are minimized as well. [ 2 ]
Two-dimensional culture also suffers from poor diffusivity of nutrients and gases, requiring added media and supplements to be manually evenly distributed, and may result in irreproducible data. [ 1 ] [ 2 ] Microcarrier cell suspensions in stirred tank bioreactors allows for an even distribution through homogenous stirring. [ 1 ] Parameters such as pH, oxygen pressure, and media supplement concentrations can be continually monitored within a bioreactor as opposed to manually testing small samples from plates. [ 2 ] However, high stir speeds can cause damaging collisions between particles and against the reactor, and too low of a speed can inhibit cell growth by causing an accumulation of particles in a ‘dead zone’ and preventing an even distribution of essential nutrients. [ 1 ] [ 4 ] Therefore, a minimum and maximum velocity gradients must be calculated so as to keep the suspension homogeneous but also sheltered from unnecessary forces. [ 2 ] [ 6 ] Often the most efficient mechanism for this is an axial stirrer within the bioreactor, which allows for efficient mixing at minimal stir speeds. [ 4 ] The homogenous nature of well-functioning bioreactors also allows for simple sampling and monitoring procedures, compared to two dimensional culture which often suffers from tedious sampling procedures. [ 4 ] [ 2 ] [ 6 ]
Furthermore, the three-dimensional and high-density suspension environment promotes natural cell morphology and differentiation through mechanical stimulation. [ 1 ] On the other hand, two-dimensional plate culture tends to de-differentiate cells over several passages and therefore total passage number must be limited. [ 1 ]
Microcarrier suspensions are also easily scaled up, through larger concentrations of microparticles in larger stirred tank reactors, while laboratory space used for culture can be still kept to a minimum. [ 2 ] However, a scale-up of the microcarrier platform also entails certain challenges in the downstream production process. [ 4 ] This includes a reworking of the cell detachment and isolation processes. [ 4 ] Larger volumes of suspension liquid must be removed from larger vats of bioreactors, and therefore more equipment must be purchased to handle tens to hundreds of liters of solution instead of the standard milliliter. [ 4 ]
Microcarriers are being investigated to deliver cells for targeted tissue engineering. [ 3 ] Hepatocytes, chondrocytes, fibroblasts and more have been successfully delivered using biocompatible microcarriers to in vivo targets for the repair of damaged tissues. [ 1 ] Microcarriers can also be used to deliver small molecules and proteins for the same purpose. [ 5 ]
A liquid-based assembly method was developed by P. Chen et al. for assembling cell-seeded microcarriers into diverse structures. Neuron -seeded microcarriers were assembled for formation of 3D neural networks with controlled global shape. This method is potentially useful for tissue engineering and neuroscience . [ 7 ] | https://en.wikipedia.org/wiki/Microcarrier |
Microcell Mediated Chromosome Transfer (or MMCT) is a technique used in cell biology and genetics to transfer a chromosome from a defined donor cell line into a recipient cell line. MMCT has been in use since the 1970s and has contributed to a multitude of discoveries including tumor , metastasis and telomerase suppressor genes as well as information about epigenetics , x-inactivation , mitochondrial function and aneuploidy . [ 1 ] [ 2 ] MMCT follows the basic procedure where donor cells (i.e. cells providing one or more chromosomes or fragments to a recipient cell) are induced to multinucleate their chromosomes. These nuclei are then forced through the cell membrane to create microcells, which can be fused to a recipient cell line. [ 1 ]
The term MMCT was first used by Fournier and Ruddle in 1977. [ 3 ] Their method was based on previous work from 1974 by Ege, Ringertz, Veomett and colleagues, [ 4 ] [ 5 ] synthesizing the techniques used at the time to induce multinucleation in cells, nuclear removal and cell-cell fusions. The next major step in MMCT came during the 1980s when new transfection techniques were utilized to introduce selectable markers onto chromosomes thus making it possible to select for the introduction of specific chromosomes and more easily create defined hybrids . [ 1 ]
Procedures for MMCT differ slightly but they all require: the induction of multinucleation, enucleation (nuclear removal), and fusion . Multinucleation is usually accomplished through causing prolonged mitotic arrest by colcemid treatment. Certain cells will then "slip" out of mitosis and form multiple nuclei. These nuclei can then be removed using cytochalasin B to disrupt the cytoskeleton and centrifugation in a density gradient to force enucleation. The newly created microcells can then be fused to recipient (target) cells by exposure to poly ethylene glycol, use of Sendai virus, or electrofusion. [ 1 ] [ 6 ]
Variations now allow construction of "humanized" mice with large pieces from human chromosomes [ 7 ] as well as new methods for human and mouse artificial chromosomes. [ 8 ] | https://en.wikipedia.org/wiki/Microcell-mediated_chromosome_transfer |
Microchannel in microtechnology is a channel with a hydraulic diameter below 1 mm, usually 1–99 μm. [ 1 ] Microchannels are used in fluid control (see Microfluidics ), heat transfer (see Micro heat exchanger ) and cell migration observation. [ 2 ] They are more efficient than their 'macro' counterparts, because of a high surface-area to volume ratio yet pose a multitude of challenges due to their small size. [ 3 ]
Different types of materials are required for the different uses of microchannels. These are the three main categories. [ 4 ]
Polymethyl methacrylate (PMMA) is used as a solution to a wide range of microfluidic devices due to its low cost and easier fabricating methods. [ 4 ] Silicon elastomers can be used for situations in which elasticity and deformation is necessary. [ 5 ]
Metallic substrates are often chosen for their advantageous metallic properties , such as withstanding high temperatures and transferring heat faster. They can be subject to corrosion . [ 4 ] [ 6 ]
Ceramic materials allow for high-temperature operation in comparison to metallic substrates and enable operation in harsh chemical environments in which metals cannot be used. [ 7 ]
The concept of the microchannel was proposed for the first time by researchers Tuckerman and Pease of Stanford Electronics Laboratories in 1981. [ 8 ] They suggested an effective method for designing microchannels in the laminar and fully developed flow. [ 9 ]
Microchannels are extensively used in the pharmaceuticals, and biochemical industries due to short diffusion distances, higher interfacial area, and higher heat/mass transfer rates. [ 10 ]
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microchannel_(microtechnology) |
A microchannel plate ( MCP ) is used to detect single particles ( electrons , ions and neutrons [ 1 ] ) and photons ( ultraviolet radiation and X-rays ). It is closely related to an electron multiplier , as both intensify single particles or photons by the multiplication of electrons via secondary emission . [ 2 ] Because a microchannel plate detector has many separate channels, it can provide spatial resolution.
A microchannel plate is a slab made from resistive material (most often glass) 0.5 to 2mm thick with a regular array of tiny tubes (microchannels) leading from one face to the other. The microchannels are typically 5-20 micrometers in diameter, parallel to each other and enter the plate at a small angle to the surface (8-13° from normal ). Plates are often round disks, but can be cut to any shape from sizes 10mm up to 200mm. They may also be curved.
At non-relativistic energies, single particles generally produce effects too small to enable their direct detection. The microchannel plate functions as a particle amplifier, turning a single impinging particle into a cloud of electrons. By applying a strong electric field across the MCP, each individual microchannel becomes a continuous-dynode electron multiplier .
A particle or photon that enters one of the channels through a small orifice is guaranteed to hit the wall of the channel, due to the channel being at an angle to the plate. The impact starts a cascade of electrons that propagates through the channel, amplifying the original signal by several orders of magnitude, depending on the electric field strength and the geometry of the microchannel plate. After the cascade, the microchannel takes time to recover (or recharge) before it can detect another signal.
The electrons exit the channels on the opposite side of the plate, where they are collected on an anode. Some anodes are designed to allow spatially resolved ion collection, producing an image of the particles or photons incident on the plate.
Although in many cases the collecting anode functions as the detecting element, the MCP itself can also be used as a detector. The discharging and recharging of the plate produced by the electron cascade, can be decoupled from the high voltage applied to the plate and measured, to directly produce a signal corresponding to a single particle or photon.
The gain of an MCP is very noisy, meaning that two identical particles detected in succession will often produce wildly different signal magnitudes. The temporal jitter resulting from the peak height variation can be removed by using a constant fraction discriminator . Thusly employed, MCPs are capable of measuring particle arrival times with high resolution, making them ideal detectors for mass spectrometers .
Most modern MCP detectors consist of two microchannel plates with angled channels, rotated 180° from each other - producing a shallow chevron (v-like) shape. In a chevron MCP, the electrons that exit the first plate start the cascade in the next plate. The angle between the channels reduces ion feedback in the device, as well as producing significantly more gain at a given voltage, compared to a straight channel MCP. The two MCPs can either be pressed together to preserve spatial resolution, or have a small gap between them to spread the charge across multiple channels, which further increases the gain.
This is an assembly of three microchannel plates with channels aligned in a Z shape. Single MCPs can have gain up to 10,000 (40 dB ) but this system can provide gain more than 10 million (70 dB ). [ 3 ]
An external voltage divider is used to apply 100 volts to the acceleration optics (for electron detection), each MCP, the gap between the MCPs, the backside of the last MCP, and the collector ( anode ). The last voltage dictates the time of flight of the electrons and in this way, the pulse-width .
The anode is a 0.4 mm thick plate with an edge of 0.2 mm radius to avoid high field strengths. It is just large enough to cover the active area of the MCP, because the backside of the last MCP, and the anode, together act as a capacitor with 2 mm separation - and large capacitance slows down the signal. The positive charge in the MCP influences positive charge in the backside metalization. A hollow torus conducts this around the edge of the anode plate. A torus is the optimum compromise between low capacitance and short path and for similar reasons, usually no dielectric (Markor) is placed into this region. After a 90° turn of the torus it is possible to attach a large coaxial waveguide . A taper permits minimizing the radius so that an SMA connector can be used. To save space and make the impedance match less critical, the taper is often reduced to a small 45° cone on the backside of the anode plate.
The typical 500 volts between the backside of the last MCP and the anode cannot be fed directly into the preamplifier; the inner or the outer conductor needs a DC block , that is, a capacitor. Often it is chosen to only have 10-fold capacitance compared to the MCP-anode capacitance and is implemented as a plate capacitor. Rounded, electro-polished metal plates and the ultra high vacuum allow very high field strengths and high capacitance without a dielectric. The bias for the center conductor is applied via resistors hanging through the waveguide (see bias tee ). If the DC block is used in the outer conductor, it is aligned in parallel with the larger capacitor in the power supply. Assuming good screening, the only noise is due to current noise from the linear power regulator. Because the current is low in this application and space for large capacitors is available, and because the DC-block capacitor is fast, it is possible to have very low voltage noise, so that even weak MCP signals can be detected. Sometimes the preamplifier is on a potential ( off ground ) and gets its power through a low-power isolation transformer and outputs its signal optically .
The gain of an MCP is very noisy, especially for single particles. With two thick MCPs (>1 mm) and small channels (< 10 μm), saturation occurs, especially at the ends of the channels after many electron multiplications have taken place. The last stages of the following semiconductor amplifier chain also go into saturation. A pulse of varying length, but stable height and a low jitter leading edge is sent to the time to digital converter . The jitter can be further reduced by means of a constant fraction discriminator . That means that the MCP and the preamplifier are used in the linear region (space charge negligible) and the pulse shape is assumed to be due to an impulse response , with variable height but fixed shape, from a single particle.
Because MCPs have a fixed charge that they can amplify in their life, the second MCP especially, has a lifetime problem. [ 4 ] It is important to use thin MCPs, low voltage and instead of greater voltage, more sensitive and fast semiconductor amplifiers after the anode. [ citation needed ] (see: Secondary emission#Special amplifying tubes , [ 5 ] [ 6 ] [ 7 ] ).
With high count rates or slow detectors (MCPs with phosphor screen or discrete photomultipliers ), pulses overlap. In this case, a high impedance (slow, but less noisy) amplifier and an ADC are used. Since the output signal from the MCP is generally small, the presence of the thermal noise limits the measurement of the time structure of the MCP signal. With fast amplification schemes, however, it is possible to have valuable information on the signal amplitude even at very low signal levels, yet not on the time structure information of the wideband signals.
In a delay line detector the electrons are accelerated to 500 eV between the back of the last MCP and a grid. They then fly for 5 mm and are dispersed over an area of 2 mm. A grid follows. Each element has a diameter of 1 mm and consists of an electrostatic lens focusing arriving electrons through a 30 μm hole of a grounded sheet of aluminium. Behind that, a cylinder of the same size follows. The electron cloud induces a 300 ps negative pulse when entering the cylinder and a positive when leaving. After that another sheet, a second cylinder follows, and a last sheet follows. Effectively the cylinders are fused into the center-conductor of a stripline . The sheets minimize cross talk between the layers and adjacent lines in the same layer, which would lead to signal dispersion and ringing. These striplines meander across the anode to connect all cylinders, to offer each cylinder 50 Ω impedance, and to generate a position dependent delay. Because the turns in the stripline adversely affect the signal quality their number is limited and for higher resolutions multiple independent striplines are needed. At both ends the meanders are connected to detector electronics. These electronics convert the measured delays into X- (first layer) and Y-coordinates (second layer). Sometimes a hexagonal grid and 3 coordinates are used. This redundancy reduces the dead space-time by reducing the maximum travel distance and thus the maximum delay, allowing for faster measurements. The microchannel plate detector must not operate over around 60 degree Celsius, otherwise it will degrade rapidly, bakeout without voltage has no influence. [ citation needed ]
The mass-market application of microchannel plates is in image intensifier tubes of night vision goggles , which amplify visible and invisible light to make dark surroundings visible to the human eye . MCP detectors are often employed in instrumentation for physical research, and they can be found in devices such as electron and mass spectrometers .
A 1 GHz real-time display CRT for an analog oscilloscope (the Tektronix 7104) used a microchannel plate placed behind the phosphor screen to intensify the image. Without the plate, the image would be excessively dim because of the electron-optical design. | https://en.wikipedia.org/wiki/Microchannel_plate_detector |
Microchimerism is the presence of a small number of cells in an individual that have originated from another individual and are therefore genetically distinct. This phenomenon may be related to certain types of autoimmune diseases although the responsible mechanisms are unclear. The term comes from the prefix "micro" + "chimerism" based on the hybrid Chimera of Greek mythology. The concept was first discovered in the 1960s with the term gaining usage in the 1970s. [ 1 ]
In humans (and perhaps in all placental mammals ), the most common form is fetomaternal microchimerism (also known as fetal cell microchimerism or fetal chimerism ) whereby cells from a fetus pass through the placenta and establish cell lineages within the mother. Fetal cells have been documented to persist and multiply in the mother for several decades. [ 2 ] [ 3 ] The exact phenotype of these cells is unknown, although several different cell types have been identified, such as various immune lineages, mesenchymal stem cells , and placental-derived cells. [ 4 ] A 2012 study at the Fred Hutchinson Cancer Research Center , Seattle, has detected cells with the Y chromosome in multiple areas of the brains of deceased women. [ 5 ]
Fetomaternal microchimerism occurs during pregnancy and shortly after giving birth for most women. However, not all women who have had children contain fetal cells. Studies suggest that fetomaternal microchimerism could be influenced by killer-cell immunoglobulin-like (KIR) ligands . [ 6 ] Lymphocytes also influence the development of persisting fetomaternal microchimerism since natural killer cells compose about 70% of lymphocytes in the first trimester of pregnancy. KIR patterns on maternal natural killer cells of the mother and KIR ligands on the fetal cells could have an effect on fetomaternal microchimerism. In one study, mothers with KIR2DS1 exhibited higher levels of fetomaternal microchimerism compared to mothers who were negative for this activating KIR. [ 6 ]
The potential health consequences of these cells are unknown. One hypothesis is that these fetal cells might trigger a graft-versus-host reaction leading to autoimmune disease . This offers a potential explanation for why many autoimmune diseases are more prevalent in middle-aged women. [ 7 ] Another hypothesis is that fetal cells home to injured or diseased maternal tissue where they act as stem cells and participate in repair. [ 8 ] [ 9 ] It is also possible that the fetal cells are merely innocent bystanders and have no effect on maternal health. [ 10 ]
After giving birth, about 50–75% of women carry fetal immune cell lines. Maternal immune cells are also found in the offspring yielding in maternal→fetal microchimerism , though this phenomenon is about half as frequent as the former. [ 11 ]
Microchimerism had also been shown to exist after blood transfusions to a severely immunocompromised population of patients who suffered trauma . [ 12 ]
Other possible sources of microchimerism include gestation , [ 13 ] an individual's older sibling, twin sibling, or vanished twin, with the cells being received in utero. Fetal-maternal microchimerism is especially prevalent after abortion or miscarriage. [ 14 ]
Microchimerism occurs in most pairs of twins in cattle . In cattle (and other bovines ), the placentas of fraternal twins usually fuse and the twins share blood circulation, resulting in exchange of cell lines. If the twins are a male–female pair, then XX/XY microchimerism results, and male hormones partially masculinize the heifer (female), creating a martin heifer or freemartin . Freemartins appear female, but are infertile and so cannot be used for breeding or dairy production . Microchimerism provides a method of diagnosing the condition, because male genetic material can be detected in a blood sample. [ 15 ]
Several studies have identified male DNA in the brains of both humans and mice who have previously been pregnant with a male fetus. [ 16 ] [ 17 ] It has been suggested that the fetal-derived cells can differentiate into those capable of presenting immunomarkers on their surface. [ 16 ] There has been no strong evidence to say microchimerism of the maternal brain leads to disease; however, Parkinson's disease correlates with a higher incidence of brain microchimeras. [ 16 ] Alzheimer's disease studies support nearly the opposite correlation: the more fetal-derived cells present, the lower the chance of the patient having had Alzheimer's. [ 17 ]
There are many mechanisms at the maternal-fetal interface to prevent immune rejection of fetal cells. Nevertheless, systemic immunological changes occur in pregnant women. For example, condition of women suffering from autoimmune disorders (e.g. rheumatoid arthritis, multiple sclerosis) improves during pregnancy. [ 18 ] [ 19 ] These changes in immune responses during pregnancy extend to maternal components specific to fetal antigens, because of feto-maternal cell transfer and their retention in mother tissues.
During pregnancy, numbers of fetal cells in maternal tissues increase and correlate with expansion of CD4+ regulatory T cells (Tregs). [ 20 ] Decreased expansion and decidual accumulation of Treg cause pregnancy complications (preeclampsia, abortions). [ 20 ] In mice models, most mother's fetal-specific CD8+ T cells undergo clonal deletion [ 21 ] and express low levels of chemokine receptors and ligands – this prevents remaining fetal-specific CD8+ T cells from entering the maternal-fetal interface. [ 22 ] [ 23 ] Mother's fetal-specific CD4+ T cells proliferate, and due to FOXP3 expression, differentiate into Treg cells. [ 24 ] Mice models show that fetal-specific Treg cells are necessary for successful pregnancy. [ 25 ]
Fetal T cells accumulate during in utero development. Even though the fetus is exposed to noninherited maternal antigens (NIMAs), fetal CD4 + T cells are capable of alloantigen-induced proliferation, preferentially differentiating to Treg cells and preventing a fetal immune response to maternal antigens. [ 26 ] This expanded immune tolerance persists in both mother and offspring after birth and allows microchimeric cells to be retained in tissues.
NIMA-specific tolerance causes some interesting immunological phenotypes: sensitization to erythrocyte Rhesus factor (Rh) antigens is reduced among Rh- women born to Rh+ women, [ 27 ] long-term kidney allograft survival is improved in NIMA-matched donor-recipient sibling pairs, [ 28 ] or acuteness of bone marrow transplantation graft-versus-host disease is reduced, when recipients of donor stem cells are NIMA-matched. [ 29 ] Cross-fostering animal studies show that when postnatal NIMA exposure though breastfeeding is eliminated, survival of NIMA-matched allografts is reduced. This suggests that to maintain NIMA-specific tolerance in offspring, breastfeeding is essential, but ingestion of mother's cells alone does not prime NIMA-specific tolerance. Both prenatal and postnatal exposure to mother's cells is required to maintain NIMA-specific tolerance. [ 30 ]
The severity of preexisting autoimmune disorders is reduced during pregnancy and it is most apparent when fetal microchimeric cells levels are highest - during the last trimester. [ 31 ] [ 19 ] These cells can also replace injured maternal cells and recover tissue function (type I diabetes mouse model showed replacement of defective maternal islet cells by fetal-derived pancreatic cells [ 32 ] ). Fetal microchimeric cells can differentiate into cell types that infiltrate and replace injured cells in models of Parkinson's disease or myocardial infarction. They also help in wound healing by neoangiogenesis. Seeding of fetal microchimeric cells into maternal tissues has been proposed to promote care of offspring after birth (seeding of maternal breast tissue may promote lactation, and seeding of brain may enhance maternal attention). [ 30 ]
Microchimerism has been implicated in autoimmune diseases. Independent studies repeatedly suggested that microchimeric cells of fetal origin may be involved in the pathogenesis of systemic sclerosis . [ 3 ] [ 33 ] Moreover, microchimeric cells of maternal origin may be involved in the pathogenesis of a group of autoimmune diseases found in children, i.e. juvenile idiopathic inflammatory myopathies (one example would be juvenile dermatomyositis ). [ 34 ] Microchimerism has now been further implicated in other autoimmune diseases, including systemic lupus erythematosus . [ 35 ] Contrarily, an alternative hypothesis on the role of microchimeric cells in lesions is that they may be facilitating tissue repair of the damaged organ. [ 36 ]
Moreover, fetal immune cells have also been frequently found in breast cancer stroma as compared to samples taken from healthy women. It is not clear, however, whether fetal cell lines promote the development of tumors or, contrarily, protect women from developing breast carcinoma. [ 37 ] [ 38 ]
The presence of fetal cells in mothers can be associated with benefits when it comes to certain autoimmune diseases. In particular, male fetal cells are related to helping mothers with systemic lupus erythematosus . When kidney biopsies were taken from patients with lupus nephritis, DNA was extracted and run with PCR . The male fetal DNA was quantified and the presence of specific Y chromosome sequences were found. Women with lupus nephritis containing male fetal cells in their kidney biopsies exhibited better renal system functioning. Levels of serum creatinine , which is related to kidney failure, were low in mothers with high levels of male fetal cells. [ 39 ] In contrast, women without male fetal cells who had lupus nephritis showed a more serious form of glomerulonephritis and higher levels of serum creatinine. [ 39 ]
The specific role that fetal cells play in microchimerism related to certain autoimmune diseases is not fully understood. However, one hypothesis states that these cells supply antigens , causing inflammation and triggering the release of different foreign antigens. [ 39 ] This would trigger autoimmune disease instead of serving as a therapeutic. A different hypothesis states that fetal microchimeric cells are involved in repairing tissues. When tissues get inflamed, fetal microchimeric cells go to the damaged site and aid in repair and regeneration of the tissue. [ 39 ]
Fetal maternal microchimerism may be related to autoimmune thyroid diseases. There have been reports of fetal cells in the lining of the blood and thyroid glands of patients with autoimmune thyroid disease. These cells could become activated after delivery of the baby after immune suppression in the mother is lost, suggesting a role of fetal cells in the pathogenesis of such diseases. [ 40 ] Two types of thyroid disease, Hashimoto's thyroiditis (HT) and Graves' disease (GD), show similarities to graft vs host disease which occurs after hematopoietic stem cell transplants. Fetal cells colonize maternal tissues like the thyroid gland and are able to survive many years postpartum. These fetal microchimeric cells in the thyroid show up in the blood of women affected by thyroid diseases. [ 40 ]
Sjögren syndrome (SS) is an autoimmune rheumatic disease of the exocrine glands. Increased incidence of SS after childbirth suggests a relationship between SS and pregnancy, and this led to the hypothesis that fetal microchimerism may be involved in SS pathogenesis. Studies showed the presence of Y-chromosome-positive fetal cells in minor salivary glands in 11 of 20 women with SS but in only one of eight normal controls. Fetal cells in salivary glands suggest that they may be involved in the development of SS. [ 41 ]
Lichen planus (LP) is a T-cell-mediated autoimmune chronic disease of unknown etiology. Females have a three times higher prevalence than men. LP is characterized by T lymphocytes infiltration of the lower levels of epithelium, where they damage basal cells and cause apoptosis. The fetal microchimerism may trigger a fetus versus host reaction and therefore may play a role in the pathogenesis of autoimmune diseases including LP. [ 42 ]
Pregnancy has a positive effect on the prognosis of breast cancer according to several studies [ 43 ] [ 44 ] [ 45 ] and it apparently increases the chance of survival after diagnosis of breast cancer. [ 46 ] Possible positive effects of pregnancy could be explained by the persistence of fetal cells in the blood and maternal tissues. [ 2 ]
Fetal cells are probably actively migrating from peripheral blood into the tumor tissue [ 47 ] where they are preferentially settled in the tumor stroma [ 38 ] and one their concentration decreases as they get closer to the healthy breast tissue. [ 48 ] There are two suggested mechanisms by which the fetal cells could have the positive effect on the breast cancer prognosis. The first mechanism suggests that fetal cells only oversee cancer cells and they attract components of the immune system if needed. The second option is that the down-regulation of the immune system induced by the presence of fetal cells could ultimately lead to cancer prevention, because women in whom FMC is present produce lower concentrations of inflammatory mediators, which may lead to the development of neoplastic tissue. [ 49 ]
The effect also depends on the level of microchimerism: Hyperchimerism (a high rate of microchimerism) and hypochimerism (a low rate of microchimerism) can be related to the negative effect of FMC and thus can promote a worse prognosis of breast cancer. [ 50 ] [ 51 ] Apparently, women with breast cancer may fail in the process of obtaining and maintaining allogeneic fetal cells. Low concentration and / or complete absence of fetal cells could indicate a predisposition to development of the malignant process.
Study of S. Hallum shows association between male origin fetal cells and ovarian cancer risk. Presence of Y chromosome was used to detect foreign cells in women's blood. Microchimerism is a result of pregnancy, possibility that foreign cells were of transfusion or transplantation origin was rejected due to women's health. Women testing positive for male origin microchimerism cells had reduced hazard rates of ovarian cancer than women testing negative. [ 52 ] Pregnancy at older ages can reduce risk of ovarian cancer. Numbers of microchimeric cells declines after pregnancy, and ovarian cancer is most frequent in postmenopausal women. This suggests that fetal microchimerism may play a protective role in ovarian cancer as well.
Microchimeric cells also cluster several times more in lung tumors than in surrounding healthy lung tissue. Fetal cells from the bone marrow go to the tumor sites where they may have tissue repair functions. [ 53 ] Microchimerism of fetomaternal cell trafficking origin might be associated with the pathogenesis or progression of cervical cancer. Male cells were observed in patients with cervical cancer but not in positive controls. Microchimeric cells might induce the alteration of the woman's immune system and make the cervical tissue more susceptible to HPV infection or provide a suitable environment for tumor growth. [ 54 ]
Microchimeric fetal cells expressed collagen I, III and TGF-β3, and they were identified in healed maternal cesarean section scars. This suggests that these cells migrate to the site of damage due to maternal skin injury signals, and help repair tissue. [ 55 ]
Fetomaternal microchimerism has been shown in experimental investigations of whether fetal cells can cross the blood brain barrier in mice. The properties of these cells allow them to cross the blood brain barrier and target injured brain tissue. [ 56 ] This mechanism is possible because umbilical cord blood cells express some proteins similar to neurons . When these umbilical cord blood cells are injected in rats with brain injury or stroke, they enter the brain and express certain nerve cell markers. Due to this process, fetal cells could enter the brain during pregnancy and become differentiated into neural cells. Fetal microchimerism can occur in the maternal mouse brain , responding to certain cues in the maternal body. [ 56 ]
Fetal microchimerism could have an implication on maternal health. Isolating cells in cultures can alter the properties of the stem cells, but in pregnancy the effects of fetal stem cells can be investigated without in vitro cultures. Once characterized and isolated, fetal cells that are able to cross the blood brain barrier could impact certain procedures. [ 56 ] For example, isolating stem cells can be accomplished through taking them from sources like the umbilical cord. These fetal stem cells can be used in intravenous infusion to repair the brain tissue. Hormonal changes in pregnancy alter neurogenesis, which could create favorable environments for fetal cells to respond to injury. [ 56 ]
The true function on fetal cells in mothers is not fully known, however, there have been reports of positive and negative health effects. The sharing of genes between the fetus and mother may lead to benefits. Due to not all genes being shared, health complications may arise as a result of resource allocation. [ 57 ] During pregnancy, fetal cells are able to manipulate the maternal system to draw resources from the placenta, while the maternal system tries to limit it. [ 57 ] | https://en.wikipedia.org/wiki/Microchimerism |
Micrococcal nuclease ( EC 3.1.31.1 , S7 Nuclease , MNase , spleen endonuclease , thermonuclease , nuclease T , micrococcal endonuclease , nuclease T' , staphylococcal nuclease , spleen phosphodiesterase , Staphylococcus aureus nuclease , Staphylococcus aureus nuclease B , ribonucleate (deoxynucleate) 3'-nucleotidohydrolase ) is an endo - exonuclease that preferentially digests single-stranded nucleic acids . The rate of cleavage is 30 times greater at the 5' side of A or T than at G or C and results in the production of mononucleotides and oligonucleotides with terminal 3'- phosphates . The enzyme is also active against double-stranded DNA and RNA and all sequences will be ultimately cleaved.
The enzyme has a molecular weight of 16.9kDa.
The pH optimum is reported as 9.2. The enzyme activity is strictly dependent on Ca 2+ and the pH optimum varies according to Ca 2+ concentration. [ 1 ] The enzyme is therefore easily inactivated by EGTA .
This enzyme is the extracellular nuclease of Staphylococcus aureus . Two strains, V8 and Foggi, yield almost identical enzymes. [ 2 ] A common source is E.coli cells carrying a cloned nuc gene encoding Staphylococcus aureus extracellular nuclease (micrococcal nuclease).
The 3-dimensional structure of micrococcal nuclease (then called Staphyloccal nuclease) was solved very early in the history of protein crystallography , in 1969, [ 3 ] deposited as now-obsolete Protein Data Bank file 1SNS. Higher-resolution, more recent crystal structures are available for the apo form as Protein Data Bank file 1SNO: [1] and for the thymidine-diphosphate-inhibited form as Protein Data Bank file 3H6M: [2] or 1SNC: [3] . As seen in the ribbon diagram above, the nuclease molecule has 3 long alpha helices and a 5-stranded, barrel-shaped beta sheet , in an arrangement known as the OB-fold (for oligonucleotide-binding fold) as classified in the SCOP database. | https://en.wikipedia.org/wiki/Micrococcal_nuclease |
A microcoil is a tiny electrical conductor such as a wire in the shape of a spiral or helix which could be a solenoid or a planar structure.
One field where these are found is nuclear magnetic resonance (NMR) spectroscopy, where it identifies radio frequency ( RF ) coils that are smaller than 1 mm. [ 3 ]
The detection limits of micro-MRI or MRM can be pushed further by taking advantage of microsystem fabrication techniques. In general, the RF receiver coil should closely conform to the sample to ensure good detection sensitivity. A properly designed NMR probe will maximize both the observe factor, which is the ratio of the sample volume being observed by the RF coil to the total sample volume required for analysis, and the filling factor, the ratio of the sample volume being observed by the RF coil to the coil volume. [ 4 ]
The miniaturization of NMR probes thus involves two advantages:
In the field of quantum sciences , microcoils play an increasing role for fast spin control in nanoscale devices as multi-qubit spin registers and quantum memories or for the actuation of single nuclear spins e.g. around a Nitrogen-vacancy center . [ 7 ] In contrast to traditional NMR, microcoils are used here as an actuator only. The nuclear spin signal is detected via the optical readout of a single electron spin.
Microcoils have found usefulness in telemetry systems, where planar microcoils are used to supply energy to miniaturized implants. [ 8 ]
Different types of microcoils with different fabrication techniques are employed for NMR:
Is the classical geometry to create a magnetic field with an electric current . Even for a limited number of windings this geometry provides a reasonable homogeneous B 1 field and a good filling factor is possible by winding the coil directly onto a holder containing the sample. Miniaturization to a scale of several hundred micrometers (μm) is not very difficult although the wire diameter (typically 20 to 50 μm) becomes very small and a freestanding coil is a very delicate object. [ 9 ] A reduction to below 100 μm diameter is possible but the machining and handling of such coils will be rather tedious. For this reason other microsystem fabrication technology such as bulk micromachining , LIGA and micro-injection molding should be applied. [ 5 ] For solenoid coils adding more turns to the coil will enhance the B 1 /i ratio and thus both the inductance and the signal response. At the same time the coil resistance will increase linearly, so the improvement in sensitivity will be proportional to the square root of the number of turns (n). At the same time we will have a larger ohmic heating at the center of
the coil and an enhanced danger for arcing, so the optimum is generally found for only a limited number of turns. Besides RF performance, static field distortions due to susceptibility effects are an important factor in the design of microcoil probeheads.
Is the most common geometry used, based on a spiral design with the center winding contacted to the outside using a connection to another layer which is electrically isolated with a thin oxide layer. In this configuration the axis of the RF coil will be oriented perpendicular to the external static field B 0 .
The saddle coil shows the most complex geometry of these three coil types.
The B 1 field is generated primarily by the four vertical wire segments. Because of this coil geometry, the B 1 field of a saddle coil is more homogeneous in z direction than that of a planar coil. The saddle coil can be formed from wire, but it is also often etched from thin copper foil, which is then adhered to glass or PTFE tubing. The latter procedure leads to a high geometric precision, resulting in better B 1 homogeneity. The saddle coil is easily accessible and provides a good ‘filling factor’ of the usable area in the magnet bore. For these reasons it is widely used in NMR microscopy. However, these advantages are achieved at the price of decreased sensitivity. Compared to a saddle coil, the sensitivity performance of a solenoidal coil of the same dimensions is approximately three times better. [ 10 ]
Self-assembled rolled-up micro coils with diameters down to 50 μm have been developed for NMR microscopy. [ 11 ] | https://en.wikipedia.org/wiki/Microcoil |
A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor . [ 2 ] The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PCB). [ 3 ] Microcomputers became popular in the 1970s and 1980s with the advent of increasingly powerful microprocessors. The predecessors to these computers, mainframes and minicomputers , were comparatively much larger and more expensive (though indeed present-day mainframes such as the IBM System z machines use one or more custom microprocessors as their CPUs). Many microcomputers (when equipped with a keyboard and screen for input and output) are also personal computers (in the generic sense). An early use of the term "personal computer" in 1962 predates microprocessor-based designs. (See "Personal Computer: Computers at Companies" reference below) . A "microcomputer" used as an embedded control system may have no human-readable input and output devices. "Personal computer" may be used generically or may denote an IBM PC compatible machine.
The abbreviation "micro" was common during the 1970s and 1980s, [ 4 ] but has since fallen out of common usage.
The term microcomputer came into popular use after the introduction of the minicomputer , although Isaac Asimov used the term in his short story " The Dying Night " as early as 1956 (published in The Magazine of Fantasy and Science Fiction in July that year). [ 5 ] Most notably, the microcomputer replaced the many separate components that made up the minicomputer's CPU with one integrated microprocessor chip .
In 1973, the French Institut National de la Recherche Agronomique (INRA) was looking for a computer able to measure agricultural hygrometry . To answer this request, a team of French engineers of the computer technology company R2E, led by its Head of Development, François Gernelle , created the first available microprocessor-based microcomputer, the Micral N. The same year the company filed their patents with the term "Micro-ordinateur", a literal equivalent of "Microcomputer", to designate a solid state machine designed with a microprocessor.
In the US the earliest models such as the Altair 8800 were often sold as kits to be assembled by the user, and came with as little as 256 bytes of RAM , and no input/output devices other than indicator lights and switches, useful as a proof of concept to demonstrate what such a simple device could do. [ 6 ] As microprocessors and semiconductor memory became less expensive, microcomputers grew cheaper and easier to use.
All these improvements in cost and usability resulted in an explosion in their popularity during the late 1970s and early 1980s.
A large number of computer makers packaged microcomputers for use in small business applications. By 1979, many companies such as Cromemco , Processor Technology , IMSAI , North Star Computers , Southwest Technical Products Corporation , Ohio Scientific , Altos Computer Systems , Morrow Designs and others produced systems designed for resourceful end users or consulting firms to deliver business systems such as accounting, database management and word processing to small businesses. This allowed businesses unable to afford leasing of a minicomputer or time-sharing service the opportunity to automate business functions, without (usually) hiring a full-time staff to operate the computers. A representative system of this era would have used an S100 bus , an 8-bit processor such as an Intel 8080 or Zilog Z80 , and either CP/M or MP/M operating system.
The increasing availability and power of desktop computers for personal use attracted the attention of more software developers. As the industry matured, the market for personal computers standardized around IBM PC compatibles running DOS , and later Windows . Modern desktop computers, video game consoles , laptops , tablet PCs , and many types of handheld devices , including mobile phones , pocket calculators , and industrial embedded systems , may all be considered examples of microcomputers according to the definition given above.
By the early 2000s, everyday use of the expression "microcomputer" (and in particular "micro") declined significantly from its peak in the mid-1980s. [ 7 ] The term is most commonly associated with the most popular 8-bit home computers (such as the Apple II , ZX Spectrum , Commodore 64 , BBC Micro , and TRS-80 ) and small-business CP/M -based microcomputers.
In colloquial usage, "microcomputer" has been largely supplanted by the term " personal computer " or "PC", which specifies a computer that has been designed to be used by one individual at a time, a term first coined in 1959. [ 8 ] IBM first promoted the term "personal computer" to differentiate the IBM PC from CP/M -based microcomputers likewise targeted at the small-business market, and also IBM's own mainframes and minicomputers. [ citation needed ] However, following its release, the IBM PC itself was widely imitated, as well as the term. [ citation needed ] The component parts were commonly available to producers and the BIOS was reverse engineered through cleanroom design techniques. IBM PC compatible "clones" became commonplace, and the terms "personal computer", and especially "PC", stuck with the general public, often specifically for a computer compatible with DOS (or nowadays Windows).
Monitors, keyboards and other devices for input and output may be integrated or separate. Computer memory in the form of RAM , and at least one other less volatile, memory storage device are usually combined with the CPU on a system bus in one unit. Other devices that make up a complete microcomputer system include batteries, a power supply unit, a keyboard and various input/output devices used to convey information to and from a human operator ( printers , monitors , human interface devices ). Microcomputers are designed to serve only one user at a time, although they can often be modified with software or hardware to concurrently serve more than one user. Microcomputers fit well on or under desks or tables, so that they are within easy access of users. Bigger computers like minicomputers , mainframes , and supercomputers take up large cabinets or even dedicated rooms.
A microcomputer comes equipped with at least one type of data storage, usually RAM . Although some microcomputers (particularly early 8-bit home micros) perform tasks using RAM alone, some form of secondary storage is normally desirable. In the early days of home micros, this was often a data cassette deck (in many cases as an external unit). Later, secondary storage (particularly in the form of floppy disk and hard disk drives) were built into the microcomputer case.
Although they did not contain any microprocessors, but were built around transistor-transistor logic (TTL), Hewlett-Packard calculators as far back as 1968 had various levels of programmability comparable to microcomputers. The HP 9100B (1968) had rudimentary conditional (if) statements, statement line numbers, jump statements ( go to ), registers that could be used as variables, and primitive subroutines. The programming language resembled assembly language in many ways. Later models incrementally added more features, including the BASIC programming language (HP 9830A in 1971). Some models had tape storage and small printers. However, displays were limited to one line at a time. [ 9 ] The HP 9100A was referred to as a personal computer in an advertisement in a 1968 Science magazine, [ 10 ] but that advertisement was quickly dropped. [ 11 ] HP was reluctant to sell them as "computers" because the perception at that time was that a computer had to be big in size to be powerful, and thus decided to market them as calculators. Additionally, at that time, people were more likely to buy calculators than computers, and, purchasing agents also preferred the term "calculator" because purchasing a "computer" required additional layers of purchasing authority approvals. [ 12 ]
The Datapoint 2200 , made by CTC in 1970, was also comparable to microcomputers. While it contains no microprocessor, the instruction set of its custom TTL processor was the basis of the instruction set for the Intel 8008 , and for practical purposes the system behaves approximately as if it contains an 8008. This is because Intel was the contractor in charge of developing the Datapoint's CPU, but ultimately CTC rejected the 8008 design because it needed 20 support chips. [ 13 ]
Another early system, the Kenbak-1 , was released in 1971. Like the Datapoint 2200, it used small-scale integrated transistor–transistor logic instead of a microprocessor. It was marketed as an educational and hobbyist tool, but it was not a commercial success; production ceased shortly after introduction. [ 14 ]
In late 1972, a French team headed by François Gernelle within a small company, Réalisations & Etudes Electroniques (R2E), developed and patented a computer based on a microprocessor – the Intel 8008 8-bit microprocessor. This Micral-N was marketed in early 1973 as a "Micro-ordinateur" or microcomputer , mainly for scientific and process-control applications. About a hundred Micral-N were installed in the next two years, followed by a new version based on the Intel 8080. Meanwhile, another French team developed the Alvan, a small computer for office automation which found clients in banks and other sectors. The first version was based on LSI chips with an Intel 8008 as peripheral controller (keyboard, monitor and printer), before adopting the Zilog Z80 as main processor.
In late 1972, a Sacramento State University team led by Bill Pentz built the Sac State 8008 computer, able to handle thousands of patients' medical records. The Sac State 8008 was designed with the Intel 8008. It had a full set of hardware and software components : a disk operating system included in a series of programmable read-only memory chips (PROMs); 8 Kilobytes of RAM; IBM's Basic Assembly Language (BAL); a hard drive; a color display; a printer output; a 150 bit/s serial interface for connecting to a mainframe; and even the world's first microcomputer front panel. [ 15 ] [ 16 ]
In early 1973, Sord Computer Corporation (now Toshiba Personal Computer System Corporation ) completed the SMP80/08, which used the Intel 8008 microprocessor. The SMP80/08, however, did not have a commercial release. After the first general-purpose microprocessor, the Intel 8080 , was announced in April 1974, Sord announced the SMP80/x, the first microcomputer to use the 8080, in May 1974. [ 17 ]
Virtually all early microcomputers were essentially boxes with lights and switches; one had to read and understand binary numbers and machine language to program and use them (the Datapoint 2200 was a striking exception, bearing a modern design based on a monitor, keyboard, and tape and disk drives). Of the early "box of switches"-type microcomputers, the MITS Altair 8800 (1975) was arguably the most famous. Most of these simple, early microcomputers were sold as electronic kits —bags full of loose components which the buyer had to solder together before the system could be used.
The period from about 1971 to 1976 is sometimes called the first generation of microcomputers. Many companies such as DEC , [ 18 ] National Semiconductor , [ 19 ] Texas Instruments [ 20 ] offered their microcomputers for use in terminal control, peripheral device interface control and industrial machine control. There were also machines for engineering development and hobbyist personal use. [ 21 ] In 1975, the Processor Technology SOL-20 was designed, which consisted of one board which included all the parts of the computer system. The SOL-20 had built-in EPROM software which eliminated the need for rows of switches and lights. The MITS Altair just mentioned played an instrumental role in sparking significant hobbyist interest, which itself eventually led to the founding and success of many well-known personal computer hardware and software companies, such as Microsoft and Apple Computer . Although the Altair itself was only a mild commercial success, it helped spark a huge industry.
By 1977, the introduction of the second microcomputer generation as consumer goods , known as home computers , made them considerably easier to use than their predecessors because their predecessors' operation often demanded thorough familiarity with practical electronics. The ability to connect to a monitor (screen) or TV set allowed visual manipulation of text and numbers. The BASIC language, which was easier to learn and use than raw machine language, became a standard feature. These features were already common in minicomputers , with which many hobbyists and early produces were familiar.
In 1979, the launch of the VisiCalc spreadsheet (initially for the Apple II ) first turned the microcomputer from a hobby for computer enthusiasts into a business tool. After the 1981 release by IBM of its IBM PC , the term personal computer became generally used for microcomputers compatible with the IBM PC architecture ( IBM PC–compatible ). | https://en.wikipedia.org/wiki/Microcomputer |
Microcomputer Associates, Inc. , was an American computer company founded by Manny Lemas and Ray Holt . It produced the low-cost Jolt Microcomputer , designed by Holt and released in 1975 for US$249 (equivalent to $1,460 in 2024). [ 1 ] [ 2 ] A Jolt microcomputer was notably used in the Atari VCS prototype by Cyan Engineering . [ 3 ]
MAI was later acquired by semiconductor manufacturer Synertek , a second source manufacturer of the 6502 , and renamed Synertek Systems . [ 4 ] It then created the SYM-1 , a 6502-based single board microcomputer and spiritual successor to the KIM-1 . In 1978 the company offered a number of processor and peripheral modules. [ 5 ]
This computing article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microcomputer_Associates |
Microconnect distributed antennas ( MDA ) are small-cell local area (100 metre radius [ 1 ] ) transmitter-receivers usually fitted to lampposts and other street furniture [ 2 ] in order to provide Wireless LAN , GSM and GPRS connectivity. They are therefore less obtrusive than the usual masts and antennas used for these purposes and meet with less public opposition.
The service provided by microconnect distributed antennas cover a market in heavily populated urban area addressing mobile and radio connection. Also MDA is suited for bustling cities and historical areas where mobile connection and ability is impaired. [ 3 ] Having many low power, small antennae preforms and covers an area equal to or better than a traditional Macrocellular site. The centrally located radio base station connects to the antennae by fibre optical cable. [ 4 ] Each antenna point contains a 63–65 GHz wireless unit alongside a large memory store providing proxy and cache services. Also users will be able to obtain 64 kbit uplink/ 384kbit downlink service. Multiple operators can share this infrastructure. So that different service providers can this technology to benefit their customers. [ 5 ]
The four part MDA system is, the DAS (Distributed Antenna System) Master unit, access network optical fibre , and the Remote Radio over Fibre (RoF) Unit (Remote Antennae Points). Followed by the Supervisory and Management facilities. [ 6 ] This system is compatible GSM (2g and 2.5G) and 3G network requirements of mobile users. [ 7 ]
The MDA is an economical device that gives a somewhat low-cost solution to give more people access to mobile and broadband connection. This solution also has a low environmental impact that might not clutter up a historical part of an urban area. As communities become more and more dependent on technology solutions like the MDA system is perfect for protecting the natural beauty. [ 8 ] | https://en.wikipedia.org/wiki/Microconnect_distributed_antenna |
Microcosms are artificial, simplified ecosystems that are used to simulate and predict the behaviour of natural ecosystems under controlled conditions. Open or closed microcosms provide an experimental area for ecologists to study natural ecological processes. Microcosm studies can be very useful to study the effects of disturbance or to determine the ecological role of key species. A Winogradsky column is an example of a microbial microcosm. | https://en.wikipedia.org/wiki/Microcosm_(experimental_ecosystem) |
Microcosm was a hypermedia system, originally developed in 1988 by the Department of Electronics and Computer Science at the University of Southampton , with a small team of researchers in the Computer Science group: Wendy Hall , Andrew Fountain, Hugh Davis and Ian Heath. [ 1 ] [ 2 ] The system pre-dates the web and builds on early hypermedia systems, such as Ted Nelson 's Project Xanadu and work of Douglas Engelbart . And like Intermedia or Hyper-G , which were other hypermedia systems created around the same time, Microcosm stores links between documents in a separate database. [ 3 ]
This multimedia software -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microcosm_(hypermedia_system) |
Microcracks in rock , also known as microfractures and cracks , [ 1 ] are spaces in rock with the longest length of 1000 μm and the other two dimensions of 10 μm. In general, the ratio of width to length of microcracks is between 10 −3 to 10 −5 . [ 1 ]
Due to the scale, microcracks are observed using microscope to obtain their basic characteristics. [ 1 ] [ 2 ] Microcrack formation provides insights into the strength and deformation behavior of rocks. [ 3 ] Experimental and numerical results both play an important role in studying microcracks, especially their kinematics and dynamics. Microcracks in rock have been studied to understand geologic problems such as the early stage of earthquakes and fault formation. In engineering, microcracks in rock have been linked to underground engineering problems, such as deep geological repository. [ 4 ]
In general, microcracks in rock can be subdivided into four groups: [ 1 ]
The characteristics of microcracks are orientation, length, width, aspect ratio, number, and density. [ 1 ] These characteristics have been tried to be explained by mathematical functions. [ 1 ] For example, distribution of microcrack lengths away from the fault has been described by lognormal or exponential distributions. [ 1 ]
The orientations of microcracks are random in unstressed rock. [ 1 ] Once a rock has been stressed, the microcracks will have a trend of orientations more or less parallel to the maximum applied stress or the fault strike. [ 1 ] For example, the average orientation of microcracks of stressed Westerly granite is 30° to the fault strike. [ 6 ]
In a thin section, the observed length and width may not necessarily be the true length and width of a microcrack in three dimensions. [ 1 ] [ 7 ] The aspect ratio is the ratio of width to length. [ 1 ] It is generally10 −3 to 10 −5 . [ 1 ] The crack length increases with increasing maximum applied stress, resulting in a decrease in the aspect ratio . [ 1 ]
Density of microcracks can be either the number of microcracks per unit area or per grain or the microcrack length per unit area. [ 1 ] [ 6 ] Densities of microcracks near a fault are dramatically high, but they decrease rapidly within a few mineral grains away from a fault. [ 1 ] [ 6 ]
Microcracks in rock can be induced by the applied stress or temperature. [ 1 ] [ 4 ]
A microcrack is formed when the stresses exceed the local strength of grains. [ 1 ] The strength of materials is the ability to resist an applied load so that failure will not occur. [ 8 ] The intrinsic properties of rock such as mineralogical heterogeneity give diverse types of mechanically induced microcracking. The following mechanisms have strong correlations to the locations that allow stress concentration in grain-scale.
Thermally induced microcracking refers to microcrack formation due to thermal effects. [ 1 ] Heating or cooling can cause thermal expansion or contraction between grains, respectively. [ 1 ] Minerals with different thermo-elastic properties have different reactions to cooling or heating, resulting in microcrack formation. [ 1 ] Also, thermal gradients at internal boundaries of grains may also allow stress concentration , thus forming microcracks. [ 1 ]
The evolution of microcracks has been studied through experiment. [ 2 ] [ 7 ] [ 9 ] When force is applied to a rock sample, microcracks initially form randomly in space. [ 1 ] They then become more and more localized and intense with continuous loading. [ 1 ] This phenomenon is called the crack localization . [ 1 ] A theory of failure helps to explain the evolution of microcracks with increased loading: [ 10 ]
After failure, the overall microcrack density increases near the fault and decreases rapidly away from the fault. [ 1 ] [ 5 ] [ 6 ] In addition, the density of transgranular cracks increases near the fault, whereas the density of grain boundary cracks is lower. [ 5 ] Connecting locally dense crack regions, crack arrays, and grain boundary eventually forms a macrocrack. [ 1 ]
Before forming a fault, there is a fracture process zone (FPZ) . [ 5 ] [ 11 ] It is a region of microcracks near the tip of a rock failure. [ 5 ] [ 11 ] It is associated with the crack localization and related to energy dissipation. [ 11 ] The size of a fracture process zone is related to the specimen size. [ 11 ] The larger the specimen size, the large the size of the fracture process zone. [ 11 ] This relationship no longer exists when the specimen size is larger than a certain size. [ 11 ]
The heterogeneity of rock makes the microcracking behavior much more complicated than other simple materials. [ 1 ] Factors controlling microcracking behavior still have been identified and studied:
In addition to microcracks formation, microcracks in rock can be recovered either by microcrack closure or microcrack healing . [ 12 ] [ 13 ] Microcrack recovery will directly cause a decrease in permeability of rock. [ 13 ]
It can be either caused by increase in the applied stress or decrease in the effective stress. [ 12 ] [ 14 ] For example, microcracks perpendicular to the maximum stress direction will close. [ 14 ] However, in nature, parts of a microcrack can be in different directions. [ 14 ] For this reason, it will result in incomplete closure that some parts of the microcrack are closed while some parts are still open. [ 14 ]
It is driven by transportation of chemical fluid in microcracks. [ 12 ] [ 13 ] For example, healing of microcracks in quartz is activated by temperature. [ 13 ] Healing in quartz becomes fast when the temperature is above 400 °C. [ 13 ] The rate of healing also depends on the crack sizes. [ 13 ] The smaller the cracks, the faster the healing. [ 13 ]
Microcracks affect the properties of rock including stiffness , strength , elastic modulus , permeability , fracture toughness , and elastic wave velocity. [ 4 ]
Studies of microcracks are focused on their distributions of the characteristics and microcracking behavior. Many experiments to study microcracks in rock have been conducted in the past decades, whereas numerical study also has been widely used to study microcracks in recent years because of the technology development. [ 1 ] [ 15 ] These studies have been used to compare with natural conditions. [ 1 ]
Experimental study is to analyze the rock specimens that have been subjected to applied stress in laboratory. There are two popular methods to study microcracks. [ 1 ] Observation of thin section using microscope is to obtain the distributions of microcrack lengths, widths and aspect ratios, numbers and densities, as well as orientations. [ 1 ] Another method is using acoustic emission to detect and monitor microcrack growth. [ 1 ] [ 9 ] Experimental results can help scientists develop numerical models, such as simulation of fracture pattern growth. [ 2 ]
Many experiments on rock fracture mechanism have been done in laboratory, but these experiments may have different requirement of specimen configuration and loading scheme. [ 6 ] [ 7 ] [ 9 ] They are the two important factors controlling microcracking behavior such as microcrack development. [ 7 ] [ 9 ] [ 16 ]
Specimen configuration refers to the dimensions of a specimen and its man-made crack. Rock samples are usually obtained from rock cores. Therefore, cylinder shape, chevron-bend shape, and semi-circular-bend shape (SCB) are the common specimen shapes used in experimental study. [ 7 ] [ 6 ] [ 9 ] [ 16 ] For example, a semi-circular bend specimen has a man-made crack, called a notch. [ 9 ] It is used to control the morphology of rock fracture. [ 9 ] Two notch types can be induced: a straight-through notch or a chevron notch. [ 9 ] A straight-through notch semi-circular-bend (SNCCB) specimen has a flat-ended notch, whereas a chevron notch semi-circular-bend (CNSCB) specimen has a V-shaped opening to the air. [ 9 ]
In fracture mechanics , there are three types of loading modes to make a crack able to propagate. They are mode I (opening), mode II (in-plane shear), and mode III (out-plane shear). [ 7 ] These loading modes can be achieved by the designed loading scheme. [ 16 ] Mode I fractures are the most common microcracks in rock in natural. [ 2 ] [ 7 ]
An acoustic emission (AE) is a high-frequency elastic wave. [ 17 ] [ 18 ] It is generated from microcrack formations, [ 18 ] and is correlated to rapid microcrack growth. [ 17 ] Acoustic emission sensors are attached to the surface of the specimen. [ 9 ] They collect the signals generated during microcrack formation. [ 9 ] The data can be used to describe the microcrack behavior. [ 9 ] [ 17 ] Noted that one detected acoustic emission event is not necessary to be one microcrack formation. [ 17 ]
The types of data collected from acoustic emission sensors are:
These two types of data imply the following information:
Numerical study is used to help understanding the complicated rock mechanics problems. [ 15 ] Four types of models using in modelling microcracks in rock are particle-based models, block-based models, grain-based models, and node-based models. [ 15 ] Since grain-based models can consider all types of microcrack, they are good at understanding microcracking behavior. [ 15 ]
Experimental study of microcracks provides insights into faulting and microcracks formation in nature. [ 2 ] Microcracks studies with CL and fluid-inclusion studies are able to reconstruct the growth of fractures from microcracks. [ 2 ] Population of microcracks is useful to distinguish whether the detachment is due to landslide or tectonic in origin. [ 2 ] The fracture process zone (FPZ) can be used to understand the permeability of fault zones which controls fluid flow. [ 5 ] Therefore, microcracks can be useful for assessing the stress history or fluid movement history of rock. [ 2 ] Acoustic emission from microcrack growth may help to understand earthquakes . [ 1 ] [ 17 ]
Microcracks can affect the thermal and transport properties of rock. [ 4 ] Studies of microcracks in rock provide an important insights into underground engineering problems as follows: [ 4 ]
A deep geological repository is an underground repository for radioactive waste disposal, such as nuclear fuel. [ 19 ] It is at depth of hundred metres in a stable rock mass. Deep geological repositories are all over the world, such as the United States ( WIPP ) and Finland ( Olkiluoto Nuclear Power Plant ). [ 19 ]
A geothermal reservoir is one of the three components of a geothermal system that acts an energy source. [ 20 ] [ 21 ] It is a porous and permeable rock mass so that convection of trapped hot water and steam and recharge of heat supply can occur. [ 20 ] [ 21 ] The ideal geothermal reservoir is a highly permeable, fractured rock matrix. [ 21 ]
A hydrocarbon reservoir is an underground reservoir that keeps hydrocarbons trapped inside. [ 22 ] Reservoir rocks have high porosity and permeability while the surrounding rocks that act as barriers have low permeability . [ 22 ] Therefore, hydrocarbons that exist as liquid and/or gas can only stay in the reservoir rocks. [ 22 ]
Underground storage of CO 2 is a solution to remove CO 2 in the atmosphere . [ 23 ] It is composed of porous rocks surrounded by nonporous rocks so that it can trap the CO 2 for a long time. [ 23 ] A depleted oil and gas reservoir that is out of energy source is one of the examples used for underground storage. [ 23 ] | https://en.wikipedia.org/wiki/Microcracks_in_rock |
Microcrystalline waxes are a type of wax produced by de-oiling petrolatum , as part of the petroleum refining process. In contrast to the more familiar paraffin wax which contains mostly unbranched alkanes , microcrystalline wax contains a higher percentage of isoparaffinic (branched) hydrocarbons and naphthenic hydrocarbons. [ 1 ] It is characterized by the fineness of its crystals in contrast to the larger crystal of paraffin wax. It consists of high molecular weight saturated aliphatic hydrocarbons . It is generally darker, more viscous , denser, tackier and more elastic than paraffin waxes, and has a higher molecular weight and melting point . The elastic and adhesive characteristics of microcrystalline waxes are related to the non-straight chain components which they contain. Typical microcrystalline wax crystal structure is small and thin, making them more flexible than paraffin wax. It is commonly used in cosmetic formulations. [ 2 ]
Microcrystalline waxes when produced by wax refiners are typically produced to meet a number of ASTM specifications. These include congeal point (ASTM D938), needle penetration (ASTM D1321), color (ASTM D6045), and viscosity (ASTM D445). Microcrystalline waxes can generally be put into two categories: "laminating" grades and "hardening" grades. The laminating grades typically have a melting point of 140–175 °F (60–80 °C) and needle penetration of 25 or above. The hardening grades will range from about 175–200 °F (80–93 °C), and have a needle penetration of 25 or below. Color in both grades can range from brown to white, depending on the degree of processing done at the refinery level.
Microcrystalline waxes are derived from the refining of the heavy distillates from lubricant oil production. This by-product must then be de-oiled at a wax refinery. Depending on the end use and desired specification, the product may then have its odor removed and color removed (which typically starts as a brown or dark yellow). This is usually done by means of a filtration method or by hydro-treating the wax material.
Microcrystalline wax is often used in industries such as tire and rubber, candles, adhesives, corrugated board, cosmetics, castings, and others. Refineries may use blending facilities to combine paraffin and microcrystalline waxes; this is prevalent in the tire and rubber industries.
Microcrystalline waxes have considerable application in the custom making of jewelry and small sculptures. Different formulations produce waxes from those soft enough to be molded by hand to those hard enough to be carved with rotary tools. The melted wax can be cast to make multiple copies that are further carved with details. Jewelry suppliers sell wax molded into the basic forms of rings as well as details that can be heat welded together and tubes and sheets for cutting and building the wax models. Rings may be attached to a wax "tree" so that many can be cast in one pouring.
A brand of microcrystalline wax, Renaissance Wax , is also used extensively in museum and conservation settings for protection and polishing of antique woods, ivory, gemstones, and metal objects. It was developed by The British Museum in the 1950s to replace the potentially unstable natural waxes that were previously used such as beeswax and carnauba.
Microcrystalline waxes are excellent materials to use when modifying the crystalline properties of paraffin wax. The microcrystalline wax has significantly more branching of the carbon chains that are the backbone of paraffin wax. This is useful when some desired functional changes in the paraffin are needed, such as flexibility, higher melt point, and increased opacity.
They are also used as slip agents in printing ink .
Microcrystalline wax is used in such sports as ice hockey , skiing and snowboarding . It is applied to the friction tape of an ice hockey stick to prevent degradation of the tape due to water destroying the glue on the tape and also to increase control of the hockey puck due to the wax’s adhesive quality. It is also applied to the underside of skis and snowboards as glide wax to reduce friction and increase the gliding ability of the board, making it easier to control; stickier grades of kick or grip wax are also used on cross-country skis to allow the ski to alternately grip the snow and slip across it as the skier shifts their weight while striding.
Microcrystalline wax was used in the final phases of the restoration of the Cosmatesque pavement, Westminster Abbey , London.
Microcrystalline wax is also a key component in the manufacture of petrolatum . The branched structure of the carbon chain backbone allows oil molecules to be incorporated into the crystal lattice structure. The desired properties of the petrolatum can be modified by using microcrystalline wax bases of different congeal points (ASTM D938) and needle penetration (ASTM D1321).
However, key industries that utilize petrolatum, such as the personal care, cosmetic, and candle industries, have pushed for more materials that are considered "green" and based on renewable resources. As an alternative, hybrid petrolatum can be used. Hybrid petrolatum utilizes a complex mixture of vegetable oils and waxes and combines them with petroleum and micro wax-based technologies. This allows a formulator to incorporate higher percentages of renewable resources while maintaining the beneficial properties of the petrolatum. | https://en.wikipedia.org/wiki/Microcrystalline_wax |
Microcrystallization (or microcrystal test ) is a method for identifying lichen metabolites that was predominantly used before the advent of more advanced techniques such as thin-layer chromatography and high-performance liquid chromatography . Developed primarily by Yasuhiko Asahina , this approach relies on the formation of distinctive crystals from lichen extracts . Although now superseded by modern analytical methods , microcrystallization still holds importance for compound purification and analysis using X-ray crystallography .
Between 1936 and 1940, [ 1 ] [ 2 ] Japanese chemist and lichenologist Yasuhiko Asahina published a series of papers in the Journal of Japanese Botany detailing the microcrystallization technique. [ 3 ] [ 4 ] This simple and rapid method allowed for the identification of major metabolites in hundreds of lichen species, contributing significantly to taxonomic research. [ 4 ] The technique was introduced to western lichenologists in a 1943 publication by Alexander Evans , [ 5 ] and was used regularly until more advanced techniques such as thin-layer chromatography and high-performance liquid chromatography were introduced and integrated into laboratories. Decades of research on the secondary metabolites of lichens culminated in the publication of Identification of Lichen Substances , a 1996 work by Siegfried Huneck and Isao Yoshimura, that summarized analytical data for hundreds of lichen molecules, including images of microcrystals. [ 6 ] Ultimately, the microcrystallization method had limitations, as it was unable to detect minor components or analyze complex mixtures of lichen substances. [ 7 ] [ 8 ] Despite these drawbacks, microcrystallization played a crucial role in the study of correlations between lichen chemistry, morphology , and geographic distribution. [ 8 ]
To perform microcrystallization, a small piece of lichen is extracted using acetone or other solvents , filtered , and evaporated to yield a residue . [ 7 ] [ 3 ] [ 9 ] The residue is transferred to a microscope slide , and a drop of microcrystallization reagent is added before capping with a cover glass . [ 7 ] Commonly used reagents include GAW (H 2 O/ glycerol / ethanol 1:1:1, v/v/v) and GE ( acetic acid /glycerol 1:3). [ 7 ] Slides using GE or GAW are gently heated and then allowed to cool, promoting the crystallization process. [ 7 ] [ 3 ] Once formed, crystals are best observed under polarized light with a 200–1,000-fold magnification. [ 7 ]
This method requires basic laboratory equipment, including a microscope equipped for polarized light, test tubes , pipettes , a micro spirit-lamp or micro Bunsen burner , spatula or scalpel , and microscope slides and cover glasses. [ 3 ] Lichen substances can be identified based on the distinctive shape and color of their crystals. [ 7 ] [ 3 ]
The process of crystal identification involves comparing them to images of crystals in different solvents found in published sources. Although the shape of the crystals depends on the solvent and, to a certain degree, the substance concentration, it is usually possible to recognize the fundamental crystalline forms. Care should be taken to differentiate between undissolved substances, which might be crystalline but lack a characteristic shape, and recrystallized substances. Microcrystal samples cannot be preserved for long, as they start to degrade within hours or days. [ 10 ]
Distinguishing between gyrophoric acid and lecanoric acid using thin-layer chromatography can be challenging. However, if one of these substances is known to be present, a microcrystal test can help differentiate them. In the GAW solvent system, lecanoric acid forms long, curved crystal clusters, although the results can be inconsistent, especially in the presence of other substances. Gyrophoric acid, when present in the GE solvent system, may manifest as small, fine crystal clusters or rounded aggregations of tiny crystals. Lecanoric acid in the GE solvent system produces needle-like crystal clusters, but these are not as well-formed as in GAW. These tests can help distinguish Punctelia borreri (which contains gyrophoric acid) from Punctelia subrudecta (which contains lecanoric acid). [ 10 ]
When two substances generate similar-looking crystals, their optical properties can be used to differentiate between them. Certain crystals alter the polarization plane of transmitted light, and when rotated between crossed polarizers, they alternate between bright and dark every 90°. The extinction angle is the angle between a specific crystal axis and the filter's polarization plane when the crystal appears dark (in extinction). For instance, this method can be employed to distinguish between perlatolic acid and imbricaric acid , which both form long, straight crystals in the GE solvent system but exhibit extinction angles of 0° and 45°, respectively, in relation to their long axis. [ 10 ] | https://en.wikipedia.org/wiki/Microcrystallization |
Microcystins —or cyanoginosins —are a class of toxins produced by certain cyanobacteria, commonly known as blue-green algae . [ 3 ] Over 250 [ 4 ] different microcystins have been discovered so far, of which microcystin-LR is the most common. Chemically they are cyclic heptapeptides produced through nonribosomal peptide synthases. [ 5 ]
Cyanobacteria can produce microcystins in large quantities during algal blooms which then pose a major threat to drinking and irrigation water supplies, and the environment at large. [ 6 ] [ 7 ]
Microcystins—or cyanoginosins—are a class of toxins [ 8 ] produced by certain freshwater cyanobacteria ; primarily Microcystis aeruginosa but also other Microcystis , as well as members of the Planktothrix , Anabaena , Oscillatoria and Nostoc genera.
Microcystin-LR (i.e. X = leucine, Z = arginine) is the most toxic form of over 80 known toxic variants, and is also the most studied by chemists, pharmacologists, biologists, and ecologists. Microcystin-containing 'blooms' are a problem worldwide, including China, Brazil, Australia, South Africa, [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] [ 14 ] [ 15 ] [ 16 ] the United States and much of Europe. Hartebeespoort Dam in South Africa is one of the most contaminated sites in Africa, and possibly in the world.
Microcystins have a common structural framework of D-Ala 1 - X 2 - D-Masp 3 - Z 4 -Adda 5 -D-γ-Glu 6 - Mdha 7 , where X and Z are variable amino acids; the systematic name "microcystin- XZ " (MC- XZ in short) is then assigned based on the one letter codes (if available; longer codes otherwise) of the amino acids. [ 4 ] If the molecule show any other modification, the differences are noted in square brackets before "MC". [ 4 ] Of these, several are uncommon non- proteinogenic amino acids : [ 17 ]
Microcystins covalently bond to and inhibit protein phosphatases PP1 and PP2A and can thus cause pansteatitis . [ 17 ] The ADDA residue is key to this functionality: greatly simplified synthetic analogues consisting of ADDA and one additional amino acid can show the same inhibiting function. [ 19 ]
The microcystin-producing Microcystis is a genus of freshwater cyanobacteria and thrives in warm water conditions, especially in stagnant waters. [ 7 ] The EPA predicted in 2013 that climate change and changing environmental conditions may lead to harmful algae growth and may negatively impact human health. [ 20 ] Algal growth is also encouraged through the process of eutrophication (oversupply of nutrients). [ 7 ] In particular, dissolved reactive phosphorus promotes algal growth. [ 21 ] [ better source needed ]
Microcystins may have evolved as a way to deal with low iron supply in cyanobacteria: the molecule binds iron, and non-producing strains are significantly worse at coping with low iron levels. [ 22 ] Low iron supply up-regulates McyD , one of the microcystin synthetic operons. [ 23 ] Sufficient iron supply, however, can still boost microcystin production by making the bacterium better at photosynthesis, therefore producing sufficient ATP for MC biosynthesis. [ 24 ]
Microcystin production is also positively correlated with temperature. [ 25 ] Bright light and red light increases transcription of McyD , but blue light reduces it. [ 26 ] A wide range of other factors such as pH may also affect MC production, but comparison is complicated due to a lack of standard testing conditions. [ 27 ]
There are several ways of exposure to these hepatotoxins that humans can encounter one of which is through recreational activities like swimming, surfing, fishing, and other activities involving direct contact with contaminated water. [ 28 ] Another rare, yet extremely toxic, route of exposure that has been identified by scientists is through hemodialysis surgeries. One of the fatal cases for microcystic intoxication through hemodialysis was studied in Brazil where 48% of patients that received the surgery in a specific period of time died because the water used in the procedure was found to be contaminated. [ 29 ]
Microcystins are chemically stable over a wide range of temperature and pH , possibly as a result of their cyclic structure. [ 30 ] Microcystin-LR water contamination is resistant to boiling and microwave treatments. [ 31 ] Microcystin-producing bacteria algal blooms can overwhelm the filter capacities of water treatment plants. Some evidence shows the toxin can be transported by irrigation into the food chain. [ 32 ] [ 33 ]
In 2011, a record outbreak of blooming microcystis occurred in Lake Erie , in part related to the wettest spring on record, and expanded lake bottom dead zones, reduced fish populations, fouled beaches, and damaged the local tourism industry, which generates more than $10 billion in revenue annually. [ 1 ]
In August 2014, the City of Toledo, Ohio detected unsafe levels of microcystin in its water supply due to harmful algal blooms in Lake Erie, the shallowest of the Great Lakes . The city issued an advisory to approximately 500,000 people that the water was not safe for drinking or cooking. [ 34 ] [ 35 ] An Ohio state task force found that Lake Erie received more phosphorus than any other Great Lake, both from crop land, due to the farming practices, and from urban water-treatment centres. [ 21 ]
In 2016, microcystin had been found in San Francisco Bay Area shellfish in seawater, apparently from freshwater runoff, exacerbated by drought . [ 36 ]
In 2018, the Iowa Department of Natural Resources found microcystins at levels of 0.3 µg/L, or micrograms per liter ( ppb ), in the raw water supplies of 15 out of 26 public water systems tested. [ 37 ]
In 2023, the Oregon Department of Environmental Quality (DEQ) and Oregon Health Authority issued a cyanobacteria advisory for much of the Willamette River as it runs through Portland . [ 38 ] The advisory affected the Willamette from the Ross Island Lagoon through Cathedral Park . [ 39 ] Testing by the DEQ showed microcystin levels at 549 ppb. [ 38 ]
Microcystins cannot be broken down by standard proteases like pepsin , trypsin , collagenase , and chymotrypsin due to their cyclic chemical nature. [ 30 ] They are hepatotoxic , i.e., able to cause serious damage to the liver . Once ingested, microcystin travels to the liver via the bile acid transport system, where most is stored, though some remains in the blood stream and may contaminate tissue. [ 40 ] [ 41 ] [ page needed ] Acute health effects of Microcystin-LR are abdominal pain, vomiting and nausea, diarrhea, headache, blistering around the mouth, and after inhalation sore throat, dry cough, and pneumonia. [ 42 ] [ 29 ]
Studies suggest that the absorption of microcystins occurs in the gastrointestinal tract. [ 28 ] Furthermore, it was found that these hepatotoxins inhibit the activity of protein enzymes phosphatase PP1 and PP2A causing hemorrhagic shock and were found to kill within 45 minutes in mice studies. [ 43 ]
There appears to be inadequate information to assess the carcinogenic potential of microcystins by applying EPA Guidelines for Carcinogen Risk Assessment. A few studies suggest a relationship may exist between liver and colorectral cancers and the occurrence of cyanobacteria in drinking water in China. [ 44 ] [ 45 ] [ 46 ] [ 47 ] [ 48 ] [ 49 ] Evidence is, however, limited due to limited ability to accurately assess and measure exposure.
In the US, the EPA issued a health advisory in 2015. [ 50 ] A ten day Health Advisory was calculated for different ages which is considered protective of non-carcinogenic adverse health effects over a ten-day exposure to microcystins in drinking water: 0.3 μg/L for bottle-fed infants and young children of pre-school age and 1.6 μg/L for children of school age through adults. [ 50 ] : 28–29 | https://en.wikipedia.org/wiki/Microcystin |
Microcystin-LR ( MC-LR ) is a toxin produced by cyanobacteria . It is the most toxic of the microcystins .
Microcystins are cyclic heptapeptides . The seven amino acids that are involved in the structure of a microcystin include the unique amino acids ADDA and D -β-methyl-isoaspartate ( D -β-Me-isoAsp). Furthermore, microcystins contain two variable residues, which make the differentiation between variants of microcystins. These two variable functionalities are always standard proteinogenic amino acids - In microcystin-LR these are leucine and arginine .
More than 250 microcystins have been identified to date, [ 1 ] representing differences in the two variable residues and some modifications in the other amino acids. These modifications include demethylation of Masp and Mdha and methylesterification of D -Glu. Different microcystins have different toxicity profiles, with microcystin-LR found to be the most toxic. [ 2 ] [ 3 ]
Microcystins are small nonribosomal peptides . In Microcystis aeruginosa microcystin-LR is synthesized by proteins that encoded by a 55 kb microcystin-gene cluster ( mcy ) that contains 6 large (over 3 kb) genes that encode proteins with polyketide synthase activity, nonribosomal peptide synthase activity ( mcyA-E and G ) and 4 smaller genes ( mcyF and H-J ). These large proteins are made up of different protein domains , coined 'modules', that each have their own specific enzymatic function. [ 4 ] Although the enzyme systems involved in the biosynthesis of microcystins is not identical among all cyanobacteria, there are large similarities and most of the essential enzymes are conserved. [ 4 ] [ 5 ]
The biosynthesis of microcystin-LR in Microcystis aeruginosa begins with the coupling of phenylacetate to the mcyG enzyme. In a series of reactions, catalysed by different enzyme modules as well as different enzymes, microcystin-LR is formed. The entire biosynthesis pathway of microcystin-LR in Microcystis aeruginosa is illustrated in the figure.
The first steps of the synthesis involve the insertion of several carbon- and oxygen atoms between the acetyl - and phenylgroup . This part of the synthesis is catalyzed by enzyme domains that possess β-ketoacylsynthase, acyltransferase, C-methyltransferase and ketoacyl reductase activity. At the end of this stage, that is, after the first condensation of glutamate, the amino acid Adda is formed. [ 4 ] The second part of the synthesis involves the condensation of the amino acids of which the microcystin is composed. Thus, in the case of microcystin-LR the consecutive condensation of the amino acids glutamic acid, methyldehydroalanine, alanine, leucine, methylaspartic acid and arginine leads to the coupled product. A nucleophilic attack of the nitrogen in the Adda residue results in the release of the cyclic microcystin-LR. [ 4 ]
The different microcystins are all synthesized by the same [ clarification needed ] enzymes as microcystin-LR. [ 6 ]
Microcystin-LR inhibits protein phosphatase type 1 and type 2A ( PP1 and PP2A ) activities in the cytoplasm of liver cells. This leads to an increase in phosphorylation of proteins in liver cells. The interaction of microcystin-LR to the phosphatases includes the formation of a covalent bond between a methylene group of microcystin-LR and a cystine residue at the catalytic subunit of the phosphoprotein phosphatase (PPP) family of serine/threonine-specific phosphatases, like PP1 and PP2A. When microcystin-LR binds directly to the catalytic center of the PPP enzymes, they block the access of the substrate to the active site completely and inhibition of the enzyme takes place. In this way the protein phosphatase is inhibited and more phosphorylated proteins in the liver cells are left, which is responsible for the hepatotoxicity of microcystin-LR.
The active site of catalytic PPP enzymes represents three surface grooves: the hydrophobic groove, the acidic groove and the C-terminal groove, which are Y-shaped with the active site at the bifurcation point. The Adda side-chain of microcystin-LR is accommodated to the hydrophobic groove, the carboxylic D-Glu site makes hydrogen bonds to metal-bound water molecules and the carboxyl group of the Masp site makes hydrogen bonds to conserved arginine and tyrosine residues in the PPP enzyme. Finally the methylene group at the Mdha site of microcystin-LR binds covalently to a S-atom of a cysteine residue, and the leucine residue packs closely to another conserved tyrosine residue. [ 2 ]
Microcystin-LR is toxic for both humans and animals. There are epidemiological results from studies that have shown symptoms of poisoning attributed to the presence of cyanotoxins in drinking water. The effects are divided in short-term and long-term effects.
There are no verifiable reports of human deaths known to have been specifically caused by microcystin-LR, although there are reports of health effects after exposure and there have been deaths attributed to microcystins in general. [ 7 ] One of the most outstanding reports was an outbreak in Caruaru , Brazil , in 1996. 116 patients experienced multiple effects: visual disturbance, nausea, vomiting and muscle weakness. One hundred developed acute liver failure and 52 suffered from symptoms of what is now called "Caruaru Syndrome." [ 8 ] The syndrome was caused by dialysis therapy with water that had not been properly treated. [ 9 ]
There are few short-term effects caused by exposure to microcystin-LR. Microcystins are primarily hepatotoxic compounds; therefore, noticeable toxic effects are not immediate. Most of the toxicity studies have been done with mice that received intra-peritoneal injections. The most common effect is liver damage, [ 10 ] Two of the most commonly seen symptoms are gastroenteritis and cholestatic liver disease .
In an experiment with mice, the animals died within a few hours after injection of a lethal dose of micocystin-LR. Liver damage could be noticed in 20 minutes. Within a few hours, liver cells died. [ 11 ]
Acute microcystin-LR intoxication may result in long-term injury, while chronic low-level exposure may cause adverse health effects. From animal studies, it is proven that there will be chronic liver injury from oral exposure to microcystin-LR. It might even be carcinogenic . Cancers have been found during animal studies. Microcystin-LR itself does not cause cancer, but it may stimulate the growth of cancer cells.
Microcystin-LR had effects on all animals, not only the domestic animals from swimming in a river of drinking water with cyanobacteria blooms. Symptoms in domestic animal poisoning include diarrhea, vomiting, weakness, recumbency and are fatal in most cases [ 12 ] [ 13 ]
Mircocystin-LR is toxic for all animals, including the animals consumed by humans. Fishes and birds are also at risk for microcystin-LR poisoning.
Cyanobacteria prefer to live in water bodies such as lake, ponds, reservoirs, and slow-moving streams. When the water is warm there are enough nutrients available for the bacteria to survive. Most cyanobacteria produce toxins, of which microcystin is only one group. When a cyanobacterium dies, its cell wall degrades while the toxins are released in the water. Microcystins are extremely stable in water and withstand chemical breakdown such as hydrolysis or oxidation. The half-life of this toxin is 3 weeks at pH 1 and 40 °C. At typical conditions in the environment, however, the half-life is 10 weeks. [ 10 ] Microcystin-LR water contamination is resistant to boiling and microwave treatments. [ 14 ]
After release in the water, microcystins are actively absorbed by fish and birds from intoxicated water and thus enter the food chain . Humans are also exposed to microcystins by performing activities in intoxicated water. [ 15 ]
Microcystin-LR is rapidly excreted from the blood plasma. Plasma half-lives for the α- and β-stages, corresponding to distribution and elimination, are respectively 0.8 and 6.9 minutes. [ 16 ] [ 17 ] The total clearance of the compound from the plasma is about 0.9 mL/min.
The excretion of the compound takes primarily place via the feces and urine. After 6 days approximately 24% of the intake is excreted from the body, of which about 9% is excreted via the feces and 14.5% via the urine. [ 17 ]
Microcystin-LR is mostly concentrated in the liver. Other tissues get exposed at much lower levels. [ 17 ]
Data about the metabolism of microcystin-LR in humans is very scarce. Data about metabolism and disposition of the toxin in mice and rats is more widely available. In these animals microcystin-LR is rapidly concentrated in the liver. [ 18 ] Intoxication of mice with microcystin-LR led to a decrease in the levels of cytochrome P450 and cytochrome b5 and an increase in cytochrome P420, to which CYP450 is converted. Together with the fact that mice with an induced higher concentration CYP450 are less affected by the toxin, this suggest that CYP450 plays an important role in the detoxification of the compound.
In phase 2 of the biotransformation the compound is conjugated with several different endogenous substances. Microcystin-LR is known to be excreted as glutathione conjugate, cysteine conjugate and an oxidized ADDA diene conjugate. The glutathione and cysteine conjugate with the Mda-moiety. The oxidized ADDA is conjugated at the conjugated bond . [ 19 ]
Toxic effects cyanotoxins are very diverse and include neurotoxicity , hepatotoxicity and cytotoxicity with chemical burns . Microcystins are generally associated with hepatotoxicity. The toxic effect of microcystins is due to their inhibition of protein phosphatases. [ 20 ]
Many studies took place with intraperitoneal administration . Because of the differences in lipophilicity and polarity between the different microcystins, it cannot be presumed that the i.p. LD50 will predict toxicity after oral administration. [ 10 ]
Microcystins are hepatotoxins. After acute exposure, severe liver damage is noticeable by a disruption of liver cell structure. The liver weight will increase due to intrahepatic hemorrhage , haemodynamic shock, heart failure and death. [ 10 ]
After nasal administration of microcystin-LR, the epithelium of nasal mucosa of both the olfactory and respiratory zones were suffering from necrosis. Even liver lesions were noticed after oral administration. The LD50 for nasal administration is equal to the intraperitoneal administration.
For the assessment of possible chronic human health effects, studies involving repeated oral administration of pure microcystins at various dose levels are most desirable.
In a mice study, pure mirocystin-LR was administered orally at doses 0, 40, 200 or 1000 μg/kg bodyweight. At the highest dose, almost all mice showed liver changes and chronic inflammation and a few other symptoms. In female mice only changes in transaminases were observed at the highest dose. [ 10 ]
Mice showed neoplastic liver nodules after 100 oral administrations at 20 μg/kg bodyweight. The nodules observed were up to 5mm in diameter. However, no mice showed liver nodules after 100 administrations of 80 μg/kg.
The IARC committee concluded that microcystin-LR is possibly carcinogenic to humans. So, microcystin-LR itself is not a carcinogen, but it stimulates tumor growth. Mice treated with the carcinogenic compound dimethylbenzathracene showed an increased number and weight of skin tumors. [ 7 ]
There is very little known about acute toxicity for humans, but there have been animal studies, showing the following results.
When microcystins are injected intravenously or intraperitoneally , they localize in the liver. This appears to be the result of uptake by hepatocytes . The WHO report states that microcystins are lethal to mice when they are exposed intraperitoneally to 25 to 150 μg/kg body weight. [ 10 ] Perhaps due to poor absorption after exposure, orally administered microscytins are less toxic, as a lethal dose in mice is about 5 to 10 μg/kg body weight. Hepatotoxicity in the form of hepatic necrosis occurs within 60 minutes after an intraveneous dose. [ 20 ] Blooms of Microcystis aeruginosa did not cause increased tumor rates in groups of mice treated for up to one year. It is shown that mice given 20 μg/kg body weight 4 times a week during a period of 28 weeks developed neoplasms of the liver. [ 20 ] There results are, however, ambiguous.
By the oral route, microcystin-LR displays acute toxicity in rodents. It is apparent that a significant amount of the oral dose passes the intestinal barrier.
Microcystins do not appear to show developmental toxicity.
The WHO states microcystin-LR has no mutagenic effect. However, the induction of DNA strand-breaks in lymphocytes has been observed in mice after single oral administration. The effect is time- and dose-dependent. There is no change in the expression of selected genes involved in the cellular response to DNA damage after a 4-hour exposure. After 24 hours, the DNA damage-responsive genes were upregulated, which indicates that microcystin-LR is an indirect genotoxic agent. [ 22 ] In China, the highest incidence of liver cancer occurs in areas with abundant cyanobacteria in the surface waters. Tumor development is associated with low-concentration exposure over a long period of time. [ 20 ]
In vitro studies showed that microcystin-LR is a potent inhibitor of protein phosphatase 1 (PP-1) and PP2A , but has no effect on protein kinase C or cyclic AMP-dependent kinase . Mutagenicity does not appear to occur for purified toxins derived from Microcystis , although the toxins were clastogenic for human lymphocytes. [ 20 ]
A metalloprotease enzyme isolated from bacteria at Lake Rotorua , among other locations, is called microcystinase . This particular enzyme turns microcystins into products with a 160-fold decrease in toxicity. [ 23 ]
The Chinese general Zhu-Ge Liang was the first to observe cyanobacteria poisoning about 1000 years ago. He reported the death of troops who drank green coloured water from a river in southern China. [ citation needed ] The first published report of an incidence of cyanobacteria poisoning dates from the poisoning of an Australian lake in 1878. [ 24 ] Also, in China and Brasil, people died after drinking water from a lake. All these incidents have been attributed to cyanobacteria and the toxic compound microcystin-LR. That is the reason why the World Health Organization (WHO) issued a guideline for microcystins in drinking water. The WHO guideline for microcystins in drinking water, based on microcystin-LR, is 1 μg/L. [ 16 ] With the high levels of Eutrophication in South Africa, typical exposures can be as high as 10 μg/L. [ 25 ] [ 26 ] [ 27 ] [ 28 ] | https://en.wikipedia.org/wiki/Microcystin-LR |
Microcystinase is a protease that selectively degrades microcystin , an extremely potent cyanotoxin that causes marine pollution and can lead to human and animal food chain poisoning. The enzyme is naturally produced by a number of bacteria isolated in Japan and New Zealand . As of 2012, the chemical structure of this enzyme has not been scientifically determined. [ 1 ]
The enzyme degrades the cyclic peptide toxin microcystin into a linear peptide, which is 160 times less toxic. [ 2 ] Other bacteria then further degrade the linear peptide.
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microcystinase |
A microdensitometer is an optical instrument used to measure optical densities in the microscopic domain. [ 1 ] [ 2 ] [ 3 ] A well-known microdensitometer, used in the photographic industry, is a granularity instrument or granularity machine. [ 2 ] The granularity measurement [ 2 ] involves the use of an optical aperture, 10-50 micrometers in diameter, and in the recording of thousands of optical density readings. The standard deviation of this series of measurements is known as the granularity [ 2 ] [ 3 ] of the measured transmission surface, optical film, or photographic film , in particular .
An alternative version to the traditional point-by-point microdensitometer is the beam expanded laser microdensitometer . [ 3 ] [ 4 ] This instrument can illuminate simultaneously an area a few centimeters wide with an ultra thin height, in the micrometer regime. [ 4 ] Advantages include increased depth of focus, significant increases in data collection speed, and superior signal to noise ratios. [ 3 ] [ 4 ] In microscopy applications, this type of ultra thin beam-expanded illumination can also be known as light sheet illumination or selective plane illumination.
This measurement technique, using ultra-thin expanded laser beams , is particularly useful to detect microscopic imperfections in optical coatings or transmission optical surfaces. [ 5 ] | https://en.wikipedia.org/wiki/Microdensitometer |
Microdialysis is a minimally-invasive sampling technique that is used for continuous measurement of free, unbound analyte concentrations in the extracellular fluid of virtually any tissue. Analytes may include endogenous molecules (e.g. neurotransmitter , hormones , glucose , etc.) to assess their biochemical functions in the body, or exogenous compounds (e.g. pharmaceuticals ) to determine their distribution within the body. The microdialysis technique requires the insertion of a small microdialysis catheter (also referred to as microdialysis probe) into the tissue of interest. The microdialysis probe is designed to mimic a blood capillary and consists of a shaft with a semipermeable hollow fiber membrane at its tip, which is connected to inlet and outlet tubing. The probe is continuously perfused with an aqueous solution (perfusate) that closely resembles the (ionic) composition of the surrounding tissue fluid at a low flow rate of approximately 0.1-5μL/min. [ 1 ] Once inserted into the tissue or (body)fluid of interest, small solutes can cross the semipermeable membrane by passive diffusion . The direction of the analyte flow is determined by the respective concentration gradient and allows the usage of microdialysis probes as sampling as well as delivery tools. [ 1 ] The solution leaving the probe (dialysate) is collected at certain time intervals for analysis.
The microdialysis principle was first employed in the early 1960s, when push-pull canulas [ 2 ] and dialysis sacs [ 3 ] were implanted into animal tissues, especially into rodent brains, to directly study the tissues' biochemistry. [ 1 ] While these techniques had a number of experimental drawbacks, such as the number of samples per animal or no/limited time resolution, the invention of continuously perfused dialytrodes in 1972 helped to overcome some of these limitations. [ 4 ] Further improvement of the dialytrode concept resulted in the invention of the "hollow fiber", a tubular semipermeable membrane with a diameter of ~200-300μm, in 1974. [ 5 ] Today's most prevalent shape, the needle probe, consists of a shaft with a hollow fiber at its tip and can be inserted by means of a guide cannula into the brain and other tissues. An alternative method, open flow micro-perfusion (OFM), replaces the membrane with macroscopic openings which facilitates sampling of lipophilic [ 6 ] [ 7 ] [ 8 ] and hydrophilic compounds, [ 9 ] protein bound and unbound drugs, [ 10 ] [ 11 ] neurotransmitters , peptides and proteins , antibodies , [ 12 ] [ 13 ] [ 14 ] nanoparticles and nanocarriers , enzymes and vesicles .
There are a variety of probes with different membrane and shaft length combinations available. The molecular weight cutoff of commercially available microdialysis probes covers a wide range of approximately 6-100kD, but also 1MD is available. While water-soluble compounds generally diffuse freely across the microdialysis membrane, the situation is not as clear for highly lipophilic analytes, where both successful (e.g. corticosteroids) and unsuccessful microdialysis experiments (e.g. estradiol, fusidic acid) have been reported. [ 15 ] However, the recovery of water-soluble compounds usually decreases rapidly if the molecular weight of the analyte exceeds 25% of the membrane’s molecular weight cutoff.
Due to the constant perfusion of the microdialysis probe with fresh perfusate, a total equilibrium cannot be established. [ 1 ] This results in dialysate concentrations that are lower than those measured at the distant sampling site. In order to correlate concentrations measured in the dialysate with those present at the distant sampling site, a calibration factor (recovery) is needed. [ 16 ] The recovery can be determined at steady-state using the constant rate of analyte exchange across the microdialysis membrane. The rate at which an analyte is exchanged across the semipermeable membrane is generally expressed as the analyte’s extraction efficiency. The extraction efficiency is defined as the ratio between the loss/gain of analyte during its passage through the probe (C in −C out ) and the difference in concentration between perfusate and distant sampling site (C in −C sample ).
In theory, the extraction efficiency of a microdialysis probe can be determined by: 1) changing the drug concentrations while keeping the flow rate constant or 2) changing the flow rate while keeping the respective drug concentrations constant. At steady-state, the same extraction efficiency value is obtained, no matter if the analyte is enriched or depleted in the perfusate. [ 1 ] Microdialysis probes can consequently be calibrated by either measuring the loss of analyte using drug-containing perfusate or the gain of analyte using drug-containing sample solutions. To date, the most frequently used calibration methods are the low-flow-rate method, the no-net-flux method, [ 17 ] the dynamic (extended) no-net-flux method, [ 18 ] and the retrodialysis method. [ 19 ] The proper selection of an appropriate calibration method is critically important for the success of a microdialysis experiment. Supportive in vitro experiments prior to the use in animals or humans are therefore recommended. [ 1 ] In addition, the recovery determined in vitro may differ from the recovery in humans. Its actual value therefore needs to be determined in every in vivo experiment. [ 15 ]
The low-flow-rate method is based on the fact that the extraction efficiency is dependent on the flow-rate. At high flow-rates, the amount of drug diffusing from the sampling site into the dialysate per unit time is smaller (low extraction efficiency) than at lower flow-rates (high extraction efficiency). At a flow-rate of zero, a total equilibrium between these two sites is established (C out = C sample ). This concept is applied for the (low-)flow-rate method, where the probe is perfused with blank perfusate at different flow-rates. Concentration at the sampling site can be determined by plotting the extraction ratios against the corresponding flow-rates and extrapolating to zero-flow. The low-flow-rate method is limited by the fact that calibration times may be rather long before a sufficient sample volume has been collected. [ citation needed ]
During calibration with the no-net-flux-method, the microdialysis probe is perfused with at least four different concentrations of the analyte of interest (C in ) and steady-state concentrations of the analyte leaving the probe are measured in the dialysate (C out ). [ 17 ] The recovery for this method can be determined by plotting C out −C in over C in and computing the slope of the regression line. If analyte concentrations in the perfusate are equal to concentrations at the sampling site, no-net flux occurs. Respective concentrations at the no-net-flux point are represented by the x-intercept of the regression line. The strength of this method is that, at steady-state, no assumptions about the behaviour of the compound in the vicinity of the probe have to be made, since equilibrium exists at a specific time and place. [ 15 ] However, under transient conditions (e.g. after drug challenge), the probe recovery may be altered resulting in biased estimates of the concentrations at the sampling site. To overcome this limitation, several approaches have been developed that are also applicable under non-steady-state conditions. One of these approaches is the dynamic no-net-flux method. [ 18 ]
While a single subject/animal is perfused with multiple concentrations during the no-net-flux method, multiple subjects are perfused with a single concentration during the dynamic no-net-flux (DNNF) method. [ 18 ] Data from the different subjects/animals is then combined at each time point for regression analysis allowing determination of the recovery over time. The design of the DNNF calibration method has proven very useful for studies that evaluate the response of endogenous compounds, such as neurotransmitters, to drug challenge. [ 18 ]
During retrodialysis, the microdialysis probe is perfused with an analyte-containing solution and the disappearance of drug from the probe is monitored. The recovery for this method can be computed as the ratio of drug lost during passage (C in −C out ) and drug entering the microdialysis probe (C in ). In principle, retrodialysis can be performed using either the analyte itself (retrodialysis by drug) or a reference compound (retrodialysis by calibrator) that closely resembles both the physiochemical and the biological properties of the analyte. [ 19 ] Despite the fact that retrodialysis by drug cannot be used for endogenous compounds as it requires absence of analyte from the sampling site, this calibration method is most commonly used for exogenous compounds in clinical settings. [ 1 ]
The microdialysis technique has undergone much development since its first use in 1972, [ 4 ] when it was first employed to monitor concentrations of endogenous biomolecules in the brain. [ 20 ] Today's area of application has expanded to monitoring free concentrations of endogenous as well as exogenous compounds in virtually any tissue. Although microdialysis is still primarily used in preclinical animal studies (e.g. laboratory rodents, dogs, sheep, pigs), it is now increasingly employed in humans to monitor free, unbound drug tissue concentrations as well as interstitial concentrations of regulatory cytokines and metabolites in response to homeostatic perturbations such as feeding and/or exercise. [ 21 ]
When employed in brain research, microdialysis is commonly used to measure neurotransmitters (e.g. dopamine , serotonin , norepinephrine , acetylcholine , [ 22 ] glutamate , GABA ) and their metabolites, as well as small neuromodulators (e.g. cAMP , cGMP , NO ), amino acids (e.g. glycine , cysteine , tyrosine ), and energy substrates (e.g. glucose , lactate , pyruvate ). Exogenous drugs to be analyzed by microdialysis include new antidepressants , antipsychotics , as well as antibiotics and many other drugs that have their pharmacological effect site in the brain. The first non-metabolite to be analyzed by microdialysis in vivo in the human brain was rifampicin . [ 23 ] [ 24 ] [ 25 ]
Applications in other organs include the skin (assessment of bioavailability and bioequivalence of topically applied dermatological drug products), [ 26 ] and monitoring of glucose concentrations in patients with diabetes (intravascular or subcutaneous probe placement). The latter may even be incorporated into an artificial pancreas system for automated insulin administration.
Microdialysis has also found increasing application in environmental research, [ 27 ] sampling a diversity of compounds from waste-water and soil solution, including saccharides, [ 28 ] metal ions, [ 29 ] micronutrients, [ 30 ] organic acids, [ 31 ] and low molecular weight nitrogen. [ 32 ] Given the destructive nature of conventional soil sampling methods, [ 33 ] microdialysis has potential to estimate fluxes of soil ions that better reflect an undisturbed soil environment. | https://en.wikipedia.org/wiki/Microdialysis |
Microdissection refers to a variety of techniques where a microscope is used to assist in dissection .
Different kinds of techniques involve microdissection :
This article related to pathology is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microdissection |
Microecology means microbial ecology or ecology of a microhabitat. It is a large field that includes many topics such as: evolution, biodiversity, exobiology, ecology, bioremediation , recycling, and food microbiology. [ 1 ] It can also refer to a hybrid urban network at the scale of the neighbourhood. [ 2 ] It is the study of the interactions between living organisms and their environment, and how these interactions affect the organisms and their environment. Additionally, it is a multidisciplinary area of study, combining elements of biology, chemistry, physics, mathematics and urban planning . It focuses on the study of the interactions between microorganisms and the environment they inhabit, their effects on the environment, and their effects on other organisms. Microecology also studies the effects of human activity on the environment and how this affects the growth and development of microorganisms or organic structures. Microecology has many applications in the fields of medicine, agriculture, biotechnology and design. It is also important for understanding the cycling of nutrients in the environment, and the behavior of microorganisms or actors in various environments.
In humans , gut microecology is the study of the microbial ecology of the human gut which includes gut microbiota composition, its metabolic activity, and the interactions between the microbiota, the host, and the environment. [ 3 ] Research in human gut microecology is important because the microbiome can have profound effects on human health. The microbiome is known to influence the immune system, digestion, and metabolism, and is thought to play a role in a variety of diseases, including diabetes, obesity, inflammatory bowel disease, and cancer. Studying the microbiome can help us better understand these diseases and develop treatments.
Moving onwards, Intestinal microecology is a new area of microecology study. It is a complex microflora that is directly related to human health. [ 4 ] Therefore, regulation of intestinal microecology will help in the treatment of many diseases. It was reported that intestinal flora is involved in anti-tumor immunotherapy and affects the curative effect of an anti-malignant tumor therapy to varying degrees.
The activity of metabolites and microbial composition of the intestinal microbiota are associated with various diseases including gastrointestinal diseases and cancer . [ 5 ] Similar to the intestinal microecosystem, the vaginal microecosystem is also complicated and plays an important role in women's health. [ 6 ] Maintaining microecological balance and the acidic environment of the vagina inhibits the proliferation of pathogenic bacteria . [ 7 ] [ 8 ]
At the urban scale, the term micro-ecology has been used by Mueller-Wolfertshofer and Boucsein [ 2 ] to describe the interdependence and interrelation of various activities within a neighbourhood. The synergy formed through socioeconomic processes, often with collaboration, profits all the actors involved and improves conditions, not just in the immediate neighbourhood, but at times even the city they are part of.
This microbiology -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microecology |
Microecosystems can exist in locations which are precisely defined by critical environmental factors within small or tiny spaces.
Such factors may include temperature , pH , chemical milieu, nutrient supply, presence of symbionts or solid substrates, gaseous atmosphere ( aerobic or anaerobic ) etc.
These microecosystems with limited water volume are often only of temporary duration and hence colonized by organisms which possess a drought-resistant spore stage in the lifecycle, or by organisms which do not need to live in water continuously. The ecosystem conditions applying at a typical pond edge can be quite different from those further from shore. Extremely space-limited water ecosystems can be found in, for example, the water collected in bromeliad leaf bases and the "pitchers" of Nepenthes .
These include the buccal region (especially cavities in the gingiva ), rumen , caecum etc. of mammalian herbivores or even invertebrate digestive tracts . In the case of mammalian gastrointestinal microecology, microorganisms such as protozoa, bacteria, as well as curious incompletely defined organisms (such as certain large structurally complex Selenomonads , Quinella ovalis "Quin's Oval", Magnoovum eadii "Eadie's Oval", Oscillospira etc.) can exist in the rumen as incredibly complex, highly enriched mixed populations, (see Moir and Masson images [ 1 ] ). This type of microecosystem can adjust rapidly to changes in the nutrition or health of the host animal (usually a ruminant such as cow, sheep, goat etc.); see Hungate's "The Rumen and its microbes 1966). Even within a small closed system such as the rumen there may exist a range of ecological conditions: Many organisms live freely in the rumen fluid whereas others require the substrate and metabolic products supplied by the stomach wall tissue with its folds and interstices. Interesting questions are also posed concerning the transfer of the strict anaerobe organisms in the gut microflora/microfauna to the next host generation. Here, mutual licking and coprophagia certainly play important roles.
A typical soil microecosystem may be restricted to less than a millimeter in its total depth range owing to steep variation in humidity and/or atmospheric gas composition. The soil grain size and physical and chemical properties of the substrate may also play important roles. Because of the predominant solid phase in these systems they are notoriously difficult to study microscopically without simultaneously disrupting the fine spatial distribution of their components.
These are defined by gradients of water temperature, nutrients, dissolved gases, salt concentrations etc. Along the path of terrestrial water flow the resulting temperature gradient continuum alone may provide many different minute microecosystems, starting with thermophilic bacteria such as Archaea "Archaebacteria" (100 °C (212 °F) or more), followed by conventional thermophiles (60–100 °C (140–212 °F)), cyanobacteria (blue-green algae) such as the motile filaments of Oscillatoria (30–60 °C (86–140 °F)), protozoa such as Amoeba, rotifers , then green algae (0–30 °C (32–86 °F)) etc.
Of course other factors than temperature also play important roles. Hot springs can provide classic and straightforward ecosystems for microecology studies as well as providing a haven for hitherto undescribed organisms.
The best known contain rare specialized organisms, found only in the immediate vicinity (sometimes within centimeters) of underwater volcanic vents (or "smokers"). These ecosystems require extremely advanced diving and collection techniques for their scientific exploration.
One that is sealed and completely independent of outside factors, except for temperature and light. A good example would be a plant contained in a sealed jar and submerged under water. No new factors would be able to enter this ecosystem. | https://en.wikipedia.org/wiki/Microecosystem |
A microelectrode is an electrode used in electrophysiology either for recording neural signals or for the electrical stimulation of nervous tissue (they were first developed by Ida Hyde in 1921). Pulled glass pipettes with tip diameters of 0.5 μm or less are usually filled with 3 molars potassium chloride solution as the electrical conductor. When the tip penetrates a cell membrane the lipids in the membrane seal onto the glass, providing an excellent electrical connection between the tip and the interior of the cell, which is apparent because the microelectrode becomes electrically negative compared to the extracellular solution. There are also microelectrodes made with insulated metal wires, made from inert metals with high Young modulus such as tungsten , stainless steel , or platinum-iridium alloy [ 1 ] and coated with glass or polymer insulator with exposed conductive tips. These are mostly used for recording from the external side of the cell membrane. More recent advances in lithography have produced silicon-based microelectrodes. | https://en.wikipedia.org/wiki/Microelectrode |
Microelectrode arrays ( MEAs ) (also referred to as multielectrode arrays [ 1 ] [ 2 ] ) are devices that contain multiple (tens to thousands) microelectrodes through which neural signals are obtained or delivered, essentially serving as neural interfaces that connect neurons to electronic circuitry . There are two general classes of MEAs: implantable MEAs, used in vivo , and non-implantable MEAs, used in vitro . In each class, there are rigid, flexible, and stretchable microelectrode array .
Neurons and muscle cells create ion currents through their membranes when excited, causing a change in voltage between the inside and the outside of the cell. When recording, the electrodes on an MEA transduce the change in voltage from the environment carried by ions into currents carried by electrons (electronic currents). When stimulating, electrodes transduce electronic currents into ionic currents through the media. This triggers the voltage-gated ion channels on the membranes of the excitable cells, causing the cell to depolarize and trigger an action potential if it is a neuron or a twitch if it is a muscle cell. [ citation needed ]
The size and shape of a recorded signal depend upon several factors: the nature of the medium in which the cell or cells are located (e.g. the medium's electrical conductivity , capacitance , and homogeneity ); the nature of contact between the cells and the MEA electrode (e.g. area of contact and tightness); the nature of the MEA electrode itself (e.g. its geometry, impedance , and noise); the analog signal processing (e.g. the system's gain , bandwidth , and behavior outside of cutoff frequencies ); and the data sampling properties (e.g. sampling rate and digital signal processing ). [ 3 ] For the recording of a single cell that partially covers a planar electrode, the voltage at the contact pad is approximately equal to the voltage of the overlapping region of the cell and electrode multiplied by the ratio the surface area of the overlapping region to the area of the entire electrode, or:
V p a d = V o v e r l a p × A o v e r l a p A e l e c t r o d e {\displaystyle V_{pad}=V_{overlap}\times {\frac {A_{overlap}}{A_{electrode}}}}
assuming the area around an electrode is well-insulated and has a very small capacitance associated with it. [ 3 ] The equation above, however, relies on modeling the electrode, cells, and their surroundings as an equivalent circuit diagram . An alternative means of predicting cell-electrode behavior is by modeling the system using a geometry-based finite element analysis in an attempt to circumvent the limitations of oversimplifying the system in a lumped circuit element diagram. [ 4 ]
An MEA can be used to perform electrophysiological experiments on tissue slices or dissociated cell cultures. With acute tissue slices, the connections between the cells within the tissue slices prior to extraction and plating are more or less preserved, while the intercellular connections in dissociated cultures are destroyed prior to plating. With dissociated neuronal cultures, the neurons spontaneously form networks . [ 5 ]
It can be seen that the voltage amplitude an electrode experiences is inversely related to the distance from which a cell depolarizes. [ 6 ] Thus, it may be necessary for the cells to be cultured or otherwise placed as close to the electrodes as possible. With tissue slices, a layer of electrically passive dead cells form around the site of incision due to edema . [ 7 ] A way to deal with this is by fabricating an MEA with three-dimensional electrodes fabricated by masking and chemical etching . These 3-D electrodes penetrate the dead cell layer of the slice tissue, decreasing the distance between live cells and the electrodes. [ 8 ] In dissociated cultures, proper adherence of the cells to the MEA substrate is important for getting robust signals.
The first implantable arrays were microwire arrays developed in the 1950s. [ 9 ] The first experiment involving the use of an array of planar electrodes to record from cultured cells was conducted in 1972 by C.A. Thomas, Jr. and his colleagues. [ 6 ] The experimental setup used a 2 x 15 array of gold electrodes plated with platinum black , each spaced 100 μm apart from each other. Myocytes harvested from embryonic chicks were dissociated and cultured onto the MEAs, and signals up to 1 mV high in amplitude were recorded. [ 10 ] MEAs were constructed and used to explore the electrophysiology of snail ganglia independently by Guenter Gross and his colleagues at the Center for Network Neuroscience in 1977 without prior knowledge of Thomas and his colleagues' work. [ 6 ] In 1982, Gross observed spontaneous electrophysiological activity from dissociated spinal cord neurons, and found that activity was very dependent on temperature. Below about 30˚C signal amplitudes decrease rapidly to relatively small value at room temperature . [ 6 ]
Before the 1990s, significant entry barriers existed for new laboratories that sought to conduct MEA research due to the custom MEA fabrication and software they had to develop. [ 5 ] However, with the advent of affordable computing power [ 3 ] and commercial MEA hardware and software, [ 5 ] many other laboratories were able to undertake research using MEAs.
Microelectrode arrays can be divided up into subcategories based on their potential use: in vitro and in vivo arrays.
The standard type of in vitro MEA comes in a pattern of 8 x 8 or 6 x 10 electrodes. Electrodes are typically composed of indium tin oxide , platinum black or titanium nitride and have diameters between 10 and 30 μm. These arrays are normally used for single-cell cultures or acute brain slices. [ 3 ]
One challenge among in vitro MEAs has been imaging them with microscopes that use high power lenses, requiring low working distances on the order of micrometers. In order to avoid this problem, "thin"-MEAs have been created using cover slip glass. These arrays are approximately 180 μm allowing them to be used with high-power lenses. [ 3 ] [ 11 ]
Another challenge among in vitro MEAs has been the rigidity of the glass substrate, which does not replicate the soft, flexible nature of biological tissues, thus impacting cellular behavior and experimental outcomes. [ 12 ] [ 13 ] To address this limitation, flexible and stretchable microelectrode arrays have been developed to better simulate the mechanical properties of living tissues. [ 13 ] [ 14 ] Manufacturers of flexible and stretchable MEAs such as BioMedical Sustainable Elastic Electronic Devices and Flexcell International Corporation are advancing MEA technologies to enhance the relevance of in vitro research by providing a more physiologically accurate environment for cells. [ 15 ] [ 16 ]
In another special design, 60 electrodes are split into 6 × 5 arrays separated by 500 μm. Electrodes within a group are separated by 30 um with diameters of 10 μm. Arrays such as this are used to examine local responses of neurons while also studying functional connectivity of organotypic slices. [ 3 ] [ 17 ]
Spatial resolution is one of the key advantages of MEAs and allows signals sent over a long distance to be taken with higher precision when a high-density MEA is used. These arrays usually have a square grid pattern of 256 electrodes that cover an area of 2.8 by 2.8 mm. [ 3 ]
Increased spatial resolution is provided by CMOS-based high-density microelectrode arrays featuring thousands of electrodes along with integrated readout and stimulation circuits on compact chips of the size of a thumbnail. [ 18 ] Even the resolution of signals propagating along single axons has been demonstrated. [ 19 ]
In order to obtain quality signals electrodes and tissue must be in close contact with one another. The perforated MEA design applies negative pressure to openings in the substrate so that tissue slices can be positioned on the electrodes to enhance contact and recorded signals. [ 3 ]
A different approach to lower the electrode impedance is by modification of the interface material, for example by using carbon nanotubes , [ 20 ] [ 21 ] or by modification of the structure of the electrodes, with for example gold nanopillars [ 22 ] or nanocavities. [ 23 ]
The three major categories of implantable MEAs are microwire, silicon -based, [ 24 ] and flexible microelectrode arrays. Microwire MEAs are largely made of stainless steel or tungsten and they can be used to estimate the position of individual recorded neurons by triangulation. Silicon-based microelectrode arrays include two specific models: the Michigan and Utah arrays. Michigan arrays allow a higher density of sensors for implantation as well as a higher spatial resolution than microwire MEAs. They also allow signals to be obtained along the length of the shank, rather than just at the ends of the shanks. In contrast to Michigan arrays, Utah arrays are 3-D, consisting of 100 conductive silicon needles. However, in a Utah array, signals are only received from the tips of each electrode, which limits the amount of information that can be obtained at one time. Furthermore, Utah arrays are manufactured with set dimensions and parameters while the Michigan array allows for more design freedom. Flexible arrays, made with polyimide , parylene , or benzocyclobutene , provide an advantage over rigid microelectrode arrays because they provide a closer mechanical match, as the Young's modulus of silicon is much larger than that of brain tissue, contributing to shear-induced inflammation . [ 9 ] [ 13 ] [ 25 ]
The fundamental unit of communication of neurons is, electrically, at least, the action potential. This all-or-nothing phenomenon originates at the axon hillock , [ 26 ] resulting in a depolarization of the intracellular environment which propagates down the axon . This ion flux through the cellular membrane generates a sharp change in voltage in the extracellular environment, which is what the MEA electrodes ultimately detect. Thus, voltage spike counting and sorting is often used in research to characterize network activity. Spike train analysis, can also save processing time and computing memory compared to voltage measurements. Spike timestamps are identified as times where the voltage measured by an individual electrode exceeds a threshold (often defined by standard deviations from the mean of an inactive time period). These timestamps can be further processed to identify bursts(multiple spikes in close proximity). Further analysis of these trains can reveal spike organization and temporal patterns. [ 27 ]
In general, the major strengths of in vitro arrays when compared to more traditional methods such as patch clamping include: [ 28 ]
Furthermore, in vitro arrays are non-invasive when compared to patch clamping because they do not require breaching of the cell membrane.
With respect to in vivo arrays however, the major advantage over patch clamping is the high spatial resolution. Implantable arrays allow signals to be obtained from individual neurons enabling information such as position or velocity of motor movement that can be used to control a prosthetic device. Large-scale, parallel recordings with tens of implanted electrodes are possible, at least in rodents, during animal behavior. This makes such extracellular recordings the method of choice to identify of neural circuits and to study their functions. Unambiguous identification of the recorded neuron using multi-electrode extracellular arrays, however, remains a problem to date.
In vitro MEAs are less suited for recording and stimulating single cells due to their low spatial resolution compared to patch clamp and dynamic clamp systems. The complexity of signals an MEA electrode could effectively transmit to other cells is limited compared to the capabilities of dynamic clamps.
There are also several biological responses to implantation of a microelectrode array, particularly in regards to chronic implantation. [ 29 ] Most notable among these effects are neuronal cell loss, glial scarring , and a drop in the number of functioning electrodes. [ 30 ] The tissue response to implantation is dependent among many factors including size of the MEA shanks, distance between the shanks, MEA material composition, and time period of insertion. The tissue response is typically divided into short term and long term response. The short term response occurs within hours of implantation and begins with an increased population of astrocytes and glial cells surrounding the device. The recruited microglia then initiate inflammation and a process of phagocytosis of the foreign material begins. Over time, the astrocytes and microglia recruited to the device begin to accumulate, forming a sheath surrounding the array that extends tens of micrometres around the device. This not only increases the space between electrode probes, but also insulates the electrodes and increases impedance measurements. Problems with chronic implantation of arrays have been a driving force in the research of these devices. One novel study examined the neurodegenerative effects of inflammation caused by chronic implantation. [ 31 ] Immunohistochemical markers showed a surprising presence of hyperphosphorylated tau, an indicator of Alzheimer's disease , near the electrode recording site. The phagocytosis of electrode material also brings into question the issue of a biocompatibility response, which research suggests has been minor and becomes almost nonexistent after 12 weeks in vivo . Research into minimizing the negative effects of device insertion includes surface coating of the devices with proteins that encourage neuron attachment, such as laminin , or drug eluting substances. [ 32 ] [ 13 ]
The nature of dissociated neuronal networks does not seem to change or diminish the character of its pharmacological response when compared to in vivo models, suggesting that MEAs can be used to study pharmacological effects on dissociated neuronal cultures in a more simple, controlled environment. [ 33 ] A number of pharmacological studies using MEAs on dissociated neuronal networks, e.g. studies with ethanol . [ 34 ] Interlaboratory validation has been conducted using MEAs. [ 35 ]
In addition, a substantial body of work on various biophysical aspects of network function was carried out by reducing phenomena usually studied at the behavioral level to the dissociated cortical network level. For example, the capacity of such networks to extract spatial [ 36 ] and temporal [ 37 ] features of various input signals, dynamics of synchronization, [ 38 ] sensitivity to neuromodulation [ 39 ] [ 40 ] [ 41 ] and kinetics of learning using closed loop regimes. [ 42 ] [ 43 ] Finally, combining MEA technology with confocal microscopy allows for studying relationships between network activity and synaptic remodeling. [ 11 ]
MEAs have been used to interface neuronal networks with non-biological systems as a controller. For example, a neural-computer interface can be created using MEAs. Dissociated rat cortical neurons were integrated into a closed stimulus-response feedback loop to control an animat in a virtual environment. [ 44 ] A closed-loop stimulus-response system has also been constructed using an MEA by Potter, Mandhavan, and DeMarse, [ 45 ] and by Mark Hammond, Kevin Warwick , and Ben Whalley in the University of Reading . About 300,000 dissociated rat neurons were plated on an MEA, which was connected to motors and ultrasound sensors on a robot, and was conditioned to avoid obstacles when sensed. [ 46 ] Along these lines, Shimon Marom and colleagues in the Technion hooked dissociated neuronal networks growing on MEAs to a Lego Mindstorms robot; the visual field of the robot was classified by the network, and commands were delivered to the robot wheels such that it completely avoids bumping into obstacles. [ 36 ] This "Braitenberg vehicle" was used to demonstrate the indeterminacy of reverse neuro-engineering showing that even in a simple setup with practically unlimited access to every piece of relevant information, [ 47 ] it was impossible to deduce with certainty the specific neural coding scheme that was used to drive the robots behavior.
MEAs have been used to observe network firing in hippocampal slices. [ 48 ]
There are several implantable interfaces that are currently available for consumer use including deep brain stimulators , cochlear implants , and cardiac pacemakers . Deep brain stimulation (DBS) has been effective at treating movement disorders such as Parkinson's disease , [ 49 ] and cochlear implants have helped many to improve their hearing by assisting stimulation of the auditory nerve . Because of their remarkable potential, MEAs are a prominent area of neuroscience research. Research suggests that MEAs may provide insight into processes such as memory formation and perception and may also hold therapeutic value for conditions such as epilepsy , depression , and obsessive-compulsive disorder [ citation needed ] . Clinical trials using interface devices for restoring motor control after spinal cord injury or as treatment for ALS have been initiated in a project entitled BrainGate (see video demo: BrainGate ). MEAs provide the high resolution necessary to record time varying signals, giving them the ability to be used to both control and obtain feedback from prosthetic devices, as was shown by Kevin Warwick , Mark Gasson and Peter Kyberd . [ 50 ] [ 51 ] Research suggests that MEA use may be able to assist in the restoration of vision by stimulating the optic pathway . [ 9 ]
A biannual scientific user meeting is held in Reutlingen , organized by the Natural and Medical Sciences Institute (NMI) at the University of Tübingen . The meetings offer a comprehensive overview of all aspects related to new developments and current applications of Microelectrode Arrays in basic and applied neuroscience as well as in industrial drug discovery, safety pharmacology and neurotechnology. The biannual conference has developed into an international venue for scientists developing and using MEAs from both industry and academia, and is recognized as an information-packed scientific forum of high quality. The meeting contributions are available as open access proceeding books.
In addition to being used for scientific purposes, MEAs have been used in contemporary art to investigate philosophical questions about the relationship between technology and biology. Traditionally within Western thought, biology and technology have been separated into two distinct categories: bios and technê. [ 52 ] In 2002, MEART: The Semi-living Artist was created as a collaborative art and science project between SymbioticA at the University of Western Australia in Perth , and the Potter Lab at the Georgia Institute of Technology in Atlanta , to question the relationship between biology and technology. [ 53 ] [ 54 ] [ 55 ] [ 56 ] MEART consisted of rat cortical neurons grown in vitro on an MEA in Atlanta, a pneumatic robot arm capable of drawing with pens on paper in Perth, and software to govern communications between the two. Signals from the neurons were relayed in a closed-loop between Perth and Atlanta as the MEA stimulated the pneumatic arm. MEART was first exhibited to the public in the exhibition Biofeel at the Perth Institute of Contemporary Arts in 2002. [ 55 ] [ 57 ] | https://en.wikipedia.org/wiki/Microelectrode_array |
Microelectromechanical system oscillators ( MEMS oscillators ) are devices that generate highly stable reference frequencies used to sequence electronic systems, manage data transfer , define radio frequencies , and measure elapsed time. The core technologies used in MEMS oscillators have been in development since the mid-1960s, but have only been sufficiently advanced for commercial applications since 2006. [ 1 ] MEMS oscillators incorporate MEMS resonators , which are microelectromechanical structures that define stable frequencies. MEMS clock generators are MEMS timing devices with multiple outputs for systems that need more than a single reference frequency. MEMS oscillators are a valid alternative to older, more established quartz crystal oscillators , offering better resilience against vibration and mechanical shock, and reliability with respect to temperature variation.
MEMS resonators are small electromechanical structures that vibrate at high frequencies. They are used for timing references, signal filtering, mass sensing, biological sensing, motion sensing, and other diverse applications.
For frequency and timing references, MEMS resonators are attached to electronic circuits, often called sustaining amplifiers, to drive them in continuous motion. In most cases these circuits are located near the resonators and in the same physical package. In addition to driving the resonators, these circuits produce output signals for downstream electronics.
By convention, the term oscillators usually denotes integrated circuits (ICs) that supply single output frequencies. MEMS oscillators include MEMS resonators, sustaining amps, and additional electronics to set or adjust their output frequencies. These circuits often include phase-locked loops (PLLs) that produce selectable or programmable output frequencies from the upstream MEMS reference frequencies. [ 2 ]
MEMS oscillators are commonly available as 4- or 6-pin ICs that conform to printed circuit board (PCB) solder footprints previously standardized for quartz crystal oscillators.
The term clock generator usually denotes a timing IC with multiple outputs. Following this custom, MEMS clock generators are multi-output MEMS timing devices. These are used to supply timing signals in complex electronic systems that require multiple frequencies or clock phases. For example, most computers require independent clocks for processor timing, disk I/O, serial I/O, video generation, Ethernet I/O, audio conversion, and other functions. [ 3 ]
Clock generators are usually specialised for their applications, including the number and selection of frequencies, various auxiliary features, and package configurations. They often include multiple PLLs to generate multiple output frequencies or phases.
MEMS Real-time clocks (RTCs) are ICs that track time of day and date. They include MEMS resonators , sustaining amps, and registers that increment with time, for instance counting days, hours, minutes and seconds. They also include auxiliary functions like alarm outputs and battery management.
RTCs must run continuously to keep track of elapsed time. To do this they must sometimes run from small batteries and therefore must operate at very low power levels. They are generally moderate-sized ICs with up to 20 pins for power, battery backup, digital interface, and various other functions.
Motivated by the shortcomings of quartz crystal oscillators, researchers have been developing the resonance properties of MEMS structures since 1965. [ 4 ] [ 5 ] However, until recently various accuracy, stability, and manufacturability issues related to sealing, packaging, and adjusting the resonator elements prevented cost-effective commercial manufacturing. Five technical challenges had to be overcome:
The first MEMS resonators were built with metallic resonator elements. [ 4 ] These resonators were envisioned as audio filters and had moderate quality factors (Qs) of 500 and frequencies of 1 kHz to 100 kHz. Filtering applications, now for high frequency radio, are still important and are an active area for MEMS research and commercial products.
However, early MEMS resonators did not have sufficiently stable frequencies to be used for timing references or clock generation. The metallic resonator elements tended to shift frequency with time (they aged) and with use (they fatigued). Under temperature variation they tended to have large and not entirely predictable frequency shifts (they had large temperature sensitivity) and when they were temperature cycled they tended to return to different frequencies (they were hysteretic).
Work in the 1970s [ 6 ] [ 7 ] [ 8 ] through the 1990s [ 9 ] identified sufficiently stable resonator materials and associated fabrication techniques. In particular, single and polycrystalline silicon was found to be suitable for frequency references with effectively zero aging, fatigue and hysteresis, and with moderate temperature sensitivity. [ 10 ] [ 11 ]
Material development is still ongoing in MEMS resonator research. Significant effort has been invested in silicon-germanium (SiGe) for its low temperature fabrication [ 12 ] and aluminium nitride (AlN) for its piezoelectric transduction. [ 13 ] Work on micromachined quartz continues, [ 14 ] while polycrystalline diamond has been used for high frequency resonators for its exceptional stiffness-to-mass ratio. [ 15 ]
MEMS resonators require cavities in which they can move freely, and for frequency references these cavities must be evacuated. Early resonators were built on top of silicon wafers and tested in vacuum chambers, [ 9 ] but individual resonator encapsulation was clearly needed.
The MEMS community had employed bonded cover techniques to enclose other MEMS components, for instance pressure sensors , accelerometers , and gyroscopes , and these techniques were adapted to resonators. [ 16 ] [ 17 ] In this approach, cover wafers were micromachined with small cavities and bonded to the resonator wafers, enclosing the resonators in small evacuated cavities. Initially these wafers were bonded with low melting temperature glass, called glass frit , [ 18 ] but recently other bonding technologies including metallic compression and metallic amalgams, have replaced glass frit. [ 19 ] [ 20 ]
Thin film encapsulation techniques were developed to form enclosed cavities by building covers directly over the resonators in the fabrication process rather than bonding covers onto the resonators. [ 21 ] [ 22 ] [ 23 ] [ 24 ] [ 25 ] [ 26 ] These techniques had the advantage that they did not use as much die area for the sealing structure, they did not require preparation of second wafers to form the covers, and the resulting device wafers were thinner.
Frequency references generally require frequency stabilities of 100 parts per million (ppm) or better. However, the early cover and encapsulation technologies left significant amounts of contamination in the cavities. Because MEMS resonators are small, and particularly because they have small volume-to-surface area, they are especially sensitive to mass loading. Even single-atomic layers of contaminants like water or hydrocarbons can shift the resonator's frequencies out of specification. [ 27 ] [ 28 ]
When resonators are aged or temperature cycled, the contaminants can move in the chambers, and transfer onto or off of the resonators. [ 10 ] [ 29 ] The change in mass on the resonators can produce hysteresis of thousands of ppm, which is unacceptable for virtually all frequency reference applications.
Early covered resonators with glass frit seals were unstable because contaminants outgassed from the sealing material. To overcome this, getters were built into the cavities. Getters are materials that can absorb gas and contaminants after cavities are sealed. However, getters can also release contaminants and can be costly, so their use in this application is being discontinued in favor of cleaner cover bonding processes.
Likewise, thin film encapsulation can trap fabrication byproducts in the cavities. A high temperature thin film encapsulation based on epitaxial silicon deposition was developed to eliminate this. This epitaxial sealing (EpiSeal) process [ 30 ] has been found to be exceptionally clean and produces the highest stability resonators. [ 31 ] [ 32 ] [ 33 ] [ 34 ] [ 35 ]
In early MEMS resonator development, researchers tried to build resonators at the target application frequencies and to maintain those frequencies over temperature. Approaches to solving this problem included trimming and temperature compensating the MEMS resonators in ways analogous to those used for quartz crystal. [ 36 ] [ 37 ] [ 38 ]
However, these techniques were found to be technically limiting and expensive. A more effective solution was to electronically shift the resonators' frequencies to the oscillators' output frequencies. [ 39 ] [ 40 ] This had the advantage that the resonators did not need to be individually trimmed; instead their frequencies could be measured and appropriate scaling coefficients recorded in the oscillator ICs. In addition, the resonators' temperatures could be electronically measured, and the frequency scaling could be adjusted to compensate for the resonators' frequency variation over temperature.
Various applications require clocks with predefined signal and performance specifications. Of these, the key specifications are phase noise and frequency stability.
Phase noise has been optimized by raising the resonator's natural frequencies (f) and quality factors (Q). The Q specifies how long resonators continue to ring after drive to them is stopped, or equivalently when viewed as filters how narrow their pass-bands are. In particular, the Q times f, or Qf product, determines the near-carrier phase noise. [ 41 ] Early MEMS resonators showed unacceptably low Qf products for reference. Significant theoretical work clarified the underlying physics [ 42 ] [ 43 ] while experimental work developed high Qf resonators. [ 44 ] The presently available MEMS Qf performance is suitable for virtually all applications.
Resonator structural design, particularly in mode control, [ 45 ] anchoring methods, [ 15 ] [ 46 ] narrow-gap transducers, [ 47 ] linearity, [ 48 ] and arrayed structures [ 49 ] consumed significant research effort.
The required frequency accuracies range from relatively loose for processor clocking, typically 50 to 100 ppm, to precise for high speed data clocking, often 2.5 ppm and below. Research demonstrated MEMS resonators and oscillators could be built to well within these levels. [ 50 ] [ 51 ] Commercial products are now available to 0.5 ppm, [ 52 ] which covers the majority of application requirements.
Finally, the frequency control electronics and associated support circuitry needed to be developed and optimized. Key areas were in temperature sensors [ 53 ] and PLL design. [ 54 ] Recent circuit developments have produced MEMS oscillators suitable for high speed serial applications [ 55 ] with sub-picosecond integrated jitter. [ 56 ]
The U.S. Defense Advanced Research Projects Agency ( DARPA ) funded a wide range of MEMS research that provided the base technologies for the developments described above. In 2001 and 2002, DARPA launched the Nano Mechanical Array Signal Processors (NMASP) and Harsh Environment Robust Micromechanical Technology (HERMIT) programs to specifically develop MEMS high stability resonator and packaging technologies. This work was fruitful and advanced the technology to a level at which venture capital funded startups could develop commercial products. These startups included Discera [ 57 ] in 2001, SiTime in 2004, Silicon Clocks in 2006, and Harmonic Devices in 2006. [ citation needed ]
SiTime introduced the first production MEMS oscillator in 2006, followed by Discera in 2007. Harmonic Devices changed its focus to sensor products and was bought by Qualcomm in 2010. Silicon Clocks never introduced commercial products and was bought by Silicon Labs in 2010. Additional entrants have announced their intention to produce MEMS oscillators, including Sand 9 [ 58 ] and VTI Technologies. [ 59 ]
By sales volume, MEMS oscillator suppliers rank in descending order as SiTime and Discera. A number of quartz oscillator suppliers resell MEMS oscillators. SiTime announced it has cumulatively shipped 50 million units as of mid-2011. [ 60 ] Others have not disclosed sales volumes.
One can think of MEMS resonators as small bells that ring at high frequencies. Small bells ring at higher frequencies than large bells, and since MEMS resonators are small they can ring at high frequencies. Common bells are meters down to centimeters across and ring at hundreds of hertz to kilohertz ; MEMS resonators are a tenth of a millimeter across and ring at tens of kilohertz to hundreds of megahertz. MEMS resonators have operated at over a gigahertz . [ 61 ]
Common bells are mechanically struck, while MEMS resonators are electrically driven. There are two base technologies used to build MEMS resonators that differ in how electrical drive and sense signals are transduced from the mechanical motion. These are electrostatic and piezoelectric . All commercial MEMS oscillators use electrostatic transduction while MEMS filters use piezoelectric transduction. Piezoelectric resonators have not shown sufficient frequency stability or quality factor (Q) for frequency reference applications.
Electronic sustaining amps drive the resonators in continuous oscillation. These amplifiers detect the resonator motion and drive additional energy into the resonators. They are carefully designed to maintain the resonators motion at appropriate amplitudes and to extract low noise output clock signals.
Additional circuits called fractional-n phase lock loops (frac-N PLLs) multiply the resonator's mechanical frequencies to the oscillator's output frequencies. [ 39 ] [ 40 ] [ 54 ] [ 56 ] These highly specialized PLLs set the output frequencies under control of digital state machines. The state machines are controlled by calibration and program data stored in non-volatile memory and adjust the PLL configurations to compensate for temperature variations.
The state machines can also be built to provide additional user functions, for instance spread-spectrum clocking and voltage controlled frequency trimming.
MEMS clock generators are built with MEMS oscillators at their core and include additional circuitry to supply the additional outputs. This additional circuitry is usually designed to provide the specific features required by the applications.
MEMS RTCs work like oscillators but are optimized for low power consumption and include auxiliary circuits to track the date and time. To operate at low power they are built with low frequency MEMS resonators. Care is taken in circuit design to minimize power consumption while providing the required timing accuracies.
Depending upon the type of resonator, the fabrication process is either done in a specialized MEMS fab or a CMOS foundry.
The manufacturing process varies with resonator and encapsulation design, but in general the resonator structures are lithographically patterned and plasma-etched in or on silicon wafers. All commercial MEMS oscillators are built from poly or single crystal silicon.
It is important in electrostatically transduced resonators to form narrow and well controlled drive and sense capacitor gaps. These can be either lateral for instance under the resonators, or vertical beside the resonators. Each option has its advantages [ further explanation needed ] and both are used commercially.
The resonators are encapsulated either by bonding cover wafers onto the resonator wafers or by depositing thin film encapsulation layers over the resonators. Here again, both methods are used commercially.
Bonded cover wafers must be attached with an adhesive. Two options are used, a glass frit bond ring or a metallic bond ring. The glass frit has been found to generate too much contamination, and thus drift, and is no longer commonly used. [ 62 ]
For thin film encapsulation the resonators' structures are covered with layers of oxide and silicon, then released by removing the surrounding oxide to form freestanding resonators, and finally sealed with an additional deposition. [ 31 ]
The sustaining amps, PLLs , and auxiliary circuits are built with standard mixed-signal CMOS processes fabricated in CMOS foundries.
Integrated MEMS oscillators with CMOS circuits on the same IC die have been demonstrated [ 9 ] [ 63 ] but to date this homogeneous integration is not commercially viable. Instead, it is advantageous to produce the MEMS resonators and CMOS circuitry on separate die and combine them at the packaging stage. Combining multiple die in a single package in this way is called heterogeneous integration or simply die stacking.
The completed MEMS devices, enclosed in small chip-level vacuum chambers , are diced from their silicon wafers , and the resonator die are stacked on CMOS die and molded into plastic packages to form oscillators.
MEMS oscillators are packaged in the same factories and with the same equipment and materials that are used for standard IC packaging. This is a significant contributor to their cost-effectiveness and reliability as compared to quartz oscillators, which are assembled with specialized ceramic packages in custom-built factories.
Package dimensions and pad shapes match those of standard quartz oscillator packages so the MEMS oscillators can be soldered directly on PCBs designed for quartz without requiring board modification or re-design.
Production tests check and calibrate the MEMS resonators and CMOS ICs to verify they are performing to specification and trim their frequencies. In addition, many MEMS oscillators have programmable output frequencies that can be configured at test time. Of course the various types of oscillators are configured from specialized CMOS and MEMS die. For instance, low power and high performance oscillators are not built with the same die. In addition, high precision oscillators often require more careful calibration than lower precision oscillators.
MEMS oscillators are tested much like standard ICs. Like packaging, this is done in standard IC factories with standard IC test equipment.
Using standard IC packaging and test facilities (called subcons in the IC industry) gives MEMS oscillators production scalability. [ 46 ] These facilities are capable of large production volumes, often hundreds of millions of ICs per day. This capacity is shared across many IC companies, so ramping production volumes of specific ICs, or in this case specific MEMS oscillators, is a function of allocating standard production equipment. Conversely, quartz oscillator factories are single-function in nature, so that ramping production requires installing custom equipment, which is more costly and time-consuming than allocating standard equipment.
Quartz oscillators are sold in much larger quantities than MEMS oscillators, and are widely used and understood by electronics engineers. Therefore, quartz oscillators provide the baseline from which MEMS oscillators are compared. [ 64 ]
Recent advances have enabled MEMS-based timing devices to offer performance levels similar, and sometimes superior, to quartz devices. MEMS oscillator signal quality as measured by phase noise is now sufficient for most applications. Phase noise of −150 dBc at 10 kHz from 10 MHz is now available, a level that is generally only needed for radio frequency (RF) applications. MEMS oscillators are now available with integrated jitter under 1.0 picosecond, measured from 12 kHz to 20 MHz, a level that is normally required for high speed serial data links, such as SONET and SyncE, and some instrumentation applications.
Short term stability, startup time, and power consumption, are similar to those of quartz. [ citation needed ] In some cases, MEMS oscillators show lower power consumption than that of quartz.
High precision MEMS temperature-compensated oscillators (TCXOs) have recently been announced with ±0.1 ppm frequency stability over temperature. [ 65 ] This exceeds the performance of all but the very high-end quartz TCXOs and oven-controlled oscillators (OCXOs). [ citation needed ] MEMS TCXOs are now available with output frequencies over 100 MHz, a capability that only a few specialized quartz oscillators (e.g., inverted mesa,) can provide. [ citation needed ]
In RTC applications MEMS oscillators are performing slightly better than the best quartz tuning forks in terms of frequency stability over temperature and solder-down shift, while quartz is still superior for the lowest power applications.
Manufacturing and stocking quartz oscillators to the wide variety of specifications that users require is difficult. [ citation needed ] Various applications require oscillators with specific frequencies, accuracy levels, signal quality levels, package sizes, supply voltages, and special features. The combination of these leads to a proliferation of part numbers which makes stocking impractical and can lead to long production lead times. [ citation needed ]
MEMS oscillator suppliers solve the diversity problem by leveraging circuit technology. While quartz oscillators are usually built with the quartz crystals driven at the desired output frequencies, [ citation needed ] MEMS oscillators commonly drive the resonators at one frequency and multiply this to the designed output frequency. In this way, the hundreds of standard application frequencies and the occasional custom frequency can be provided without redesigning the MEMS resonators or circuits.
There are, of course, differences in the resonator, circuits, or calibration required for different categories of parts, but within these categories the frequency translation parameters can often be programmed into the MEMS oscillators late in the production process. Because the components are not differentiated until late in the process the lead times can be short, typically a few weeks. Technologically, quartz oscillators can be made with circuit-centric programmable architectures like those used in MEMS, but historically only a minority have been built this way.
MEMS oscillators are also significantly immune to shock and vibration and have shown production quality levels higher than those associated with quartz. [ citation needed ]
Quartz oscillators are secure in specific applications where suitable MEMS oscillators have not been introduced. One of those applications, for instance, is voltage-controlled TCXOs (VCTCXOs) for cell phone handsets. This application requires a very specific set of capabilities for which quartz products are highly optimized. [ citation needed ]
Quartz oscillators are superior in the extreme high ends of the performance range. These include OCXOs that can maintain stabilities within a few parts per billion (ppb), and surface acoustic wave (SAW) oscillators that can deliver jitter under 100 femtoseconds at high frequencies. Until recently, MEMS oscillators did not compete in the TCXO product range, but new product introductions have brought MEMS oscillators into that market.
Quartz is still dominant in clock generator applications. These applications require highly specialized output combinations and custom packages. The supply chain for these products is specialized and does not include a MEMS oscillator supplier.
MEMS oscillators are replacing quartz oscillators in a variety of applications such as computing, consumer, networking, communications, automotive and industrial systems.
Programmable MEMS oscillators can be used in most applications where fixed-frequency quartz oscillators are used, such as PCI-Express, SATA, SAS, PCI, USB, Gigabit Ethernet, MPEG video, and cable modems.
MEMS clock generators are useful in complex systems that require multiple frequencies, such as data servers and telecom switches.
MEMS real-time clocks are used in systems that require precise time measurements. Smart meters for gas and electricity are an example that is consuming significant quantities of these devices.
and
VC-TCXO – Voltage Controlled TCXO
The "X" in the names of oscillator types originally denoted "crystal". Some manufacturers have adopted this convention to include MEMS oscillators. Others are substituting "M" for "X" (as in "VCMO" versus "VCXO") to differentiate MEMS-based oscillators from quartz-based oscillators.
MEMS oscillators may be detrimentally affected by helium . In 2018, a helium leak from a hospital MRI machine caused widespread failure of nearby iPhones due to their MEMS oscillators. [ 66 ] [ 67 ] A helium concentration of as little as 2% has been shown to cause complete failure of a MEMS oscillator. | https://en.wikipedia.org/wiki/Microelectromechanical_system_oscillator |
Microevolution is the change in allele frequencies that occurs over time within a population. [ 1 ] This change is due to four different processes: mutation , selection ( natural and artificial ), gene flow and genetic drift . This change happens over a relatively short (in evolutionary terms) amount of time compared to the changes termed macroevolution .
Population genetics is the branch of biology that provides the mathematical structure for the study of the process of microevolution. Ecological genetics concerns itself with observing microevolution in the wild. Typically, observable instances of evolution are examples of microevolution; for example, bacterial strains that have antibiotic resistance .
Microevolution provides the raw material for macroevolution . [ 2 ] [ 3 ]
Macroevolution is guided by sorting of interspecific variation ("species selection" [ 2 ] ), as opposed to sorting of intraspecific variation in microevolution. [ 3 ] Species selection may occur as (a) effect-macroevolution, where organism-level traits (aggregate traits) affect speciation and extinction rates, and (b) strict-sense species selection, where species-level traits (e.g. geographical range) affect speciation and extinction rates. [ 4 ] Macroevolution does not produce evolutionary novelties, but it determines their proliferation within the clades in which they evolved, and it adds species-level traits as non-organismic factors of sorting to this process. [ 3 ]
Mutations are changes in the DNA sequence of a cell's genome and are caused by radiation , viruses , transposons and mutagenic chemicals , as well as errors that occur during meiosis or DNA replication . [ 5 ] [ 6 ] [ 7 ] Errors are introduced particularly often in the process of DNA replication , in the polymerization of the second strand. These errors can also be induced by the organism itself, by cellular processes such as hypermutation . Mutations can affect the phenotype of an organism, especially if they occur within the protein coding sequence of a gene. Error rates are usually very low—1 error in every 10–100 million bases—due to the proofreading ability of DNA polymerases . [ 8 ] [ 9 ] (Without proofreading error rates are a thousandfold higher; because many viruses rely on DNA and RNA polymerases that lack proofreading ability, they experience higher mutation rates.) Processes that increase the rate of changes in DNA are called mutagenic : mutagenic chemicals promote errors in DNA replication, often by interfering with the structure of base-pairing, while UV radiation induces mutations by causing damage to the DNA structure. [ 10 ] Chemical damage to DNA occurs naturally as well, and cells use DNA repair mechanisms to repair mismatches and breaks in DNA—nevertheless, the repair sometimes fails to return the DNA to its original sequence.
In organisms that use chromosomal crossover to exchange DNA and recombine genes, errors in alignment during meiosis can also cause mutations. [ 11 ] Errors in crossover are especially likely when similar sequences cause partner chromosomes to adopt a mistaken alignment making some regions in genomes more prone to mutating in this way. These errors create large structural changes in DNA sequence— duplications , inversions or deletions of entire regions, or the accidental exchanging of whole parts between different chromosomes (called translocation ).
Mutation can result in several different types of change in DNA sequences; these can either have no effect, alter the product of a gene , or prevent the gene from functioning. Studies in the fly Drosophila melanogaster suggest that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70 percent of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial. [ 12 ] Due to the damaging effects that mutations can have on cells, organisms have evolved mechanisms such as DNA repair to remove mutations. [ 5 ] Therefore, the optimal mutation rate for a species is a trade-off between costs of a high mutation rate, such as deleterious mutations, and the metabolic costs of maintaining systems to reduce the mutation rate, such as DNA repair enzymes. [ 13 ] Viruses that use RNA as their genetic material have rapid mutation rates, [ 14 ] which can be an advantage since these viruses will evolve constantly and rapidly, and thus evade the defensive responses of e.g. the human immune system . [ 15 ]
Mutations can involve large sections of DNA becoming duplicated , usually through genetic recombination . [ 16 ] These duplications are a major source of raw material for evolving new genes, with tens to hundreds of genes duplicated in animal genomes every million years. [ 17 ] Most genes belong to larger families of genes of shared ancestry . [ 18 ] Novel genes are produced by several methods, commonly through the duplication and mutation of an ancestral gene, or by recombining parts of different genes to form new combinations with new functions. [ 19 ] [ 20 ]
Here, domains act as modules, each with a particular and independent function, that can be mixed together to produce genes encoding new proteins with novel properties. [ 21 ] For example, the human eye uses four genes to make structures that sense light: three for color vision and one for night vision ; all four arose from a single ancestral gene. [ 22 ] Another advantage of duplicating a gene (or even an entire genome ) is that this increases redundancy ; this allows one gene in the pair to acquire a new function while the other copy performs the original function. [ 23 ] [ 24 ] Other types of mutation occasionally create new genes from previously noncoding DNA. [ 25 ] [ 26 ]
Selection is the process by which heritable traits that make it more likely for an organism to survive and successfully reproduce become more common in a population over successive generations.
It is sometimes valuable to distinguish between naturally occurring selection, natural selection, and selection that is a manifestation of choices made by humans, artificial selection. This distinction is rather diffuse. Natural selection is nevertheless the dominant part of selection.
The natural genetic variation within a population of organisms means that some individuals will survive more successfully than others in their current environment . Factors which affect reproductive success are also important, an issue which Charles Darwin developed in his ideas on sexual selection .
Natural selection acts on the phenotype , or the observable characteristics of an organism, but the genetic (heritable) basis of any phenotype which gives a reproductive advantage will become more common in a population (see allele frequency ). Over time, this process can result in adaptations that specialize organisms for particular ecological niches and may eventually result in the speciation (the emergence of new species).
Natural selection is one of the cornerstones of modern biology . The term was introduced by Darwin in his groundbreaking 1859 book On the Origin of Species , [ 27 ] in which natural selection was described by analogy to artificial selection , a process by which animals and plants with traits considered desirable by human breeders are systematically favored for reproduction. The concept of natural selection was originally developed in the absence of a valid theory of heredity ; at the time of Darwin's writing, nothing was known of modern genetics. The union of traditional Darwinian evolution with subsequent discoveries in classical and molecular genetics is termed the modern evolutionary synthesis . Natural selection remains the primary explanation for adaptive evolution .
Genetic drift is the change in the relative frequency in which a gene variant ( allele ) occurs in a population due to random sampling . That is, the alleles in the offspring in the population are a random sample of those in the parents. And chance has a role in determining whether a given individual survives and reproduces. A population's allele frequency is the fraction or percentage of its gene copies compared to the total number of gene alleles that share a particular form. [ 28 ]
Genetic drift is an evolutionary process which leads to changes in allele frequencies over time. It may cause gene variants to disappear completely, and thereby reduce genetic variability. In contrast to natural selection , which makes gene variants more common or less common depending on their reproductive success, [ 29 ] the changes due to genetic drift are not driven by environmental or adaptive pressures, and may be beneficial, neutral, or detrimental to reproductive success.
The effect of genetic drift is larger in small populations, and smaller in large populations. Vigorous debates wage among scientists over the relative importance of genetic drift compared with natural selection. Ronald Fisher held the view that genetic drift plays at the most a minor role in evolution, and this remained the dominant view for several decades. In 1968 Motoo Kimura rekindled the debate with his neutral theory of molecular evolution which claims that most of the changes in the genetic material are caused by genetic drift. [ 30 ] The predictions of neutral theory, based on genetic drift, do not fit recent data on whole genomes well: these data suggest that the frequencies of neutral alleles change primarily due to selection at linked sites , rather than due to genetic drift by means of sampling error . [ 31 ]
Gene flow is the exchange of genes between populations, which are usually of the same species. [ 32 ] Examples of gene flow within a species include the migration and then breeding of organisms, or the exchange of pollen . Gene transfer between species includes the formation of hybrid organisms and horizontal gene transfer .
Migration into or out of a population can change allele frequencies, as well as introducing genetic variation into a population. Immigration may add new genetic material to the established gene pool of a population. Conversely, emigration may remove genetic material. As barriers to reproduction between two diverging populations are required for the populations to become new species , gene flow may slow this process by spreading genetic differences between the populations. Gene flow is hindered by mountain ranges, oceans and deserts or even man-made structures such as the Great Wall of China , which has hindered the flow of plant genes. [ 33 ]
Depending on how far two species have diverged since their most recent common ancestor , it may still be possible for them to produce offspring, as with horses and donkeys mating to produce mules . [ 34 ] Such hybrids are generally infertile , due to the two different sets of chromosomes being unable to pair up during meiosis . In this case, closely related species may regularly interbreed, but hybrids will be selected against and the species will remain distinct. However, viable hybrids are occasionally formed and these new species can either have properties intermediate between their parent species, or possess a totally new phenotype. [ 35 ] The importance of hybridization in developing new species of animals is unclear, although cases have been seen in many types of animals, [ 36 ] with the gray tree frog being a particularly well-studied example. [ 37 ]
Hybridization is, however, an important means of speciation in plants, since polyploidy (having more than two copies of each chromosome) is tolerated in plants more readily than in animals. [ 38 ] [ 39 ] Polyploidy is important in hybrids as it allows reproduction, with the two different sets of chromosomes each being able to pair with an identical partner during meiosis. [ 40 ] Polyploid hybrids also have more genetic diversity, which allows them to avoid inbreeding depression in small populations. [ 41 ]
Horizontal gene transfer is the transfer of genetic material from one organism to another organism that is not its offspring; this is most common among bacteria . [ 42 ] In medicine, this contributes to the spread of antibiotic resistance , as when one bacteria acquires resistance genes it can rapidly transfer them to other species. [ 43 ] Horizontal transfer of genes from bacteria to eukaryotes such as the yeast Saccharomyces cerevisiae and the adzuki bean beetle Callosobruchus chinensis may also have occurred. [ 44 ] [ 45 ] An example of larger-scale transfers are the eukaryotic bdelloid rotifers , which appear to have received a range of genes from bacteria, fungi, and plants. [ 46 ] Viruses can also carry DNA between organisms, allowing transfer of genes even across biological domains . [ 47 ] Large-scale gene transfer has also occurred between the ancestors of eukaryotic cells and prokaryotes, during the acquisition of chloroplasts and mitochondria . [ 48 ]
Gene flow is the transfer of alleles from one population to another.
Migration into or out of a population may be responsible for a marked change in allele frequencies. Immigration may also result in the addition of new genetic variants to the established gene pool of a particular species or population.
There are a number of factors that affect the rate of gene flow between different populations. One of the most significant factors is mobility, as greater mobility of an individual tends to give it greater migratory potential. Animals tend to be more mobile than plants, although pollen and seeds may be carried great distances by animals or wind.
Maintained gene flow between two populations can also lead to a combination of the two gene pools, reducing the genetic variation between the two groups. It is for this reason that gene flow strongly acts against speciation , by recombining the gene pools of the groups, and thus, repairing the developing differences in genetic variation that would have led to full speciation and creation of daughter species.
For example, if a species of grass grows on both sides of a highway, pollen is likely to be transported from one side to the other and vice versa. If this pollen is able to fertilise the plant where it ends up and produce viable offspring, then the alleles in the pollen have effectively been able to move from the population on one side of the highway to the other.
The term microevolution was first used by botanist Robert Greenleaf Leavitt in the journal Botanical Gazette in 1909, addressing what he called the "mystery" of how formlessness gives rise to form. [ 49 ]
However, Leavitt was using the term to describe what we would now call developmental biology ; it was not until Russian Entomologist Yuri Filipchenko used the terms "macroevolution" and "microevolution" in 1927 in his German language work, Variabilität und Variation , that it attained its modern usage. The term was later brought into the English-speaking world by Filipchenko's student Theodosius Dobzhansky in his book Genetics and the Origin of Species (1937). [ 1 ]
In young Earth creationism and baraminology a central tenet is that evolution can explain diversity in a limited number of created kinds which can interbreed (which they call "microevolution") while the formation of new "kinds" (which they call "macroevolution") is impossible. [ 50 ] [ 51 ] This acceptance of "microevolution" only within a "kind" is also typical of old Earth creationism . [ 52 ]
Scientific organizations such as the American Association for the Advancement of Science describe microevolution as small scale change within species, and macroevolution as the formation of new species, but otherwise not being different from microevolution. In macroevolution, an accumulation of microevolutionary changes leads to speciation. [ 53 ] The main difference between the two processes is that one occurs within a few generations, whilst the other takes place over thousands of years (i.e. a quantitative difference). [ 54 ] Essentially they describe the same process; although evolution beyond the species level results in beginning and ending generations which could not interbreed, the intermediate generations could.
Opponents to creationism argue that changes in the number of chromosomes can be accounted for by intermediate stages in which a single chromosome divides in generational stages, or multiple chromosomes fuse, and cite the chromosome difference between humans and the other great apes as an example. [ 55 ] Creationists insist that since the actual divergence between the other great apes and humans was not observed, the evidence is circumstantial.
Describing the fundamental similarity between macro and microevolution in his authoritative textbook "Evolutionary Biology," biologist Douglas Futuyma writes,
One of the most important tenets of the theory forged during the Evolutionary Synthesis of the 1930s and 1940s was that "macroevolutionary" differences among organisms - those that distinguish higher taxa - arise from the accumulation of the same kinds of genetic differences that are found within species. Opponents of this point of view believed that "macroevolution" is qualitatively different from "microevolution" within species, and is based on a totally different kind of genetic and developmental patterning... Genetic studies of species differences have decisively disproved [this] claim. Differences between species in morphology, behavior, and the processes that underlie reproductive isolation all have the same genetic properties as variation within species : they occupy consistent chromosomal positions, they may be polygenic or based on few genes, they may display additive, dominant, or epistatic effects, and they can in some instances be traced to specifiable differences in proteins or DNA nucleotide sequences. The degree of reproductive isolation between populations, whether prezygotic or postzygotic, varies from little or none to complete . Thus, reproductive isolation, like the divergence of any other character, evolves in most cases by the gradual substitution of alleles in populations .
Contrary to the claims of some antievolution proponents, evolution of life forms beyond the species level (i.e. speciation ) has indeed been observed and documented by scientists on numerous occasions. [ 57 ] In creation science , creationists accepted speciation as occurring within a "created kind" or "baramin", but objected to what they called "third level-macroevolution" of a new genus or higher rank in taxonomy . There is ambiguity in the ideas as to where to draw a line on "species", "created kinds", and what events and lineages fall within the rubric of microevolution or macroevolution. [ 58 ] | https://en.wikipedia.org/wiki/Microevolution |
Microextrusion is a microforming extrusion process performed at the submillimeter range. Like extrusion , material is pushed through a die orifice, but the resulting product's cross section can fit through a 1mm square. Several microextrusion processes have been developed since microforming was envisioned in 1990. [ 1 ] [ 2 ] [ 3 ] Forward (ram and billet move in the same direction) and backward (ram and billet move in the opposite direction) microextrusion were first introduced, with forward rod-backward cup and double cup extrusion methods developing later. [ 2 ] [ 4 ] Regardless of method, one of the greatest challenges of creating a successful microextrusion machine is the manufacture of the die and ram. "The small size of the die and ram, along with the stringent accuracy requirement, needs suitable manufacturing processes." [ 2 ] Additionally, as Fu and Chan pointed out in a 2013 state-of-the-art technology review, several issues must still be resolved before microextrusion and other microforming technologies can be implemented more widely, including deformation load and defects , forming system stability, mechanical properties, and other size-related effects on the crystallite (grain) structure and boundaries. [ 2 ] [ 3 ]
Microextrusion is an outgrowth of microforming, a science that was in its infancy in the early 1990s. In 2002, Engel et al. expressed that up to that point, only a few research experiments involving micro-deep drawing and extruding processes had been attempted, citing limitations in shearing on billets and difficulties in tool manufacturing and handling. [ 1 ] By the mid- to late 2000s, researchers were working on issues such as billet flow, interfacial friction, extrusion force, and size effects, "the deviations from the expected results that occur when the dimension of a workpiece or sample is reduced." [ 2 ] Most recently, research into using ultrafine-grained material at higher formation temperatures and applying ultrasonic vibration to the process has pushed the science further. [ 3 ] [ 4 ] However, before bulk production of microparts such as pins, screws, fasteners, connectors, and sockets using microforming and microextrusion techniques can occur, more research into billet production, transportation, positioning, and ejection are required. [ 3 ] [ 4 ]
Microextrusion techniques have also been applied to bioceramic and plastic extrusion and the manufacture of components for resorbable and implantable medical devices , from bioresorbable stents to controlled drug release systems. [ 5 ] [ 6 ]
Like normal macro-level extrusion, several similar microextrusion processes have been described over the years. The most basic processes were forward (direct) and backward (indirect) microextrusion. The ram (which propels the billet forward) and billet both move in the same direction with forward microextrusion, while in backward microextrusion has the ram and billet moving in opposite directions. These in turn have been applied to specialized applications such as the manufacture of microbillet, brass micropins, microgear shafts, and microcondensers. [ 2 ] [ 4 ] However, other processes have been applied to microextrusion, including forward rod–backward cup extrusion and double cup (one forward, one backward) extrusion. [ 4 ]
Strengths of microextrusion over other manufacturing processes include its ability to create very complex cross-sections, preserve chemical properties, condition physical properties, and process materials which are delicate or dependent on physical or chemical properties. [ 2 ] [ 3 ] [ 5 ] [ 6 ] However, microextrusion has some limitations, though primarily related to the need for improvement of the relatively young process. Dixit and Das described it thus in 2012:
With the scaling down of dimensions and increasing geometric complexity of objects, currently available technologies and systems may not be able to meet the development needs. New measuring devices, principles and instrumentation, tolerance rules , and procedures have to be developed. Materials databases with detailed information on various materials and their properties/interface properties including microstructures and size effect would be very useful for product innovation and process design. More studies are necessary on micro/nanowear and damages/failures of the micromanufacturing tools. The forming limits for different types of materials at the microlevel must be prescribed. More specific considerations must be incorporated into the design of machines that are scaled down for microforming to meet engineering applications and requirements. [ 2 ] | https://en.wikipedia.org/wiki/Microextrusion |
Microfabrication is the process of fabricating miniature structures of micrometre scales and smaller. Historically, the earliest microfabrication processes were used for integrated circuit fabrication, also known as " semiconductor manufacturing " or "semiconductor device fabrication". In the last two decades, microelectromechanical systems (MEMS), microsystems (European usage), micromachines (Japanese terminology) and their subfields have re-used, adapted or extended microfabrication methods. These subfields include microfluidics /lab-on-a-chip, optical MEMS (also called MOEMS), RF MEMS, PowerMEMS, BioMEMS and their extension into nanoscale (for example NEMS, for nano electro mechanical systems). The production of flat-panel displays and solar cells also uses similar techniques.
Miniaturization of various devices presents challenges in many areas of science and engineering: physics , chemistry , materials science , computer science , ultra-precision engineering, fabrication processes, and equipment design. It is also giving rise to various kinds of interdisciplinary research. [ 1 ] The major concepts and principles of microfabrication are microlithography , doping , thin films , etching , bonding , and polishing .
Microfabricated devices include:
Microfabrication technologies originate from the microelectronics industry, and the devices are usually made on silicon wafers even though glass , plastics and many other substrate are in use. Micromachining, semiconductor processing, microelectronic fabrication, semiconductor fabrication , MEMS fabrication and integrated circuit technology are terms used instead of microfabrication, but microfabrication is the broad general term.
Traditional machining techniques such as electro-discharge machining , spark erosion machining , and laser drilling have been scaled from the millimeter size range to micrometer range, but they do not share the main idea of microelectronics-originated microfabrication: replication and parallel fabrication of hundreds or millions of identical structures. This parallelism is present in various imprint , casting and moulding techniques which have successfully been applied in the microregime. For example, injection moulding of DVDs involves fabrication of submicrometer-sized spots on the disc.
Microfabrication is actually a collection of technologies which are utilized in making microdevices. Some of them have very old origins, not connected to manufacturing , like lithography or etching . Polishing was borrowed from optics manufacturing , and many of the vacuum techniques come from 19th century physics research . Electroplating is also a 19th-century technique adapted to produce micrometre scale structures, as are various stamping and embossing techniques.
To fabricate a microdevice, many processes must be performed, one after the other, many times repeatedly. These processes typically include depositing a film , patterning the film with the desired micro features, and removing (or etching ) portions of the film. Thin film metrology is used typically during each of these individual process steps, to ensure the film structure has the desired characteristics in terms of thickness ( t ), refractive index ( n ) and extinction coefficient ( k ), [ 2 ] for suitable device behavior. For example, in memory chip fabrication there are some 30 lithography steps, 10 oxidation steps, 20 etching steps, 10 doping steps, and many others are performed. The complexity of microfabrication processes can be described by their mask count . This is the number of different pattern layers that constitute the final device. Modern microprocessors are made with 30 masks while a few masks suffice for a microfluidic device or a laser diode . Microfabrication resembles multiple exposure photography, with many patterns aligned to each other to create the final structure.
Microfabricated devices are not generally freestanding devices but are usually formed over or in a thicker support substrate . For electronic applications, semiconducting substrates such as silicon wafers can be used. For optical devices or flat panel displays, transparent substrates such as glass or quartz are common. The substrate enables easy handling of the micro device through the many fabrication steps. Often many individual devices are made together on one substrate and then singulated into separated devices toward the end of fabrication.
Microfabricated devices are typically constructed using one or more thin films (see Thin film deposition ). The purpose of these thin films depends upon the type of device. Electronic devices may have thin films which are conductors (metals), insulators (dielectrics) or semiconductors. Optical devices may have films which are reflective, transparent, light guiding or scattering. Films may also have a chemical or mechanical purpose as well as for MEMS applications. Examples of deposition techniques include:
It is often desirable to pattern a film into distinct features or to form openings (or vias) in some of the layers. These features are on the micrometer or nanometer scale and the patterning technology is what defines microfabrication. This patterning technique typically uses a 'mask' to define portions of the film which will be removed. Examples of patterning techniques include:
Etching is the removal of some portion of the thin film or substrate. The substrate is exposed to an etching (such as an acid or plasma) which chemically or physically attacks the film until it is removed. Etching techniques include:
Microforming is a microfabrication process of microsystem or microelectromechanical system (MEMS) "parts or structures with at least two dimensions in the submillimeter range." [ 3 ] [ 4 ] [ 5 ] It includes techniques such as microextrusion , [ 4 ] microstamping , [ 6 ] and microcutting. [ 7 ] These and other microforming processes have been envisioned and researched since at least 1990, [ 3 ] leading to the development of industrial- and experimental-grade manufacturing tools. However, as Fu and Chan pointed out in a 2013 state-of-the-art technology review, several issues must still be resolved before the technology can be implemented more widely, including deformation load and defects , forming system stability, mechanical properties, and other size-related effects on the crystallite (grain) structure and boundaries: [ 4 ] [ 5 ] [ 8 ]
In microforming, the ratio of the total surface area of grain boundaries to the material volume decreases with the decrease of specimen size and the increase of grain size. This leads to the decrease of grain boundary strengthening effect. Surface grains have lesser constraints compared to internal grains. The change of flow stress with part geometry size is partly attributed to the change of volume fraction of surface grains. In addition, the anisotropic properties of each grain become significant with the decrease of workpiece size, which results in the inhomogeneous deformation, irregular formed geometry and the variation of deformation load. There is a critical need to establish the systematic knowledge of microforming to support the design of part, process, and tooling with the consideration of size effects. [ 8 ]
a wide variety of other processes for cleaning, planarizing, or modifying the chemical properties of microfabricated devices can also be performed. Some examples include:
Microfabrication is carried out in cleanrooms , where air has been filtered of particle contamination and temperature , humidity , vibrations and electrical disturbances are under stringent control. Smoke , dust , bacteria and cells are micrometers in size, and their presence will destroy the functionality of a microfabricated device.
Cleanrooms provide passive cleanliness but the wafers are also actively cleaned before every critical step. RCA-1 clean in ammonia -peroxide solution removes organic contamination and particles; RCA-2 cleaning in hydrogen chloride -peroxide mixture removes metallic impurities. Sulfuric acid - peroxide mixture (a.k.a. Piranha) removes organics. Hydrogen fluoride removes native oxide from silicon surface. These are all wet cleaning steps in solutions. Dry cleaning methods include oxygen and argon plasma treatments to remove unwanted surface layers, or hydrogen bake at elevated temperature to remove native oxide before epitaxy . Pre-gate cleaning is the most critical cleaning step in CMOS fabrication: it ensures that the ca. 2 nm thick oxide of a MOS transistor can be grown in an orderly fashion. Oxidation , and all high temperature steps are very sensitive to contamination, and cleaning steps must precede high temperature steps.
Surface preparation is just a different viewpoint, all the steps are the same as described above: it is about leaving the wafer surface in a controlled and well known state before you start processing. Wafers are contaminated by previous process steps (e.g. metals bombarded from chamber walls by energetic ions during ion implantation ), or they may have gathered polymers from wafer boxes, and this might be different depending on wait time.
Wafer cleaning and surface preparation work similarly to the machines in a bowling alley : first they remove all unwanted bits and pieces, and then they reconstruct the desired pattern so that the game can go on.
Journals
Books | https://en.wikipedia.org/wiki/Microfabrication |
Microfauna (from Ancient Greek mikros ' small ' and from Latin fauna ' animal ' ) are microscopic animals and organisms that exhibit animal-like qualities and have body sizes that are usually <0.1 mm. [ 1 ] [ 2 ] Microfauna are represented in the animal kingdom (e.g. nematodes , small arthropods ) and the protist kingdom (i.e. protozoans ). A large amount of microfauna are soil microfauna which includes protists, rotifers, and nematodes. These types of animal-like protists are heterotrophic , largely feeding on bacteria. However, some microfauna can consume other things, making them detritivores , fungivores , or even predators. [ 3 ]
Microfauna are present in every habitat on Earth. They fill essential roles as decomposers and food sources for lower trophic levels, and are necessary to drive processes within larger organisms. Populations of microfauna can reach up to ~10 7 (~10 million) individuals per g −1 (0.1 g, or 1/10th of a gram) and are very common in plant litter, surface soils, and water films. [ 3 ] Many microfauna, such as nematodes, inhabit soil habitats. Plant parasitic nematodes inhabit the roots of various plants, while free-living nematodes live in soil water films. [ 3 ]
Microfauna also inhabit freshwater ecosystems. For example, freshwater microfauna in Australia include rotifers, ostracods, copepods, and cladocerans. [ 4 ] Rotifers are filter feeders that are usually found in fresh water and water films. They consume a variety of things including bacteria, algae, plant cells and organic material. [ 3 ]
Tardigrades inhabit a variety of lichens and mosses . They need water in these areas to allow for gas exchange and to prevent them from desiccating . [ 5 ] Because of this they are considered aquatic . However, they have also been found in all types of environments, ranging from the deep sea to dunes. [ 5 ]
One particular example of the role of microfauna can be seen in soil, where they are important in the cycling of nutrients in ecosystems . [ 6 ] The ecological functions of the rhizosphere can be influenced by microfauna, specifically by nematodes and protozoa, which are abundant in soil. For instance, the carbon cycling within the soil can be affected by nematodes who will feed on the roots of plants, impacting the organic carbon in the soil. Similarly, soil protozoa are able to release phosphorus and nitrogen into the soil and higher trophic levels by dissolving the organic material and nutrients available. [ 7 ]
Soil micro-fauna can also impact microorganisms within the rhizosphere by affecting their diversity and accelerating microorganism turnover. This happens because of the microfauna's selective grazing and their ability to influence the resources within the soil. [ 8 ] For example, protozoa can help maintain the quality of the soil by grazing on soil bacteria. Through their grazing, the protozoa can help maintain populations of bacteria, allowing the bacteria to more efficiently decompose dead organic material which will improve the fertility of the soil . [ 9 ]
Soil microfauna are capable of digesting just about any organic substance and some inorganic substances. [ citation needed ] These organisms are often essential links in the food chain between primary producers and larger species. For example, zooplankton are widespread microscopic animals and protists that feed on algae and detritus in the ocean, such as foraminifera .
Microfauna also aid in digestion and other processes in larger organisms.
Examples of notable phyla that include some microfauna:
Macrofauna are organisms that are greater than 2 mm in size that usually inhabit soft sediments. [ 12 ] They are also found in the benthic zone, and are suspension feeders or deposit feeders. [ 13 ] They are important to the marine food web as they are preyed upon by other organisms. Macrofauna, such as flatworms, are able to be separated into small parts through fragmentation , and are able to decompose organic matter. [ 14 ]
Microflora are organisms that reside within intestines and assist with the digestion of food. [ 15 ] In soil, there are three main groups of microflora: viruses, fungi and bacteria. | https://en.wikipedia.org/wiki/Microfauna |
A microfibril is a very fine fibril , or fiber-like strand, consisting of glycoproteins and cellulose . It is usually, but not always, used as a general term in describing the structure of protein fiber, e.g. hair and sperm tail. Its most frequently observed structural pattern is the 9+2 pattern in which two central protofibrils are surrounded by nine other pairs. Cellulose inside plants is one of the examples of non-protein compounds that are using this term with the same purpose. Cellulose microfibrils are laid down in the inner surface of the primary cell wall . As the cell absorbs water, its volume increases and the existing microfibrils separate and new ones are formed to help increase cell strength.
Cellulose is synthesized by cellulose synthase or Rosette terminal complexes which reside on a cells membrane. As cellulose fibrils are synthesized and grow extracellularly they push up against neighboring cells. Since the neighboring cell can not move easily the Rosette complex is instead pushed around the cell through the fluid phospholipid membrane. Eventually this results in the cell becoming wrapped in a microfibril layer. This layer becomes the cell wall. The organization of microfibrils forming the primary cell wall is rather disorganized. However, another mechanism is used in secondary cell walls leading to its organization. Essentially, lanes on the secondary cell wall are built with microtubules. These lanes force microfibrils to remain in a certain area while they wrap. During this process microtubules can spontaneously depolymerize and repolymerize in a different orientation. This leads to a different direction in which the cell continues getting wrapped.
Fibrillin microfibrils are found in connective tissues , which mainly makes up fibrillin-1 [ 1 ] and provides elasticity. During the assembly, mirofibrils exhibit a repeating stringed-beads arrangement produced by the cross-linking of molecules forming a striated pattern with a given periodicity when viewed stained under an electron microscope. In the formation of elastic fiber , fibrillin microfibrils guides the deposit of tropoelastin and remains in the outer layer of mature elastin fibers. [ 2 ] The microfibril is also associated in cell communication. Formation of fibrillin microfibrils in the pericellular region affects the activity of a growth factor called TGFβ . [ 1 ]
In Marfan syndrome , a connective tissue disorder, mutations in the gene encoding for the fibrillin-1 protein impact nearly every one of its domains. [ 3 ] Such defects in fibrillin-1 affect the signaling of TGFβ , as microfibrils directly govern the activity of TGFβ. [ 1 ] This hinders the formation of the extracellular matrix , and ultimately results in a severe phenotype which involves a few organ systems, including the central nervous system , circulatory system , ocular system , and skeletal system . [ 4 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microfibril |
Microfilaments , also called actin filaments , are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton . They are primarily composed of polymers of actin , but are modified by and interact with numerous other proteins in the cell. Microfilaments are usually about 7 nm in diameter and made up of two strands of actin. Microfilament functions include cytokinesis , amoeboid movement , cell motility , changes in cell shape, endocytosis and exocytosis , cell contractility, and mechanical stability. Microfilaments are flexible and relatively strong, resisting buckling by multi-piconewton compressive forces and filament fracture by nanonewton tensile forces. In inducing cell motility , one end of the actin filament elongates while the other end contracts, presumably by myosin II molecular motors. [ 1 ] Additionally, they function as part of actomyosin -driven contractile molecular motors, wherein the thin filaments serve as tensile platforms for myosin's ATP -dependent pulling action in muscle contraction and pseudopod advancement. Microfilaments have a tough, flexible framework which helps the cell in movement. [ 2 ]
Actin was first discovered in rabbit skeletal muscle in the mid 1940s by F.B. Straub . [ 3 ] Almost 20 years later, H.E. Huxley demonstrated that actin is essential for muscle constriction. The mechanism in which actin creates long filaments was first described in the mid 1980s. Later studies showed that actin has an important role in cell shape, motility, and cytokinesis.
Actin filaments are assembled in two general types of structures: bundles and networks. Bundles can be composed of polar filament arrays, in which all barbed ends point to the same end of the bundle, or non-polar arrays, where the barbed ends point towards both ends. A class of actin-binding proteins , called cross-linking proteins, dictate the formation of these structures. Cross-linking proteins determine filament orientation and spacing in the bundles and networks. These structures are regulated by many other classes of actin-binding proteins, including motor proteins, branching proteins, severing proteins, polymerization promoters, and capping proteins. [ citation needed ]
Measuring approximately 6 nm in diameter , [ 4 ] microfilaments are the thinnest fibers of the cytoskeleton. They are polymers of actin subunits (globular actin, or G-actin), which as part of the fiber are referred to as filamentous actin, or F-actin. Each microfilament is made up of two helical , interlaced strands of subunits. Much like microtubules , actin filaments are polarized. Electron micrographs have provided evidence of their fast-growing barbed-ends and their slow-growing pointed-end. This polarity has been determined by the pattern created by the binding of myosin S1 fragments: they themselves are subunits of the larger myosin II protein complex . The pointed end is commonly referred to as the minus (−) end and the barbed end is referred to as the plus (+) end. [ citation needed ]
In vitro actin polymerization, or nucleation , starts with the self-association of three G-actin monomers to form a trimer . ATP -bound actin then itself binds the barbed end, and the ATP is subsequently hydrolyzed . ATP hydrolysis occurs with a half time of about 2 seconds, [ 5 ] while the half time for the dissociation of the inorganic phosphate is about 6 minutes. [ 5 ] This autocatalyzed event reduces the binding strength between neighboring subunits, and thus generally destabilizes the filament. In vivo actin polymerization is catalyzed by a class of filament end-tracking molecular motors known as actoclampins . Recent evidence suggests that the rate of ATP hydrolysis and the rate of monomer incorporation are strongly coupled. [ citation needed ]
Subsequently, ADP -actin dissociates slowly from the pointed end, a process significantly accelerated by the actin-binding protein, cofilin . ADP bound cofilin severs ADP-rich regions nearest the (−)-ends. Upon release, the free actin monomer slowly dissociates from ADP, which in turn rapidly binds to the free ATP diffusing in the cytosol , thereby forming the ATP-actin monomeric units needed for further barbed-end filament elongation. This rapid turnover is important for the cell's movement. End-capping proteins such as CapZ prevent the addition or loss of monomers at the filament end where actin turnover is unfavorable, such as in the muscle apparatus. [ citation needed ]
Actin polymerization together with capping proteins were recently used to control the 3-dimensional growth of protein filament so as to perform 3D topologies useful in technology and the making of electrical interconnect. Electrical conductivity is obtained by metallisation of the protein 3D structure. [ 6 ] [ 7 ]
As a result of ATP hydrolysis, filaments elongate approximately 10 times faster at their barbed ends than their pointed ends. At steady-state , the polymerization rate at the barbed end matches the depolymerization rate at the pointed end, and microfilaments are said to be treadmilling . Treadmilling results in elongation in the barbed end and shortening in the pointed-end, so that the filament in total moves. Since both processes are energetically favorable, this means force is generated, the energy ultimately coming from ATP. [ 1 ]
Intracellular actin cytoskeletal assembly and disassembly are tightly regulated by cell signaling mechanisms. Many signal transduction systems use the actin cytoskeleton as a scaffold, holding them at or near the inner face of the peripheral membrane . This subcellular location allows immediate responsiveness to transmembrane receptor action and the resulting cascade of signal-processing enzymes. [ citation needed ]
Because actin monomers must be recycled to sustain high rates of actin-based motility during chemotaxis , cell signalling is believed to activate cofilin, the actin-filament depolymerizing protein which binds to ADP-rich actin subunits nearest the filament's pointed-end and promotes filament fragmentation, with concomitant depolymerization in order to liberate actin monomers. In most animal cells, monomeric actin is bound to profilin and thymosin beta-4 , both of which preferentially bind with one-to-one stoichiometry to ATP-containing monomers. Although thymosin beta-4 is strictly a monomer-sequestering protein, the behavior of profilin is far more complex. Profilin enhances the ability of monomers to assemble by stimulating the exchange of actin-bound ADP for solution-phase ATP to yield actin-ATP and ADP. Profilin is transferred to the leading edge by virtue of its PIP 2 binding site, and it employs its poly-L-proline binding site to dock onto end-tracking proteins. Once bound, profilin-actin-ATP is loaded into the monomer-insertion site of actoclampin motors. [ citation needed ]
Another important component in filament formation is the Arp2/3 complex , which binds to the side of an already existing filament (or "mother filament"), where it nucleates the formation of a new daughter filament at a 70-degree angle relative to the mother filament, effecting a fan-like branched filament network. [ 8 ]
Specialized unique actin cytoskeletal structures are found adjacent to the plasma membrane. Four remarkable examples include red blood cells , human embryonic kidney cells , neurons , and sperm cells. In red blood cells, a spectrin -actin hexagonal lattice is formed by interconnected short actin filaments. [ 9 ] In human embryonic kidney cells, the cortical actin forms a scale-free fractal structure. [ 10 ] First found in neuronal axons , actin forms periodic rings that are stabilized by spectrin and adducin [ 11 ] [ 12 ] – and this ring structure was then found by He et al 2016 to occur in almost every neuronal type and glial cells , across seemingly every animal taxon including Caenorhabditis elegans , Drosophila , Gallus gallus and Mus musculus . [ 13 ] And in mammalian sperm, actin forms a helical structure in the midpiece, i.e., the first segment of the flagellum . [ 14 ]
In non-muscle cells, actin filaments are formed proximal to membrane surfaces. Their formation and turnover are regulated by many proteins, including: [ citation needed ]
The actin filament network in non-muscle cells is highly dynamic. The actin filament network is arranged with the barbed-end of each filament attached to the cell's peripheral membrane by means of clamped-filament elongation motors, the above-mentioned "actoclampins", formed from a filament barbed-end and a clamping protein (formins, VASP, Mena, WASP, and N-WASP). [ 15 ] The primary substrate for these elongation motors is profilin-actin-ATP complex which is directly transferred to elongating filament ends. [ 16 ] The pointed-end of each filament is oriented toward the cell's interior. In the case of lamellipodial growth, the Arp2/3 complex generates a branched network, and in filopodia a parallel array of filaments is formed. [ citation needed ]
Myosin motors are intracellular ATP-dependent enzymes that bind to and move along actin filaments. Various classes of myosin motors have very different behaviors, including exerting tension in the cell and transporting cargo vesicles. [ citation needed ]
One proposed model suggests the existence of actin filament barbed-end-tracking molecular motors termed "actoclampin". [ 17 ] The proposed actoclampins generate the propulsive forces needed for actin-based motility of lamellipodia , filopodia , invadipodia, dendritic spines , intracellular vesicles , and motile processes in endocytosis , exocytosis , podosome formation, and phagocytosis . Actoclampin motors also propel such intracellular pathogens as Listeria monocytogenes , Shigella flexneri , Vaccinia and Rickettsia . When assembled under suitable conditions, these end-tracking molecular motors can also propel biomimetic particles. [ citation needed ]
The term actoclampin is derived from acto - to indicate the involvement of an actin filament, as in actomyosin, and clamp to indicate a clasping device used for strengthening flexible/moving objects and for securely fastening two or more components, followed by the suffix - in to indicate its protein origin. An actin filament end-tracking protein may thus be termed a clampin. [ citation needed ]
Dickinson and Purich recognized that prompt ATP hydrolysis could explain the forces achieved during actin-based motility. [ 15 ] They proposed a simple mechanoenzymatic sequence known as the Lock, Load & Fire Model, in which an end-tracking protein remains tightly bound ("locked" or clamped) onto the end of one sub-filament of the double-stranded actin filament. After binding to Glycyl-Prolyl-Prolyl-Prolyl-Prolyl-Prolyl-registers on tracker proteins, Profilin-ATP-actin is delivered ("loaded") to the unclamped end of the other sub-filament, whereupon ATP within the already clamped terminal subunit of the other subfragment is hydrolyzed ("fired"), providing the energy needed to release that arm of the end-tracker, which then can bind another Profilin-ATP-actin to begin a new monomer-addition round. [ citation needed ]
The following steps describe one force-generating cycle of an actoclampin molecular motor:
When operating with the benefit of ATP hydrolysis, AC motors generate per-filament forces of 8–9 pN, which is far greater than the per-filament limit of 1–2 pN for motors operating without ATP hydrolysis. [ 15 ] [ 17 ] [ 18 ] The term actoclampin is generic and applies to all actin filament end-tracking molecular motors, irrespective of whether they are driven actively by an ATP-activated mechanism or passively. [ citation needed ]
Some actoclampins (e.g., those involving Ena/VASP proteins, WASP, and N-WASP) apparently require Arp2/3-mediated filament initiation to form the actin polymerization nucleus that is then "loaded" onto the end-tracker before processive motility can commence. To generate a new filament, Arp2/3 requires a "mother" filament, monomeric ATP-actin, and an activating domain from Listeria ActA or the VCA region of N-WASP. The Arp2/3 complex binds to the side of the mother filament, forming a Y-shaped branch having a 70-degree angle with respect to the longitudinal axis of the mother filament. Then upon activation by ActA or VCA, the Arp complex is believed to undergo a major conformational change, bringing its two actin-related protein subunits near enough to each other to generate a new filament gate. Whether ATP hydrolysis may be required for nucleation and/or Y-branch release is a matter under active investigation. [ citation needed ] | https://en.wikipedia.org/wiki/Microfilament |
Microfiltration is a type of physical filtration process where a contaminated fluid is passed through a special pore-sized membrane filter to separate microorganisms and suspended particles from process liquid . It is commonly used in conjunction with various other separation processes such as ultrafiltration and reverse osmosis to provide a product stream which is free of undesired contaminants .
Microfiltration usually serves as a pre-treatment for other separation processes such as ultrafiltration , and a post-treatment for granular media filtration . The typical particle size used for microfiltration ranges from about 0.1 to 10 μm . [ 1 ] In terms of approximate molecular weight these membranes can separate macromolecules of molecular weights generally less than 100,000 g/mol. [ 2 ] The filters used in the microfiltration process are specially designed to prevent particles such as, sediment , algae , protozoa or large bacteria from passing through a specially designed filter. More microscopic, atomic or ionic materials such as water (H 2 O), monovalent species such as Sodium (Na + ) or Chloride (Cl − ) ions, dissolved or natural organic matter , and small colloids and viruses will still be able to pass through the filter. [ 3 ]
The suspended liquid is passed through at a relatively high velocity of around 1–3 m/s and at low to moderate pressures (around 100-400 kPa ) parallel or tangential to the semi-permeable membrane in a sheet or tubular form. [ 4 ] A pump is commonly fitted onto the processing equipment to allow the liquid to pass through the membrane filter. There are also two pump configurations, either pressure driven or vacuum . A differential or regular pressure gauge is commonly attached to measure the pressure drop between the outlet and inlet streams. See Figure 1 for a general setup. [ 5 ]
The most abundant use of microfiltration membranes are in the water , beverage and bio-processing industries (see below). The exit process stream after treatment using a micro-filter has a recovery rate which generally ranges to about 90-98 %. [ 6 ]
Perhaps the most prominent use of microfiltration membranes pertains to the treatment of potable water supplies. The membranes are a key step in the primary disinfection of the uptake water stream. Such a stream might contain pathogens such as the protozoa Cryptosporidium and Giardia lamblia which are responsible for numerous disease outbreaks. Both species show a gradual resistance to traditional disinfectants (i.e. chlorine ). [ 7 ] The use of MF membranes presents a physical means of separation (a barrier) as opposed to a chemical alternative. In that sense, both filtration and disinfection take place in a single step, negating the extra cost of chemical dosage and the corresponding equipment (needed for handling and storage).
Similarly, the MF membranes are used in secondary wastewater effluents to remove turbidity but also to provide treatment for disinfection. At this stage, coagulants ( iron or aluminum ) may potentially be added to precipitate species such as phosphorus and arsenic which would otherwise have been soluble. [ 8 ]
Another crucial application of MF membranes lies in the cold sterilisation of beverages and pharmaceuticals . [ 9 ] Historically, heat was used to sterilize refreshments such as juice, wine and beer in particular, however a palatable loss in flavour was clearly evident upon heating. Similarly, pharmaceuticals have been shown to lose their effectiveness upon heat addition. MF membranes are employed in these industries as a method to remove bacteria and other undesired suspensions from liquids, a procedure termed as 'cold sterilisation', which negate the use of heat.
Furthermore, microfiltration membranes are finding increasing use in areas such as petroleum refining, [ 10 ] in which the removal of particulates from flue gases is of particular concern. The key challenges/requirements for this technology are the ability of the membrane modules to withstand high temperatures (i.e. maintain stability), but also the design must be such to provide a very thin sheeting (thickness < 2000 angstroms ) to facilitate an increase of flux . In addition the modules must have a low fouling profile and most importantly, be available at a low-cost for the system to be financially viable.
Aside from the above applications, MF membranes have found dynamic use in major areas within the dairy industry, particularly for milk and whey processing. The MF membranes aid in the removal of bacteria and the associated spores from milk, by rejecting the harmful species from passing through. This is also a precursor for pasteurisation , allowing for an extended shelf-life of the product. However, the most promising technique for MF membranes in this field pertains to the separation of casein from whey proteins (i.e. serum milk proteins). [ 11 ] This results in two product streams both of which are highly relied on by consumers; a casein -rich concentrate stream used for cheese making, and a whey/serum protein stream which is further processed (using ultrafiltration ) to make whey protein concentrate. The whey protein stream undergoes further filtration to remove fat in order to achieve higher protein content in the final WPC (Whey Protein Concentrate) and WPI (Whey Protein Isolate) powders.
Other common applications utilising microfiltration as a major separation process include
Membrane filtration processes can be distinguished by three major characteristics: driving force, retentate stream and permeate streams. The microfiltration process is pressure driven with suspended particles and water as retentate and dissolved solutes plus water as permeate. The use of hydraulic pressure accelerates the separation process by increasing the flow rate ( flux ) of the liquid stream but does not affect the chemical composition of the species in the retentate and product streams. [ 15 ]
A major characteristic that limits the performance of microfiltration or any membrane technology is a process known as fouling . Fouling describes the deposition and accumulation of feed components such as suspended particles, impermeable dissolved solutes or even permeable solutes, on the membrane surface and or within the pores of the membrane. Fouling of the membrane during the filtration processes decreases the flux and thus overall efficiency of the operation. This is indicated when the pressure drop increases to a certain point. It occurs even when operating parameters are constant (pressure, flow rate, temperature and concentration) Fouling is mostly irreversible although a portion of the fouling layer can be reversed by cleaning for short periods of time. [ 16 ]
Microfiltration membranes can generally operate in one of two configurations.
Cross-flow filtration : where the fluid is passed through tangentially with respect to the membrane. [ 17 ] Part of the feed stream containing the treated liquid is collected below the filter while parts of the water are passed through the membrane untreated. Cross flow filtration is understood to be a unit operation rather than a process. Refer to Figure 2 for a general schematic for the process.
Dead-end filtration ; all of the process fluid flows and all particles larger than the pore sizes of the membrane are stopped at its surface. All of the feed water is treated at once subject to cake formation. [ 18 ] This process is mostly used for batch or semicontinuous filtration of low concentrated solutions. [ 19 ] Refer to Figure 3 for a general schematic for this process.
The major issues that influence the selection of the membrane include [ 20 ]
A few important design heuristics and their assessment are discussed below:
Like any other membranes, microfiltration membranes are prone to fouling. (See Figure 4 below) It is therefore necessary that regular maintenance be carried out to prolong the life of the membrane module.
The cost to design and manufacture a membrane per unit of area are about 20% less compared to the early 1990s and in a general sense are constantly declining. [ 28 ] Microfiltration membranes are more advantageous in comparison to conventional systems. Microfiltration systems do not require expensive extraneous equipment such as flocculates, addition of chemicals, flash mixers, settling and filter basins. [ 29 ] However the cost of replacement of capital equipment costs (membrane cartridge filters etc.) might still be relatively high as the equipment may be manufactured specific to the application. Using the design heuristics and general plant design principles (mentioned above), the membrane life-span can be increased to reduce these costs.
Through the design of more intelligent process control systems and efficient plant designs some general tips to reduce operating costs are listed below [ 30 ]
Table 1 (below) expresses an indicative guide of membrane filtration capital and operating costs per unit of flow.
Table 1 Approximate Costing of Membrane Filtration per unit of flow [ 31 ]
Note:
The materials which constitute the membranes used in microfiltration systems may be either organic or inorganic depending upon the contaminants that are desired to be removed, or the type of application.
General Membrane structures for microfiltration include
Membrane modules for dead-end flow microfiltration are mainly plate-and-frame configurations. They possess a flat and thin-film composite sheet where the plate is asymmetric. A thin selective skin is supported on a thicker layer that has larger pores. These systems are compact and possess a sturdy design, Compared to cross-flow filtration, plate and frame configurations possess a reduced capital expenditure; however the operating costs will be higher. The uses of plate and frame modules are most applicable for smaller and simpler scale applications (laboratory) which filter dilute solutions. [ 32 ]
This particular design is used for cross-flow filtration. The design involves a pleated membrane which is folded around a perforated permeate core, akin to a spiral, that is usually placed within a pressure vessel. This particular design is preferred when the solutions handled is heavily concentrated and in conditions of high temperatures and extreme pH . This particular configuration is generally used in more large scale industrial applications of microfiltration. [ 32 ]
This design involves bundling several hundred to several thousand hollow fiber membranes in a tube filter housing. Feed water is delivered into the membrane module. It passes through from the outside surface of the hollow fibers and the filtered water exits through the center of the fibers. With the flux rate in excess of 75 gallon per square foot per day, this design can be used for large scale facilities. [ 33 ]
As separation is achieved by sieving, the principal mechanism of transfer for microfiltration through micro porous membranes is bulk flow. [ 34 ]
Generally, due to the small diameter of the pores the flow within the process is laminar ( Reynolds Number < 2100) The flow velocity of the fluid moving through the pores can thus be determined (by Hagen-Poiseuille 's equation), the simplest of which assuming a parabolic velocity profile .
Transmembrane Pressure (TMP) [ 35 ]
The transmembrane pressure (TMP) is defined as the mean of the applied pressure from the feed to the concentrate side of the membrane subtracted by the pressure of the permeate. This is applied to dead-end filtration mainly and is indicative of whether a system is fouled sufficiently to warrant replacement.
Where
Permeate Flux [ 36 ]
The permeate flux in microfiltration is given by the following relation, based on Darcy's Law
Where
The cake resistance is given by:
Where
For micron sized particles the Specific Cake Resistance is roughly. [ 37 ]
Where
Rigorous design equations [ 38 ]
To give a better indication regarding the exact determination of the extent of the cake formation, one-dimensional quantitative models have been formulated to determine factors such as
See External Links for further details
Although environmental impacts of membrane filtration processes differ according to the application, a generic method of evaluation is the life-cycle assessment (LCA), a tool for the analysis of the environmental burden of membrane filtration processes at all stages and accounts for all types of impacts upon the environment including emission to land, water and air.
In regards to microfiltration processes, there are a number of potential environmental impacts to be considered. They include global warming potential , photo-oxidant formation potential, eutrophication potential, human toxicity potential, freshwater ecotoxicity potential, marine ecotoxicity potential and terrestrial ecotoxicity potential. In general, the potential environmental impact of the process is largely dependent on flux and the maximum transmembrane pressure, however other operating parameters remain a factor to be considered. A specific comment on which exact combination of operational condition will yield the lowest burden on the environment cannot be made as each application will require different optimisations. [ 39 ]
In a general sense, membrane filtration processes are relative "low risk" operations, that is, the potential for dangerous hazards are small. There are, however several aspects to be mindful of. All pressure-driven filtration processes including microfiltration requires a degree of pressure to be applied to the feed liquid stream as well as imposed electrical concerns. Other factors contributing to safety are dependent on parameters of the process. For example, processing dairy product will lead to bacteria formations that must be controlled to comply with safety and regulatory standards. [ 40 ]
Membrane microfiltration is fundamentally the same as other filtration techniques utilising a pore size distribution to physically separate particles. It is analogous to other technologies such as ultra/nanofiltration and reverse osmosis, however, the only difference exists in the size of the particles retained, and also the osmotic pressure. The main of which are described in general below:
Ultrafiltration membranes have pore sizes ranging from 0.1 μm to 0.01 μm and are able to retain proteins, endotoxins, viruses and silica. UF has diverse applications which span from waste water treatment to pharmaceutical applications.
Nanofiltration membranes have pores sized from 0.001 μm to 0.01 μm and filters multivalent ions, synthetic dyes, sugars and specific salts. As the pore size drops from MF to NF, the osmotic pressure requirement increases.
Reverse osmosis (RO) is the finest separation membrane process available, pore sizes range from 0.0001 μm to 0.001 μm. Reverse osmosis is able to retain almost all molecules except for water, and due to the size of the pores, the required osmotic pressure is significantly greater than that for microfiltration. Both reverse osmosis and nanofiltration are fundamentally different from microfiltration since the flow goes against the concentration gradient, because those systems use pressure as a means of forcing water to go from low osmotic pressure to high osmotic pressure.
Recent advances in MF have focused on manufacturing processes for the construction of membranes and additives to promote coagulation and therefore reduce the fouling of the membrane. Since MF, UF, NF and RO are closely related, these advances are applicable to multiple processes and not MF alone.
Recently studies have shown dilute KMnO 4 preoxidation combined FeCl 3 is able to promote coagulation, leading to decreased fouling, in specific the KMnO 4 preoxidation exhibited an effect which decreased irreversible membrane fouling. [ 41 ]
Similar research has been done into the construction high flux poly(trimethylene terephthalate) (PTT) nanofiber membranes, focusing on increased throughput. Specialised heat treatment and manufacturing processes of the membrane's internal structure exhibited results indicating a 99.6% rejection rate of TiO 2 particles under high flux. The results indicate that this technology may be applied to existing applications to increase their efficiency via high flux membranes. [ 42 ] | https://en.wikipedia.org/wiki/Microfiltration |
Microflotation is a further development of standard dissolved air flotation (DAF). [ 1 ] Microflotation is a water treatment technology operating with microbubbles of 10–80 μm in size instead of 80-300 μm like conventional DAF units.
The general operating method of microflotation is similar to standard recycled stream DAF units. The advancements of microflotation are lower pressure operation, smaller footprints and less energy consumption. [ 2 ]
The method of Microflotation is comparable to recycled stream DAF .
A portion of the clarified effluent water leaving the Microflotation tank is pumped into a small pressure vessel into which compressed air is also introduced. This results in saturating the pressurized effluent water with air. The air-saturated water stream is recycled to the front of the Microflotation cell and flows through a pressure release valve just as it enters the front of the float tank, which results in the air being released in the form of tiny bubbles. Bubbles form at nucleation sites on the surface of the suspended particles, adhering to the particles. As more bubbles form, the lift from the bubbles eventually overcomes the force of gravity. This causes the suspended matter to float to the surface where it forms a froth layer which is then removed by a skimmer. The froth-free water exits the float tank as the clarified effluent from the Microflotation unit. A particular circular DAF system is called "Zero speed", allowing quite water status then highest performances; a typical example is an Easyfloat 2K DAF system. [ citation needed ]
Microflotation is an enhanced method to float particles to the surface with the aid of adherent air bubbles. [ citation needed ]
The adherence of suspended solids to bubbles is easier and more intensive, the smaller the bubbles are. Because of the improved adherence capacity of small microbubbles, the saturation of the introduced air as well as the reduction capability of particles lead to an improved suspended solids reduction, a higher solids content in the float sludge and a more stable float sludge on the surface of the microflotation cell. [ 2 ]
A difference has to be made to dispersed flotation used in mining industry in mineral segregation processes where the bubble are bigger being 500-2000 μm in size and volume of air is many fold compared to the water volume. Traditional Dissolved Air flotation ( DAF ) mainly operates with bubble sizes ranging from 80 to 300 μm with very inhomogeneous bubble size distribution.
A major difference of low pressure dissolved air flotation and other flotation processes lies in the volumes of bubbles, amount of air and raising speeds. One macro bubble can be 1000 times bigger in volume compared to one micro bubble. And vice versa the number of micro bubbles can be 1000 fold in number compared to one macro bubble having same volume.
Microflotation enables bubbles in size 40-70 μm with rise rates from 3–10 m/h. The rise rate is slow enough not to destroy the fragile flocks forming an agglomeration of particles with weak mutual bonding and high enough to allow time for separation of the agglomeration. With the attachment of particles to bubbles the size range of "flock-bubble" grows, and the rise velocities grow simultaneously. The separation rate is accelerated leading to residence times of combined chemical precipitation and flotation from 10 to 60 minutes with need of small footprint areas of treatment plants and decreasing the cost structures of treatment processes.
A distribution of bubble sizes between 20 and 50 microns is the necessary requirement for an optimum flotation result. Even a small number of bubbles with diameters of above 100 microns can disable a flotation separation process , because larger bubbles rise more quickly and cause turbulence, which severely destroys already build air-flocks-agglomerates. [ 3 ]
Microflotation is technically appropriately and primarily economic to substitute classic technology like sand filtration and sedimentation. Beyond there are several applications at which low pressure Microflotation is an alternative to membrane technology or represents a convincing addition.
Microflotation can be used as: [ 4 ] | https://en.wikipedia.org/wiki/Microflotation |
Microfluidic cell culture integrates knowledge from biology, biochemistry, engineering, and physics to develop devices and techniques for culturing, maintaining, analyzing, and experimenting with cells at the microscale. [ 1 ] [ 2 ] It merges microfluidics , a set of technologies used for the manipulation of small fluid volumes (μL, nL, pL) within artificially fabricated microsystems , and cell culture , which involves the maintenance and growth of cells in a controlled laboratory environment. [ 3 ] [ 4 ] Microfluidics has been used for cell biology studies as the dimensions of the microfluidic channels are well suited for the physical scale of cells (in the order of magnitude of 10 micrometers). [ 2 ] For example, eukaryotic cells have linear dimensions between 10 and 100 μm which falls within the range of microfluidic dimensions. [ 4 ] A key component of microfluidic cell culture is being able to mimic the cell microenvironment which includes soluble factors that regulate cell structure, function, behavior, and growth. [ 2 ] Another important component for the devices is the ability to produce stable gradients that are present in vivo as these gradients play a significant role in understanding chemotactic , durotactic , and haptotactic effects on cells. [ 2 ]
Some considerations for microfluidic devices relating to cell culture include:
Fabrication material is crucial as not all polymers are biocompatible, with some materials such as PDMS causing undesirable adsorption or absorption of small molecules. [ 9 ] [ 10 ] Additionally, uncured PDMS oligomers can leach into the cell culture media, which can harm the microenvironment. [ 9 ] As an alternative to commonly used PDMS, there have been advances in the use of thermoplastics (e.g., polystyrene) as a replacement material. [ 11 ] [ 12 ]
Spatial organization of cells in microscale devices largely depends on the culture region geometry for cells to perform functions in vivo . [ 13 ] [ 14 ] For example, long, narrow channels may be desired to culture neurons . [ 13 ] The perfusion system chosen might also affect the geometry chosen. For example, in a system that incorporates syringe pumps, channels for perfusion inlet, perfusion outlet, waste, and cell loading would need to be added for the cell culture maintenance. [ 15 ] Perfusion in microfluidic cell culture is important to enable long culture periods on-chip and cell differentiation . [ 16 ]
Other critical aspects for controlling the microenvironment include: cell seeding density, reduction of air bubbles as they can rupture cell membranes, evaporation of media due to an insufficiently humid environment, and cell culture maintenance (i.e. regular, timely media changes). [ 17 ] [ 16 ] [ 18 ]
Cell's health is defined as the collective equilibrium activities of essential and specialized cellular processes; while a cell stressor is defined as a stimulus that causes excursion from its equilibrium state. Hence, cell health may be perturbed within microsystems based on platform design or operating conditions. Exposure to stressors within microsystems can impact cells through direct and indirect ways. Therefore, it is important to design the microfluidics system for cell culture in a manner that minimizes cell stress situations. For example, by minimizing cell suspension, by avoiding abrupt geometries (which tend to favor bubble formation), designing higher and wider channels (to avoid shear stress), or avoiding thermosensitive hydrogels. [ 19 ]
Some of the major advantages of microfluidic cell culture include reduced sample volumes (especially important when using primary cells, which are often limited) and the flexibility to customize and study multiple microenvironments within the same device. [ 3 ] A reduced cell population can also be used in a microscale system (e.g., a few hundred cells) in comparison to macroscale culture systems (which often require 10 5 – 10 7 cells); this can make studying certain cell-cell interactions more accessible. [ 10 ] These reduced cell numbers make studying non-dividing or slow dividing cells (e.g., stem cells ) easier than traditional culture methods (e.g., flasks, petri dishes, or well plates) due to the smaller sample volumes. [ 10 ] [ 20 ] Given the small dimensions in microfluidics, laminar flow can be achieved, allowing manipulations with the culture system to be done easily without affecting other culture chambers. [ 20 ] Laminar flow is also useful as is it mimics in vivo fluid dynamics more accurately, often making microscale culture more relevant than traditional culture methods. [ 21 ] Compartmentalized microfluidic cultures have also been combined with live cell calcium imaging, where depolarizing stimuli have been delivered to the peripheral terminals of neurons, and calcium responses recorded in the cell body. [ 22 ] This technique has demonstrated a stark difference in the sensitivity of the peripheral terminals compared to the neuronal cell body to certain stimuli such as protons. [ 22 ] This gives an excellent example as to why it is so important to study the peripheral terminals in isolation using microfluidic cell culture devices.
Traditional two-dimensional (2D) cell culture is cell culture that takes place on a flat surface, e.g. the bottom of a well-plate, and is known as the conventional method. [ 1 ] While these platforms are useful for growing and passaging cells to be used in subsequent experiments, they are not ideal environments to monitor cell responses to stimuli as cells cannot freely move or perform functions as observed in vivo that are dependent on cell-extracellular matrix material interactions. [ 1 ] To address this issue many methods have been developed to create a three-dimensional (3D) native cell environment. One example of a 3D method is the hanging drop, where a droplet with growing cells is suspended and hangs downwards, which allows cells to grow around and atop of one another, forming a spheroid. [ 23 ] The hanging drop method has been used to culture tumor cells but is limited to the geometry of a sphere. [ 24 ] Since the advent of poly(dimethylsiloxane) (PDMS) microfluidic device fabrication through soft lithography [ 25 ] [ 26 ] microfluidic devices have progressed and have proven to be very beneficial for mimicking a natural 3D environment for cell culture. [ 27 ]
Microfluidic devices make possible the study of a single cell to a few hundred cells in a 3D environment. Comparatively, macroscopic 2D cultures have 10 4 to 10 7 cells on a flat surface. [ 10 ] Microfluidics also allow for chemical gradients, the continuous flow of fresh media, high through put testing, and direct output to analytical instruments. [ 10 ] Additionally, open microfluidic cell cultures such as "microcanals" allow for direct physical manipulation of cells with micropipettes. [ 28 ] Many microfluidic systems employ the use of hydrogels as the extracellular matrix (ECM) support which can be modulated for fiber thickness and pore size and have been demonstrated to allow the growth of cancer cells. [ 29 ] Gel free 3D cell cultures have been developed to allow cells to grow in either a cell dense environment or an ECM poor environment. [ 30 ] Although these devices have proven very useful, there are certain disadvantages such as cells sticking to the PDMS surface, small molecules diffusing into the PDMS, and unreacted PDMS polymers washing into cell culture media. [ 10 ]
The use of 3D cell cultures in microfluidic devices has led to a field of study called organ-on-a-chip . The first report of these types of microfluidic cultures was used to study the toxicity of naphthalene metabolites on the liver and lung (Viravaidya et al.). These devices can grow a stripped-down version of an organ-like system that can be used to understand many biological processes. [ 1 ] By adding an additional dimension, more advanced cell architectures can be achieved, and cell behavior is more representative of in vivo dynamics; cells can engage in enhanced communication with neighboring cells and cell-extracellular matrix interactions can be modeled. [ 1 ] [ 31 ] In these devices, chambers or collagen layers containing different cell types can interact with one another for multiple days while various channels deliver nutrients to the cells. [ 1 ] [ 32 ] An advantage of these devices is that tissue function can be characterized and observed under controlled conditions (e.g., effect of shear stress on cells, effect of cyclic strain or other forces) to better understand the overall function of the organ. [ 1 ] [ 33 ] While these 3D models offer better model organ function on a cellular level compared with 2D models, there are still challenges. Some of the challenges include: imaging of the cells, control of gradients in static models (i.e., without a perfusion system), and difficulty recreating vasculature . [ 33 ] Despite these challenges, 3D models are still used as tools for studying and testing drug responses in pharmacological studies. [ 1 ] In recent years, there are microfluidic devices reproducing the complex in vivo microvascular network. Organs-on-a-chip have also been used to replicate very complex systems like lung epithelial cells in an exposed airway and provides valuable insight for how multicellular systems and tissues function in vivo. [ 34 ] These devices are able to create a physiologically realistic 3D environment, which is desirable as a tool for drug screening, drug delivery, cell-cell interactions, tumor metastasis etc. [ 35 ] [ 36 ] In one study, researchers grew tumor cells and tested the drug delivery of cis platin, resveratrol, tirapazamine (TPZ) and then measured the effects the drugs have on cell viability. [ 37 ]
Microfluidic systems can be used to culture several cell types.
Mammalian cell cultures can be seeded, grown for several weeks, detached, and passaged to a fresh culture medium ad nauseam by digital microfluidic (DMF) devices on a macro-scale. [ 38 ]
Algae can be incubated, and their growth rate and lipid production can be monitored in a hanging-drop microfluidic system. For example, Mishra et al. developed a 25x75 mm, easily accessible microfluidic device. This design is used to optimize the conditions by changing well diameters, UV light exposure (causing mutagenesis), and light/no light tests for culturing Botryococcus braunii , which is one of the most common freshwater microalgae for biofuel production. [ 39 ]
Microfluidic systems can be used to incubate high volumes of bacteria and yeast colonies . [ 40 ] The two-layer microchemostat device is made to allow scientists to culture cells under chemostatic and thermostatic conditions without moving cells around and causing intercellular interaction. [ 40 ] Yeast cell suspension droplets can be placed on a plate with patterned hydrophilic areas and incubated for 24 hours; then the droplets are split the produced proteins from yeast are analyzed by MALDI-MS without killing the cells in the original droplets. [ 41 ]
Compared to the highly complex microenvironment in vivo , traditional mono-culture of single cell types in vitro only provides limited information about cellular behavior due to the lack of interactions with other cell types. Typically, cell-to-cell signaling can be divided into four categories depending on the distance: endocrine signaling , paracrine signaling , autocrine signaling , and juxtacrine signaling . [ 42 ] For example, in paracrine signaling, growth factors secreted from one cell diffuse over a short distance to the neighboring target cell, [ 43 ] whereas in juxtacrine signaling, membrane-bound ligands of one cell directly bind to surface receptors of adjacent cells. [ 44 ] There are three conventional approaches to incorporate cell signaling in in vitro cell culture: conditioned media transfer, mixed (or direct) co-culture, and segregated (or indirect) co-culture. [ 45 ] The use of conditioned media, where the cultured medium of one cell type (the effector) is introduced to the culture of another cell type (the responder), is a traditional way to include the effects of soluble factors in cell signaling. [ 46 ] However, this method only allows one-way signaling, does not apply to short-lived factors (which often degrade before transfer to the responder cell culture), and does not allow temporal observations of the secreted factors. [ 47 ] Recently, co-culture has become the predominant approach to study the effect of cellular communication by culturing two biologically related cell types together. Mixed co-culture is the simplest co-culture method, where two types of cells are in direct contact within a single culture compartment at the desired cell ratio. [ 48 ] Cells can communicate by paracrine and juxtacrine signaling, but separated treatments and downstream analysis of a single cell type are not readily feasible due to the completely mixed population of cells. [ 49 ] [ 50 ] The more common method is segregated co-culture, where the two cell types are physically separated but can communicate in shared media by paracrine signaling. The physical barrier can be a porous membrane, a solid wall, or a hydrogel divider. [ 49 ] [ 50 ] [ 51 ] [ 52 ] [ 53 ] [ 54 ] If the physical barrier is removable (such as in PDMS or hydrogel), the assay can also be used to study cell invasion or cell migration. [ 50 ] [ 53 ] Co-culture designs can be adapted to tri- or multi-culture, which are often more representative of in vivo conditions relative to co-culture. [ 50 ] [ 51 ] [ 55 ] [ 56 ]
The flexibility of microfluidic devices greatly contributes to the development of multi-culture studies by improved control over spatial patterns. Closed channel systems made by PDMS are most commonly used because PDMS has traditionally enabled rapid prototyping. For example, mixed co-culture can be achieved in droplet-based microfluidics easily by a co-encapsulation system to study paracrine and juxtacrine signaling . [ 57 ] Two types of cells are co-encapsulated in droplets by combining two streams of cell-laden agarose solutions. After gelation, the agarose microgels will serve as a 3D microenvironment for cell co-culture. [ 57 ] Segregated co-culture is also realized in microfluidic channels to study paracrine signaling. Human alveolar epithelial cells and microvascular endothelial cells can be co-cultured in compartmentalized PDMS channels, separated by a thin, porous, and stretchable PDMS membrane to mimic alveolar-capillary barrier . [ 52 ] Endothelial cells can also be co-cultured with cancer cells in a monolayer while separated by a 3D collagen scaffold to study endothelial cell migration and capillary growth. [ 58 ] When embedded in gels, salivary gland adenoid cystic carcinoma (ACC) cells can be co-cultured with carcinoma-associated fibroblast (CAF) in a 3D extracellular matrix to study stroma-regulated cancer invasion in the 3D environment. [ 59 ] If juxtacrine signaling is to be investigated solely without paracrine signaling, a single cell coupling co-culture microfluidic array can be designed based on a cellular valving principle. [ 60 ]
Although closed channel microfluidics (discussed in the section above ) offers high customizability and biological complexity for multi-culture, the operation often requires handling expertise and specialized equipment, such as pumps and valves . [ 50 ] [ 54 ] In addition, the use of PDMS is known to cause adverse effects to cell culture, including leaching of oligomers or absorption of small molecules, thus often doubted by biologists. [ 61 ] Therefore, open microfluidic devices made of polystyrene (PS), a well-established cell culture material, started to emerge. [ 61 ] The advantages of open multi-culture designs are direct pipette accessibility and easy fabrication ( micro-milling , 3D printing , injection molding , or razor-printing – without the need for a subsequent bonding step or channel clearance techniques). [ 50 ] [ 54 ] [ 62 ] [ 63 ] [ 64 ] They can also be incorporated into traditional cultureware (well plate or petri dish ) while remaining the complexity for multi-culture experiments. [ 50 ] [ 54 ] [ 63 ] [ 64 ] For example, the "monorail device" which patterns hydrogel walls along a rail via spontaneous capillary flow can be inserted into commercially available 24-well plates. [ 63 ] Flexible patterning geometries are achieved by merely changing 3D printed or milled inserts. The monorail device can also be adapted to study multikingdom soluble factor signaling, which is difficult in traditional shared media co-culture due to the different media and culture requirements for microbial and mammalian cells. [ 63 ] Another open multi-culture device fabricated by razor-printing is capable of integrating numerous culture modalities, including 2D, 3D, Transwell, and spheroid culture. [ 50 ] It also shows improved diffusion to promote soluble factor paracrine signaling. [ 50 ]
Microfluidic systems expand their ability to control the local cell microenvironment beyond what is possible with conventional culture systems . Being able to provide different environments in a steady, sustainable and precise manner has a significant impact on cell culture research and study. Those environmental factors include physical ( shear stress ), biochemical ( cell-cell interactions , cell-molecule interactions, cell-substrate interactions), and physicochemical (pH, CO 2 , temperature , O 2 ) factors. [ 65 ]
Oxygen plays an essential role in biological systems. [ 66 ] Oxygen concentration control is one of the key elements when designing the microfluidic systems, whether the aerobic species or when modulating cellular functions in vivo , such as baseline metabolism and function. [ 66 ] Multiple microfluidic systems have been designed to control the desired gas concentrations for cell culture. For example, generating oxygen gradients was achieved by single-thin-layer PDMS construction within channels (thicknesses less than 50 μm, diffusion coefficient of oxygen in native PDMS at 25 °C, D= 3.55x10 −5 cm 2 s −1 ) without using gas cylinders or oxygen scavenging agents; thus the microfluidic cell culture device can be placed in incubators and be operated easily. [ 67 ] However, the PDMS may be problematic for the adsorption of small hydrophobic species. [ 68 ] Poly(methyl pentene) (PMP) may be an alternative material, because it has high oxygen permeability and biocompatibility like PDMS. [ 69 ] [ 70 ] In addition to the challenges of controlling gas concentration, monitoring oxygen in the microfluidic system is another challenge to address. There are numerous different dye indicators that can be used as optical, luminescence -based oxygen sensing, which is based on the phenomenon of luminescence quenching by oxygen, without consuming oxygen in the system. [ 71 ] This technique makes monitoring oxygen in microscale environments feasible and can be applied in biological laboratories. [ 71 ]
Temperature can be sensed by cells and influences their behavior, such as biochemical reaction kinetics . [ 72 ] However, it is hard to control high-resolution temperature in traditional cell culture systems; whereas, microfluidic systems are proven to successfully reach the desired temperature under different temperature conditions through several techniques. [ 72 ] For example, the temperature gradient in the microfluidic system can be achieved by mixing two or more inputs at different temperatures and flow rates, and the temperature is measured in the outlet channels by embedding polymer -based aquarium thermocouples . [ 73 ] Also, by installing heaters and digital temperature sensors at the base of the microfluidic system, it has been demonstrated that a microfluidic cell culture system can continuously operate for at least 500 hours. [ 74 ] The circulating water channels in the microfluidic system are also used to precisely control temperatures of the cell culture channels and chambers. [ 40 ] Furthermore, putting the device inside a cell culture incubator can also easily control the cell culture temperature. [ 75 ] | https://en.wikipedia.org/wiki/Microfluidic_cell_culture |
Microfluidic diffusional sizing ( MDS ) is a method to measure the size of particles based on the degree to which they diffuse within a microfluidic laminar flow. [ 1 ] It allows size measurements to be taken from extremely small quantities of material (nano-grams) and is particularly useful when sizing molecules which may vary in size depending on their environment - e.g. protein molecules which may unfold or become denatured in unfavourable conditions.
MDS is primarily used in protein analyses, where size, concentration and interactions are important.
Measuring the size of a protein molecule is useful as an overall quality indicator, since misfolding , unfolding, oligomerization , aggregation or degradation can all affect size.
The literature specifically demonstrates the use of MDS in sizing protein-nanobody complexes, monitoring the formation of α-synuclein amyloid fibrils. [ 2 ] and in observing protein assembly into oligomers [ 3 ]
MDS can also be used to size membrane proteins, as the use of a protein specific labelling and detection system allows other species present in the solution (such as free lipid micelles or detergents) to be ignored.
MDS has been used to characterise interactions between biomolecules under native conditions, and has been demonstrated to detect specific interactions within complex mixtures. [ 4 ] It has also been used in detecting and quantifying protein-ligand interactions [ 5 ] and protein-lipid interactions. [ 6 ]
The concentration of purified protein solutions in the laboratory is useful in determining yield and measuring the success of a prep. MDS reports concentration as well as size for each test.
Since the detection is not based on inherent fluorescence of tryptophan or tyrosine residues, MDS has been used as an alternative to A280 UV-Vis quantification. [ 7 ]
If protein specific labelling is applied, MDS allows membrane proteins to be sized. This is particularly useful as it is an area where other biophysical techniques can struggle - for example dynamic light scattering (DLS) is of limited use, since free detergent molecules may also scatter light and affect the results. [ 8 ]
Furthermore, as the size reported is an average of all detectable species present there is no bias towards large species, as is found in DLS measurements. [ 9 ]
Another key advantage is that results can be obtained with very small quantities of material [ 10 ] which may be particularly important where samples are scarce or expensive.
With commercially available MDS instruments, testing is very simple and there is no need to input test parameters or sample conditions. This makes it a very repeatable method of testing as most of the functions such as flow rates, detector settings etc. are automated by the instrument rather than set by the operator.
In addition to size, MDS is able to calculate concentration so two parameters can be assessed in one test.
Finally the method does not require calibration, as it relies on a ratio-metric measurement to determine diffusion rate. [ 11 ]
In an MDS analysis, a stream of liquid containing the particles to be sized is introduced alongside an auxiliary stream in a laminar flow in a microfluidic channel. Because there is no convective mixing of the two streams, the only way particles can move to the auxiliary stream is by diffusion. The rate of this diffusion is dependent on the particle's size, as determined by the Stokes–Einstein equation , so small particles diffuse quicker than large particles.
After a period of diffusion the original and auxiliary streams are split and the degree of diffusion is fixed. The number of particles in each stream can then be detected (in the case of proteins this is achieved by addition of an amine reactive fluorogenic dye). The ratio between the two streams is used to determine the diffusion co-efficient, which is used to calculate the hydrodynamic radius . The sum of particles in both streams can also be used to measure the concentration of the analyte. [ 12 ] | https://en.wikipedia.org/wiki/Microfluidic_diffusional_sizing |
Microfluidics refers to a system that manipulates a small amount of fluids (10 −9 to 10 −18 liters) using small channels with sizes of ten to hundreds of micrometres. It is a multidisciplinary field that involves molecular analysis, molecular biology , and microelectronics . [ 1 ] It has practical applications in the design of systems that process low volumes of fluids to achieve multiplexing , automation, and high-throughput screening . Microfluidics emerged in the beginning of the 1980s and is used in the development of inkjet printheads, DNA chips , lab-on-a-chip technology, micro-propulsion, and micro-thermal technologies.
Typically, micro means one of the following features:
Typically microfluidic systems transport, mix, separate, or otherwise process fluids. Various applications rely on passive fluid control using capillary forces , in the form of capillary flow modifying elements, akin to flow resistors and flow accelerators. In some applications, external actuation means are additionally used for a directed transport of the media. Examples are rotary drives applying centrifugal forces for the fluid transport on the passive chips. Active microfluidics refers to the defined manipulation of the working fluid by active (micro) components such as micropumps or microvalves . Micropumps supply fluids in a continuous manner or are used for dosing. Microvalves determine the flow direction or the mode of movement of pumped liquids. Often, processes normally carried out in a lab are miniaturised on a single chip, which enhances efficiency and mobility, and reduces sample and reagent volumes.
The behaviour of fluids at the microscale can differ from "macrofluidic" behaviour in that factors such as surface tension , energy dissipation, and fluidic resistance start to dominate the system. Microfluidics studies how these behaviours change, and how they can be worked around, or exploited for new uses. [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ]
At small scales (channel size of around 100 nanometers to 500 micrometers ) some unintuitive properties appear. In particular, the Reynolds number (which compares the effect of the momentum of a fluid to the effect of viscosity ) can become very low. One consequence is co-flowing fluids do not necessarily mix in the traditional sense, as flow becomes laminar rather than turbulent ; molecular transport between them must often be through diffusion . [ 7 ]
High specificity of chemical and physical properties (concentration, pH, temperature, shear force, etc.) can also be ensured resulting in more uniform reaction conditions and higher grade products in single and multi-step reactions. [ 8 ] [ 9 ]
Microfluidic flows need only be constrained by geometrical length scale – the modalities and methods used to achieve such a geometrical constraint are highly dependent on the targeted application. [ 10 ] Traditionally, microfluidic flows have been generated inside closed channels with the channel cross section being in the order of 10 μm x 10 μm. Each of these methods has its own associated techniques to maintain robust fluid flow which have matured over several years. [ citation needed ]
The behavior of fluids and their control in open microchannels came into focus around 2005 [ 11 ] and applied in air-to-liquid sample collection [ 12 ] [ 13 ] and chromatography. [ 14 ] In open microfluidics , at least one boundary of the system is removed, exposing the fluid to air or another interface (i.e. liquid). [ 15 ] [ 16 ] [ 17 ] Advantages of open microfluidics include accessibility to the flowing liquid for intervention, larger liquid-gas surface area, and minimized bubble formation. [ 18 ] [ 15 ] [ 17 ] [ 19 ] Another advantage of open microfluidics is the ability to integrate open systems with surface-tension driven fluid flow, which eliminates the need for external pumping methods such as peristaltic or syringe pumps. [ 20 ] Open microfluidic devices are also easy and inexpensive to fabricate by milling, thermoforming, and hot embossing. [ 21 ] [ 22 ] [ 23 ] [ 24 ] In addition, open microfluidics eliminates the need to glue or bond a cover for devices, which could be detrimental to capillary flows. Examples of open microfluidics include open-channel microfluidics, rail-based microfluidics, paper-based , and thread-based microfluidics. [ 15 ] [ 20 ] [ 25 ] Disadvantages to open systems include susceptibility to evaporation, [ 26 ] contamination, [ 27 ] and limited flow rate. [ 17 ]
Continuous flow microfluidics rely on the control of a steady state liquid flow through narrow channels or porous media predominantly by accelerating or hindering fluid flow in capillary elements. [ 28 ] In paper based microfluidics, capillary elements can be achieved through the simple variation of section geometry. In general, the actuation of liquid flow is implemented either by external pressure sources, external mechanical pumps , integrated mechanical micropumps , or by combinations of capillary forces and electrokinetic mechanisms. [ 29 ] [ 30 ] Continuous-flow microfluidic operation is the mainstream approach because it is easy to implement and less sensitive to protein fouling problems. Continuous-flow devices are adequate for many well-defined and simple biochemical applications, and for certain tasks such as chemical separation, but they are less suitable for tasks requiring a high degree of flexibility or fluid manipulations. These closed-channel systems are inherently difficult to integrate and scale because the parameters that govern flow field vary along the flow path making the fluid flow at any one location dependent on the properties of the entire system. Permanently etched microstructures also lead to limited reconfigurability and poor fault tolerance capability.
Process monitoring capabilities in continuous-flow systems can be achieved with highly sensitive microfluidic flow sensors based on MEMS technology, which offers resolutions down to the nanoliter range. [ 31 ]
Droplet-based microfluidics is differs from continuous microfluidics; droplet-based microfluidics manipulates discrete volumes of fluids in immiscible phases with low Reynolds number and laminar flow regimes. Interest in droplet-based microfluidics systems has been growing substantially in past decades. Microdroplets allow for handling miniature volumes (μL to fL) of fluids conveniently, provide better mixing, encapsulation, sorting, and sensing, and suit high throughput experiments. [ 33 ] Exploiting the benefits of droplet-based microfluidics efficiently requires a deep understanding of droplet generation [ 34 ] to perform various logical operations [ 35 ] [ 36 ] such as droplet manipulation, [ 37 ] droplet sorting, [ 38 ] droplet merging, [ 39 ] and droplet breakup. [ 40 ]
Alternatives to the above closed-channel continuous-flow systems include novel open structures, where discrete, independently controllable droplets
are manipulated on a substrate using electrowetting . Following the analogy of digital microelectronics, this approach is referred to as digital microfluidics . Le Pesant et al. pioneered the use of electrocapillary forces to move droplets on a digital track. [ 41 ] The "fluid transistor" pioneered by Cytonix [ 42 ] also played a role. The technology was subsequently commercialised by Duke University. By using discrete unit-volume droplets, [ 34 ] a microfluidic function can be reduced to a set of repeated basic operations, i.e., moving one unit of fluid over one unit of distance. This "digitisation" method facilitates the use of a hierarchical and cell-based approach for microfluidic biochip design. Therefore, digital microfluidics offers a flexible and scalable system architecture as well as high fault-tolerance capability. Moreover, because each droplet can be controlled independently, these systems also have dynamic reconfigurability, whereby groups of unit cells in a microfluidic array can be reconfigured to change their functionality during the concurrent execution of a set of bioassays. Although droplets are manipulated in confined microfluidic channels, since the control on droplets is not independent, it should not be confused as "digital microfluidics". One common actuation method for digital microfluidics is electrowetting -on-dielectric ( EWOD ). [ 43 ] Many lab-on-a-chip applications have been demonstrated within the digital microfluidics paradigm using electrowetting.
Paper-based microfluidic devices are proposed to provide portable, cheap, and user-friendly medical diagnostic systems. [ 44 ] Paper based microfluidics rely on the phenomenon of capillary penetration in porous media. [ 45 ] To tune fluid penetration in porous substrates such as paper in two and three dimensions, the pore structure, wettability and geometry of the microfluidic devices can be controlled while the viscosity and evaporation rate of the liquid play a further significant role. Many such devices feature hydrophobic barriers on hydrophilic paper that passively transport aqueous solutions to outlets where biological reactions take place. [ 46 ] Paper-based microfluidics are considered as portable point-of-care biosensors used in a remote setting where advanced medical diagnostic tools are not accessible. [ 47 ] Current applications include portable glucose detection [ 48 ] and environmental testing, [ 49 ] with hopes of reaching areas that lack advanced medical diagnostic tools.
One potential application area involves particle detection in fluids. Particle detection of small fluid-borne particles down to about 1 μm in diameter is typically achieved using a Coulter counter , in which electrical signals are generated when a weakly-conducting fluid such as in saline water is passed through a small (~100 μm diameter) pore, so that an electrical signal is generated that is directly proportional to the ratio of the particle volume to the pore volume. The physics behind this is relatively simple, described in a classic paper by DeBlois and Bean, [ 50 ] and the implementation first described in Coulter's original patent. [ 51 ] This is the method used to e.g. size and count erythrocytes ( red blood cells ) as well as leukocytes ( white blood cells ) for standard blood analysis. The generic term for this method is resistive pulse sensing (RPS); Coulter counting is a trademark term. However, the RPS method does not work well for particles below 1 μm diameter, as the signal-to-noise ratio falls below the reliably detectable limit, set mostly by the size of the pore in which the analyte passes and the input noise of the first-stage amplifier . [ citation needed ]
The limit on the pore size in traditional RPS Coulter counters is set by the method used to make the pores, which while a trade secret, most likely [ according to whom? ] uses traditional mechanical methods. This is where microfluidics can have an impact: The lithography -based production of microfluidic devices, or more likely the production of reusable molds for making microfluidic devices using a molding process, is limited to sizes much smaller than traditional machining . Critical dimensions down to 1 μm are easily fabricated, and with a bit more effort and expense, feature sizes below 100 nm can be patterned reliably as well. This enables the inexpensive production of pores integrated in a microfluidic circuit where the pore diameters can reach sizes of order 100 nm, with a concomitant reduction in the minimum particle diameters by several orders of magnitude.
As a result, there has been some university-based development of microfluidic particle counting and sizing [ 52 ] [ 53 ] [ 54 ] with the accompanying commercialization of this technology. This method has been termed microfluidic resistive pulse sensing (MRPS).
One application for microfluidic devices is the separation and sorting of different fluids or cell types. Microfluidic devices have been integrated with magnetophoresis : the migration of particles by a magnetic field . [ 55 ] This can be accomplished by sending a fluid containing at least one magnetic component through a microfluidic channel that has a magnet positioned along the length of the channel. This creates a magnetic field inside the microfluidic channel which draws magnetically active substances towards it, effectively separating the magnetic and non-magnetic components of the fluid. This technique can be readily utilized in industrial settings where the fluid at hand already contains magnetically active material. For example, a handful of metallic impurities can find their way into certain consumable liquids, namely milk and other dairy products. [ 56 ] Conveniently, in the case of milk, many of these metal contaminants exhibit paramagnetism . Therefore, before packaging, milk can be flowed through channels with magnetic gradients as a means of purifying out the metal contaminants.
cell separations are of interest in microfluidics. This is accomplished. First, a paramagnetic substance (usually micro/ nanoparticles or a paramagnetic fluid ) [ 57 ] needs to be functionalized to target the cell type of interest. This can be accomplished by identifying a transmembranal protein unique to the cell type of interest and subsequently functionalizing magnetic particles with the complementary antigen or antibody . [ 56 ] [ 58 ] [ 59 ] [ 60 ] [ 61 ] Once the magnetic particles are functionalized, they are dispersed in a cell mixture where they bind to only the cells of interest. The resulting cell/particle mixture can then be flowed through a microfluidic device with a magnetic field to separate the targeted cells from the rest.
Conversely, microfluidic-assisted magnetophoresis may be used to facilitate efficient mixing within microdroplets or plugs. To accomplish this, microdroplets are injected with paramagnetic nanoparticles and are flowed through a straight channel which passes through rapidly alternating magnetic fields. This causes the magnetic particles to be quickly pushed from side to side within the droplet and results in the mixing of the microdroplet contents. [ 60 ] This eliminates the need for tedious engineering considerations that are necessary for traditional, channel-based droplet mixing. Other research has also shown that the label-free separation of cells may be possible by suspending cells in a paramagnetic fluid and taking advantage of the magneto-Archimedes effect. [ 62 ] [ 63 ] While this does eliminate the complexity of particle functionalization, more research is needed to fully understand the magneto-Archimedes phenomenon and how it can be used to this end. This is not an exhaustive list of the various applications of microfluidic-assisted magnetophoresis; the above examples merely highlight the versatility of this separation technique in both current and future applications.
Microfluidic structures include micropneumatic systems, i.e. microsystems for the handling of off-chip fluids (liquid pumps, gas valves, etc.), and microfluidic structures for the on-chip handling of nanoliter (nl) and picoliter (pl) volumes. [ 64 ] To date, the most successful commercial application of microfluidics is the inkjet printhead . [ 65 ] Additionally, microfluidic manufacturing advances mean that makers can produce the devices in low-cost plastics such as polymethymethacrylate (PMMA), polystyrene , cyclic olefin polymer (COP) and polyvinyl chloride (PVC) [ 66 ] [ 67 ] and automatically verify part quality. [ 68 ]
Advances in microfluidics technology promise to improve molecular biology procedures for enzymatic analysis (e.g., glucose and lactate assays ), DNA analysis (e.g., polymerase chain reaction and high-throughput sequencing ), proteomics , and in chemical synthesis. [ 28 ] [ 69 ] Microfluidic biochips integrate assay operations such as detection, with sample pre-treatment and sample preparation. [ 70 ] [ 71 ]
A promising application area for biochips is clinical pathology , especially the point-of-care diagnosis of diseases . [ 72 ] In addition, microfluidics-based devices, capable of continuous sampling and real-time testing of air/water samples for biochemical toxins and other dangerous pathogens , [ 73 ] can serve as an always-on "bio-smoke alarm" for early warning.
Microfluidic technology has provide tools for biologists to control the cellular environment. Potential advantages of this technology for microbiology are listed below:
Some of these areas are further elaborated in the sections below:
Early biochips were based on the idea of a DNA microarray , e.g., the GeneChip DNAarray from Affymetrix , which is a piece of glass, plastic or silicon substrate, on which pieces of DNA (probes) are affixed in a microscopic array. Similar to a DNA microarray , a protein array is a miniature array where a multitude of different capture agents, most frequently monoclonal antibodies , are deposited on a chip surface; they are used to determine the presence and/or amount of proteins in biological samples, e.g., blood . A drawback of DNA and protein arrays is that they are neither reconfigurable nor scalable after manufacture. Digital microfluidics has been described as a means for carrying out Digital PCR .
In addition to microarrays, biochips have been designed for two-dimensional electrophoresis , [ 85 ] transcriptome analysis, [ 86 ] and PCR amplification. [ 87 ] Other applications include various electrophoresis and liquid chromatography applications for proteins and DNA , cell separation, in particular, blood cell separation, protein analysis, cell manipulation and analysis including cell viability analysis [ 33 ] and microorganism capturing. [ 71 ]
By combining microfluidics with landscape ecology and nanofluidics , a nano/micro fabricated fluidic landscape can be constructed by building local patches of bacterial habitat and connecting them by dispersal corridors. The resulting landscapes can be used as physical implementations of an adaptive landscape , [ 88 ] by generating a spatial mosaic of patches of opportunity distributed in space and time. The patchy nature of these fluidic landscapes allows for the study of adapting bacterial cells in a metapopulation system. The evolutionary ecology of these bacterial systems in these synthetic ecosystems allows for using biophysics to address questions in evolutionary biology .
The ability to create precise and carefully controlled chemoattractant gradients makes microfluidics the ideal tool to study motility, [ 89 ] chemotaxis and the ability to evolve / develop resistance to antibiotics in small populations of microorganisms and in a short period of time. These microorganisms including bacteria [ 90 ] and the broad range of organisms that form the marine microbial loop , [ 91 ] responsible for regulating much of the oceans' biogeochemistry.
Microfluidics has also greatly aided the study of durotaxis by facilitating the creation of durotactic (stiffness) gradients.
By rectifying the motion of individual swimming bacteria, [ 92 ] microfluidic structures can be used to extract mechanical motion from a population of motile bacterial cells. [ 93 ] This way, bacteria-powered rotors can be built. [ 94 ] [ 95 ]
The merger of microfluidics and optics is typical known as optofluidics . Examples of optofluidic devices are tunable microlens arrays [ 96 ] [ 97 ] and optofluidic microscopes.
Microfluidic flow enables fast sample throughput, automated imaging of large sample populations, as well as 3D capabilities, [ 98 ] [ 99 ] or superresolution. [ 100 ]
Due to the increase in safety concerns and operating costs of common analytic methods ( ICP-MS , ICP-AAS , and ICP-OES [ 101 ] ), the Photonics Lab on a Chip (PhLOC) is becoming an increasingly popular tool for the analysis of actinides and nitrates in spent nuclear waste. The PhLOC is based on the simultaneous application of Raman and UV-Vis-NIR spectroscopy, [ 102 ] which allows for the analysis of more complex mixtures which contain several actinides at different oxidation states. [ 103 ] Measurements made with these methods have been validated at the bulk level for industrial tests, [ 101 ] [ 104 ] and are observed to have a much lower variance at the micro-scale. [ 105 ] This approach has been found to have molar extinction coefficients (UV-Vis) in line with known literature values over a comparatively large concentration span for 150 μL [ 103 ] via elongation of the measurement channel, and obeys Beer's Law at the micro-scale for U(IV). [ 106 ] Through the development of a spectrophotometric approach to analyzing spent fuel, an on-line method for measurement of reactant quantities is created, increasing the rate at which samples can be analyzed and thus decreasing the size of deviations detectable within reprocessing. [ 104 ]
Through the application of the PhLOC, flexibility and safety of operational methods are increased. Since the analysis of spent nuclear fuel involves extremely harsh conditions, the application of disposable and rapidly produced devices (Based on castable and/or engravable materials such as PDMS, PMMA, and glass [ 107 ] ) is advantageous, although material integrity must be considered under specific harsh conditions. [ 106 ] Through the usage of fiber optic coupling, the device can be isolated from instrumentation, preventing irradiative damage and minimizing the exposure of lab personnel to potentially harmful radiation, something not possible on the lab scale nor with the previous standard of analysis. [ 103 ] The shrinkage of the device also allows for lower amounts of analyte to be used, decreasing the amount of waste generated and exposure to hazardous materials. [ 103 ]
Expansion of the PhLOC to miniaturize research of the full nuclear fuel cycle is currently being evaluated, with steps of the PUREX process successfully being demonstrated at the micro-scale. [ 102 ] Likewise, the microfluidic technology developed for the analysis of spent nuclear fuel is predicted to expand horizontally to analysis of other actinide, lanthanides, and transition metals with little to no modification. [ 103 ]
HPLC in the field of microfluidics comes in two different forms. Early designs included running liquid through the HPLC column then transferring the eluted liquid to microfluidic chips and attaching HPLC columns to the microfluidic chip directly. [ 108 ] The early methods had the advantage of easier detection from certain machines like those that measure fluorescence. [ 109 ] HPLC columns have been integrated into microfluidic chips. The main advantage of integrating HPLC columns into microfluidic devices is the smaller form factor that can be achieved, which allows for additional features to be combined within one microfluidic chip. Integrated chips can also be fabricated from multiple different materials, including glass and polyimide which are quite different from the standard material of PDMS used in many different droplet-based microfluidic devices. [ 110 ] [ 111 ] This is an important feature because different applications of HPLC microfluidic chips may call for different pressures. PDMS fails in comparison for high-pressure uses compared to glass and polyimide. High versatility of HPLC integration ensures robustness by avoiding connections and fittings between the column and chip. [ 112 ] The ability to build off said designs in the future allows the field of microfluidics to continue expanding its potential applications.
The potential applications surrounding integrated HPLC columns within microfluidic devices have proven expansive over the last 10–15 years. The integration of such columns allows for experiments to be run where materials were in low availability or very expensive, like in biological analysis of proteins. This reduction in reagent volumes allows for new experiments like single-cell protein analysis, which due to size limitations of prior devices, previously came with great difficulty. [ 113 ] The coupling of HPLC-chip devices with other spectrometry methods like mass-spectrometry allow for enhanced confidence in identification of desired species, like proteins. [ 114 ] Microfluidic chips have also been created with internal delay-lines that allow for gradient generation to further improve HPLC, which can reduce the need for further separations. [ 115 ] Some other practical applications of integrated HPLC chips include the determination of drug presence in a person through their hair [ 116 ] and the labeling of peptides through reverse phase liquid chromatography. [ 117 ]
Acoustic droplet ejection uses a pulse of ultrasound to move low volumes of fluids (typically nanoliters or picoliters) without any physical contact. This technology focuses acoustic energy into a fluid sample to eject droplets as small as a millionth of a millionth of a litre (picoliter = 10 −12 litre). ADE technology is a very gentle process, and it can be used to transfer proteins, high molecular weight DNA and live cells without damage or loss of viability. This feature makes the technology suitable for a wide variety of applications including proteomics and cell-based assays.
Microfluidic fuel cells can use laminar flow to separate the fuel and its oxidant to control the interaction of the two fluids without the physical barrier that conventional fuel cells require. [ 118 ] [ 119 ] [ 120 ]
To understand the prospects for life to exist elsewhere in the universe, astrobiologists are interested in measuring the chemical composition of extraplanetary bodies. [ 121 ] Because of their small size and wide-ranging functionality, microfluidic devices are uniquely suited for these remote sample analyses. [ 122 ] [ 123 ] [ 124 ] From an extraterrestrial sample, the organic content can be assessed using microchip capillary electrophoresis and selective fluorescent dyes. [ 125 ] These devices are capable of detecting amino acids , [ 126 ] peptides , [ 127 ] fatty acids , [ 128 ] and simple aldehydes , ketones , [ 129 ] and thiols . [ 130 ] These analyses coupled together could allow powerful detection of the key components of life, and hopefully inform our search for functioning extraterrestrial life. [ 131 ]
Microfluidic techniques such as droplet microfluidics, paper microfluidics, and lab-on-a-chip are used in the realm of food science in a variety of categories. [ 132 ] Research in nutrition, [ 133 ] [ 134 ] food processing, and food safety benefit from microfluidic technique because experiments can be done with less reagents. [ 132 ]
Food processing requires the ability to enable shelf stability in foods, such as emulsions or additions of preservatives. Techniques such as droplet microfluidics are used to create emulsions that are more controlled and complex than those created by traditional homogenization due to the precision of droplets that is achievable. Using microfluidics for emulsions is also more energy efficient compared to homogenization in which “only 5% of the supplied energy is used to generate the emulsion, with the rest dissipated as heat” . [ 135 ] Although these methods have benefits, they currently lack the ability to be produced at large scale that is needed for commercialization. [ 136 ] Microfluidics are also used in research as they allow for innovation in food chemistry and food processing. [ 132 ] [ 136 ] An example in food engineering research is a novel micro-3D-printed device fabricated to research production of droplets for potential food processing industry use, particularly in work with enhancing emulsions. [ 137 ]
Paper and droplet microfluidics allow for devices that can detect small amounts of unwanted bacteria or chemicals, making them useful in food safety and analysis. [ 138 ] Paper-based microfluidic devices are often referred to as microfluidic paper-based analytical devices (μPADs) and can detect such things as nitrate, [ 139 ] preservatives, [ 140 ] or antibiotics [ 141 ] in meat by a colorimetric reaction that can be detected with a smartphone. These methods are being researched because they use less reactants, space, and time compared to traditional techniques such as liquid chromatography. μPADs also make home detection tests possible, which is of interest to those with allergies and intolerances. [ 139 ] In addition to paper-based methods, research demonstrates droplet-based microfluidics shows promise in drastically shortening the time necessary to confirm viable bacterial contamination in agricultural waters in the domestic and international food industry. [ 138 ]
Personalized cancer treatment is a tuned method based on the patient's diagnosis and background. Microfluidic technology offers sensitive detection with higher throughput, as well as reduced time and costs. For personalized cancer treatment, tumor composition and drug sensitivities are very important. [ 142 ]
A patient's drug response can be predicted based on the status of biomarkers , or the severity and progression of the disease can be predicted based on the atypical presence of specific cells. [ 143 ] Drop - qPCR is a droplet microfluidic technology in which droplets are transported in a reusable capillary and alternately flow through two areas maintained at different constant temperatures and fluorescence detection. It can be efficient with a low contamination risk to detect Her2 . [ 142 ] A digital droplet‐based PCR method can be used to detect the KRAS mutations with TaqMan probes , to enhance detection of the mutative gene ratio. [ 144 ] In addition, accurate prediction of postoperative disease progression in breast or prostate cancer patients is essential for determining post-surgery treatment. A simple microfluidic chamber, coated with a carefully formulated extracellular matrix mixture is used for cells obtained from tumor biopsy after 72 hours of growth and a thorough evaluation of cells by imaging. [ 145 ]
Microfluidics is also suitable for circulating tumor cells (CTCs) and non- CTCs liquid biopsy analysis. Beads conjugate to anti‐ epithelial cell adhesion molecule (EpCAM) antibodies for positive selection in the CTCs isolation chip (iCHIP) . [ 146 ] CTCs can also be detected by using the acidification of the tumor microenvironment and the difference in membrane capacitance. [ 147 ] [ 148 ] CTCs are isolated from blood by a microfluidic device, and are cultured on-chip , which can be a method to capture more biological information in a single analysis. For example, it can be used to test the cell survival rate of 40 different drugs or drug combinations. [ 149 ] Tumor‐derived extracellular vesicles can be isolated from urine and detected by an integrated double‐filtration microfluidic device; they also can be isolated from blood and detected by electrochemical sensing method with a two‐level amplification enzymatic assay . [ 150 ] [ 151 ]
Tumor materials can directly be used for detection through microfluidic devices. To screen primary cells for drugs, it is often necessary to distinguish cancerous cells from non-cancerous cells. A microfluidic chip based on the capacity of cells to pass small constrictions can sort the cell types, metastases . [ 152 ] Droplet‐based microfluidic devices have the potential to screen different drugs or combinations of drugs, directly on the primary tumor sample with high accuracy. To improve this strategy, the microfluidic program with a sequential manner of drug cocktails, coupled with fluorescent barcodes, is more efficient. [ 153 ] Another advanced strategy is detecting growth rates of single-cell by using suspended microchannel resonators, which can predict drug sensitivities of rare CTCs . [ 154 ]
Microfluidics devices also can simulate the tumor microenvironment , to help to test anticancer drugs. Microfluidic devices with 2D or 3D cell cultures can be used to analyze spheroids for different cancer systems (such as lung cancer and ovarian cancer ), and are essential for multiple anti-cancer drugs and toxicity tests. This strategy can be improved by increasing the throughput and production of spheroids. For example, one droplet-based microfluidic device for 3D cell culture produces 500 spheroids per chip. [ 155 ] These spheroids can be cultured longer in different surroundings to analyze and monitor. The other advanced technology is organs‐on‐a‐chip , and it can be used to simulate several organs to determine the drug metabolism and activity based on vessels mimicking, as well as mimic pH , oxygen ... to analyze the relationship between drugs and human organ surroundings. [ 155 ]
One strategy relevant to single-cell chromatin immunoprecipitation (ChiP)‐Sequencing is droplets , which operates by combining droplet‐based single cell RNA sequencing with DNA‐barcoded antibodies, possibly to explore the tumor heterogeneity by the genotype and phenotype to select the personalized anti-cancer drugs and prevent the cancer relapse. [ 156 ]
One significant advancement in the field is the development of integrated capillary electrophoresis (CE) systems on microchips , as demonstrated by Z. Hugh Fan and D. Jed. Harrison. They created a planar glass chip incorporating a sample injector and separation channels using micromachining techniques. This setup allowed for the rapid separation of amino acids in just a few seconds, achieving high separation efficiencies with up to 6800 theoretical plates . The use of high electric fields , possible due to the thermal mass and conductivity of glass, minimized Joule heating effects, making the system highly efficient and fast. Such innovations highlight the potential of microfluidic devices in analytical chemistry, particularly in applications requiring quick and precise analyses. [ 157 ] | https://en.wikipedia.org/wiki/Microfluidics |
Microfluorimetry is an adaption of fluorimetry for studying the biochemical and biophysical properties of cells by using microscopy to image cell components tagged with fluorescent molecules. It is a type of microphotometry that gives a quantitative measure of the qualitative nature of fluorescent measurement and therefore, allows for definitive results that would have been previously indiscernible to the naked eye. [ 1 ]
Microfluorimetry has uses for many different fields including cell biology , microbiology , immunology , cell cycle analysis and "flow karyotyping " of cells. [ 2 ] In flow karotyping, isolated metaphase chromosomes are stained and measured in a flow microfluorometer. Fluorescent staining of chromosomes can also give distribution about the relative frequency of occurrence and the chromosomal DNA content of the measured chromosomes. This technique allows for karyotyping at higher speeds than with previous methods and was shown to be accurate using Chinese hamster chromosomes. [ 3 ] Flow microfluorimetry (FMF) can also be used to determine different populations of cells using fluorescent markers with small cell samples. The markers used for measurement in flow microfluorimetry are made up of fluorescent antigens or DNA binding agents. [ 2 ] It allows for the accurate measure of an antibody reacting with an antigen. [ 1 ] Flow microfluorimetry is also used in pharmaceutical research to determine cell type, protein and DNA expression, cell cycle, and other properties of a cell during drug treatment. [ 4 ] For example, microfluorimetry is used in neurons to compare the effects of neurotoxins on both calcium ion concentration and mitochondrial membrane potential in individual cells. [ 5 ] Microfluorimetry can also be used as a method to distinguish different microorganisms from one another by analyzing and comparing the DNA content of each cell. [ 6 ] This same concept can also be applied to distinguish between cell types using a suitable fluorescent dye which varies depending on purpose and is a critical technique in modern cell biology and genomics. [ 7 ]
Another use of microfluorometry is flow cytometry which uses the emission of fluorochrome molecules and usually a laser as a light source to create data from particles and cells. [ 8 ] It can be used to separate chromosomes at a very high rate and used easily with next-gen sequencing. This technique can simply results by separating only the relevant chromosomes at a very fast rate. [ 9 ] For example, E. coli bacteriophages lambda and T4 were able to be separated by flow cytometry which allowed for genomic analysis which was previously difficult. [ 10 ]
Microfluorimetry is building upon the established method of fluorimetric measurement. Using a dye that fluoresces in the presence of a target compound, fluorimetry can detect the presence of the compound by determining the presence and intensity of fluorescence. Differences in the intensity can be used to determine concentration of the compound. Additionally, if the dye undergoes a spectral shift then you can determine the absolute concentration of the target regardless of knowledge of the concentration of the dye. Fura-2 is an example of a fluorescent dye used to measure calcium. Microfluorimetry expands on fluorimetry by adding a microscopic component to measurements to allow analysis of single cells and other microscopic interests. [ 11 ]
A microfluorometer is a fluorescence spectrophotometer combined with a microscope, designed to measure fluorescence spectra of microscopic samples or areas or can be configured to measure the transmission and reflectance spectra of microscopic sample areas. It can either be a complete microfluorometer built exclusively for fluorescence microspectroscopy or the fluorescence spectrometer unit which attaches to the optical port of a microscope. [ 12 ] A microfluorometer can be used to estimate amounts and distributions of chemical components in individual cells or in chromosomes. In order to estimate the amount of chemical components, its fluorescent intensity is measured by photoelectrical photometry while distribution is found by measuring the intensities of photos of negative chromosomes' metaphase plates. [ 13 ] A microspectrophotometer can measure transmission, absorbance, reflectance and emission spectra then using built in algorithms a spectra is produced that can be compared against previous data in order to determine composition, concentration, etc. [ 12 ]
There are many sources of error in the process but biological errors such as an inability to prepare homogenous samples are more likely to be a limitation than technical errors. [ 1 ] | https://en.wikipedia.org/wiki/Microfluorimetry |
Microfoam is finely textured milk used for making espresso -based coffee drinks, particularly those with latte art . It is typically made with the steam wand of an espresso machine , which pumps steam into a pitcher of milk.
The opposite of microfoam is Macrofoam (also called dry foam, in contrast to the wet foam of microfoam), which has visibly large bubbles, a style of milk, traditionally used for cappuccinos .
Microfoam is shiny, slightly thickened, and should have microscopic, uniform bubbles. [ 1 ] It is not as viscous or "foamy" as macrofoam [ 2 ] – it is better described as "gooey" and resembles melted marshmallows or wet paint. There have been a variety of names used for this ideal standard, such as "microfoam", "velvet milk", [ 3 ] "microbubbles", and so forth.
The decorative application of microfoam is called latte art , which involves making patterns in espresso-based drinks. Microfoam is essential for this as the microscopic bubbles give definition and stability to the patterns, which are harder to achieve with macrofoam which disperses more readily. [ 4 ] Latte art is traditionally associated with lattes , as the name suggests, but can also be used in cappuccinos and other drinks.
A cappuccino made with microfoam is sometimes called a "wet" cappuccino. [ 5 ] However, cappuccinos typically use thicker macrofoam, with a layer of dry foam floating on the top of the drink. Latte macchiato is another drink which generally has separate layers of dry foam and liquid milk, but microfoam is occasionally used instead. Microfoam may also be added to brewed coffee in a café au lait , and faint latte art can be produced. [ 6 ] Microfoam may also be used in a steamer (a "coffee-free" cappuccino), though this can instead be made with dry foam.
As it requires a skilled barista to produce microfoam (especially when used for latte art), it is a sign of attention to quality, and a defining characteristic of the third wave of coffee .
Microfoam is usually created with the steam wand of an espresso machine . This is the quickest method and provides precise control over the timing and depth of air injection. Alternative methods are rarely as effective for producing microfoam, but some are acceptable for macrofoam. These include whisking, shaking, and hand pumps. [ 4 ] Dedicated electric milk frothers may also be used, usually consisting of a motorized whisk. [ 7 ]
When using a steam wand, the volume and type of foam is controlled by the barista during the steaming process, [ 1 ] and loosely follows these steps:
The details of the above method vary between baristas, and are influenced by the machine and the desired outcome.
The basic requirements for formation of foam are an abundance of gas, water, a surfactant, and energy. [ citation needed ] The steam wand of an espresso machine supplies energy, in the form of heat, and gas, in the form of steam. The other two components, water and surfactants, are naturally occurring ingredients of milk. [ 11 ] Varying the balance of these factors affects the size of bubbles, the foam dissipation rate, and the volume of foam. [ 12 ]
Microfoam may be represented simply as a metastable liquid-gas colloid of milk and air, consisting of gaseous bubbles suspended in the liquid milk. In reality, the suspension is more complex because milk consists of two different colloids itself - an emulsion of fat and a sol of protein. In fact, these two colloids are what enable milk to form such a mechanically strong foam which does not collapse under its own weight. [ 6 ] The interaction between fat and air creates a structure of microscopic bubbles strong enough to support itself, and even be submerged (i.e. suspended within the liquid milk). [ 13 ]
Like in whipped cream, air bubbles are initially stabilized by the protein β -casein, prior to their adsorption of fat. [ 14 ] This adsorption causes destabilization of the bubbles, because the fat molecules are amphiphilic (i.e. they have polar and non-polar ends), competing with protein molecules which are more conducive to bubbles. [ 15 ] The denaturation of milk fat occurs around 40 °C (104 °F), so milk at higher temperatures is not significantly affected by this problem. [ 15 ] At higher temperatures, the protein β -lactoglobulin enables the foam to maintain its structure and is the prime factor in the formation of foam. [ citation needed ] This can be shown trivially by adding various quantities of skim milk powder which contains a high concentration of β -lactoglobulin.
Since fat reduces the likelihood of bonding at the surface of bubbles, it follows that fat content in milk is inversely proportional to its frothing potential. [ 15 ] Whilst this is true, an excessive fat constituent also enables larger bubbles, leading to macrofoam rather than microfoam. As a result, most baristas prefer to use whole milk rather than skim milk, due to its tendency to form smaller, more homogeneous bubbles. [ 15 ]
Several studies have confirmed that the foamability of pasteurized whole milk, measured by the volume of foam produced, reaches a minimum at 25 °C (77 °F). [ 12 ] [ 13 ] [ 16 ] This value is higher for raw milk - around 35 °C (95 °F). The dip in foamability occurs due to fat globules consisting of both solid and liquid phases at this temperature. Solid fat crystals in a globule may penetrate the film which separates them from the surrounding air, causing spreading of the membrane material which is then adsorbed onto air bubbles. [ 13 ] At temperatures above the minimum foamability temperature, the volume of foam steadily increases, which has been attributed to the trends of decreasing viscosity and surface tension with temperature. [ 17 ]
If milk is heated above 82 °C (180 °F), it becomes scalded and its texture is compromised. Microfoam cannot exist in overheated milk due to the missing tertiary structure in the protein. [ 18 ] When milk is scalded, the suspended protein casein becomes denatured and cannot maintain the intermolecular bonds necessary for microfoam. [ 19 ]
The stability of milk foam, measured by the half-life of its volume, is also greatly influenced by temperature. [ 13 ] For pasteurized whole milk, stability increases with temperature up to about 40 °C (104 °F), then rises steeply until 60 °C (140 °F), where it starts steadily decreasing. Skim milk generally produces more stable foam, owing to its lower concentration of micellar casein. For regular pasteurized, homogenized whole milk, steamed at 70 °C (158 °F), the half-life is roughly 150 minutes. [ 13 ] However, microfoam tends to separate into layers more quickly than it reduces in volume, so baristas usually steam milk immediately before serving it. [ 10 ] This is especially important when serving latte art which may degrade within minutes.
When using a steam wand, a slight but audible hissing sound occurs when the air enters the milk, mainly due to microscopic cavitation . [ 20 ] [ 21 ] A louder screaming sound may be heard if the steam orifice becomes blocked or the machine cannot pump enough air. [ 22 ] | https://en.wikipedia.org/wiki/Microfoam |
Microfungi or micromycetes are fungi — eukaryotic organisms such as molds , mildews and rusts —which have microscopic spore -producing structures. [ 1 ] They exhibit tube tip-growth and have cell walls composed of chitin , a polymer of N -acetylglucosamine . Microfungi are a paraphyletic group, distinguished from macrofungi only by the absence of a large, multicellular fruiting body. They are ubiquitous in all terrestrial and freshwater and marine environments, and grow in plants, soil, water, insects, cattle rumens , hair, and skin. Most of the fungal body consists of microscopic threads, called hyphae , extending through the substrate in which it grows. The mycelia of microfungi produce spores that are carried by the air, spreading the fungus. [ citation needed ]
Many microfungi species are benign, existing as soil saprotrophs , for example, largely unobserved by humans. Many thousands of microfungal species occur in lichens , forming symbiotic relationships with algae . Other microfungi, such as those of the genera Penicillium , Aspergillus and Neurospora , were first discovered as molds causing spoilage of fruit and bread. [ citation needed ]
Certain species have commercial value. Penicillium species are used in the manufacture of blue cheeses and as the source of the antibiotic penicillin , discovered by Sir Alexander Fleming in 1928, while Fusarium venenatum is used to produce Quorn, a mycoprotein food product. [ citation needed ]
Microfungi can be harmful, causing diseases of plants, animals and humans with varying degrees of severity and economic impact. The irritating human skin disease known as athlete's foot or tinea pedis is caused by species of the microfungal genus Trichophyton . Microfungi may cause diseases of crops and trees which range in severity from mild to disastrous, and in economic importance from beneficial to seriously costly. The mold Botrytis cinerea can cause spoilage of crops including grapes, but is also responsible for the " noble rot ", which concentrates sugars in the grapes used to make the intensely sweet and concentrated Sauternes dessert wines from the Bordeaux region of France . Dutch elm disease , which has ravaged elms across Europe and North America in the last 50 years, is caused by the microfungi of the genus Ophiostoma . Rice blast , a devastating fungal disease of cereals including rice , wheat and millet , is caused by the phytopathogenic Ascomycete fungus Magnaporthe grisea . In the built environment , the toxic fungus Stachybotrys chartarum causes damage to damp walls and furnishings, and may be responsible for sick building syndrome . [ citation needed ]
Types of epidermal microfungal infections are: [ citation needed ]
Within the United States, approximately 13,000 species of microfungi on plants or plant products are thought to exist. Specimens of microfungi are housed in the U.S. National Fungus Collections and other institutions like herbaria and culture collections that serve as reservoirs of information and documentation about the nation's natural heritage. Based on the number of species reported in the literature and those represented in the collections; the number of microfungi known in the United States is estimated at 29,000 species. In certain areas of the temperate northern hemisphere where fungi have been well studied, the ratio of vascular plant to fungal species is about 6 to 1. [ 2 ] This suggests that there may be as many as 120,000 species of fungi within the United States, surpassing the 29,000 U.S. species of microfungi estimated based on collection and literature data, [ 3 ] and 1.5 million worldwide. [ citation needed ] However, as of 1991, the microfungi of the tropical United States had not been well studied. [ 2 ] | https://en.wikipedia.org/wiki/Microfungi |
Microglobulin is a globulin of relatively small molecular weight. [ 1 ] It can be contrasted to macroglobulin .,
Examples include:
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microglobulin |
A micrograph is an image, captured photographically or digitally, taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a microscope but is only slightly magnified, usually less than 10 times. Micrography is the practice or art of using microscopes to make photographs. A photographic micrograph is a photomicrograph , and one taken with an electron microscope is an electron micrograph .
A micrograph contains extensive details of microstructure. A wealth of information can be obtained from a simple micrograph like behavior of the material under different conditions, the phases found in the system, failure analysis, grain size estimation, elemental analysis and so on. Micrographs are widely used in all fields of microscopy.
A light micrograph or photomicrograph is a micrograph prepared using an optical microscope , a process referred to as photomicroscopy . At a basic level, photomicroscopy may be performed simply by connecting a camera to a microscope, thereby enabling the user to take photographs at reasonably high magnification .
Scientific use began in England in 1850 by Richard Hill Norris FRSE for his studies of blood cells. [ 1 ]
Roman Vishniac was a pioneer in the field of photomicroscopy, specializing in the photography of living creatures in full motion. He also made major developments in light-interruption photography and color photomicroscopy .
Photomicrographs may also be obtained using a USB microscope attached directly to a home computer or laptop.
An electron micrograph is a micrograph prepared using an electron microscope .
Micrographs usually have micron bars, or magnification ratios, or both.
Magnification is a ratio between the size of an object on a picture and its real size. Magnification can be a misleading parameter as it depends on the final size of a printed picture and therefore varies with picture size. A scale bar , or micron bar , is a line of known length displayed on a picture. The bar can be used for measurements on a picture. When the picture is resized the bar is also resized making it possible to recalculate the magnification. Ideally, all pictures destined for publication/presentation should be supplied with a scale bar; the magnification ratio is optional. All but one (limestone) of the micrographs presented on this page do not have a micron bar; supplied magnification ratios are likely incorrect, as they were not calculated for pictures at the present size.
The microscope has been mainly used for scientific discovery. It has also been linked to the arts since its invention in the 17th century. Early adopters of the microscope, such as Robert Hooke and Antonie van Leeuwenhoek , were excellent illustrators. Cornelius Varley 's graphic microscope made sketching from a microscope easier with a camera-lucida-like mechanism. After the invention of photography in the 1820s the microscope was later combined with the camera to take pictures instead of relying on an artistic rendering.
Since the early 1970s individuals have been using the microscope as an artistic instrument. Websites and traveling art exhibits such as the Nikon Small World and Olympus Bioscapes have featured a range of images for the sole purpose of artistic enjoyment. Some collaborative groups, such as the Paper Project have also incorporated microscopic imagery into tactile art pieces as well as 3D immersive rooms and dance performances.
In 2015, photographer and gemologist Danny J. Sanchez photographed mineral and gemstone interiors in works referred to as "otherworldly". [ 2 ] [ 3 ] [ 4 ]
A paper published in 2009 described a method of photomicrography in a smartphone using a free-hand technique. [ 5 ] An operator only need focus the camera through the eyepiece of a microscope and capture a photo normally. Later, adapters were designed for the purpose and sold commercially or home-made. [ 6 ] A home-made adapter was also made using scrap materials and a Coca-Cola aluminum can. [ 7 ] | https://en.wikipedia.org/wiki/Micrograph |
Micrographia: or Some Physiological Descriptions of Minute Bodies Made by Magnifying Glasses. With Observations and Inquiries Thereupon is a historically significant book by Robert Hooke about his observations through various lenses. It was the first book to include illustrations of insects and plants as seen through microscopes.
Published in January 1665, the first major publication of the Royal Society , it became the first scientific best-seller, inspiring a wide public interest in the new science of microscopy . [ 1 ] The book originated the biological term cell .
Hooke most famously describes a fly 's eye and a plant cell (where he coined that term because plant cells, which are walled, reminded him of the cells of a monastery [ 2 ] ). Known for its spectacular copperplate of the miniature world, particularly its fold-out plates of insects , the text itself reinforces the tremendous power of the new microscope . The plates of insects fold out to be larger than the large folio itself, the engraving of the louse in particular folding out to four times the size of the book. Although the book is best known for demonstrating the power of the microscope, Micrographia also describes distant planetary bodies , the wave theory of light , the organic origin of fossils , and other philosophical and scientific interests of its author.
Hooke also selected several objects of human origin; among these objects were the jagged edge of a honed razor and the point of a needle, seeming blunt under the microscope. His goal may well have been to contrast the flawed products of mankind with the perfection of nature (and hence, in the spirit of the times, of biblical creation). [ 3 ]
Published under the aegis of the Royal Society , the popularity of the book helped further the society's image and mission of being England's leading scientific organization. Micrographia 's illustrations of the miniature world captured the public's imagination in a radically new way; Samuel Pepys called it "the most ingenious book that ever I read in my life". [ 4 ]
In 2007, Janice Neri , a professor of art history and visual culture, studied Hooke's artistic influences and processes with the help of some newly rediscovered notes and drawings that appear to show some of his work leading up to Micrographia. [ 5 ] She observes, "Hooke's use of the term "schema" to identify his plates indicates that he approached his images in a diagrammatic manner and implies the study or visual dissection of the objects portrayed." Identifying Hooke's schema as 'organization tools,' she emphasizes: [ 6 ]
Hooke built up his images from numerous observations made from multiple vantage points, under varying lighting conditions, and with lenses of differing powers. Similarly his specimens required a great deal of manipulation and preparation in order to make them visible through the microscope.
Additionally: "Hooke often enclosed the objects he presented within a round frame, thus offering viewers an evocation of the experience of looking through the lens of a microscope." [ 6 ] | https://en.wikipedia.org/wiki/Micrographia |
Microinjection is the use of a glass micropipette to inject a liquid substance at a microscopic or borderline macroscopic level. The target is often a living cell but may also include intercellular space. Microinjection is a simple mechanical process usually involving an inverted microscope with a magnification power of around 200x (though sometimes it is performed using a dissecting stereo microscope at 40–50x or a traditional compound upright microscope at similar power to an inverted model).
For processes such as cellular or pronuclear injection the target cell is positioned under the microscope and two micromanipulators —one holding the pipette and one holding a microcapillary needle usually between 0.5 and 5 μm in diameter (larger if injecting stem cells into an embryo)—are used to penetrate the cell membrane and/or the nuclear envelope . [ 1 ] In this way the process can be used to introduce a vector into a single cell. Microinjection can also be used in the cloning of organisms, in the study of cell biology and viruses, and for treating male subfertility through intracytoplasmic sperm injection (ICSI, / ˈ ɪ k s i / IK -see ).
The use of microinjection as a biological procedure began in the early twentieth century, although even through the 1970s it was not commonly used. By the 1990s, its use had escalated significantly and it is now considered a common laboratory technique, along with vesicle fusion , electroporation , chemical transfection , and viral transduction , for introducing a small amount of a substance into a small target. [ 2 ]
There are two basic types of microinjection systems. The first is called a constant flow system and the second is called a pulsed flow system . In a constant flow system, which is relatively simple and inexpensive though clumsy and outdated, a constant flow of a sample is delivered from a micropipette and the amount of the sample which is injected is determined by how long the needle remains in the cell. This system typically requires a regulated pressure source, a capillary holder, and either a coarse or a fine micromanipulator. A pulsed flow system, however, allows for greater control and consistency over the amount of sample injected: the most common arrangement for intracytoplasmic sperm injection includes an Eppendorf "Femtojet" injector coupled with an Eppendorf "InjectMan", though procedures involving other targets usually take advantage of much less expensive equipment of similar capability. Because of its increased control over needle placement and movement and in addition to the increased precision over the volume of substance delivered, the pulsed flow technique usually results in less damage to the receiving cell than the constant flow technique. However, the Eppendorf line, at least, has a complex user interface and its particular system components are usually much more expensive than those necessary to create a constant flow system or than other pulsed flow injection systems. [ 3 ]
Pronuclear injection is a technique used to create transgenic organisms by injecting genetic material into the nucleus of a fertilized oocyte . This technique is commonly used to study the role of genes using mouse animal models.
The pronuclear injection of mouse sperm is one of the two most common methods for producing transgenic animals (along with the genetic engineering of embryonic stem cells ). [ 4 ] In order for pronuclear injection to be successful, the genetic material (typically linear DNA ) must be injected while the genetic material from the oocyte and sperm are separate (i.e., the pronuclear phase ). [ 5 ] In order to obtain these oocytes, mice are commonly superovulated using gonadotrophins . [ 6 ] Once plugging has occurred, oocytes are harvested from the mouse and injected with the genetic material. The oocyte is then implanted in the oviduct of a pseudopregnant animal . [ 5 ] While efficiency varies, 10-40% of mice born from these implanted oocytes may contain the injected construct . [ 6 ] Transgenic mice can then be bred to create transgenic lines. | https://en.wikipedia.org/wiki/Microinjection |
A microlens is a small lens , generally with a diameter less than a millimetre (mm) and often as small as 10 micrometres (μm). The small sizes of the lenses means that a simple design can give good optical quality but sometimes unwanted effects arise due to optical diffraction at the small features. A typical microlens may be a single element with one plane surface and one spherical convex surface to refract the light. Because micro-lenses are so small, the substrate that supports them is usually thicker than the lens and this has to be taken into account in the design. More sophisticated lenses may use aspherical surfaces and others may use several layers of optical material to achieve their design performance.
A different type of microlens has two flat and parallel surfaces and the focusing action is obtained by a variation of refractive index across the lens. These are known as gradient-index (GRIN) lenses . Some micro-lenses achieve their focusing action by both a variation in refractive index and by the surface shape.
Another class of microlens, sometimes known as micro- Fresnel lenses , focus light by refraction in a set of concentric curved surfaces. Such lenses can be made very thin and lightweight. Binary-optic micro-lenses focus light by diffraction . They have grooves with stepped edges or multilevels that approximate the ideal shape. They have advantages in fabrication and replication by using standard semiconductor processes such as photolithography and reactive-ion etching (RIE).
Micro-lens arrays contain multiple lenses formed in a one-dimensional or two-dimensional array on a supporting substrate. If the individual lenses have circular apertures and are not allowed to overlap, they may be placed in a hexagonal array to obtain maximum coverage of the substrate. However, there will still be gaps between the lenses which can only be reduced by making the micro-lenses with non-circular apertures. With optical sensor arrays , tiny lens systems serve to focus and concentrate the light onto the photo-diode surface, instead of allowing it to fall on non-photosensitive areas of the pixel device. Fill-factor is the ratio of the active refracting area, i.e. that area which directs light to the photo-sensor, to the total contiguous area occupied by the microlens array.
In the 17th century, Robert Hooke and Antonie van Leeuwenhoek both developed techniques to make small glass lenses for use with their microscopes . Hooke melted small filaments of Venetian glass and allowed the surface tension in the molten glass to form the smooth spherical surfaces required for lenses, then mounting and grinding the lenses using conventional methods. [ 1 ] The principle has been repeated by performing photolithography into materials such as photoresist or UV curable epoxy and melting the polymer to form arrays of multiple lenses. [ 2 ] [ 3 ] More recently microlens arrays have been fabricated using convective assembly of colloidal particles from suspension. [ 4 ]
Advances in technology have enabled micro-lenses to be designed and fabricated to close tolerances by a variety of methods. In most cases multiple copies are required and these can be formed by moulding or embossing from a master lens array. The master lens array may also be replicated through the generation of an electroform using the master lens array as a mandrel . The ability to fabricate arrays containing thousands or millions of precisely spaced lenses has led to an increased number of applications. [ 5 ]
The optical efficiency of diffracting lenses depends on the shape of the groove structure and, if the ideal shape can be approximated by a series of steps or multilevels, the structures may be fabricated using technology developed for the integrated circuit industry, such as wafer-level optics . The study of such diffracting lenses is known as binary optics . [ 6 ]
Micro-lenses in recent imaging chips have attained smaller and smaller sizes. The Samsung NX1 mirrorless system camera packs 28.2 million micro-lenses onto its CMOS imaging chip, one per photo-site, each with a side length of just 3.63 micrometer. For smartphones this process is miniaturized even further: The Samsung Galaxy S6 has a CMOS sensor with pixels only 1.12 micrometer each. These pixels are covered with micro-lenses of an equally small pitch.
Micro-lenses can be also made from liquids. [ 7 ] Recently, a glass-like resilient free-form micro-lenses were realized via ultra-fast laser 3D nanolithography technique. The sustained ~2 GW/cm 2 intensity for femtosecond pulsed irradiation shows its potential in high power and/or harsh environment applications. [ 8 ]
Bio-microlenses have been developed to image biological specimens without causing damage. [ 9 ] [ 10 ] These can be made from a single cell attached to a fiber probe.
Wafer-level optics (WLO) enables the design and manufacture of miniaturized optics at the wafer level using advanced semiconductor -like techniques. The end product is cost effective, miniaturized optics that enable the reduced form factor of camera modules for mobile devices . [ 11 ]
The technology is scalable from a single-element CIF/VGA lens to a multi-element mega pixel lens structure, where the lens wafers are precision aligned, bonded together and diced to form multi-element lens stacks. As of 2009 the technology was used in about 10 percent of the mobile phone camera lens market. [ 12 ]
Semiconductor stacking methodology can now be used to fabricate wafer-level optical elements in a chip scale package. The result is a wafer-level camera module that measures .575 mm x 0.575 mm. The module can be integrated into a catheter or endoscope with a diameter as small as 1.0 mm. [ 13 ]
Single micro-lenses are used to couple light to optical fibres ; microlens arrays are often used to increase the light collection efficiency of CCD arrays and CMOS sensors , to collect and focus light that would have otherwise fallen onto the non-sensitive areas of the sensor. Micro-lens arrays are also used in some digital projectors , to focus light to the active areas of the LCD used to generate the image to be projected. Current research also relies on micro-lenses of various types to act as concentrators for high efficiency photovoltaics for electricity production. [ 14 ]
Combinations of microlens arrays have been designed that have novel imaging properties, such as the ability to form an image at unit magnification and not inverted as is the case with conventional lenses. Micro-lens arrays have been developed to form compact imaging devices for applications such as photocopiers and mobile-phone cameras .
Another application is in 3D imaging and displays . In 1902, Frederic E. Ives proposed the use of an array of alternately transmitting and opaque strips to define the viewing directions for a pair of interlaced images and hence enable the observer to see a 3D stereoscopic image . [ 15 ] The strips were later replaced by Hess with an array of cylindrical lenses known as a lenticular screen , to make more efficient use of the illumination. [ 16 ]
Hitachi have 3D displays free of 3D glasses using arrays of microlens to create the stereoscopic effect. [ citation needed ]
More recently, the availability of arrays of spherical micro-lenses has enabled Gabriel Lippmann 's idea for integral photography to be explored and demonstrated. [ 17 ] [ 18 ] Colloidal micro-lenses have also enabled single molecule detection when used in conjunction with a long working distance, low light collection efficiency objective lens. [ 19 ]
Micro-lens arrays are also used by Lytro to achieve light field photography ( plenoptic camera ) that eliminates the need for initial focusing prior to capturing images. Instead, focus is achieved in software during post-processing. [ 20 ]
In order to characterize micro-lenses it is necessary to measure parameters such as the focal length and quality of transmitted wavefront . [ 21 ] Special techniques and new definitions have been developed for this.
For example, because it is not practical to locate the principal planes of such small lenses, measurements are often made with respect to the lens or substrate surface. Where a lens is used to couple light into an optical fibre the focused wavefront may exhibit spherical aberration and light from different regions of the microlens aperture may be focused to different points on the optical axis . It is useful to know the distance at which the maximum amount of light is concentrated in the fibre aperture and these factors have led to new definitions for focal length. To enable measurements on micro-lenses to be compared and parts to be interchanged, a series of international standards has been developed to assist users and manufacturers by defining microlens properties and describing appropriate measurement methods. [ 22 ] [ 23 ] [ 24 ] [ 25 ]
Examples of micro-optics are to be found in nature ranging from simple structures to gather light for photosynthesis in leaves to compound eyes in insects . As methods of forming micro-lenses and detector arrays are further developed, the ability to mimic optical designs found in nature will lead to new compact optical systems. [ 26 ] [ 27 ] | https://en.wikipedia.org/wiki/Microlens |
Micromachines are mechanical objects that are fabricated in the same general manner as integrated circuits . They are generally considered to be between 100 nanometres to 100 micrometres in size, although that is debatable. The applications of micromachines include accelerometers that detect when a car has hit an object and trigger an airbag . Complex systems of gears and levers are another application.
The fabrication of these devices is usually done by two techniques, surface micromachining and bulk micromachining . To do bulk micromachining, the region needed is highly doped with boron and the unwanted silicon is etched in liquid silicon etches. This technique is termed an etchstop as the doping of boron produces an unetchable layer/pattern. [ 1 ]
Most micromachines act as transducers ; in other words, they are either sensors or actuators .
Sensors convert information from the environment into interpretable electrical signals. One example of a micromachine sensor is a resonant chemical sensor. A lightly damped mechanical object vibrates much more at one frequency than any other, and this frequency is called its resonance frequency. A chemical sensor is coated with a special polymer that attracts certain molecules , such as those found in anthrax , and when those molecules attach to the sensor, its mass increases. The increased mass alters the resonance frequency of the mechanical object, which is detected with circuitry.
Actuators convert electrical signals and energy into motion of some kind. The three most common types of actuators are electrostatic , thermal , and magnetic . Electrostatic actuators use the force of electrostatic energy to move objects. Two mechanical elements, one that is stationary (the stator ) and one that is movable (the rotor ) have two different voltages applied to them, which creates an electric field . The field competes with a restoring force on the rotor (normally a spring force produced by the bending or stretching of the rotor) to move it. The greater the electric field, the further the rotor will move. Thermal actuators use the force of thermal expansion to move objects. When a material is heated, it expands an amount depending on material properties. Two objects can be connected in such a way that one object is heated more than the other and expands more, and this imbalance creates motion. The direction of motion depends on the connection between the objects. This is seen in a "heatuator", which is a U-shaped beam with one wide arm and one narrow arm. When a current is passed through the object, heat is created. The narrow arm is heated more than the wide arm because they have the same current density. Since the two arms are connected at the top, the stretching hot arm pushes in the direction of the cold arm. Magnetic actuators used fabricated magnetic layers to create forces. | https://en.wikipedia.org/wiki/Micromachinery |
Micromagnetics is a field of physics dealing with the prediction of magnetic behaviors at sub-micrometer length scales. The length scales considered are large enough for the atomic structure of the material to be ignored (the continuum approximation ), yet small enough to resolve magnetic structures such as domain walls or vortices.
Micromagnetics can deal with static equilibria , by minimizing the magnetic energy, and with dynamic behavior, by solving the time-dependent dynamical equation.
Micromagnetics originated from a 1935 paper
by Lev Landau and Evgeny Lifshitz on antidomain walls. [ 1 ] : 133 [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] : 440 Micromagnetics was then expanded upon by William Fuller Brown Jr. in several works in 1940-1941 [ 1 ] : 133 [ 3 ] [ non-primary source needed ] [ 7 ] [ 8 ] [ 6 ] : 440 using energy expressions taken from a 1938 paper by William Cronk Elmore . [ 3 ] [ 9 ] According to D. Wei, Brown introduced the name "micromagnetics" in 1958. [ 10 ] : 41 [ 11 ] The field prior to 1960 was summarised in Brown's book Micromagnetics . [ 10 ] : 41 [ 12 ] In the 1970s computational methods were developed for the analysis of recording media due to the introduction of personal computers. [ 10 ] : 44
The purpose of static micromagnetics is to solve for the spatial distribution of the magnetization M {\displaystyle \mathbf {M} } at equilibrium. In most cases, as the temperature is much lower than the Curie temperature of the material considered, the modulus | M | {\displaystyle |\mathbf {M} |} of the magnetization is assumed to be everywhere equal to the saturation magnetization M s {\displaystyle M_{s}} . The problem then consists in finding the spatial orientation of the magnetization, which is given by the magnetization direction vector m = M / M s {\displaystyle \mathbf {m} =\mathbf {M} /M_{s}} , also called reduced magnetization .
The static equilibria are found by minimizing the magnetic energy, [ 13 ] : 138
subject to the constraint | M | = M s {\displaystyle |\mathbf {M} |=M_{s}} or | m | = 1 {\displaystyle |\mathbf {m} |=1} .
The contributions to this energy are the following:
The exchange energy is a phenomenological continuum description of the quantum-mechanical exchange interaction . It is written as: [ 1 ] [ 13 ] : 101–104
where A {\displaystyle A} is the exchange constant ; m x {\displaystyle m_{x}} , m y {\displaystyle m_{y}} and m z {\displaystyle m_{z}} are the components of m {\displaystyle \mathbf {m} } ;
and the integral is performed over the volume of the sample.
The exchange energy tends to favor configurations where the magnetization varies slowly across the sample. This energy is minimized when the magnetization is perfectly uniform. [ 1 ] : 135 The exchange term is isotropic,
so any direction is equally acceptable. [ 1 ] : 83
Magnetic anisotropy arises due to a combination of crystal structure and spin-orbit interaction . [ 1 ] : 84 It can be generally written as:
where F anis {\displaystyle F_{\text{anis}}} , the anisotropy energy density, is a function of the orientation of the magnetization. Minimum-energy directions for F anis {\displaystyle F_{\text{anis}}} are called easy axes .
Time-reversal symmetry ensures that F anis {\displaystyle F_{\text{anis}}} is an even function of m {\displaystyle \mathbf {m} } . [ 13 ] : 108 The simplest such function is
where K 1 is called the anisotropy constant . In this approximation, called uniaxial anisotropy , the easy axis is the z {\displaystyle z} axis. [ 1 ] : 85
The anisotropy energy favors magnetic configurations where the magnetization is everywhere aligned along an easy axis.
The Zeeman energy is the interaction energy between the magnetization and any externally applied field. It is written as: [ 1 ] : 174 [ 13 ] : 109
where H a {\displaystyle \mathbf {H} _{\text{a}}} is the applied field and μ 0 {\displaystyle \mu _{0}} is the vacuum permeability .
The Zeeman energy favors alignment of the magnetization parallel to the applied field.
The demagnetizing field is the magnetic field created by the magnetic sample upon itself. The associated energy is: [ 13 ] : 110
where H d {\displaystyle \mathbf {H} _{\text{d}}} is the demagnetizing field . The field satisfies
and hence can be written as the gradient of a potential H d = − ∇ U {\displaystyle \mathbf {H} _{\text{d}}=-\nabla U} . This field depends on the magnetic configuration itself, and it can be found by solving
inside of the body and
outside of the body.
These are supplemented with the boundary conditions on the surface of the body
where n {\displaystyle \mathbf {n} } is the unit normal to the surface. Furthermore, the potential satisfies the condition that | r U | {\displaystyle |rU|} and | r 2 ∇ U | {\displaystyle |r^{2}\nabla U|} remain bounded as r → ∞ {\displaystyle r\to \infty } . [ 1 ] : 109–111 The solution of these equations (cf. magnetostatics ) is:
The quantity − ∇ ⋅ M {\displaystyle -\nabla \cdot \mathbf {M} } is often called the volume charge density , and M ⋅ n {\displaystyle \mathbf {M} \cdot \mathbf {n} } is called the surface charge density . [ 1 ] : 125–126 [ 13 ] : 110 [ 6 ] : 441 The energy of the demagnetizing field favors magnetic configurations that minimize magnetic charges. In particular, on the edges of the sample, the magnetization tends to run parallel to the surface. In most cases it is not possible to minimize this energy term at the same time as the others. [ citation needed ] The static equilibrium then is a compromise that minimizes the total magnetic energy, although it may not minimize individually any particular term.
This interaction arises when a crystal lacks inversion symmetry, encouraging the magnetization to be perpendicular to its neighbours. It directly competes with the exchange energy. It is modelled with the energy contribution [ 14 ]
E DMI = ∫ V D : ( ∇ m × m ) {\displaystyle E_{\text{DMI}}=\int _{V}\mathbf {D} :(\nabla \mathbf {m} \times \mathbf {m} )}
where D {\displaystyle \mathbf {D} } is the spiralization tensor,
that depends upon the crystal class. [ 15 ] For bulk DMI,
and for a thin film in the x − y {\displaystyle x-y} plane
interfacial DMI takes the form
and for materials with symmetry class D 2 d {\displaystyle D_{2d}} the energy contribution is
This term is important for the formation of magnetic skyrmions .
The magnetoelastic energy describes the energy storage due to elastic lattice distortions. It may be neglected if magnetoelastic coupled effects are neglected.
There exists a preferred local distortion of the crystalline solid associated with the magnetization director m {\displaystyle \mathbf {m} } .
For a simple small-strain model, one can assume this strain to be isochoric and fully
isotropic in the lateral direction, yielding the deviatoric ansatz [ 13 ] : 128 [ 16 ] : 250–251 ε 0 ( m ) = 3 2 λ s [ m ⊗ m − 1 3 1 ] {\displaystyle \mathbf {\varepsilon } _{0}(\mathbf {m} )={\frac {3}{2}}\lambda _{\text{s}}\,\left[\mathbf {m} \otimes \mathbf {m} -{\frac {1}{3}}\mathbf {1} \right]} where the material parameter λ s {\displaystyle \lambda _{\text{s}}} is the isotropic magnetostrictive
constant. The elastic
energy density is assumed to be a function of the elastic, stress-producing
strains ε e := ε − ε 0 {\displaystyle \mathbf {\varepsilon } _{e}:=\mathbf {\varepsilon } -\mathbf {\varepsilon } _{0}} . A quadratic form for the magnetoelastic energy is [ 13 ] : 138 E m-e = 1 2 ∫ V [ ε − ε 0 ( m ) ] : C : [ ε − ε 0 ( m ) ] {\displaystyle E_{\text{m-e}}={\frac {1}{2}}\int _{V}[\mathbf {\varepsilon } -\mathbf {\varepsilon } _{0}(\mathbf {m} )]:\mathbb {C} :[\mathbf {\varepsilon } -\mathbf {\varepsilon } _{0}(\mathbf {m} )]} where C := λ 1 ⊗ 1 + 2 μ I {\displaystyle \mathbb {C} :=\lambda \mathbf {1} \otimes \mathbf {1} +2\mu \mathbb {I} } is the fourth-order elasticity tensor. Here the elastic response is assumed to be isotropic (based on
the two Lamé constants λ {\displaystyle \lambda } and μ {\displaystyle \mu } ).
Taking into account the constant length of m {\displaystyle \mathbf {m} } , we obtain the invariant-based representation E m-e = ∫ V λ 2 tr 2 [ ε ] + μ tr [ ε 2 ] − 3 μ E { tr [ ε ( m ⊗ m ) ] − 1 3 tr [ ε ] } . {\displaystyle E_{\text{m-e}}=\int _{V}{\frac {\lambda }{2}}{\mbox{tr}}^{2}[\mathbf {\varepsilon } ]+\mu \,{\mbox{tr}}[\mathbf {\varepsilon } ^{2}]-3\mu E{\big \{}{\mbox{tr}}[\mathbf {\varepsilon } (\mathbf {m} \otimes \mathbf {m} )]-{\frac {1}{3}}{\mbox{tr}}[\mathbf {\varepsilon } ]{\big \}}.}
This energy term contributes to magnetostriction .
The purpose of dynamic micromagnetics is to predict the time evolution of the magnetic configuration. [ 1 ] : 181–182 This is especially important if the sample is subject to some non-steady conditions such as the application of a field pulse or an AC field. This is done by solving the Landau-Lifshitz-Gilbert equation , which is a partial differential equation describing the evolution of the magnetization in terms of the local effective field acting on it.
The effective field is the local field felt by the magnetization. The only real fields however are the magnetostatic field and the applied field. [ 12 ] It can be described informally as the derivative of the magnetic energy density with respect to the orientation of the magnetization, as in:
where d E /d V is the energy density. In variational terms, a change d m of the magnetization and the associated change d E of the magnetic energy are related by:
Since m is a unit vector, d m is always perpendicular to m . Then the above definition leaves unspecified the component of H eff that is parallel to m . [ 12 ] This is usually not a problem, as this component has no effect on the magnetization dynamics.
From the expression of the different contributions to the magnetic energy, the effective field can be found to be (excluding the DMI and magnetoelastic contributions): [ 1 ] : 178
This is the equation of motion of the magnetization. It describes a Larmor precession of the magnetization around the effective field, with an additional damping term arising from the coupling of the magnetic system to the environment. The equation can be written in the so-called Gilbert form (or implicit form) as: [ 1 ] : 181 [ 6 ] : 462
where γ {\displaystyle \gamma } is the electron gyromagnetic ratio and α {\displaystyle \alpha } the Gilbert damping constant.
It can be shown that this is mathematically equivalent to the following Landau-Lifshitz (or explicit) form: [ 17 ] [ 1 ] : 181–182
where α {\displaystyle \alpha } is the Gilbert Damping constant, characterizing how quickly the damping term takes away energy from the system ( α {\displaystyle \alpha } = 0, no damping, permanent precession).
These equations preserve the constraint | m | = 1 {\displaystyle |\mathbf {m} |=1} , as [ 1 ] : 181
The interaction of micromagnetics with mechanics is also of interest in the context of industrial applications that deal with magneto-acoustic resonance such as in hypersound speakers, high frequency magnetostrictive transducers etc.
FEM simulations taking into account the effect of magnetostriction into micromagnetics are of importance. Such simulations use models described above within a finite element framework. [ 18 ]
Apart from conventional magnetic domains and domain-walls, the theory also treats the statics and dynamics of topological line and point configurations, e.g. magnetic vortex and antivortex states; [ 19 ] or even 3d-Bloch points, [ 20 ] [ 21 ] where, for example, the magnetization leads radially into all directions from the origin, or into topologically equivalent configurations. Thus in space, and also in time, nano- (and even pico-)scales are used.
The corresponding topological quantum numbers [ 21 ] are thought [ by whom? ] to be used as information carriers, to apply the most recent, and already studied, propositions in information technology .
Another application that has emerged in the last decade is the application of micromagnetics towards neuronal stimulation. In this discipline, numerical methods such as finite-element analysis are used to analyze the electric/magnetic fields generated by the stimulation apparatus; then the results are validated or explored further using in-vivo or in-vitro neuronal stimulation. Several distinct set of neurons have been studied using this methodology including retinal neurons, cochlear neurons, [ 22 ] vestibular neurons, and cortical neurons of embryonic rats. [ 23 ] | https://en.wikipedia.org/wiki/Micromagnetics |
Micromatabilin , the green pigment of the spider species Micrommata virescens , is characterized as a mixture of biliverdin conjugates . The two isolated fractions have identical absorption bands (free base: 620–630 μm, hydrochloride: 690 μm, zinc complex: 685–690 μm). Chromic acid degradation yields imides I, II, IIIa, and IIIb. Differences in the non-hydrolytic degradation and in polarity lead to the conclusion that fraction 1 is a monoconjugate and fraction 2a diconjugate of biliverdin. [ 1 ]
This biochemistry article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Micromatabilin |
Micromeritics is the science of the behavior of particulate materials smaller than 75 μm. [ 1 ] It is thus the study of the fundamental and derived properties of individual as well as a collection of particles. Micromeritics involves materials with larger particles than nanoparticles where they are smaller than 0.1 μm.
The knowledge and control of the size of particles has importance in pharmacy and materials science . The size, and hence the surface area of a particle , can be related to the physical, chemical and pharmacological properties of drugs. Clinically, the particle size of a drug can affect its release from dosage forms that are administered orally, parenterally , rectally and topically . The successful formulation of suspensions , emulsions and tablets ; both physical stability and pharmacological response also depends on the particle size achieved in the product. [ 2 ] [ 3 ] [ 4 ] [ 5 ]
The term was coined by Joseph Marius DallaValle in his book Micromeritics: The Technology of Fine Particles (1948). [ 6 ] It was derived from the Greek words Greek : μικρο , romanized : micro meaning "small" and Greek : μέρος , romanized : méros meaning "part". [ 7 ] The size range which he covered in the book was from 100 nm to 100 mm. Anything smaller than this but bigger than a molecule was referred to at the time as a colloid but is now often referred to as a nanoparticle .
Applications included soil physics , mineral physics , chemical engineering , geology , and hydrology . Characteristics discussed included particle size and shape, packing , electrical , optical , chemical and surface science .
Particle size and surface area influence the release of a drug from a dosage form that is administered orally , rectally, parenterally , and topically . Higher surface area brings about intimate contact of the drug with the dissolution fluids in vivo and increases the drug solubility and dissolution.
Particle size and surface area influence the drug absorption and subsequently the therapeutic action. The higher the dissolution, the faster the absorption and hence the quicker and greater the drug action.
Micromeritic properties of a particle , i.e. the particle size in a formulation , influence the physical stability of the suspensions and emulsions . The smaller the size of the particle , the better the physical stability of the dosage form owing to the Brownian motion of the particles in the dispersion .
Good flow properties of granules and powders are important in the manufacturing of tablets and capsules . The distribution of particles should be uniform in terms of number and weight . Very small particle size causes attraction, which in turn destabilises the suspension by coagulating. | https://en.wikipedia.org/wiki/Micromeritics |
A micrometeorite is a micrometeoroid that has survived entry through the Earth's atmosphere . Usually found on Earth 's surface, micrometeorites differ from meteorites in that they are smaller in size, more abundant, and different in composition. The IAU officially defines meteoroids as 30 micrometers to 1 meter; micrometeorites are the small end of the range (~submillimeter). [ 1 ] They are a subset of cosmic dust , which also includes the smaller interplanetary dust particles (IDPs). [ 2 ]
Micrometeorites enter Earth's atmosphere at high velocities (at least 11 km/s) and undergo heating through atmospheric friction and compression . Micrometeorites individually weigh between 10 −9 and 10 −4 g and collectively comprise most of the extraterrestrial material that has come to the present-day Earth. [ 3 ]
Fred Lawrence Whipple first coined the term "micro-meteorite" to describe dust-sized objects that fall to the Earth. [ 4 ] Sometimes meteoroids and micrometeoroids entering the Earth's atmosphere are visible as meteors or "shooting stars" , whether or not they reach the ground and survive as meteorites and micrometeorites.
Micrometeorite (MM) textures vary as their original structural and mineral compositions are modified by the degree of heating that they experience entering the atmosphere—a function of their initial speed and angle of entry. They range from unmelted particles that retain their original mineralogy (Fig. 1 a, b), to partially melted particles (Fig. 1 c, d) to round melted cosmic spherules (Fig. 1 e, f, g, h, Fig. 2) some of which have lost a large portion of their mass through vaporization (Fig. 1 i). Classification is based on composition and degree of heating. [ 5 ] [ 6 ]
The extraterrestrial origins of micrometeorites are determined by microanalyses that show that:
An estimated 40,000 ± 20,000 tonnes per year (t/yr) [ 3 ] of cosmic dust enters the upper atmosphere each year of which less than 10% (2700 ± 1400 t/yr) is estimated to reach the surface as particles. [ 15 ] Therefore the mass of micrometeorites deposited is roughly 50 times higher than that estimated for meteorites, which represent approximately 50 t/yr, [ 16 ] and the huge number of particles entering the atmosphere each year (~10 17 > 10 μm) suggests that large MM collections contain particles from all dust-producing objects in the Solar System including asteroids, comets, and fragments from the Moon and Mars. Large MM collections provide information on the size, composition, atmospheric heating effects and types of materials accreting on Earth while detailed studies of individual MMs give insights into their origin, the nature of the carbon , amino acids and pre-solar grains they contain. [ 17 ]
Chemical analysis of the microscopic chromite crystals, or chrome-spinels, retrieved from micrometeorites in acid baths has shown that primitive achondrites , which represent less than half a percent of the MM reaching Earth today, were common among MMs accreting more than 466 million years ago. [ 18 ]
Micrometeorites have been collected from deep-sea sediments , sedimentary rocks and polar sediments. They were previously collected primarily from polar snow and ice because of their low concentrations on the Earth's surface, but in 2016 a method to extract micrometeorites in urban environments [ 19 ] was discovered. [ 20 ]
Melted micrometeorites (cosmic spherules) were first collected from deep-sea sediments during the 1873 to 1876 expedition of HMS Challenger . In 1891, Murray and Renard found "two groups [of micrometeorites]: first, black magnetic spherules, with or without a metallic nucleus; second, brown-coloured spherules resembling chondr(ul)es, with a crystalline structure". [ 21 ] In 1883, they suggested that these spherules were extraterrestrial because they were found far from terrestrial particle sources, they did not resemble magnetic spheres produced in furnaces of the time, and their nickel-iron (Fe-Ni) metal cores did not resemble metallic iron found in volcanic rocks. The spherules were most abundant in slowly accumulating sediments, particularly red clays deposited below the carbonate compensation depth , a finding that supported a meteoritic origin. [ 22 ] In addition to those spheres with Fe-Ni metal cores, some spherules larger than 300 μm contain a core of elements from the platinum group. [ 23 ]
Since the first collection of HMS Challenger , cosmic spherules have been recovered from ocean sediments using cores, box cores, clamshell grabbers, and magnetic sleds. [ 24 ] Among these a magnetic sled, called the "Cosmic Muck Rake", retrieved thousands of cosmic spherules from the top 10 cm of red clays on the Pacific Ocean floor. [ 25 ]
Terrestrial sediments also contain micrometeorites. These have been found in samples that:
The oldest MMs are totally altered iron spherules found in 140- to 180-million-year-old hardgrounds. [ 27 ]
In 2016 a new study showed that flat roofs in urban areas are fruitful places to extract micrometeorites. [ 19 ] The "urban" cosmic spherules have a shorter terrestrial age and are less altered than the previous findings. [ 32 ]
Amateur collectors may find micrometeorites in areas where dust from a large area has been concentrated, such as from a roof downspout. [ 33 ] [ 34 ] [ 35 ]
Micrometeorites found in polar sediments are much less weathered than those found in other terrestrial environments, as evidenced by little etching of interstitial glass, and the presence of large numbers of glass spherules and unmelted micrometeorites, particle types that are rare or absent in deep-sea samples. [ 5 ] The MMs found in polar regions have been collected from Greenland snow, [ 36 ] Greenland cryoconite, [ 37 ] [ 38 ] [ 39 ] Antarctic blue ice [ 40 ] Antarctic aeolian (wind-driven) debris, [ 41 ] [ 42 ] [ 43 ] ice cores, [ 44 ] the bottom of the South Pole water well, [ 5 ] [ 15 ] Antarctic sediment traps [ 45 ] and present day Antarctic snow. [ 14 ]
Modern classification of meteorites and micrometeorites is complex; the 2007 review paper of Krot et al. [ 46 ] summarizes modern meteorite taxonomy. Linking individual micrometeorites to meteorite classification groups requires a comparison of their elemental, isotopic and textural characteristics. [ 47 ]
Whereas most meteorites originate from asteroids , the contrasting make-up of micrometeorites suggests that most originate from comets .
Fewer than 1% of MMs are achondritic and are similar to HED meteorites , which are thought to be from the asteroid 4 Vesta . [ 48 ] [ 49 ] Most MMs are compositionally similar to carbonaceous chondrites , [ 50 ] [ 51 ] [ 52 ] whereas approximately 3% of meteorites are of this type. [ 53 ] The dominance of carbonaceous chondrite-like MMs and their low abundance in meteorite collections suggests that most MMs derive from sources different from those of most meteorites. Since most meteorites derive from asteroids, an alternative source for MMs might be comets. The idea that MMs might originate from comets originated in 1950. [ 4 ]
Until recently the greater-than-25-km/s entry velocities of micrometeoroids, measured for particles from comet streams, cast doubts against their survival as MMs. [ 11 ] [ 54 ] However, recent dynamical simulations [ 55 ] suggest that 85% of cosmic dust could be cometary. Furthermore, analyses of particles returned from the comet, Wild 2 , by the Stardust spacecraft show that these particles have compositions that are consistent with many micrometeorites. [ 56 ] [ 57 ] Nonetheless, some parent bodies of micrometeorites appear to be asteroids with chondrule -bearing carbonaceous chondrites . [ 58 ]
The influx of micrometeoroids also contributes to the composition of regolith (planetary/lunar soil) on other bodies in the Solar System. Mars has an estimated annual micrometeoroid influx of between 2,700 and 59,000 t/yr. This contributes to about 1 m of micrometeoritic content to the depth of the Martian regolith every billion years. Measurements from the Viking program indicate that the Martian regolith is composed of 60% basaltic rock and 40% rock of meteoritic origin. The lower-density Martian atmosphere allows much larger particles than on Earth to survive the passage through to the surface, largely unaltered until impact. While on Earth particles that survive entry typically have undergone significant transformation, a significant fraction of particles entering the Martian atmosphere throughout the 60 to 1200-μm diameter range probably survive unmelted. [ 59 ]
Solar System → Local Interstellar Cloud → Local Bubble → Gould Belt → Orion Arm → Milky Way → Milky Way subgroup → Local Group → Local Sheet → Virgo Supercluster → Laniakea Supercluster → Local Hole → Observable universe → Universe Each arrow ( → ) may be read as "within" or "part of". | https://en.wikipedia.org/wiki/Micrometeorite |
Micromirror devices are devices based on microscopically small mirrors. The mirrors are microelectromechanical systems (MEMS), which means that their states are controlled by applying a voltage between the two electrodes around the mirror arrays. Digital micromirror devices are used in video projectors and optics and micromirror devices for light deflection and control.
Digital Micromirror Devices (DMD) were invented by Texas Instruments in 1987 and are the core of the DLP technology used for video projection. The mirrors are arranged in a matrix and have two states, "on" or "off" (digital). In the on state, light from the projector bulb is reflected into the lens making the pixel appear bright on the screen. In the off state, the light is directed elsewhere (usually onto a heatsink ), making the pixel appear dark. Colours could be produced by various technologies like different light sources or gratings.
The mirrors could not only be switched between two states, their rotation is in fact continuous. This could be used for controlling the intensity and direction of incident light. One future application is controlling the light in buildings, based on micromirrors between the two panes of Insulated glazing . The power and direction of the incident light is determined by the mirrors state, which itself is controlled electrostatically. [ 1 ]
A MEMS scanning micromirror consists of a silicon device with a millimeter-scale mirror at the center. The mirror is typically connected to flexures that allow it to oscillate on a single axis or biaxially, to project or capture light. [ 2 ] | https://en.wikipedia.org/wiki/Micromirror_device |
In mechanics, a micromixer is a device based on mechanical microparts used to mix fluids . This device represents a key technology to fields such as Chemical industry , Pharmaceutical industry , Analytical chemistry , Biochemistry , and high-throughput synthesis, since it makes use of the miniaturization of the fluids associated in the mixing to reduce quantities involved in the chemical and/or biochemical processes.
There are two types of micromixers: passive and active. [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ clarification needed ] Active mixers use an external energy source, either electric or magnetic, to perform the mixing of the fluids. Passive mixers have no power source and use pressure to guide the flow. [ 5 ] | https://en.wikipedia.org/wiki/Micromixer |
Micromodels are a type of card model or paper model that was popular during the 1940s and 1950s in the United Kingdom . In 1941, Geoffrey Heighway invented and marketed a new concept in card models. He took the available concept of card models and miniaturized them so that an entire train or building could be wrapped in a packet of post cards. These packets usually sold for about a shilling, or pocket change.
When he released his product in the 1940s it caught on and Micro-modeling became a national pastime. The slogan "Your Workshop in a Cigar Box" is still widely quoted today among paper modelers. Their other slogan was: Three-Dimensional, Volumetric. During the war years, the models were especially popular as they were extremely portable and builders were able to work on them anywhere. Anecdotes say people liked them because they were small enough to take with you, so if you got stuck in a bomb shelter during an air raid, you had something interesting to do. Several of the railway Micromodels were distributed in Australia in the form of small stapled books, rather than individual postcards.
The subjects of original Micromodels included among other things, Trains, Planes, Ships, Boats, Buildings, Cars and a Dragon. There were 82 original Micromodel Packets. From these packets one could make up 121 separate models. Micromodels also released some items including how-to booklets and powdered glue. Heighway continued to release models from 1941 until he became seriously ill in 1956. He died in 1959. There were several models that Heighway had mentioned in his catalogs and advertising, that for one reason or another were never released. These were known as the "Might have beens."
Micromodels are considered collectable, and some rare originals can only be had for thousands of dollars. [ citation needed ] Others are more easily obtainable.
There have been other products similar to or based on Micromodels, including Modelcraft Ltd. and a set of books based on enlargements of some of Heighway's Micromodels, finished by Myles Mandell. Several designers have released new Micromodel style models, including MicromodelsUSA.
Cardboard engineering | https://en.wikipedia.org/wiki/Micromodel |
See text.
Synonyms of Micromonosporales
Synonyms of Micromonosporaceae
Micromonosporaceae is a family of bacteria of the class Actinomycetia . They are gram-positive , spore -forming soil organisms that form a true mycelium .
The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) [ 2 ] and National Center for Biotechnology Information (NCBI). [ 3 ]
Actinocatenispora
Longispora
Catelliglobosispora
Hamadaea
Dactylosporangium
Catenuloplanes
Pseudosporangium
Actinoplanes
Asanoa
Salinispora Maldonado et al. 2005
Micromonospora
Actinocatenispora Thawai et al. 2006
Actinorhabdospora Mingma et al. 2016
Phytomonospora Li et al. 2011
Stackebrandtia species-group 2
Stackebrandtia Labeda & Kroppenstedt 2005
Natronoglycomyces Sorokin et al. 2021
Salilacibacter Li et al. 2016b
Haloglycomyces Guan et al. 2009
Salininema corrig. Nikou et al. 2015
Glycomyces Labeda et al. 1985
Longispora Matsumoto et al. 2003
Micromonospora ~6
Pilimelia Kane 1966
Planosporangium Wiese et al. 2008
Polymorphospora Tamura et al. 2006
Micromonospora pisi
Micromonospora ~5
Luedemannella Ara and Kudo 2007
Hamadaea Ara et al. 2008
Allorhizocola Sun et al. 2019
Catelliglobosispora Ara et al. 2008
Rhizocola Matsumoto et al. 2014
Allocatelliglobosispora Lee and Lee 2011
Catellatospora Asano and Kawamoto 1986
Rugosimonospora Monciardini et al. 2009
Virgisporangium corrig. Tamura et al. 2001
Dactylosporangium Thiemann et al. 1967
Phytohabitans Inahashi et al. 2010
Phytohabitans houttuyneae
Asanoa Lee and Hah 2002
Catenuloplanes Yokota et al. 1993
Mangrovihabitans Liu et al. 2017
Actinoplanes ~1
Couchioplanes caeruleus azureus
Krasilnikovia Ara and Kudo 2007
Jidongwangia Jia et al. 2013 ex Han et al. 2023
Nucisporomicrobium Han et al. 2022
Couchioplanes Tamura et al. 1994
Pseudosporangium Ara et al. 2008
Actinoplanes Couch 1950
Micromonospora Ørskov 1923 (incl. Plantactinospora ; Salinispora ; Spirilliplanes )
Phytomonospora
Stackebrandtia
Natronoglycomyces
Haloglycomyces
Glycomyces
Actinocatenispora
Longispora
" Natronosporangium " Sorokin et al. 2022
Rugosimonospora
Planosporangium
Virgisporangium
Dactylosporangium
Allocatelliglobosispora
Hamadaea
Allorhizocola
Catelliglobosispora
Rhizocola
Catellatospora
Pilimelia
Phytohabitans
Asanoa
Catenuloplanes
Spirilliplanes Tamura et al. 1997
Actinoplanes (incl. Krasilnikovia ; Mangrovihabitans ; Pseudosporangium )
Micromonospora pattaloongensis
Polymorphospora
Micromonospora polyrhachis
Micromonospora pisi
Plantactinospora Qin et al. 2009
Micromonospora [incl. Salinispora ]
Genera incertae sedis:
This Actinomycetota -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Micromonosporaceae |
Micromotors are very small particles (measured in microns ) that can move themselves. [ 1 ] The term is often used interchangeably with " nanomotor ," despite the implicit size difference. These micromotors actually propel themselves in a specific direction autonomously when placed in a chemical solution. There are many different micromotor types operating under a host of mechanisms. Easily the most important examples are biological motors such as bacteria and any other self-propelled cells. Synthetically, researchers have exploited oxidation-reduction reactions to produce chemical gradients, local fluid flows, or streams of bubbles that then propel these micromotors through chemical media. [ 2 ] Different stimuli, both external (light, [ 3 ] magnetism [ 4 ] ) and internal (fuel concentration, material composition, [ 5 ] particle asymmetry [ 6 ] ) can be used to control the behavior of these micromotors.
Micromotors may have applications in medicine since they have been shown to be able to deliver materials to living cells within an organism. They also have been shown to be effective in degrading certain chemical and biological warfare agents.
Janus particle micromotors consist of two or more components with distinct physical properties, such as a titanium dioxide particle capped with gold, [ 7 ] or a polystyrene bead coated on one side with a layer of platinum [ 8 ] [ 9 ] which both display a difference in catalytic activity between halves. When these motors are placed in a fuel, such as hydrogen peroxide, one redox half-reaction occurs on each pole according to catalytic activity. As the oxidation reaction produces electrons and protons, the reduction reaction consumes these as reactants on the opposite pole of the particle, this movement of molecules generates a fluid flow across the surface of the motor and this drives the particle forward. The catalytic difference between each pole of the Janus motor can be characteristic of the material [ 10 ] such as metals which catalyze at different rates, or induced by external stimuli like UV light [ 7 ] which can be absorbed by semi-conductor materials like titanium dioxide to excite electrons for the redox reaction.
Catalytic activity is not the only way to generate motion using Janus materials; self-propelled Janus droplets can be made using a complex emulsion of two different surfactant oils [ 11 ] which move forward spontaneously due to the difference in surface tension as the two oils solubilize.
However, a Janus structure is not always required to break symmetry. For enzyme-attached particles or lipid vesicles, symmetry can be disrupted by the uneven distribution of enzymes on their surface. [ 12 ] [ 13 ] [ 14 ] [ 15 ] These discoveries offer new insights into designing synthetic micro/nanomotors.
Nano particle incorporation into micromotors has been recently studied and observed further. Specifically, gold nanoparticles have been introduced to the traditional titanium dioxide outer layer of most micromotors. [ 16 ] The size of these gold nanoparticles typically is distributed from anywhere around 3 nm to 30 nm. [ 17 ] Since these gold nanoparticles are layered on top of the inner core (usually a reducing agent, such as magnesium), there is enhanced macrogalvanic corrosion observed. [ 18 ] Technically, this is where the cathode and anode are in contact with each other, creating a circuit. The cathode, as a result of the circuit, is corroded. The depletion of this inner core leads to the reduction of the chemical environment as a fuel source. For example, in a TiO 2 /Au/Mg micromotor in a seawater environment, the magnesium inner core would experience corrosion and reduce water to begin a chain of reactions that results in hydrogen gas as a fuel source. The reduction reaction is as follows: M g + 2 H 2 O → M g ( O H ) 2 + H 2 {\displaystyle Mg+2H_{2}O\to Mg(OH)_{2}+H_{2}} [ 16 ]
Researchers hope that micromotors will be used in medicine to deliver medication and do other precise small-scale interventions. [ 19 ] A study has shown that micromotors could deliver gold particles to the stomach layer of living mice. [ 20 ]
Micromotors are capable of photocatalytic degradation with the appropriate composition. [ 21 ] [ 22 ] Specifically, micromotors with a titanium dioxide/gold nanoparticle outer layer and magnesium inner core are currently being examined and studied for their degradation efficacy against chemical and biological warfare agents (CBWA). These new TiO 2 /Au/Mg micromotors produce no reagents or toxic byproducts from the propulsion and degradation mechanisms. However, they are very effective against CBWAs and present a complete and rapid degradation of certain CBWAs. There has been recent research of TiO 2 /Au/Mg micromotors and their use and degradation efficacy against biological warfare agents, such as Bacillus anthracis, and chemical warfare agents, such as organophosphate nerve agents - a class of acetylcholinesterase inhibitors . Therefore, application of these micromotors is a possibility for medical and environmental applications.
These new micromotors are composed of a photoactive photocatalyst outer/surface layer that often has active metal nanoparticles (platinum, gold, silver, etc.) on the surface as well. [ 23 ] Under UV irradiation, the adsorbed water produces strongly oxidizing hydroxyl radicals. Also, adsorbed molecular O 2 reacts with electrons producing superoxide anions. Those superoxide anions also produce to the production of peroxide radicals, hydroxyl radicals, and hydroxyl anions. Transformation into carbon dioxide and water, otherwise known as mineralization , of CWAs has been observed as a result of the radicals and anions . Also, the active metal nanoparticles effectively shift the Fermi level of the photocatalyst, enhancing the distribution of the electron charge. Therefore, the lifetime of the radicals and anions is extended, so the implementation of the active metal nanoparticles has greatly improved photocatalytic efficiency.
Metal–organic frameworks (MOFs) are a class of compounds that are composed of a metal ion cluster coordinated to an organic linker. These compounds can form 1D, 2D and 3D structures. They possess a porous morphology which can be tuned in terms of shape and size depending on the metal ion and organic linker used to form the MOF. These pores grants them great catalytic properties which is why MOF research focused on the catalytic degradation of contaminants for environmental remediation has been gaining more attention. The major limitation of MOFs is that they tend to settle at the bottom of the solution, reducing their effectiveness since they are not coming into contact with the contaminant. Thus, in the past years more and more research focused on MOF for catalytic degradation have been implementing micromotors. The MOF particles are half-coated with a metal, creating a Janus motor particle (half metal, half MOF). The motor aspect of the particle enhances its diffusion, increasing the probability of the MOF and contaminant encountering each other in solution, thus increasing its degradation rate. These MOF based micromotors have proven to be extremely efficient at decontaminating water, and after the fuel used for propulsion (in most cases hydrogen peroxide) is completely consumed, they settle at the bottom of the solution, facilitating the removal of the Janus motor particles from the solution. [ 24 ] [ 25 ] | https://en.wikipedia.org/wiki/Micromotor |
Micron is a monthly peer-reviewed scientific journal in the field of microscopy . It was established in 1969 and is published by Elsevier .
This article about a biology journal is a stub . You can help Wikipedia by expanding it .
See tips for writing articles about academic journals . Further suggestions might be found on the article's talk page . | https://en.wikipedia.org/wiki/Micron_(journal) |
A micronekton is a group of organisms of 2 to 20 cm in size which are able to swim independently of ocean currents . The word ' nekton ' is derived from the Greek νήκτον , translit. nekton , meaning "to swim", and was coined by Ernst Haeckel in 1890.
Micronekton organisms are ubiquitous in the world's oceans and they can be divided into broad taxonomic groups . [ 1 ] [ 2 ] The distinction between micronekton and micro-, meso- and macro- zooplankton is based on size. Micronekton typically ranges in size from 2 to 20 cm, macro-zooplankton from 2 mm to 2 cm, meso-zooplankton from 0.2 to 2 mm and micro-zooplankton from 20 μm to 0.2 mm. Micronekton represents 3.8-11.8 billion tons of mesopelagic fishes worldwide, [ 3 ] [ 4 ] approximately 380 million tons of Antarctic krill in the Southern Ocean [ 5 ] and a global estimated biomass of at least 55 million tons of a single group of Ommastrephid squid. [ 6 ] This diverse group assemblage is distributed between the sea surface and approximately 1000 m deep (in the mesopelagic zone ). Micronekton shows a diverse range of migration patterns including diel vertical migration over several hundreds of metres from below 400 m (deeper layers) to the top 200 m (shallower layers) of the water column at dusk and inversely at dawn, [ 7 ] [ 8 ] [ 9 ] reverse migration (organisms stay in the shallow layer during the day) [ 10 ] [ 11 ] mid-water migration (organisms stay in the intermediate layer, i.e. between 200 and 400 m) or non-migration (organisms stay in the deep layer at night and shallow layer during the day). [ 8 ] [ 12 ] Micronekton plays a key role in the oceanic biological pump by transporting organic carbon from the euphotic zone to deeper parts of the oceans [ 13 ] [ 14 ] It is also preyed upon by various predators such as tunas , billfishes, sharks , marine birds and marine mammals . [ 15 ] [ 16 ] [ 17 ] [ 18 ] [ 19 ]
Generally, the taxonomy of global existing micronekton is not yet complete due to the paucity of faunal surveys, net avoidance (organisms sensing the approach of the net and swimming out of its path) and escapement (animals escape through the meshes after entering the net), and gear in-adaptability. New species are continually being discovered and described in new regions of the world's oceans. [ 20 ]
Crustaceans are highly diverse, with a single group, the decapods, consisting of 15,000 species in around 2,700 genera. [ 21 ] Euphausiids consist of 10 genera with a total of 85 species. Hyperiids are also widely distributed in the world's oceans with approximately 233 species across 72 genera. [ 22 ]
Cephalopods comprise less than 1000 species distributed across 43 families. They occur in all marine habitats such as benthic, burrowing on coral reefs, grass flats, sand, mud, rocks; are epibenthic, pelagic and epipelagic in bays, seas and the open ocean. [ 23 ]
Bristlemouths (Gonostomatidae), largely Cyclothone , account for more than 50% of the total vertebrate abundance between 100 and 1000 m. Twenty-one species of bristlemouths have been described globally. Lanternfishes are the secondmost abundant marine vertebrates, having diversified into 252 species. [ 24 ]
Hatchetfishes (Sternoptychidae) and dragonfishes (Stomiidae) are other common mesopelagic taxa in the deep-sea environment. [ 25 ] [ 26 ]
The crustacean body is divided into three sections: head, thorax and tail. They typically have 2 antennae and a varying number of pairs of thoracic legs called pereiopods (or thoracopods). [ 22 ] Crustacean species such as Systelaspis debilis and Oplophorus spinosus have specific visual pigments thought to facilitate congener recognition. [ 27 ] The oplophorid genera Systellaspis , Acanthephyra and Oplophorus secrete luminous fluids as part of their distress response. [ 28 ]
Cephalopods are soft-bodied animals with a cranium and, in most forms, a mantle/fin (cuttlebone or gladius) as primary skeletal features. [ 23 ] They have highly developed central nervous systems with well-organized eyes. Cephalopods can be divided into four main groups: squids, cuttlefishes, octopuses and chambered nautiluses, which have distinguishable morphological features. [ 23 ] Squids can have chromatic vision through the presence of various visual pigments.
Few anatomical and physiological studies of mesopelagic fishes have been conducted, except for research of the swimbladder of these organisms. The deepest-living mesopelagic fishes have no swimbladder. Most species inhabiting the upper mesopelagic zone have gas-filled swimbladders (which aid in buoyancy). Other species have a gas-filled swimbladder when young which becomes filled with fat with age. [ 29 ] Polyunsaturated wax esters are common in muscle or adipose tissue of lanternfishes, [ 30 ] posing an obstacle to human consumption.
Lanternfishes possess retina with a single pigment capable of absorbing bioluminescent light ranging from 480 to 492 nm at a distance of up to 30 m in the deep ocean. [ 31 ]
Bioluminescence is the production and emission of light from a living organism as a result of a natural chemical reaction, typically the molecular decomposition of luciferin substrates by the luciferase enzyme in the presence of oxygen. [ 31 ] Bioluminescence in animals is used to communicate, defend against predation, and find or attract prey. [ 28 ] It is mainly generated endogenously (e.g. photophores of lanternfish es) or through bacterially-mediated symbiosis (e.g. most anglerfish lures, flashlightfish subocular organs), within teleosts . [ 28 ] [ 32 ] It is common in micronekton (including many types of planktonic crustaceans, mesopelagic fishes such as myctophids/lanternfishes and stomiiformes, and squids). [ 28 ] [ 33 ] [ 34 ]
Many mesopelagic species (midwater squids, fish and shrimps) have counter shading ventral bioluminescent photophores which serve to match the intensity of downwelling light so as to hide from predators lurking below. [ 28 ] [ 35 ] To conceal itself with bioluminescence, the animal must precisely match its luminescence to the intensity, angular distribution and color of the downwelling light. [ 35 ]
Stomiiformes have barbels, ventral arrays, and red and blue suborbital photophores. [ 28 ] Lanternfishes have also developed lateral photophores on the sides of their bodies (for species recognition) [ 31 ] and sexually dimorphic luminescent organs on the tail or head. [ 25 ] [ 33 ] The sexual dimorphism of bioluminescent signalling and sensory systems may help facilitate sexual encounters in the deep ocean. [ 33 ] At the onset of sexual maturity, secondary light organs develop in some of the arms of certain female squids e.g. cranchiids ( Liocranchia and Leachia pacifica ) for use in sexual recognition. Females of the octopod Japetella develop a ring of bioluminescent tissue around their mouth just prior to mating and this tissue atrophies once the eggs are spent. [ 33 ] [ 35 ] [ 36 ] In the squid Ctenopteryx siculus , males develop a large photophore within the posterior region of their body at sexual maturity. [ 35 ] Bioluminescent signaling by micronekton also carries some degree of risk for it may expose the organism to a predator. [ 35 ]
Crustaceans show omnivorous feeding patterns since they prey on zooplankton, such as euphausiids and copepods, and are also known for occasional herbivory. [ 37 ] All squids have carnivorous foraging patterns. [ 38 ] Most mesopelagic fishes are carnivores . [ 39 ] [ 40 ] [ 41 ] Some mesopelagic fishes, for example Ceratoscopelus warmingii , have some herbivorous feeding strategies, and can thus be classified as omnivores. [ 42 ] Mesopelagic fishes mostly feed at night or dusk, with a few species being acyclic. [ 43 ]
Micronekton plays an important role in oceanic food webs by connecting top predators such as tunas and billfishes to lower trophic level zooplankton . [ 44 ] [ 8 ] Crustaceans, cephalopods and mesopelagic fishes generally have overlapping isotopic niche widths [ 44 ] [ 8 ] suggesting some degree of similarity in their diet with low level of resource partitioning and a high level of competition among these broad categories. [ 45 ] In low productive environments, predators such as swordfish were shown to forage on larger-sized squids since micronekton prey density is reduced and the costs associated with finding prey are higher than the energy intake when consuming smaller-sized micronekton. [ 8 ] Crustaceans and mesopelagic fishes generally occupy trophic level 3, smaller-sized squids occupy trophic level 3 to 4 and large nektonic squids such as Ommastrephes bartramii occupy trophic level 5. [ 8 ] [ 44 ]
Crustaceans, such as krill, may form several aggregation types, from high to low densities distributed throughout the water column, that are influenced by current velocities, direction, mean depth, and predator foraging. [ 46 ] Cephalopods may form large schools of neritic and oceanic species with millions of individuals, or small schools with a few dozens of individuals or may be found as isolated territorial individuals. [ 23 ] Some mesopelagic fishes form schools or are aggregated in scattering layers while others are dispersed [ 43 ]
Krill individuals of 45.4 mm in length can maintain horizontal sustained swimming speeds of 0.2 cm s −1 and are able to swim into currents for several hours at speeds of 0.17 cm s −1 . [ 47 ] [ 48 ] Krill are able to dart rapidly backwards to escape predators. [ 49 ] Cephalopods such as Illex illecebrosus are able to swim continuously. [ 38 ] During daytime, mesopelagic fish often hang motionless in the water column with head up or down in a state of torpor. [ 43 ] Myctophids have sustained swimming speeds of approximately 75 cm s −1 , with larger individuals having higher rates than smaller ones. [ 50 ] At night, fishes in the upper layers of the water column are active and swim horizontally, while those which stayed at depth are immobile and vertically oriented. Mesopelagic fishes are capable of rapid evasive movements to escape predators. [ 43 ]
However, crustaceans, cephalopods and mesopelagic fishes can adapt their swimming speeds, with the fastest swimming during escape, intermediate during foraging and lowest speed during migration: [ 51 ]
Sexual differences in gonads of krill first occur in subadults (> 24 mm), and secondary sexual (external) characteristics develop progressively in the late sub-adult stage (35 mm for females and 43 mm or larger for males). [ 52 ] The reproductive cycle of krill usually spans from December to April. [ 52 ]
Cephalopods have a wide range of reproductive strategies and may spawn once or more than once, with the latter including: (1) polycyclic spawning, with eggs laid in separate batches during the spawning season and growth between the production of egg batches, (2) multiple spawning, with group-synchronous ovulation, monocyclic spawning and growth between egg batches, (3) intermittent terminal spawning, with group-synchronous ovulation, monocyclic spawning and no growth between egg batches, (4) continuous spawning, with asynchronous ovulation, monocyclic spawning and growth between egg batches. [ 53 ] Cephalopods typically grow fast and mature rapidly, with their life cycle generally terminating with reproduction. [ 38 ]
The age of mesopelagic fishes can be determined from their otoliths and their growth rate can be calculated from the von Bertalanffy growth equation. [ 43 ] Most mesopelagic fishes become sexually mature one year after hatching in highly productive areas, and more than two years in low productive areas. [ 43 ] Most tropical myctophids and smaller gonostomatids are believed to have a one-year life cycle compared to mesopelagic fishes from colder waters which have a longer life cycle. [ 43 ] In temperate and subtropical regions, myctophids spawn mainly from late winter to summer. [ 43 ] The spawning season for Gonostomatids differ among species, with Sigmops elongatus spawning in spring and summer, Gonostoma ebelingi in early fall, Gonostoma atlanticum during all seasons in the subtropical central Pacific, and Gonostoma gracile in fall and winter in the western Pacific. [ 43 ] Other mesopelagic fishes such Maurolicus muelleri , Vinciguerria nimbaria and Vinciguerria poweriae spawn mainly in spring and summer. [ 43 ]
The vertical migration patterns of micronekton are species dependent. Most micronekton show an extensive diel vertical migration whereby they are concentrated below 400 m of the water column during the day and migrate to the top 200 m at dusk, and they migrate in the opposite direction to below 400 m at dawn. [ 8 ] Diel vertical migration of the mesopelagic community represents one of the Earth's largest daily animal migrations. The change in light intensity is believed to be the stimulus for triggering this vertical movement, with the main biological reason being enhanced foraging opportunities at the surface and decreased predation at night than in daytime. [ 54 ] Migrant micronekton may be following the movements of their main prey which undergo diel vertical migration at dusk. [ 55 ] Upward and downward migrations seem to occur in a series of events by different micronekton groups, with for example, smaller fishes which swim at smaller speeds leaving their location first than larger fishes. [ 12 ] [ 50 ]
Other micronekton species, however, are non-migrating or weakly migrating and hence stay below 400 m depth at dusk, for e.g., members of the Cyclothone genus and some sternoptychids . [ 12 ] Mid-water migration, i.e., migration to the lower limit of the shallow scattering layer (at approximately 200 m depth) at nighttime and back to 400 m before daytime, is also seen in some taxa. [ 12 ]
Almost all mesopelagic species are believed to change their vertical distribution range during their life history, with younger individuals generally inhabiting shallower depths than older ones. [ 43 ]
The distributional patterns of micronekton generally seem to coincide with water mass distribution, mesoscale oceanographic processes such as eddies , and presence of seamounts . [ 9 ] [ 12 ] [ 56 ] Micronekton showed reverse migration patterns, being located in the top 200 m of the water column during daytime, in a cyclonic mesoscale eddy in the South West Indian Ocean . [ 9 ] Cyclonic eddies also showed greater micronekton densities than anti-cyclonic eddies. [ 9 ] Mesoscale cyclonic eddies may hence create favorable conditions, such as enhanced foraging opportunities, for micronekton. [ 9 ]
Most micronekton species are oceanic [ 43 ] but neritic patterns have also been observed. Some micronekton taxa, such as Diaphus suborbitalis , preferentially associate with seamounts. [ 12 ] Large populations of D. suborbitalis have been reported off the slopes of the Equator, La Pérouse and MAD-Ridge seamounts in the Indian Ocean. They are located at depths around the seamounts' flanks during the day, and ascend in dense schools to the upper portion of the flanks and over the summits at dusk. [ 12 ] [ 57 ]
Fishes may interact with seamounts in different ways:
Some micronekton taxa may show the "feed-rest" hypothesis, whereby they would rest in the quiescent shelter offered by the seamount topography and sense the environment around the seamount to take advantage of the flow-advected prey, while avoiding advective loss by strong currents. [ 58 ] Some cephalopod species may use seamounts as spawning and foraging grounds. [ 59 ]
The high protein and low-fat content of cephalopods make them interesting components in human diets. [ 23 ] Mesopelagic fishes are good sources of "Omega-3" n-3 PUFA ( polyunsaturated fatty acids ), EPA (icosapentaenoic acid) and DHA ( docosahexaenoic acid ), [ 60 ] making them attractive candidates as dietary supplements for human consumption, as fishmeal in aquaculture farms, or for use as nutraceuticals. [ 61 ]
Compared to pelagic species such as tuna , sharks , and marine mammals , trace element concentrations in micronekton have been poorly studied. Trace elements are defined as those occurring in trace amounts (typically < 0.01% of the organism), and excluding the macronutrients calcium , magnesium , potassium and sodium . [ 62 ] Some trace elements, such as iron , manganese , selenium , and zinc are essential to the normal functioning of an organism. Cadmium, lead, and mercury , however, are non-essential elements (i.e., with no known biological function). [ 63 ] Other elements such as copper, zinc and selenium, are important in metabolic processes but toxic in high doses. [ 64 ] Trace elements, such as mercury, can bioaccumulate to harmful levels when they are stored in tissues of organisms faster than they can be detoxified and/or excreted. [ 64 ] Marine vertebrates have specific proteins, metallothionein , which bind trace elements such as cadmium, copper and zinc when in excess. [ 65 ] [ 66 ] The trace element selenium may reduce the availability of methylmercury by sequestering mercury, thus decreasing its toxicity. [ 67 ]
Trace element concentrations vary between micronekton broad categories and between metals, with crustaceans having higher levels of arsenic, copper, and zinc, compared to mesopelagic fishes. [ 68 ] [ 69 ] Copper and zinc are both known to associate with the respiratory pigment hemocyanin in crustaceans. [ 70 ] Cephalopods are known to bioaccumulate higher cadmium, copper and zinc concentrations in their digestive glands compared to fishes. [ 69 ] [ 71 ]
Myctophids sampled in the Indian Ocean and Gulf of California were enriched in iron, zinc and cobalt. [ 69 ] [ 72 ] [ 73 ] The mesopelagic fishes Chauliodus sloani , Sigmops elongatus , and Ceratoscopelus warmingii of the South West Indian Ocean, and the Sulu, Celebes and Philippine Seas (South China), have similar range of values of arsenic, cadmium, cobalt, copper, chromium, manganese, lead, selenium, silver, and zinc, suggesting that these organisms have similar biochemical processes, irrespective of their location. [ 69 ] [ 74 ]
Some micronekton organisms showed trace element concentrations above the permitted levels determined by European and worldwide legislations, and will hence have to be regularly monitored for their trace element content so as not to pose a threat to human consumption. [ 69 ] [ 75 ] [ 76 ]
There are growing interests in the commercial exploitation of micronekton for human consumption, as fishmeal in aquaculture farms and for nutraceutical products. [ 61 ] Cephalopod fisheries already exist, targeting a wide range of species, and with more than half of the total catch taken in the northeast and northwest Pacific, and the northeast and northwest Atlantic. [ 23 ] The fisheries target neritic and oceanic squids (e.g., Todarodes , Loligo , Illex , etc.), cuttlefish (e.g., Sepia , Sepiella , and allied genera), and octopuses (Octopus and Eledone ). [ 23 ]
The cephalopod fisheries use the following principal types of fishing methods and gear: [ 77 ]
some bottom trawling and
purse seine
trawling
some bottom trawling
Interest in mesopelagic fish exploitation is also rapidly growing due to their sheer number and ubiquitous nature. [ 78 ] The mesopelagic fish stock has been estimated at 20-100 billion tons with a potential yield of approximately 200 000 tons per year in the Arabian Sea, [ 43 ] [ 79 ] and a total global fish biomass of 2-19.5 gigatons between 70°N and 70°S. [ 80 ] Catches of mesopelagic fishes for scientific surveys are made using various types of trawls (Isaacs-Kidd midwater trawl, Cobb trawl, rectangular midwater trawl, Hokkaido University Frame Trawl, International Young Gadoid Pelagic Trawl, etc.), with mouth areas of 1–10 m 2 . Experiments have been conducted with commercial trawls having large mouth openings (100–1000 m 2 ) and large meshes (e.g., 20 cm) in the front part and gradually decreasing towards the codend. These commercial-sized trawls catch larger mesopelagic fishes but poorly sample small Cyclothone species. [ 43 ] | https://en.wikipedia.org/wiki/Micronekton |
Micronization is the process of reducing the average diameter of a solid material's particles. Traditional techniques for micronization focus on mechanical means, such as milling and grinding . Modern techniques make use of the properties of supercritical fluids and manipulate the principles of solubility .
The term micronization usually refers to the reduction of average particle diameters to the micrometer range, but can also describe further reduction to the nanometer scale. Common applications include the production of active chemical ingredients, foodstuff ingredients, and pharmaceuticals . These chemicals need to be micronized to increase efficacy.
Traditional micronization techniques are based on friction to reduce particle size. Such methods include milling , bashing and grinding . A typical industrial mill is composed of a cylindrical metallic drum that usually contains steel spheres. As the drum rotates the spheres inside collide with the particles of the solid, thus crushing them towards smaller diameters. In the case of grinding, the solid particles are formed when the grinding units of the device rub against each other while particles of the solid are trapped in between.
Methods like crushing and cutting are also used for reducing particle diameter, but produce more rough particles compared to the two previous techniques (and are therefore the early stages of the micronization process). Crushing employs hammer-like tools to break the solid into smaller particles by means of impact. Cutting uses sharp blades to cut the rough solid pieces into smaller ones.
Modern methods use supercritical fluids in the micronization process. These methods use supercritical fluids to induce a state of supersaturation , which leads to precipitation of individual particles. The most widely applied techniques of this category include the RESS process (Rapid Expansion of Supercritical Solutions), the SAS method (Supercritical Anti-Solvent) and the PGSS method (Particles from Gas Saturated Solutions). These modern techniques allow for greater tuneability of the process. Supercritical carbon dioxide (scCO 2 ) is a commonly used medium in micronization processes. [ 1 ] This is because scCO 2 is not very reactive and has easily accessible critical point state parameters. As a result, scCO2 can be effectively used to obtain pure crystalline or amorphous micronized forms. [ 2 ] Parameters like relative pressure and temperature, solute concentration, and antisolvent to solvent ratio are varied to adjust the output to the producer's needs. Control of particle size in micronization can be influenced by macroscopic factors, such as geometric parameters of the spray nozzle and flow rate, and molecular level changes due to adjustments in state parameters. These adjustments can lead to the nucleation of particles of varying sizes by polymorphic or amorphous transformations, as well as due to the characteristics of aggregation processes, which in some cases is accompanied by changes in conformational equilibria. [ 3 ] [ 4 ] [ 5 ] The supercritical fluid methods result in finer control over particle diameters, distribution of particle size and consistency of morphology. [ 6 ] [ 7 ] [ 8 ] Because of the relatively low pressure involved, many supercritical fluid methods can incorporate thermolabile materials. Modern techniques involve renewable, nonflammable and nontoxic chemicals. [ 9 ]
In the case of RESS (Rapid Expansion of Supercritical Solutions), the supercritical fluid is used to dissolve the solid material under high pressure and temperature, thus forming a homogeneous supercritical phase . Thereafter, the mixture is expanded through a nozzle to form the smaller particles. Immediately upon exiting the nozzle, rapid expansion occurs, lowering the pressure. The pressure will drop below supercritical pressure, causing the supercritical fluid - usually carbon dioxide - to return to the gas state. This phase change severely decreases the solubility of the mixture and results in precipitation of particles. [ 10 ] The less time it takes the solution to expand and the solute to precipitate, the narrower the particle size distribution will be. Faster precipitation times also tend to result in smaller particle diameters. [ 11 ]
In the SAS method (Supercritical Anti-Solvent), the solid material is dissolved in an organic solvent. The supercritical fluid is then added as an antisolvent, which decreases the solubility of the system. As a result, particles of small diameter are formed. [ 8 ] There are various submethods to SAS which differ in the method of introduction of the supercritical fluid into the organic solution. [ 12 ]
In the PGSS method (Particles from Gas Saturated Solutions) the solid material is melted and the supercritical fluid is dissolved in it. [ 13 ] However, in this case the solution is forced to expand through a nozzle, and in this way nanoparticles are formed. The PGSS method has the advantage that because of the supercritical fluid, the melting point of the solid material is reduced. Therefore, the solid melts at a lower temperature than the normal melting temperature at ambient pressure.
Pharmaceuticals and foodstuff ingredients are the main industries in which micronization is utilized. Particles with reduced diameters have higher dissolution rates, which increases efficacy. [ 9 ] Progesterone , for example, can be micronized by making very tiny crystals of the progesterone. [ 14 ] Micronized progesterone is manufactured in a laboratory from plants. It is available for use as HRT , infertility treatment, progesterone deficiency treatment, including dysfunctional uterine bleeding in premenopausal women. Compounding pharmacies can supply micronized progesterone in sublingual tablets, oil caps, or transdermal creams. [ 15 ] Creatine is among the other drugs that are micronized. [ 11 ] | https://en.wikipedia.org/wiki/Micronization |
A micronova is a putative type of thermonuclear explosion on the surface of a white dwarf much smaller than the strength of a nova ; being about 1 × 10 39 ergs (1.0 × 10 −12 foe ; 1.0 × 10 32 J ) in strength, about a millionth that of a typical nova. The phenomenon was first described in April 2022. [ 1 ] [ 2 ] [ 3 ]
A team led by Durham University researchers announced on 20 April 2022 that they identified three micronovae using data from the Transiting Exoplanet Survey Satellite (TESS). [ 4 ] The team discovered with TESS that two of the micronovae occurred on white dwarfs, with the astronomers confirming with the Very Large Telescope that the third occurred on a white dwarf as well. [ 5 ]
The phenomenon had previously been observed in the white dwarf binary TV Columbae using data from the International Ultraviolet Explorer. [ 6 ] However the data was not sufficient to infer the physical mechanism behind the explosion.
Micronovae specifically form on white dwarfs that have strong magnetic fields, as fields send material toward the star's magnetic poles. This causes the hydrogen fusion explosions on the surface to be more localized and smaller than a typical nova. [ 5 ]
An alternative explanation for the phenomenon is that these represent magnetic reconnection events either in the accretion disks or in the coronae of the companion stars. The system V2487 Oph is one of the candidate micronovae, and has also shown standard recurrent novae. The properties of its short duration flares also do not agree with predictions for nuclear fusion events. [ 7 ] | https://en.wikipedia.org/wiki/Micronova |
Microoptomechanical systems ( MOMS ), also written as micro-optomechanical systems , are a special class of microelectromechanical systems (MEMS) which use optical and mechanical, but not electronic components. [ 1 ]
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microoptomechanical_systems |
Micropaleontology (American spelling; spelled micropalaeontology in European usage) is the branch of paleontology ( palaeontology ) that studies microfossils , or fossils that require the use of a microscope to see the organism, its morphology and its characteristic details.
Microfossils are fossils that are generally between 0.001mm and 1 mm in size, [ 1 ] the study of which requires the use of light or electron microscopy . Fossils which can be studied by the naked eye or low-powered magnification, such as a hand lens, are referred to as macrofossils .
For example, some colonial organisms, such as Bryozoa (especially the Cheilostomata ) have relatively large colonies , but are classified by fine skeletal details of the small individuals of the colony.
In another example, many fossil genera of Foraminifera , which are protists are known from shells (called "tests") that were as big as coins, such as the genus Nummulites .
Microfossils are a common feature of the geological record , from the Precambrian to the Holocene . They are most common in deposits of marine environments, but also occur in brackish water, fresh water and terrestrial sedimentary deposits. While every kingdom of life is represented in the microfossil record, the most abundant forms are protist skeletons or cysts from the Chrysophyta , Pyrrhophyta , Sarcodina , acritarchs and chitinozoans , together with pollen and spores from the vascular plants .
In 2017, fossilized microorganisms , or microfossils, were announced to have been discovered in hydrothermal vent precipitates in the Nuvvuagittuq Belt of Quebec, Canada that may be as old as 4.28 billion years old, the oldest record of life on Earth , suggesting "an almost instantaneous emergence of life" (in a geological time-scale sense), after ocean formation 4.41 billion years ago , and not long after the formation of the Earth 4.54 billion years ago. [ 2 ] [ 3 ] [ 4 ] [ 5 ] Nonetheless, life may have started even earlier, at nearly 4.5 billion years ago, as claimed by some researchers. [ 6 ] [ 7 ]
Micropaleontology can be roughly divided into four areas of study on the basis of microfossil composition: (a) calcareous , as in coccoliths and foraminifera , (b) phosphatic , as in the study of some vertebrates , (c) siliceous , as in diatoms and radiolaria , or (d) organic , as in the pollen and spores studied in palynology .
This division reflects differences in the mineralogical and chemical composition of microfossil remains (and therefore in the methods of fossil recovery) rather than any strict taxonomic or ecological distinctions. Most researchers in this field , known as micropaleontologists , are typically specialists in one or more taxonomic groups .
Calcareous ( CaCO 3 ) microfossils include coccoliths , foraminifera , calcareous dinoflagellate cysts , and ostracods (seed shrimp).
Phosphatic microfossils include conodonts (tiny oral structures of an extinct chordate group), some scolecodonts ("worm" jaws), shark spines and teeth, and other fish remains (collectively called " ichthyoliths ").
Siliceous microfossils include diatoms , radiolarians , silicoflagellates , ebridians , phytoliths , some scolecodonts ("worm" jaws), and sponge spicules .
The study of organic microfossils is called palynology . Organic microfossils include pollen , spores , chitinozoans (thought to be the egg cases of marine invertebrates), scolecodonts ("worm" jaws), acritarchs , dinoflagellate cysts , and fungal remains.
Sediment or rock samples are collected from either cores or outcrops, and the microfossils they contain are extracted by a variety of physical and chemical laboratory techniques, including sieving, density separation by centrifuge or in heavy liquids, and chemical digestion of the unwanted fraction. The resulting concentrated sample of microfossils is then mounted on a slide for analysis, usually by light microscope. Taxa are then identified and counted. The enormous numbers of microfossils that a small sediment sample can often yield allows the collection of statistically robust datasets which can be subjected to multivariate analysis. A typical microfossil study will involve identification of a few hundred specimens from each sample.
Microfossils are specially noteworthy for their importance in biostratigraphy . Since microfossils are often extremely abundant, widespread, and quick to appear and disappear from the stratigraphic record, they constitute ideal index fossils from a biostratigraphic perspective. Also, the planktonic and nektonic habits of some microfossils give them the bonus of appearing across a wide range of facies or paleoenvironments, as well as having near-global distribution, making biostratigraphic correlation even more powerful and effective.
Microfossils, particularly from deep-sea sediments, also provide some of the most important records of global environmental change on long, medium or short timescales. [ 8 ] Across vast areas of the ocean floor, the shells of planktonic micro-organisms sinking from surface waters provide the dominant source of sediment, and they continuously accumulate (typically at rates of 20–50 million per million years). Study of changes in assemblages of microfossils and changes in their shell chemistry (e.g., oxygen isotope composition) are fundamental to research on climate change in the geological past.
In addition to providing an excellent tool for sedimentary rock dating and for paleoenvironmental reconstruction – heavily used in both petroleum geology and paleoceanography – micropaleontology has also found a number of less orthodox applications, such as its growing role in forensic police investigation or in determining the provenance of archaeological artefacts.
Micropaleontology is also a tool of geoarchaeology used in the archaeological reconstruction of human habitation sites and environments. Changes in the microfossil population abundance in the stratigraphy of current and former water bodies reflect changes in environmental conditions. Naturally occurring ostracods in freshwater bodies are impacted by changes in salinity and pH due to human activities. When correlated with other dating techniques, prehistoric environments can be reconstructed. Work on Lake Tanganyika provided a profile of human-induced environmental changes of a 4,000-year period. [ 9 ]
Similar work in the arid American Southwest has provided information on irrigation canals used by prehistoric peoples from 2100 B.C. to 500 B.C. [ 10 ] Other archaeological work in arid climates throughout the Americas has incorporated Micropaleontological analysis to build a more complete picture of prehistoric climate and human activity. | https://en.wikipedia.org/wiki/Micropaleontology |
The Microparticle Performance Rating ( MPR ) is an air filter rating system created by the company 3M . It rates the ability of an air filter to filter out micro particles.
Because MPR was created by 3M, it only applies to filters produced by the 3M brand. [ 1 ]
The higher the MPR, the better the filter's ability to capture particles from the air as it passes through the filter.
MPR is different from MERV , the Minimum Efficiency Reporting Value. The MERV system measures a filter's ability to capture large particles. The MPR only takes into account the microscopic particles between 0.3 and 1 μm.
This science article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microparticle_performance_rating |
Micropatterning is the art of miniaturisation of patterns . Especially used for electronics , it has recently [ when? ] become a standard in biomaterials engineering and for fundamental research on cellular biology by mean of soft lithography . It generally uses photolithography methods but many techniques have been developed. [ 1 ]
In cellular biology , micropatterns can be used to control the geometry of adhesion and substrate rigidity. This tool helped scientists to discover how the environment influences processes such as the orientation of the cell division axis, organelle positioning, cytoskeleton rearrangement cell differentiation and directionality of cell migration. [ 2 ] [ 3 ] Micropatterns can be made on a wide range of substrates, from glass to polyacrylamide and polydimethylsiloxane (PDMS). The polyacrylamide and PDMS in particular come into handy because they let scientists specifically regulate the stiffness of the substrate, and they allow researchers to measure cellular forces ( traction force microscopy ). Advanced custom micropatterning [ 4 ] allow precise and relatively rapid experiments controlling cell adhesion, cell migration, guidance, 3D confinement and microfabrication of microstructured chips. [ 5 ] Using advanced tools, protein patterns can be produced in virtually unlimited numbers (2D/ 3D shapes and volumes).
Nanopatterning of proteins has been achieved through using top-down lithography techniques. [ 6 ]
Aerosol micropatterning for biomaterials uses spray microscopic characteristics to obtain semi-random patterns particularly well adapted for biomaterials.
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Micropatterning |
Microphotographs are photographs shrunk to microscopic scale. [ 2 ] Microphotography is the art of making such images. Applications of microphotography include espionage such as in the Hollow Nickel Case , where they are known as microfilm .
Using the daguerreotype process, John Benjamin Dancer was one of the first to produce microphotographs, in 1839. [ 3 ] He achieved a reduction ratio of 160:1. Dancer perfected his reduction procedures with Frederick Scott Archer 's wet collodion process , developed in 1850–51, but he dismissed his decades-long work on microphotographs as a personal hobby, and did not document his procedures. The idea that microphotography could be no more than a novelty was an opinion shared by the 1858 Dictionary of Photography , which called the process "somewhat trifling and childish." [ 4 ]
Novelty viewing devices such as Stanhopes were once a popular way to carry and view microphotographs. [ 2 ] | https://en.wikipedia.org/wiki/Microphotograph |
Microphotonics is a branch of technology that deals with directing light on a microscopic scale and is used in optical networking . Particularly, it refers to the branch of technology that deals with wafer-level integrated devices and systems that emit, transmit, detect, and process light along with other forms of radiant energy with photon as the quantum unit. [ 1 ]
Microphotonics employs at least two different materials with a large differential index of refraction to squeeze the light down to a small size. Generally speaking, virtually all of microphotonics relies on Fresnel reflection to guide the light. If the photons reside mainly in the higher index material, the confinement is due to total internal reflection . If the confinement is due many distributed Fresnel reflections , the device is termed a photonic crystal . There are many different types of geometries used in microphotonics including optical waveguides , optical microcavities , and Arrayed waveguide gratings .
Photonic crystals are non-conducting materials that reflect various wavelengths of light almost perfectly. Such a crystal can be referred to as a perfect mirror . Other devices employed in microphotonics include micromirrors and photonic wire waveguides. These tools are used to "mold the flow of light", a famous phrase for describing the goal of microphotonics. The crystals serve as structures that allow the manipulation, confinement, and control of light in one, two, or three dimensions of space. [ 2 ]
An optical microdisk , optical microtoroid , or optical microsphere uses internal reflection in a circular geometry to hold on to the photons . This type of circularly symmetric optical resonance is called a Whispering gallery mode , after Lord Rayleigh coined the term.
Microphotonics has biological applications and these can be demonstrated in the case of the "biophotonic chips", which are developed to increase efficiency in terms of "photonic yield" or the collected luminescent signal emitted by fluorescent markers used in biological chips. [ 3 ]
Currently, microphotonics technology is also being developed to replace electronics devices and bio-compatible intracellular devices. [ 4 ] For instance, the long-standing goal of an all-optical router would eliminate electronic bottlenecks, speeding up the network. Perfect mirrors are being developed for use in fiber-optic cables .
This technology-related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microphotonics |
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4286
17342
ENSG00000187098
ENSMUSG00000035158
O75030
Q08874
NM_198159 NM_198177 NM_198178 NM_001354604 NM_001354605 NM_001354606 NM_001354607 NM_001354608
NM_001113198 NM_001178049 NM_008601
NP_937802 NP_937820 NP_937821 NP_001341533 NP_001341534 NP_001341535 NP_001341536 NP_001341537
NP_001106669 NP_001171520 NP_032627
Microphthalmia-associated transcription factor also known as class E basic helix-loop-helix protein 32 or bHLHe32 is a protein that in humans is encoded by the MITF gene .
MITF is a basic helix-loop-helix leucine zipper transcription factor involved in lineage-specific pathway regulation of many types of cells including melanocytes , osteoclasts , and mast cells . [ 5 ] The term "lineage-specific", since it relates to MITF, means genes or traits that are only found in a certain cell type. Therefore, MITF may be involved in the rewiring of signaling cascades that are specifically required for the survival and physiological function of their normal cell precursors. [ 6 ]
MITF, together with transcription factor EB ( TFEB ), TFE3 and TFEC , belong to a subfamily of related bHLHZip proteins, termed the MiT-TFE family of transcription factors. [ 7 ] [ 8 ] The factors are able to form stable DNA-binding homo- and heterodimers. [ 9 ] The gene that encodes for MITF resides at the mi locus in mice, [ 10 ] and its protumorogenic targets include factors involved in cell death, DNA replication , repair, mitosis, microRNA production, membrane trafficking, mitochondrial metabolism, and much more. [ 11 ] Mutation of this gene results in deafness, bone loss, small eyes, and poorly pigmented eyes and skin. [ 12 ] In human subjects, because it is known that MITF controls the expression of various genes that are essential for normal melanin synthesis in melanocytes, mutations of MITF can lead to diseases such as melanoma , Waardenburg syndrome , and Tietz syndrome . [ 13 ] Its function is conserved across vertebrates, including in fishes such as zebrafish [ 14 ] and Xiphophorus . [ 15 ]
An understanding of MITF is necessary to understand how certain lineage-specific cancers and other diseases progress. In addition, current and future research can lead to potential avenues to target this transcription factor mechanism for cancer prevention. [ 16 ]
As mentioned above, changes in MITF can result in serious health conditions. For example, mutations of MITF have been implicated in both Waardenburg syndrome and Tietz syndrome .
Waardenburg syndrome is a rare genetic disorder. Its symptoms include deafness, minor defects, and abnormalities in pigmentation. [ 17 ] Mutations in the MITF gene have been found in certain patients with Waardenburg syndrome, type II. Mutations that change the amino acid sequence of that result in an abnormally small MITF are found. These mutations disrupt dimer formation, and as a result cause insufficient development of melanocytes. [ citation needed ] The shortage of melanocytes causes some of the characteristic features of Waardenburg syndrome. [ citation needed ]
Tietz syndrome, first described in 1923, is a congenital disorder often characterized by deafness and leucism. Tietz is caused by a mutation in the MITF gene. [ 18 ] The mutation in MITF deletes or changes a single amino acid base pair specifically in the base motif region of the MITF protein. The new MITF protein is unable to bind to DNA and melanocyte development and subsequently melanin production is altered. A reduced number of melanocytes can lead to hearing loss, and decreased melanin production can account for the light skin and hair color that make Tietz syndrome so noticeable. [ 13 ]
Melanocytes are commonly known as cells that are responsible for producing the pigment melanin which gives coloration to the hair, skin, and nails. The exact mechanisms of how exactly melanocytes become cancerous are relatively unclear, but there is ongoing research to gain more information about the process. For example, it has been uncovered that the DNA of certain genes is often damaged in melanoma cells, most likely as a result of damage from UV radiation, and in turn increases the likelihood of developing melanoma. [ 19 ] Specifically, it has been found that a large percentage of melanomas have mutations in the B-RAF gene which leads to melanoma by causing an MEK-ERK kinase cascade when activated. [ 20 ] In addition to B-RAF, MITF is also known to play a crucial role in melanoma progression. Since it is a transcription factor that is involved in the regulation of genes related to invasiveness, migration, and metastasis, it can play a role in the progression of melanoma.
MITF recognizes E-box (CAYRTG) and M-box (TCAYRTG or CAYRTGA) sequences in the promoter regions of target genes. Known target genes (confirmed by at least two independent sources) of this transcription factor include,
Additional genes identified by a microarray study (which confirmed the above targets) include the following, [ 22 ]
The LysRS -Ap 4 A-MITF signaling pathway was first discovered in mast cells , in which, the A mitogen-activated protein kinase (MAPK) pathway is activated upon allergen stimulation. The binding of immunoglobulin E to the high-affinity IgE receptor ( FcεRI ) provides the stimulus that starts the cascade.
Lysyl- tRNA synthetase (LysRS) normally resides in the multisynthetase complex. This complex consists of nine different aminoacyl-tRNA synthetases and three scaffold proteins and has been termed the "signalosome" due to its non-catalytic signalling functions. [ 40 ] After activation, LysRS is phosphorylated on Serine 207 in a MAPK-dependent manner. [ 41 ] This phosphorylation causes LysRS to change its conformation, detach from the complex and translocate into the nucleus, where it associates with the encoding histidine triad nucleotide–binding protein 1 (HINT1) thus forming the MITF-HINT1 inhibitory complex. The conformational change also switches LysRS activity from aminoacylation of Lysine tRNA to diadenosine tetraphosphate (Ap4A) production. Ap4A, which is an adenosine joined to another adenosine through a 5‘-5’tetraphosphate bridge, binds to HINT1 and this releases MITF from the inhibitory complex, allowing it to transcribe its target genes. [ 42 ] Specifically, Ap4A causes a polymerization of the HINT1 molecule into filaments. The polymerization blocks the interface for MITF and thus prevents the binding of the two proteins. This mechanism is dependent on the precise length of the phosphate bridge in the Ap4A molecule so other nucleotides such as ATP or AMP will not affect it. [ 43 ]
MITF is also an integral part of melanocytes, where it regulates the expression of a number of proteins with melanogenic potential. Continuous expression of MITF at a certain level is one of the necessary factors for melanoma cells to proliferate, survive and avoid detection by host immune cells through the T-cell recognition of the melanoma-associated antigen (melan-A). [ 44 ] Post-translational modifications of the HINT1 molecules have been shown to affect MITF gene expression as well as the binding of Ap4A. [ 45 ] Mutations in HINT1 itself have been shown to be the cause of axonal neuropathies . [ 46 ] The regulatory mechanism relies on the enzyme diadenosine tetraphosphate hydrolase, a member of the Nudix type 2 enzymatic family (NUDT2), to cleave Ap4A, allow the binding of HINT1 to MITF and thus suppress the expression of the MITF transcribed genes. [ 47 ] NUDT2 itself has also been shown to be associated with human breast carcinoma, where it promotes cellular proliferation. [ 48 ] The enzyme is 17 kDa large and can freely diffuse between the nucleus and cytosol explaining its presence in the nucleus. It has also been shown to be actively transported into the nucleus by directly interacting with the N-terminal domain of importin-β upon immunological stimulation of the mast cells. Growing evidence is pointing to the fact that the LysRS-Ap4A-MITF signalling pathway is in fact an integral aspect of controlling MITF transcriptional activity. [ 49 ]
Activation of the LysRS-Ap4A-MITF signalling pathway by isoproterenol has been confirmed in cardiomyocytes. A heart specific isoform of MITF is a major regulator of cardiac growth and hypertrophy responsible for heart growth and for the physiological response of the cardiomyocytes to beta-adrenergic stimulation. [ 50 ]
MITF is phosphorylated on several serine and tyrosine residues. [ 51 ] [ 52 ] [ 53 ] Serine phosphorylation is regulated by several signaling pathways including MAPK/BRAF/ERK , receptor tyrosine kinase KIT , GSK-3 and mTOR . In addition, several kinases including PI3K , AKT , SRC and P38 are also critical activators of MITF phosphorylation. [ 54 ] In contrast, tyrosine phosphorylation is induced by the presence of the KIT oncogenic mutation D816V. [ 53 ] This KIT D816V pathway is dependent on SRC protein family activation signaling. The induction of serine phosphorylation by the frequently altered MAPK/BRAF pathway and the GSK-3 pathway in melanoma regulates MITF nuclear export and thereby decreasing MITF activity in the nucleus. [ 55 ] Similarly, tyrosine phosphorylation mediated by the presence of the KIT oncogenic mutation D816V also increases the presence of MITF in the cytoplasm. [ 53 ]
Most transcription factors function in cooperation with other factors by protein–protein interactions . Association of MITF with other proteins is a critical step in the regulation of MITF-mediated transcriptional activity. Some commonly studied MITF interactions include those with MAZR, PIAS3 , Tfe3 , hUBC9, PKC1, and LEF1 . Looking at the variety of structures gives insight into MITF's varied roles in the cell.
The Myc-associated zinc-finger protein related factor (MAZR) interacts with the Zip domain of MITF. When expressed together, both MAZR and MITF increase promoter activity of the mMCP-6 gene. MAZR and MITF together transactivate the mMCP-6 gene. MAZR also plays a role in the phenotypic expression of mast cells in association with MITF. [ 56 ]
PIAS3 is a transcriptional inhibitor that acts by inhibiting STAT3 's DNA binding activity. PIAS3 directly interacts with MITF, and STAT3 does not interfere with the interaction between PIAS3 and MITF. PIAS3 functions as a key molecule in suppressing the transcriptional activity of MITF. This is important when considering mast cell and melanocyte development. [ 57 ]
MITF, TFE3 and TFEB are part of the basic helix-loop-helix-leucine zipper family of transcription factors. [ 7 ] [ 9 ] Each protein encoded by the family of transcription factors can bind DNA. MITF is necessary for melanocyte and eye development and new research suggests that TFE3 is also required for osteoclast development, a function redundant of MITF. The combined loss of both genes results in severe osteopetrosis, pointing to an interaction between MITF and other members of its transcription factor family. [ 58 ] [ 59 ] In turn, TFEB has been termed as the master regulator of lysosome biogenesis and autophagy. [ 60 ] [ 61 ] Interestingly, MITF, TFEB and TFE3 separate roles in modulating starvation-induced autophagy have been described in melanoma. [ 62 ] Moreover, MITF and TFEB proteins, directly regulate each other’s mRNA and protein expression while their subcellular localization and transcriptional activity are subject to similar modulation, such as the mTOR signaling pathway. [ 8 ]
UBC9 is a ubiquitin conjugating enzyme whose proteins associates with MITF. Although hUBC9 is known to act preferentially with SENTRIN/SUMO1, an in vitro analysis demonstrated greater actual association with MITF. hUBC9 is a critical regulator of melanocyte differentiation. To do this, it targets MITF for proteasome degradation. [ 63 ]
Protein kinase C-interacting protein 1 (PKC1) associates with MITF. Their association is reduced upon cell activation. When this happens MITF disengages from PKC1. PKC1 by itself, found in the cytosol and nucleus, has no known physiological function. It does, however, have the ability to suppress MITF transcriptional activity and can function as an in vivo negative regulator of MITF induced transcriptional activity. [ 64 ]
The functional cooperation between MITF and the lymphoid enhancing factor (LEF-1) results in a synergistic transactivation of the dopachrome tautomerase gene promoter, which is an early melanoblast marker. LEF-1 is involved in the process of regulation by Wnt signaling. LEF-1 also cooperates with MITF-related proteins like TFE3. MITF is a modulator of LEF-1, and this regulation ensures efficient propagation of Wnt signals in many cells. [ 28 ]
Translational regulation of MITF is still an unexplored area with only two peer-reviewed papers (as of 2019) highlighting the importance. [ 65 ] [ 66 ] During glutamine starvation of melanoma cells ATF4 transcripts increases as well as the translation of the mRNA due to eIF2α phosphorylation. [ 65 ] This chain of molecular events leads to two levels of MITF suppression: first, ATF4 protein binds and suppresses MITF transcription and second, eIF2α blocks MITF translation possibly through the inhibition of eIF2B by eIF2α.
MITF can also be directly translationally modified by the RNA helicase DDX3X . [ 66 ] The 5' UTR of MITF contains important regulatory elements ( IRES ) that is recognized, bound and activated by DDX3X. Although, the 5' UTR of MITF only consists of a nucleotide stretch of 123-nt, this region is predicted to fold into energetically favorable RNA secondary structures including multibranched loops and asymmetric bulges that is characteristics of IRES elements. Activation of this cis-regulatory sequences by DDX3X promotes MITF expression in melanoma cells. [ 66 ] | https://en.wikipedia.org/wiki/Microphthalmia-associated_transcription_factor |
Microphysiometry is the in vitro measurement of the functions and activities of life or of living matter (as organs, tissues, or cells) and of the physical and chemical phenomena involved on a very small (micrometer) scale. [ 1 ] [ 2 ] The term microphysiometry emerged in the scientific literature at the end of the 1980s. [ 3 ] [ 4 ]
The primary parameters assessed in microphysiometry comprise pH and the concentration of dissolved oxygen , glucose , and lactic acid , with an emphasis on the first two. Measuring these parameters experimentally in combination with a fluidic system for cell culture maintenance and a defined application of drugs or toxins provides the quantitative output parameters extracellular acidification rates (EAR), oxygen uptake rates (OUR), and rates of glucose consumption or lactate release to characterize the metabolic situation.
Due to the label-free nature of sensor-based measurements, dynamic monitoring of cells or tissues for several days or even longer is feasible. [ 5 ] On an extended timescale, a dynamic analysis of a cell's metabolic response to an experimental treatment can distinguish acute effects (e.g., one hour after a treatment), early effects (e.g., at 24 hours), and delayed, chronic responses (e.g., at 96 hours). As stated by Alajoki et al., "The concept is that it is possible to detect receptor activation and other physiological changes in living cells by monitoring the activity of energy metabolism". [ 6 ] | https://en.wikipedia.org/wiki/Microphysiometry |
A micropipe , also called a micropore , microtube , capillary defect or pinhole defect , is a crystallographic defect in a single crystal substrate. Minimizing the presence of micropipes is important in semiconductor manufacturing , as their presence on a wafer can result in the failure of integrated circuits made from that wafer.
Micropipes are also relevant to makers of silicon carbide (SiC) substrates, used in a variety of industries such as power semiconductor devices for vehicles and high frequency communication devices; during the production of these materials, the crystal undergoes internal and external stresses causing growth of defects, or dislocations , within the atomic lattice .
A screw dislocation is a common dislocation that transforms successive atomic planes within a crystal lattice into the shape of a helix . Once a screw dislocation propagates through the bulk of a sample during the wafer growth process, a micropipe is formed.
Micropipes and screw dislocations in epitaxial layers are normally derived from the substrates on which the epitaxy is performed. Micropipes are considered to be empty-core screw dislocations with large strain energy (i.e. they have large Burgers vector ); they follow the growth direction (c-axis) in silicon carbide boules and substrates propagating into the deposited epitaxial layers.
Factors which influence formation of micropipes (and other defects) are such growth parameters as temperature, supersaturation , vapor phase stoichiometry , impurities and the polarity of the seed crystal surface.
This crystallography -related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Micropipe |
The microplane model , conceived in 1984, [ 1 ] is a material constitutive model for progressive softening damage. Its advantage over the classical tensorial constitutive models is that it can capture the oriented nature of damage such as tensile cracking , slip, friction , and compression splitting, as well as the orientation of fiber reinforcement. Another advantage is that the anisotropy of materials such as gas shale or fiber composites can be effectively represented. To prevent unstable strain localization (and spurious mesh sensitivity in finite element computations), this model must be used in combination with some nonlocal continuum formulation (e.g., the crack band model). Prior to 2000, these advantages were outweighed by greater computational demands of the material subroutine, but thanks to huge increase of computer power, the microplane model is now routinely used in computer programs, even with tens of millions of finite elements .
The basic idea of the microplane model is to express the constitutive law not in terms of tensors , but in terms of the vectors of stress and strain acting on planes of various orientations called the microplanes. The use of vectors was inspired by G. I. Taylor 's idea in 1938 [ 2 ] which led to Taylor models for plasticity of polycrystalline metals. [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] But the microplane models [ 1 ] [ 8 ] [ 9 ] [ 10 ] [ 11 ] [ 12 ] [ 13 ] differ conceptually in two ways.
Firstly, to prevent model instability in post-peak softening damage , the kinematic constraint must be used instead of the static one. Thus, the strain (rather than stress) vector on each microplane is the projection of the macroscopic strain tensor , i.e.,
where ε N , ε M {\displaystyle \varepsilon _{N},\varepsilon _{M}} and ε L {\displaystyle \varepsilon _{L}} are the normal vector and two strain vectors corresponding to each microplane, and N i j = n i n j , M i j = ( n i m j + m i n j ) / 2 {\displaystyle N_{ij}=n_{i}n_{j},M_{ij}=(n_{i}m_{j}+m_{i}n_{j})/2} and L i j = ( n i ℓ j + ℓ i n j ) / 2 {\displaystyle L_{ij}=(n_{i}\ell _{j}+\ell _{i}n_{j})/2} where n i , m i {\displaystyle n_{i},m_{i}} and ℓ i {\displaystyle \ell _{i}} are three mutually orthogonal vectors , one normal and two tangential, characterizing each particular microplane (subscripts i , j = 1 , 2 , 3 {\displaystyle i,j=1,2,3} refer to Cartesian coordinates).
Secondly, a variational principle (or the principle of virtual work ) relates the stress vector components on the microplanes ( σ N , σ M {\displaystyle \sigma _{N},\sigma _{M}} and σ L {\displaystyle \sigma _{L}} ) to the macro-continuum stress tensor σ i j {\displaystyle \sigma _{ij}} , to ensure equilibrium. This yields for the stress tensor the expression: [ 9 ] [ 13 ]
with
Here Ω {\displaystyle \Omega } is the surface of a unit hemisphere, and the sum is an approximation of the integral . The weights, w μ ( μ = 1 , 2 , … , n M ) {\displaystyle w_{\mu }(\mu =1,2,\ldots ,n_{M})} , are based on an optimal Gaussian integration formula for a spherical surface. [ 9 ] [ 14 ] [ 15 ] At least 21 microplanes are needed for acceptable accuracy but 37 are distinctly more accurate.
The inelastic or damage behavior is characterized by subjecting the microplane stresses σ N , σ M {\displaystyle \sigma _{N},\sigma _{M}} and σ L {\displaystyle \sigma _{L}} to strain-dependent strength limits called stress-strain boundaries imposed on each microplane. They are of four types, [ 13 ] viz.:
Each step of explicit analysis begins with an elastic predictor and, if the boundary has been exceeded, the stress vector component on the microplane is then dropped at constant strain to the boundary.
The microplane constitutive model for damage in concrete evolved since 1984 through a series of progressively improved models labeled M0, M1, M2, ..., M7. [ 13 ] It was also extended to fiber composites (woven or braided laminates), rock , jointed rock mass, clay , sand , foam, polymers and metal . [ 8 ] [ 11 ] [ 16 ] [ 17 ] [ 18 ] [ 19 ] [ 20 ] [ 21 ] [ 22 ] [ 23 ] [ 24 ] [ 25 ] The microplane model has been shown to allow close fits of the concrete test data for uniaxial , biaxial and triaxial loadings with post-peak softening, compression-tension load cycles, opening and mixed mode fractures, tension-shear and compression-shear failures, axial compression followed by torsion (i.e., the vertex effect) and fatigue. The loading rate effect and long-term aging creep of concrete have also been incorporated. Models M4 and M7 have been generalized to finite strain. The microplane model has been introduced into various commercial programs (ATENA, OOFEM, DIANA, SBETA,...) and large proprietary wavecodes (EPIC, PRONTO, MARS,...). Alternatively, it is often being used as the user's subroutine such as UMAT or VUMAT in ABAQUS. | https://en.wikipedia.org/wiki/Microplane_model_for_constitutive_laws_of_materials |
Microplastics are "synthetic solid particles or polymeric matrices, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water." [ 1 ] Microplastics are dangerous to human health [ citation needed ] and the environment because they contain harmful chemicals which leak into the air, water, and food.
Microplastics cause pollution by entering natural ecosystems from a variety of sources, including cosmetics , clothing , construction , renovation , food packaging , and industrial processes.
The term microplastics is used to differentiate from larger, non-microscopic plastic waste . Two classifications of microplastics are currently recognized. Primary microplastics include any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment . These include microfibers from clothing, microbeads , plastic glitter [ 2 ] and plastic pellets (also known as nurdles). [ 3 ] [ 4 ] [ 5 ] Secondary microplastics arise from the degradation (breakdown) of larger plastic products through natural weathering processes after entering the environment. Such sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers , tea bags and tire wear. [ 6 ] [ 5 ] [ 7 ] [ 8 ]
Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems , where they cause water pollution . [ 9 ]
Approximately 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester , acrylic , or nylon -based clothing, often during the washing process. [ 10 ] Microplastics also accumulate in the air and terrestrial ecosystems . Airborne microplastics have been detected in the atmosphere, as well as indoors and outdoors.
Because plastics degrade slowly (often over hundreds to thousands of years), [ 11 ] [ 12 ] microplastics have a high probability of ingestion, incorporation into, and accumulation in the bodies and tissues of many organisms. The toxic chemicals that come from both the ocean and runoff can also biomagnify up the food chain. [ 13 ] [ 14 ] In terrestrial ecosystems, microplastics have been demonstrated to reduce the viability of soil ecosystems. [ 15 ] [ 16 ] As of 2023, the cycle and movement of microplastics in the environment was not fully known. Microplastics in surface sample ocean surveys might have been underestimated as deep layer ocean sediment surveys in China found that plastics are present in deposition layers far older than the invention of plastics.
Microplastics are likely to degrade into smaller nanoplastics through chemical weathering processes, mechanical breakdown, and even through the digestive processes of animals. Nanoplastics are a subset of microplastics and they are smaller than 1 μm (1 micrometer or 1000 nm). Nanoplastics cannot be seen by the human eye. [ 17 ]
The term "microplastics" was introduced in 2004 by Professor Richard Thompson , a marine biologist at the University of Plymouth in the United Kingdom. [ 18 ] [ 19 ] [ 20 ] [ 21 ]
Microplastics are common in our world today. In 2014, it was estimated that there are between 15 and 51 trillion individual pieces of microplastic in the world's oceans, which was estimated to weigh between 93,000 and 236,000 metric tons. [ 22 ] [ 23 ] [ 24 ] Under the influence of sunlight, wind , waves and other factors, plastic degrades into small fragments known as microplastics, or even nanoplastics. [ 25 ]
Primary microplastics are small pieces of plastic that are purposefully manufactured. [ 26 ] They are usually used in facial cleansers and cosmetics , or in air blasting technology. In some cases, their use in medicine as vectors for drugs was reported. [ 27 ] Microplastic "scrubbers", used in exfoliating hand cleansers and facial scrubs, have replaced traditionally used natural ingredients , including ground almond shells, oatmeal , and pumice . Primary microplastics have also been produced for use in air-blasting technology. This process involves blasting acrylic , melamine , or polyester microplastic scrubbers at machinery, engines, and boat hulls to remove rust and paint. As these scrubbers are used repeatedly until they diminish in size and their cutting power is lost, they often become contaminated with heavy metals such as cadmium , chromium , and lead . [ 28 ] Although many companies have committed to reducing the production of microbeads , [ 29 ] there are still many bioplastic microbeads that also have a long degradation life cycle, for example in cosmetics. [ 30 ]
Secondary microplastics are small pieces of plastic derived from the physical breakdown and mechanical degradation of larger plastic debris, both at sea and on land. Over time, a culmination of physical, biological, and photochemical degradation, including photo-oxidation caused by sunlight exposure, can reduce the structural integrity of plastic debris to a size that is eventually undetectable to the naked eye. [ 31 ] This process of breaking down large plastic material into much smaller pieces is known as fragmentation. [ 28 ] It is considered that microplastics might further degrade to be smaller in size, although the smallest microplastic reportedly detected in the oceans in 2017 was 1.6 micrometres (6.3×10 −5 in) in diameter. [ 32 ] The prevalence of microplastics with uneven shapes suggests that fragmentation is a key source. [ 13 ] One study suggested that more microplastics might be formed from biodegradable polymer than from non-biodegradable polymer in both seawater and fresh water. [ 33 ] [ 34 ] [ additional citation(s) needed ]
"It's actually classified as a very high priority high contaminant by the EPA... when they litter or put something in a landfill, the plastic will break down into smaller and smaller particles. And eventually, they become microplastics... They're in the air, they're in the water, they're in the soil." – University of Tennessee professor Mike McKinney. [ 35 ]
Microplastic fibers enter the environment as a by-product during wear and tear and from the washing of synthetic clothing . [ 36 ] [ 7 ] Tires, composed partly of synthetic styrene-butadiene rubber, erode into tiny plastic and rubber particles as they are used and become dust particles. 2.0-5.0 mm plastic pellets, used to create other plastic products, enter ecosystems due to spillages and other accidents . [ 5 ]
A 2015 Norwegian Environment Agency review report about microplastics stated it would be beneficial to classify these sources as primary, as long as microplastics from these sources are added from human society since the "start of the pipe", and their emissions are inherently a result of human material and product use and not secondary to fragmentation in the nature. [ 37 ] [ incomplete short citation ]
Depending on the definition used, nanoplastics are less than 1 μm (i.e. 1000 nm) or less than 100 nm in size. [ 38 ] [ 39 ] Speculations over nanoplastics in the environment range from it being a temporary byproduct during the fragmentation of microplastics to it being an invisible environmental threat at potentially high and continuously rising concentrations. [ 40 ] The presence of nanoplastics in the North Atlantic Subtropical Gyre has been confirmed [ 41 ] and recent developments in Raman spectroscopy coupled with optical tweezers (Raman Tweezers) [ 42 ] as well as nano-fourier-transform infrared spectroscopy (nano- FTIR ) or atomic force infrared ( AFM-IR ) are promising answers in the near future regarding the nanoplastic quantity in the environment. Fluorescence could represent a unique tool for the identification and quantification of nanoplastics, since it allows the development of fast, easy, cheap, and sensitive methods. [ 43 ] However, the nanoplastic problem is complex and nanoscale properties as well as interaction with biomolecules need to be explored at the fundamental level with high spatial and temporal resolution. [ 44 ]
Nanoplastics are thought to be a risk to environmental and human health. [ 38 ] [ 45 ] Due to their small size, nanoplastics can cross cellular membranes and affect the functioning of cells. Nanoplastics are lipophilic and models show that polyethylene nanoplastics can be incorporated into the hydrophobic core of lipid bilayers. [ 46 ] Nanoplastics are also shown to cross the epithelial membrane of fish accumulating in various organs including the gallbladder, pancreas, and the brain. [ 47 ] [ 48 ] Nanoplastics are believed to cause interruptions in bone cell activities, causing improper bone formation. [ 49 ] [ 50 ] Little is known on adverse health effects of nanoplastics in organisms including humans. In zebrafish ( Danio rerio ), polystyrene nanoplastics can induce a stress response pathway altering glucose and cortisol levels, which is potentially tied to behavioral changes in stress phases. [ 51 ] In Daphnia , polystyrene nanoplastic can be ingested by the freshwater cladoceran Daphnia pulex and affect its growth and reproduction as well as induce stress defense, including the ROS production and MAPK-HIF-1/NF-κB-mediated antioxidant system. [ 52 ] [ 53 ] [ 54 ] Nanoplastics can also adsorb toxic chemical pollutants, such as antibiotics, which enable the selective association with antibiotic-resistant bacteria, resulting in the dissemination of nanoplastics and antibiotic-resistant bacteria by bacterivorous nematode Caenorhabditis elegans across the soil. [ 55 ]
The existence of microplastics in the environment is often established through aquatic studies. These include taking plankton samples, analyzing sandy and muddy sediments , observing vertebrate and invertebrate consumption, and evaluating chemical pollutant interactions. [ 56 ] Through such methods, it has been shown that there are microplastics from multiple sources in the environment. [ citation needed ]
Textiles, tires, and urban dust [ 57 ] account for over 80% of all microplastics in the seas and the environment. [ 9 ] Microplastic is also a type of airborne particulates and is found to prevail in air. [ 58 ] [ 59 ] [ 60 ] Paint appears as the largest source of microplastic leakage into the ocean and waterways (1.9 Mt/year), outweighing all other sources of microplastic leakage. [ 61 ] Microplastics could contribute up to 30% of the Great Pacific Garbage Patch polluting the world's oceans and, in many developed countries, are a bigger source of marine plastic pollution than the visible larger pieces of marine litter, according to a 2017 IUCN report. [ 5 ] Oceanic microplastics are a common source of heavy metals [ 62 ] due to the inclusion of coloring compounds containing chromium, manganese, cobalt, copper, zinc, zirconium, molybdenum, silver, tin, praseodymium, neodymium, erbium, tungsten, iridium, gold, lead, or uranium. [ 63 ]
Oral intake is the main pathway of human exposure to microplastics. [ 64 ] Microplastics exist in our daily necessities like drinking water, bottled water, seafood, salt, sugar, tea bags, milk, and so on. [ 65 ]
65 million microplastics are released into water sources everyday. [ 66 ] In 2017, more than eight million tons of plastics entered the oceans, greater than 33 times as much as that of the total plastics accumulated in the oceans by 2015. [ 67 ] One consequence of this is marine life consumption of microplastics. It is estimated that Europeans are exposed to about 11,000 particles/person/year of microplastics due to shellfish consumption. [ 68 ]
Microplastics may enter drinking-water sources in a number of ways: from surface run-off (e.g. after a rain event), to wastewater effluent (both treated and untreated), combined sewer overflows, industrial effluent, degraded plastic waste, and atmospheric deposition. [ 69 ] Surface run-off and wastewater effluent are recognized as the two main sources, but better data are required to quantify the sources and associate them with more specific plastic waste streams. Plastic bottles and caps that are used in bottled water may also be sources of microplastics in drinking-water. [ 69 ]
Microplastics may also have been widely distributed in soil, especially in agricultural systems. [ 70 ] They (especially with negative charge) can get into the water transport system of plants, and then move to the roots, stems, leaves, and fruits. [ 71 ] Once microplastics enter agricultural systems through sewage sludge, compost, and plastic mulching, they will cause food pollution, which may increase the risk of human exposure. [ 72 ]
Studies have shown that many synthetic fibers , such as polyester, nylon, acrylics, and spandex , can be shed from clothing and persist in the environment. [ 73 ] [ 74 ] [ 75 ] Each garment in a load of laundry can shed more than 1900 fibers of microplastics, with fleeces releasing the highest percentage of fibers, over 170% more than other garments. [ 76 ] [ 77 ] For an average wash load of 6 kilograms (13 lb), over 700,000 fibers could be released per wash. [ 78 ]
Washing machine manufacturers have also reviewed research into whether washing machine filters can reduce the amount of microfiber fibers that need to be treated by sewage treatment facilities. [ 79 ]
These microfibers have been found to persist throughout the food chain from zooplankton to larger animals such as whales. [ 5 ] The primary fiber that persists throughout the textile industry is polyester which is a cheap cotton alternative that can be easily manufactured. However, these types of fibers contribute greatly to the persistence to microplastics in terrestrial, aerial, and marine ecosystems. The process of washing clothes causes garments to lose an average of over 100 fibers per liter of water. [ 77 ] This has been linked with health effects possibly caused by the release of monomers , dispersive dyes, mordants , and plasticizers from manufacturing. The occurrence of these types of fibers in households has been shown to represent 33% of all fibers in indoor environments. [ 77 ]
Textile fibers have been studied in both indoor and outdoor environments to determine the average human exposure. The indoor concentration was found to be 1.0–60.0 fibers/m 3 , whereas the outdoor concentration was much lower at 0.3–1.5 fibers/m 3 . [ 80 ] The deposition rate indoors was 1586–11,130 fibers per day/m 3 which accumulates to around 190-670 fibers/mg of dust. [ 80 ] The largest concern with these concentrations is that it increases exposure to children and the elderly, which can cause adverse health effects. [ citation needed ]
Plastic containers can shed microplastics and nanoparticles into foods and beverages. [ 81 ]
In one study, 93% of the bottled water from 11 different brands showed microplastic contamination. Per liter, researchers found an average of 325 microplastic particles. [ 82 ] Of the tested brands, Nestlé Pure Life and Gerolsteiner bottles contained the most microplastic with 930 and 807 microplastic particles per liter (MPP/L), respectively. [ 82 ] San Pellegrino products showed the least quantity of microplastic densities. Compared to water from taps, water from plastic bottles contained twice as much microplastic. [ 82 ] Another study capable of detecting nanoplastics found 240,000 fragments per liter: 10% between 5 mm and 1 μm and 90% under 1 μm in diameter. [ 83 ] [ 84 ]
Some of the contamination likely comes from the process of bottling and packaging the water, [ 82 ] and possibly from filters used to purify the water. [ 83 ]
In 2020 researchers reported that polypropylene infant feeding bottles with contemporary preparation procedures were found to cause microplastics exposure to infants ranging from 14,600 to 4,550,000 particles per capita per day in 48 regions. Microplastics release is higher with warmer liquids and similar with other polypropylene products such as lunchboxes. [ 85 ] [ 86 ] [ 87 ] Unexpectedly, silicone rubber baby bottle nipples degrade over time from repeated steam sterilization, shedding micro- and nano-sized particles of silicone rubber, researchers found in 2021. They estimated that, using such heat-degraded nipples for a year, a baby will ingest more than 660,000 particles. [ 88 ] [ 89 ]
Common single-use plastic products, such as plastic cups, or even paper coffee cups that are lined with a thin plastic film inside, release trillions of microplastic- nanoparticles per liter into water during normal use. [ 91 ] [ 92 ] [ 93 ] Single-use plastic products enter aquatic environments [ 94 ] and "[l]ocal and statewide policies that reduce single-use plastics were identified as effective legislative actions that
communities can take to address plastic pollution". [ 95 ] [ 96 ]
Plastics are extensively used in the construction and renovation industry. [ 97 ] Airborne microplastic dust is produced during renovation , building, bridge and road reconstruction projects [ 98 ] and the use of power tools . [ 99 ]
Materials containing polyvinyl chloride (PVC), polycarbonate , polypropylene , and acrylic , can degrade overtime releasing microplastics. [ 97 ] During the construction process single use plastic containers and wrappers are discarded adding to plastic waste . [ 100 ] These plastics are difficult to recycle and end up in landfills where they break down over a long period of time causing potential leaching into the soil and the release of airborne microplastics. [ 101 ] [ 102 ] Airborne microplastic dust is also generated by deterioration of building materials [ 60 ]
Due to the environmental impact from plastic waste creation in the construction and renovation sectors waste management practices that address this issue are required. [ 103 ] [ 104 ] [ 105 ] Although many researchers have investigated the use of wastes, such as plastic, in the construction process in an effort to reduce waste and increase sustainability, construction is not an environmentally-friendly activity by nature. Efforts have been made to reduce plastic waste by adding it to concrete as agglomerates. However, one solution for resolving the problem from the large amount of plastic wastes generated could bring another serious problem of leaching of microplastics. The unknown part of this area is huge and needs prompt investigation. [ 104 ]
Around twenty percent of all plastics and seventy percent of all polyvinyl chloride (PVC) produced in the world each year are used by the construction industry. [ 106 ] [ 107 ] It is predicted that much more will be produced and used in the future. [ 106 ] "In Europe, approximately 20% of all plastics produced are used in the construction sector including different classes of plastics, waste and nanomaterials." [ 107 ]
Common types: [ 107 ]
Indirect use (packaging of construction materials) examples: [ 107 ]
Direct use (construction materials containing plastics) examples: [ 107 ]
Some companies have replaced natural exfoliating ingredients with microplastics, usually in the form of " microbeads " or "micro-exfoliates". These products are typically composed of polyethylene , a common component of plastics, but they can also be manufactured from polypropylene , polyethylene terephthalate (PET), and nylon . [ 108 ] They are often found in face washes, hand soaps , and other personal care products; the beads are usually washed into the sewage system immediately after use. Their small size prevents them from fully being retained by preliminary treatment screens at wastewater plants, thereby allowing some to enter rivers and oceans. [ 109 ] Wastewater treatment plants only remove an average of 95–99.9% of microbeads because of their small design. This leaves an average of 0–7 microbeads per litre being discharged. [ 110 ] Considering that the treatment plants of the world discharge 160 trillion liters of water per day, around 8 trillion microbeads are released into waterways every day. This number does not account for the sewage sludge that is reused as fertilizer after the waste water treatment that has been known to still contain these microbeads. [ 111 ]
Although many companies have committed to phasing out the use of microbeads in their products, there are at least 80 different facial scrub products that are still being sold with microbeads as a main component. [ 110 ] [ failed verification ] This contributes to the 80 metric tons of microbead discharge per year by the United Kingdom alone, which not only has a negative impact upon the wildlife and food chain, but also upon levels of toxicity, as microbeads have been proven to absorb dangerous chemicals such as pesticides and polycyclic aromatic hydrocarbons . [ 110 ] The restriction proposal by the European Chemicals Agency (ECHA) and reports by the United Nations Environment Programme ( UNEP ) and TAUW suggest that there are more than 500 microplastic ingredients that are widely used in cosmetics and personal care products. [ 112 ]
Even when microbeads are removed from cosmetic products, there are still harmful products being sold with plastics in them. For example, acrylate copolymers cause toxic effects for waterways and animals if they are polluted. [ 113 ] Acrylate copolymers also can emit styrene monomers when used in body products which increases a person's chances of cancer. [ 114 ] Countries like New Zealand which have banned microbeads often pass over other polymers such as acrylate copolymers, which can be just as toxic to people and the environment. [ 115 ]
After the Microbead-Free Waters Act of 2015 , the use of microbeads in toothpaste and other rinse-off cosmetic products has been discontinued in the US, [ 116 ] however since 2015 many industries have instead shifted toward using FDA -approved "rinse-off" metallized-plastic glitter as their primary abrasive agent . [ 117 ] [ 118 ] [ 119 ]
Recreational and commercial fishing , marine vessels , and marine industries are all sources of plastic that can directly enter the marine environment, posing a risk to biota both as macroplastics, and as secondary microplastics following long-term degradation. Marine debris observed on beaches also arises from beaching of materials carried on inshore and ocean currents. Fishing gear is a form of plastic debris with a marine source. Discarded or lost fishing gear, including plastic monofilament line and nylon netting (sometimes called ghost nets ), is typically neutrally buoyant and can, therefore, drift at variable depths within the oceans. Various countries have reported that microplastics from the industry and other sources have been accumulating in different types of seafood. In Indonesia, 55% of all fish species had evidence of manufactured debris similar to America which reported 67%. [ 120 ] However, the majority of debris in Indonesia was plastic, while in North America the majority was synthetic fibers found in clothing and some types of nets. The implication from the fact that fish are being contaminated with microplastic is that those plastics and their chemicals will bioaccumulate in the food chain. [ 121 ]
One study analyzed the plastic-derived chemical called polybrominated diphenyl ethers (PBDEs) in the stomachs of short-tailed shearwaters . It found that one-fourth of the birds had higher-brominated congeners that are not naturally found in their prey. However, the PBDE got into the birds' systems through plastic that was found in the stomachs of the birds. It is therefore not just the plastics that are being transferred through the food chain but the chemicals from the plastics as well. [ 122 ]
The manufacture of plastic products uses granules and small resin pellets as their raw material. In the United States, production increased from 2.9 million pellets in 1960 to 21.7 million pellets in 1987. [ 123 ] In 2019, plastic world production was 368 million tonnes; 51% were produced in Asia. China, the world's largest producer, created 31% of the world total. [ 124 ] Through accidental spillage during land or sea transport, inappropriate use as packing materials , and direct outflow from processing plants, these raw materials can enter aquatic ecosystems . In an assessment of Swedish waters using an 80 μm mesh, KIMO Sweden found typical microplastic concentrations of 150–2,400 microplastics per m 3 ; in a harbor adjacent to a plastic production facility, the concentration was 102,000 per m 3 . [ 28 ]
Many industrial sites in which convenient raw plastics are frequently used are located near bodies of water. If spilled during production, these materials may enter the surrounding environment, polluting waterways. [ 37 ] "More recently, Operation Cleansweep, a joint initiative of the American Chemistry Council and Society of the Plastics Industry , is aiming for industries to commit to zero pellet loss during their operations". [ 28 ] Overall, there is a significant lack of research aimed at specific industries and companies that contribute to microplastics pollution.
Since the emergence of the COVID-19 pandemic , the usage of medical face masks has sharply increased to reach approximately 89 million masks each. [ 125 ] Single use face masks are made from polymers, such as polypropylene , polyurethane , polyacrylonitrile , polystyrene , polycarbonate , polyethylene , or polyester . The increase in production, consumption, and littering of face masks was added to the list of environmental challenges, due to the addition of plastic particles waste in the environment. After degrading, disposable face masks could break down into smaller size particles (under 5mm) emerging a new source of microplastic. [ 126 ] A single surgical weathered face mask may release up to 173,000 fibers/ day. [ 125 ]
A report made in February 2020 by Oceans Asia, an organization committed to advocacy and research on marine pollution, confirms "the presence of face masks of different types and colors in an ocean in Hong Kong". [ 126 ]
Sewage treatment plants, also known as wastewater treatment plants (WWTPs), remove contaminants from wastewater, primarily from household sewage, using various physical, chemical, and biological processes. [ 127 ] Most plants in developed countries have both primary and secondary treatment stages. In the primary stage of treatment, physical processes are employed to remove oils, sand, and other large solids using conventional filters, clarifiers , and settling tanks. [ 128 ] Secondary treatment uses biological processes involving bacteria and protozoa to break down organic matter. Common secondary technologies are activated sludge systems, trickling filters , and constructed wetlands . [ 128 ] The optional tertiary treatment stage may include processes for nutrient removal ( nitrogen and phosphorus ) and disinfection . [ 128 ]
Microplastics have been detected in both the primary and secondary treatment stages of the plants. A groundbreaking 1998 study suggested that microplastic fibers would be a persistent indicator of sewage sludges and wastewater treatment plant outfalls. [ 129 ] A study estimated that about one particle per liter of microplastics are being released back into the environment, with a removal efficiency of about 99.9%. [ 127 ] [ 130 ] [ 131 ] A 2016 study showed that most microplastics are actually removed during the primary treatment stage where solid skimming and sludge settling are used. [ 127 ] When these treatment facilities are functioning properly, the contribution of microplastics into oceans and surface water environments from WWTPs is not disproportionately large. [ 127 ] [ 132 ] Many studies show that while wastewater treatment plants certainly reduce the microplastic load on waterways, with current technological developments they are not able to clean the waters fully of this pollutant. [ 133 ] [ 134 ]
Sewage sludge is used for soil fertilizer in some countries, which exposes plastics in the sludge to the weather, sunlight, and other biological factors, causing fragmentation. As a result, microplastics from these biosolids often end up in storm drains and eventually into bodies of water. [ 135 ] In addition, some studies show that microplastics do pass through filtration processes at some WWTPs. [ 28 ] According to a study from the UK, samples taken from sewage sludge disposal sites on the coasts of six continents contained an average one particle of microplastic per liter. A significant amount of these particles was of clothing fibers from washing machine effluent. [ 77 ]
Wear and tear from tires significantly contributes to the flow of (micro-)plastics into the environment. Estimates of emissions of microplastics to the environment in Denmark are between 5,500 and 14,000 tonnes (6,100 and 15,400 tons) per year. Secondary microplastics (e.g. from car and truck tires or footwear) are more important than primary microplastics by two orders of magnitude. The formation of microplastics from the degradation of larger plastics in the environment is not accounted for in the study. [ 136 ]
The estimated per capita emission ranges from 0.23 to 4.7 kg/year, with a global average of 0.81 kg/year. The emissions from car tires (wear reaching 100%) are substantially higher than those of other sources of microplastics, e.g., airplane tires (2%), artificial turf (wear 12–50%), brakes (wear 8%), and road markings (wear 5%). In the case of road markings, recent field study indicated that they were protected by a layer of glass beads and their contribution was only between 0.1 and 4.3 g/person/year, [ 137 ] which would constitute approximately 0.7% of all of the secondary microplastics emissions; this value agrees with some emissions estimates. [ 138 ] [ 139 ] Emissions and pathways depend on local factors like road type or sewage systems. The relative contribution of tire wear and tear to the total global amount of plastics ending up in our oceans is estimated to be 5–10%. In air, 3–7% of the particulate matter (PM 2.5 ) is estimated to consist of tire wear and tear, indicating that it may contribute to the global health burden of air pollution which has been projected by the World Health Organization at 3 million deaths in 2012. Pollution from tire wear and tear also enters the food chain, but further research is needed to assess human health risks. [ 140 ]
Shipping has significantly contributed to marine pollution . Some statistics indicate that in 1970, commercial shipping fleets around the world dumped over 23,000 tons of plastic waste into the marine environment. In 1988, an international agreement ( MARPOL 73/78 , Annex V) prohibited the dumping of waste from ships into the marine environment. In the United States, the Marine Plastic Pollution Research and Control Act of 1987 prohibits discharge of plastics in the sea, including from naval vessels. [ 141 ] [ 142 ] However, shipping remains a dominant source of plastic pollution , having contributed around 6.5 million tons of plastic in the early 1990s. [ 143 ] [ 144 ] Research has shown that approximately 10% of the plastic found on the beaches in Hawaii are nurdles. [ 145 ] In one incident on 24 July 2012, 150 tonnes of nurdles and other raw plastic material spilled from a shipping vessel off the coast near Hong Kong after a major storm. This waste from the Chinese company Sinopec was reported to have piled up in large quantities on beaches. [ 37 ] While this is a large incident of spillage, researchers speculate that smaller accidents also occur and further contribute to marine microplastic pollution. [ 37 ]
Airborne microplastics have been detected in the atmosphere , as well as indoors and outdoors. Microplastic can be atmospherically transported to remote areas by the wind. [ 146 ] A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics). [ 147 ] Another study looked at microplastic in the street dust of Tehran and found 2,649 particles of microplastic within 10 samples of street dust, with ranging samples concentrations from 83 particle – 605 particles (±10) per 30.0 g of street dust. [ 148 ] Microplastics and microfibers were also found in snow samples, [ 149 ] and high up in "clean" air in high mountains at vast distances from their source. [ 150 ] [ 151 ] Much like freshwater ecosystems and soil, more studies are needed to understand the full impact and significance of airborne microplastics. [ 152 ]
A growing concern regarding plastic pollution in the marine ecosystem is the use of microplastics. Microplastics are beads of plastic less than 5 millimeters wide, [ 153 ] and they are commonly found in hand soaps, face cleansers, and other exfoliators. When these products are used, the microplastics go through the water filtration system and into the ocean, but because of their small size they are likely to escape capture by the preliminary treatment screens on wastewater plants. [ 154 ] These beads are harmful to the organisms in the ocean, especially filter feeders, because they can easily ingest the plastic and become sick. The microplastics are such a concern because it is difficult to clean them up due to their size, so humans can try to avoid using these harmful plastics by purchasing products that use environmentally safe exfoliates.
Plastic pollution has previously been recorded in Antarctic surface waters and sediments as well as in the Arctic sea ice , [ 157 ] but in 2009, for the first time, plastic was found in Antarctic sea ice, with 96 microplastic particles from 14 different types of polymers in an ice core sampled from east Antarctica . [ 158 ] Relatively large particle sizes in Antarctic sea ice suggest local pollution sources.
Microplastics have been widely detected in the world's aquatic environments. [ 159 ] [ 160 ] The first study on microplastics in freshwater ecosystems was published in 2011 that found an average of 37.8 fragments per square meter of Lake Huron sediment samples. Additionally, studies have found MP (microplastic) to be present in all of the Great Lakes with an average concentration of 43,000 MP particle km −2 . [ 161 ] Microplastics have also been detected in freshwater ecosystems outside of the United States, for example in 2019 study conducted in Poland showed that microplastic was present in all 30 studied lakes of the Masurian Lakeland with density from 0.27 to 1.57 particles per liter. [ 162 ] In Canada, a three-year study found a mean microplastic concentration of 193,420 particles km −2 in Lake Winnipeg . None of the microplastics detected were micro-pellets or beads and most were fibers resulting from the breakdown of larger particles, synthetic textiles, or atmospheric fallout. [ 163 ] The highest concentration of microplastic ever discovered in a studied freshwater ecosystem was recorded in the Rhine river at 4000 MP particles kg −1 . [ 164 ]
Researchers from Western Carolina University, Highlands Biological Station, and Virginia Tech found microplastics in Richland Creek watershed in Western North Carolina. 90% of the microplastics were fibers, largely attributed to clothing, city runoff, and atmospheric deposition. [ 165 ] [ 166 ] [ 167 ]
A substantial portion of microplastics are expected to end up in the world's soil , yet very little research has been conducted on microplastics in soil outside of aquatic environments. [ 168 ] In wetland environments microplastic concentrations have been found to exhibit a negative correlation with vegetation cover and stem density. [ 159 ] There exists some speculation that fibrous secondary microplastics from washing machines could end up in soil through the failure of water treatment plants to completely filter out all of the microplastic fibers. Furthermore, geophagous soil fauna, such as earthworms, mites, and collembolans could contribute to the amount of secondary microplastic present in soil by converting consumed plastic debris into microplastic via digestive processes. Further research, however, is needed. There is concrete data linking the use of organic waste materials to synthetic fibers being found in the soil; but most studies on plastics in soil merely report its presence and do not mention origin or quantity. [ 5 ] [ 169 ] Controlled studies on fiber-containing land-applied wastewater sludges (biosolids) applied to soil reported semiquantitative [ clarification needed ] recoveries of the fibers a number of years after application. [ 170 ]
A 2015 review of 15 brands of table salts commercially available in China found microplastics were much more prevalent in sea salts compared to lake, rock, or well salts, attributing this to sea salts being contaminated by ocean water pollution while the rock/well salts were more likely contaminated during the production stages of collecting, wind drying, and packaging. [ 171 ] According to a 2017 estimate, a person who consumes seafood will ingest 11,000 bits of microplastics per year. A 2019 study found a kilo of sugar had 440 microplastic particles, a kilo of salt contained 110 particles, and a litre of bottled water contained 94 particles. [ 172 ] [ 173 ] [ 174 ]
The composition of microplastics are complex. A study in 2023 tested some fish species and found that "about 80% of the MPs detected were fibrous in shape and were made of polyethylene (25%), polyester (20%), and polyamide (10%). Most microplastic particles observed were black (61%) or blue (27%) in color." [ 175 ]
Microplastics contain two different types of chemicals. The first are additives and polymeric raw materials such as monomers or oligomers. Additives are chemicals intentionally added during plastic production to give plastic qualities like color and transparency and to enhance the performance of plastic products to improve both the resistance to degradation by ozone, temperature, light radiation, mold, bacteria and humidity, and mechanical, thermal and electrical resistance. Examples of additives in microplastics are inert or reinforcing fillers, plasticizers, antioxidants, UV stabilizers, lubricants, dyes and flame-retardants [ 176 ] The second type of chemicals are ones absorbed from the surrounding environment.
In 2008, an International Research Workshop at the University of Washington at Tacoma concluded that microplastics were a problem in the marine environment, based on their documented occurrence, the long residence times of these particles, their likely buildup in the future, and their demonstrated ingestion by marine organisms . [ 177 ]
According to a comprehensive review of scientific evidence published by the European Union 's Scientific Advice Mechanism in 2019, microplastics were present in every part of the environment. While there was no evidence of widespread ecological risk from microplastic pollution yet, risks were likely to become widespread within a century if pollution continued at its current rate. [ 152 ]
As of 2020 microplastics had been detected in freshwater systems including marshes, streams, ponds, lakes, and rivers in Europe, North America, South America, Asia, and Australia. [ 159 ] [ 178 ] Samples collected across 29 Great Lakes tributaries from six states in the United States were found to contain plastic particles, 98% of which were microplastics ranging in size from 0.355mm to 4.75mm. [ 179 ] Likewise, they have been found in high mountains, at great distances from their source. [ 150 ]
Deep layer ocean sediment surveys in China (2020) show the presence of plastics in deposition layers far older than the invention of plastics, leading to suspected underestimation of microplastics in surface sample ocean surveys. [ 180 ]
In September 2021 Hurricane Larry deposited, during the storm peak, 113,000 particles/m 2 /day as it passed over Newfoundland , Canada. Back-trajectory modelling and polymer type analysis indicated that those microplastics may have been ocean-sourced as the hurricane traversed the North Atlantic garbage patch of the North Atlantic Gyre . [ 181 ]
As of 2023 there was rapid growth of microplastic pollution research, with marine and estuarine environments most frequently studied. Researchers have called for better sharing of research data that might lead to effective solutions. [ 182 ]
A 2023 study formally identified plasticosis as a fibrotic disease caused by plastic ingestion, distinguishing it from general physical damage by detailing the chronic tissue remodeling and inflammation it induces in seabird digestive systems. [ 183 ]
Consequences of plastic degradation and pollution release over long term have mostly been overlooked. The large amounts of plastic in the environment, exposed to degradation, with years of decay and release of toxic compounds to follow was referred to as toxicity debt . [ 40 ]
Microplastics are inconspicuous, being less than 5 mm. Particles of this size are available to every species, enter the food chain at the bottom, and become embedded in animal tissue.
Micro- and nanoplastics can become embedded in animals' tissue through ingestion or respiration. The initial demonstration of bioaccumulation of these particles in animals was conducted under controlled conditions by exposing them to high concentrations of microplastics over extended periods, accumulating these particles in their gut and gills due to ingestion and respiration, respectively. Various annelid species, such as deposit-feeding lugworms ( Arenicola marina ), have been shown to accumulate microplastics embedded in their gastrointestinal tract . Similarly, many crustaceans , like the shore crab Carcinus maenas , have been seen to integrate microplastics into both their respiratory and digestive tracts. [ 74 ] [ 184 ] [ 185 ] Plastic particles are often mistaken by fish for food, which can block their digestive tracts, sending incorrect feeding signals to the brains of the animals. [ 9 ] However, research in 2021 revealed that fish ingest microplastics inadvertently rather than intentionally. [ 186 ] The first occurrence of bioaccumulation of micro and nanoplastics in wild animals was documented in the skin mucosa of salmon, and it was attributed to the resemblance between nanoplastics and the outer shell of the viruses that the mucosa traps. [ 187 ] This discovery was entirely serendipitous, as the research team had developed a detailed molecular separation process for the components of fish skin with the primary objective of isolating chitin from a vertebrate for the first time. [ 188 ]
A study done at the Argentinean coastline of the Rio de la Plata estuary , found the presence of microplastics in the guts of 11 species of coastal freshwater fish. These 11 species of fish represented four different feeding habits: detritivore , planktivore , omnivore and ichthyophagous . [ 189 ] This study is one of the few so far to show the ingestion of microplastics by freshwater organisms.
It can take up to 14 days for microplastics to pass through an animal (as compared to a normal digestion period of 2 days), but enmeshment of the particles in animals' gills can prevent elimination entirely. [ 184 ] When microplastic-laden animals are consumed by predators, the microplastics are then incorporated into the bodies of higher trophic-level feeders. For example, scientists have reported plastic accumulation in the stomachs of lantern fish which are small filter feeders and are the main prey for commercial fish like tuna and swordfish . [ 190 ] [ 191 ] Microplastics also absorb chemical pollutants that can be transferred into the organism's tissues. [ 192 ] Small animals are at risk of reduced food intake due to false satiation and resulting starvation or other physical harm from the microplastics. [ citation needed ]
Zooplankton ingest microplastics beads (1.7–30.6 μm) and excrete fecal matter contaminated with microplastics. Along with ingestion, the microplastics stick to the appendages and exoskeleton of the zooplankton. [ 3 ] Zooplankton, among other marine organisms, consume microplastics because they emit similar infochemicals, notably dimethyl sulfide , just as phytoplankton do. [ 193 ] [ verification needed ] [ 194 ] Plastics such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) produce dimethyl sulfide odors. [ 193 ] These types of plastics are commonly found in plastic bags, food storage containers, and bottle caps. [ 195 ] Green and red filaments of plastics are found in the planktonic organisms and in seaweeds. [ 196 ]
Bottom feeders , such as benthic sea cucumbers , who are non-selective scavengers that feed on debris on the ocean floor , ingest large amounts of sediment. It has been shown that four species of sea cucumber ( Thyonella gemmate , Holothuria floridana , H. grisea and Cucumaria frondosa ) ingested between 2- and 20-fold more PVC fragments and between 2- and 138-fold more nylon line fragments (as much as 517 fibers per organism) based on plastic-to-sand grain ratios from each sediment treatment. These results suggest that individuals may be selectively ingesting plastic particles. This contradicts the accepted indiscriminate feeding strategy of sea cucumbers, and may occur in all presumed non-selective feeders when presented with microplastics. [ 197 ]
Bivalves , important aquatic filter feeders, have also been shown to ingest microplastics and nanoplastics. [ 198 ] Upon exposure to microplastics, bivalve filtration ability decreases. [ 199 ] Multiple cascading effects occur as a result, such as immunotoxicity and neurotoxicity . [ 200 ] [ 201 ] [ 202 ] Decreased immune function occurs due to reduced phagocytosis and NF-κB gene activity. [ 200 ] [ 202 ] Impaired neurological function is a result of the inhibition of ChE and suppression of neurotransmitter regulatory enzymes. [ 202 ] When exposed to microplastics, bivalves also experience oxidative stress , indicating an impaired ability to detoxify compounds within the body, which can ultimately damage DNA. [ 201 ] Bivalve gametes and larvae are also impaired when exposed to microplastics. Rates of developmental arrest, and developmental malformities increase, while rates of fertilization decrease. [ 198 ] [ 203 ] When bivalves have been exposed to microplastics as well as other pollutants such as POPs , mercury or hydrocarbons in lab settings, toxic effects were shown to be aggravated. [ 199 ] [ 200 ] [ 201 ]
Not only fish and free-living organisms can ingest microplastics. Some corals such as Pocillopora verrucosa have also been found to ingest microplastics. [ 204 ] Scleractinian corals , which are primary reef-builders, have been shown to ingest microplastics under laboratory conditions. [ 205 ] Researchers from Japan and Thailand investigating microplastics in coral have found that all three parts of the coral anatomy (surface mucus, tissue, and skeleton) contain microplastics. [ 206 ] According to recent study, mall-polyp corals (P. cf. damicornis and P. lutea) demonstrated a higher degree of MP accumulation than the large-polyp corals. [ 207 ] The interplay of precipitation, wind patterns, and ocean currents considerably influences MP abundance in corals by increasing the exposure of corals to elevated MP concentrations. Additionally, since the reef site was situated near a large rock formation, it experienced strong water movements due to constant wave action. MPs deposited in skeletons are likely to be preserved on a millennium timescale, even if the corals die. Thus, given the extensive presence of coral reefs worldwide, corals can accumulate a considerable number of MPs, thereby acting as a sink for ocean plastics. [ 208 ]
While the effects of ingestion on these corals has not been studied, corals can easily become stressed and bleach. Microplastics have been shown to stick to the exterior of the corals after exposure in the laboratory. [ 205 ] The adherence to the outside of corals can potentially be harmful, because corals cannot handle sediment or any particulate matter on their exterior and slough it off by secreting mucus, expending energy in the process, increasing the likelihood of mortality. [ 209 ] The thermodynamic properties, development, and nutrition of corals are thought to be negatively impacted by the engaged consumption and detached exterior bond strength of MPs. This could result in decreased feed intake, decreased photosynthetic efficiency, altered metabolic rates, decreased bone calcification, and even skin chlorination and necrotizing. [ 210 ]
Marine biologists in 2017 discovered that three-quarters of the underwater seagrass in the Turneffe Atoll off the coast of Belize had microplastic fibers, shards, and beads stuck to it. The plastic pieces had been overgrown by epibionts (organisms that naturally stick themselves to seagrass). Seagrass is part of the barrier reef ecosystem and is fed on by parrotfish , which in turn are eaten by humans. These findings, published in Marine Pollution Bulletin, may be "the first discovery of microplastics on aquatic vascular plants... [and] only the second discovery of microplastics on marine plant life anywhere in the world." [ 211 ]
Research published in 2023 demonstrated that microplastic exposure impaired the cognitive performance of hermit crabs, which could potentially impact their survivability. [ 212 ]
Microplastics can affect the soil ecosystem and stunt the growth of terrestrial plants due to the increased uptake of toxic metals such as cadmium. [ 213 ] [ 214 ] [ 215 ] [ 216 ] Microplastics can reduce weight of earthworms . [ 217 ]
Microbes also live on the surface of microplastics, and can form a biofilm which, according to a 2019 study, [ 218 ] has a unique structure and possesses a special risk, because microplastic biofilms have been proven to provide a novel habitat for colonization that increases overlap between different species, thus spreading pathogens and antibiotic resistant genes [ 219 ] through horizontal gene transfer . Then, due to rapid movement through waterways, these pathogens can be moved from their origin to another location where a specific pathogen may not be naturally present, spreading potential disease. [ 218 ] There is concern microplastic pollutants may act as a vector for antibiotic resistant genes and bacteria. [ 220 ] Clinically important bacterial genus like Eggerthella were more than three times enriched on riverine microplastics compared to water. [ 219 ]
In 2019, the first European records of microplastic items in amphibians' stomach content was reported in specimens of the common European newt ( Triturus carnifex ) . This also represented the first evidence for Caudata worldwide, highlighting that the emerging issue of plastics is a threat even in remote high-altitude environments. [ 221 ] The microplastic has also been found in common blackbirds ( Turdus merula ) and song thrushes ( Turdus philomelos ) which shows a ubiquity of microplastics in terrestrial environments. [ 222 ]
In 2023, plasticosis , a new disease caused solely by plastics, was discovered in seabirds who had scarred digestive tracts from ingesting plastic waste. [ 223 ] "When birds ingest small pieces of plastic, [...]it inflames the digestive tract. Over time, the persistent inflammation causes tissues to become scarred and disfigured, affecting digestion, growth and survival." [ 224 ]
Plastic particles may highly concentrate and transport synthetic organic compounds (e.g. persistent organic pollutants and emerging organic contaminants), commonly present in the environment and ambient seawater, on their surface through adsorption . [ 225 ] Microplastics can act as carriers for the transfer of POPs from the environment to organisms, also termed as the Trojan Horse effect . [ 226 ] [ 143 ] [ 144 ] Recent articles have also shown that microplastics can sorb emerging organic chemicals such as pharmaceuticals and personal care products. [ 227 ] [ 228 ] The sorption potential is affected by water matrix, pH, ionic strength and aging of microparticles. [ 227 ]
Additives added to plastics during manufacture may leach out upon ingestion, potentially causing serious harm to the organism. Endocrine disruption by plastic additives may affect the reproductive health of humans and wildlife alike. [ 144 ]
Microplastics can increase the stability of breaking waves or sea foam , potentially affecting sea albedo or atmosphere-ocean gas exchange. [ 229 ] Microplastics in the ocean may re-enter the atmosphere via sea spray . [ 230 ]
Although the impacts of microplastics on human health are still being tested, their possible effects can be studied through human absorption models of nanomaterials that are produced by various industrial production processes. [ 231 ] Several in vitro and in vivo studies have shown that micro- and nanoplastics were able to cause serious impacts on the human body, including physical stress and damage, apoptosis, necrosis, inflammation, oxidative stress and immune responses. [ 232 ] Microplastic pollution has been associated with various adverse human health conditions, including respiratory disease and inflammation , but it was not known whether this was a causative effect. [ 233 ]
Microplastics often contain chemical additives like phthalates and bisphenol A (BPA), which are known endocrine-disrupting chemicals. Microplastics and their additives can disrupt the hypothalamic-pituitary-gonadal (HPG) axis, a critical regulator of male reproductive function [ 234 ]
A study from Harvard found that microplastics have been linked to "inflammation, cell death, lung and liver effects, changes in the gut microbiome, and altered lipid and hormone metabolism." [ 235 ]
A number of studies have concluded that microplastics create inflammatory effects in the human body. An in vitro study found that ultrafine particles composed of low-toxicity material, such as polystyrene, have proinflammatory activity as a consequence of their large surface area. [ 236 ] Another study found pro-inflammatory factors and debris in human joints from polyethylene components used as prostheses, for example knee and hip replacements. [ 237 ]
In vitro studies have also shown that different polystyrene nanoparticles can induce oxidative stress, apoptosis and autophagic cell death in cell context-dependent manner. [ 238 ] Despite these toxic effects, no obvious severe toxicity was observed in liver, duodenum, ileum, jejunum, large intestine, testes, lungs, heart, spleen, and kidneys of mice following oral exposure of a mixture of microplastics. [ 239 ]
Recent studies have revealed that microplastics and nanoplastics can impair cellular metabolism in both in vitro and in vivo models. [ 238 ] After exposure to negatively charged carboxylated polystyrene nanoparticles measuring 20 nm, basolateral K+ ion channels were found to be activated in human lung cells. The nanoplastic particles caused persistent and concentration-dependent increases in short-circuit currents by the activation of the ion channels and the stimulation of Cl− and HCO3− ion efflux. [ 240 ] Furthermore, 30 nm polystyrene nanoparticles induced large vesicle-like structures in the endocytic route in macrophages and human cancer cell lines A549, HepG-2, and HCT116. As a result, vesicle transport and the distribution of proteins involved in cytokinesis are blocked, thus stimulating the formation of binucleated cells. [ 241 ]
Some of the suggested dust control measures include "lining cutting areas with tarps, cutting inside a protective tent, and using vacuum bags on power tool" when cutting materials like Trex and Azek . The cost of these measures is low." [ 99 ] Street sweeping may also inhibited the spread of pollutants by gathering significant amounts of dirty materials from the extensive construction, renovation and reconstruction projects of road tunnels, bridges, roads and buildings. [ 104 ]
Some researchers have proposed incinerating plastics to use as energy, which is known as energy recovery. As opposed to losing the energy from plastics into the atmosphere in landfills , this process turns some of the plastics back into energy that can be used. However, as opposed to recycling, this method does not diminish the amount of plastic material that is produced. Therefore, recycling plastics is considered a more efficient solution. [ 145 ]
Biodegradation is another possible solution to large amounts of microplastic waste. In this process, microorganisms consume and decompose synthetic polymers by means of enzymes. [ 242 ] These plastics can then be used in the form of energy and as a source of carbon once broken down. The microbes could potentially be used to treat sewage wastewater, which would decrease the amount of microplastics that pass through into the surrounding environments. [ 242 ]
Efficient removal of microplastics via waste water treatment plants is critical to prevent the transfer of microplastics from society to natural water systems. The captured microplastics in the treatment plants become part of the sludge produced by the plants. The problem is that this sludge is often used as farm fertilizer meaning the plastics enter waterways through runoff. [ 9 ]
Fionn Ferreira , winner of the 2019 Google Science Fair , is developing a device for the removal of microplastic particles from water using a ferrofluid . [ 243 ]
The Ocean Cleanup , a Dutch foundation, has developed various proposals, with the stated aim of "clearing 90% of the ocean's microplastics". [ 244 ] [ 245 ] [ 246 ] The project has been met with widespread criticism from oceanographers and plastic pollution experts, despite positive news articles. [ 247 ] [ 248 ] [ 249 ] It has been dismissed by almost all microplastics experts as unlikely to have any impact on the microplastics issue. Some of the reasons for this are it only targets plastics larger than 2 cm (this is larger than the criteria for a microplastic), is infeasible from an engineering standpoint and likely to fail rapidly, and it only captures plastic from the top 3m of depth (most plastic circulates much deeper than this. [ 247 ]
In addition, some bacteria have adapted to eat plastic, and some bacteria species have been genetically modified to eat (certain types of) plastics. [ 250 ] Other than degrading microplastics, microbes had been engineered in a novel way to capture microplastics in their biofilm matrix from polluted samples for easier removal of such pollutants. [ 251 ] The microplastics in the biofilms can then be released with an engineered 'release' mechanism via biofilm dispersal to facilitate with microplastics recovery. [ 252 ]
Absorption devices include sponges made of cotton and squid bones, which may be scalable for water remediation projects. [ 253 ]
Increasing education through recycling campaigns is another proposed solution for microplastic contamination. While this would be a smaller-scale solution, education has been shown to reduce littering, especially in urban environments where there are often large concentrations of plastic waste. [ 145 ] If recycling efforts are increased, a cycle of plastic use and reuse would be created to decrease our waste output and production of new raw materials. In order to achieve this, states would need to employ stronger infrastructure and investment around recycling. [ 254 ] Some advocate for improving recycling technology to be able to recycle smaller plastics to reduce the need for production of new plastics. [ 145 ]
In April 2013, Italian artist Maria Cristina Finucci founded The Garbage Patch State in order to create awareness, [ 255 ] under the patronage of UNESCO and the Italian Ministry of the Environment. [ 256 ]
In February 2013 the U.S. Environmental Protection Agency (EPA) launched its "Trash-Free Waters" initiative to prevent single-use plastic wastes from ending up in waterways and ultimately the ocean. [ 257 ] As of 2018, EPA collaborated with the United Nations Environment Programme –Caribbean Environment Programme (UNEP-CEP) and the Peace Corps to reduce and remove trash in the Caribbean Sea . [ 258 ] EPA also funded various projects in the San Francisco Bay Area including one that is aimed at reducing the use of single-use plastics such as disposable cups , spoons and straws, from three University of California campuses. [ 259 ]
The Florida Microplastic Awareness Project (FMAP), a group of volunteers who search for microplastics in coastal water samples Many organizations advocate action to counter microplastic, spreading microplastic awareness. [ 260 ] Global advocacy aimed at achieving the target of the United Nations Sustainable Development Goal 14 hopes to prevent and significantly reduce all forms of marine pollution by 2025. [ 261 ]
The Clean Oceans Initiative is a project launched in 2018 by the public institutions European Investment Bank , Agence Française de Développement and KfW Entwicklungsbank . Their goal was to provide up to €2 billion in lending, grants and technical assistance until 2023 to develop projects that removed pollution from waterways (with a focus on macroplastics and microplastics) before it reached the oceans. [ 9 ] The effort focuses on initiatives that demonstrate efficient methods of minimising plastic waste and microplastics output, emphasising on riverine and coastal areas. [ 262 ] Cassa Depositi e Prestiti (CDP), the Italian national promotional institution and financial institution for development cooperation, and the Instituto de Crédito Oficial (ICO), the Spanish promotional bank, became new partners in October 2020. [ 263 ] [ 264 ] [ 265 ] As of December 2023, The Clean Oceans Initiative had funded almost €3.2 billion, exceeding 80% of its €4 billion objective. Over 20 million people were supposed to benefit from the signed project proposals, which include better wastewater treatment in Sri Lanka, China, Egypt, and South Africa, solid waste management in Togo and Senegal, and stormwater management and flood protection in Benin, Morocco, and Ecuador. [ 266 ] [ 267 ]
In February 2022, the initiative stated that it would increase its financing aim to €4 billion by the end of 2025. At the same time, the European Bank for Reconstruction and Development (EBRD) became the Clean Oceans Initiative's sixth member. [ 262 ] By February 2023, the program had met 65% of its goal, with €2.6 billion spent in 60 projects benefiting more than 20 million people across Africa, Asia, Latin America , and Europe. [ 263 ] [ 268 ] By the beginning of 2022, more than 80% of this target was achieved, with €1.6 billion being used in long-term financing for public and private sector initiatives that minimise the discharge of plastics, microplastics, and other pollutants through enhanced solid waste, wastewater, and storm water management. [ 262 ]
In January 2021, the European Investment Bank and the Asian Development Bank had formed the Clean and Sustainable Ocean Partnership to promote cooperative projects for a clean and sustainable ocean and blue economy in the Asia-Pacific region. [ 269 ] [ 270 ]
With increasing awareness of the detrimental effects of microplastics on the environment, groups are now advocating for the removal and ban of microplastics from various products. [ 271 ] One such campaign is "Beat the Microbead", which focuses on removing plastics from personal care products. [ 108 ] The Adventurers and Scientists for Conservation run the Global Microplastics Initiative, a project to collect water samples to provide scientists with better data about microplastic dispersion in the environment. [ 272 ] UNESCO has sponsored research and global assessment programs due to the trans-boundary issue that microplastic pollution constitutes. [ 273 ] These environmental groups will keep pressuring companies to remove plastics from their products in order to maintain healthy ecosystems. [ 274 ]
In 2018, China banned the import of recyclables from other countries, forcing those other countries to re-examine their recycling schemes. [ 275 ] The Yangtze River in China contributes 55% of all plastic waste going to the seas. Including microplastics, the Yangtze bears an average of 500,000 pieces of plastic per square kilometer. [ 276 ] Scientific American reported that China dumps 30% of all plastics in the ocean. [ 277 ]
In 2024, the Hong Kong government implemented the first phase of its plastic restriction regulation. Promotional videos have also been produced to encourage citizens to bring their own utensils when dining out, to refrain from using disposable utensils, and to bring their own shopping bags when shopping. Merchants are prohibited from providing related plastic products to customers. [ 278 ] [ 279 ] [ 280 ]
In the US, some states have taken action to mitigate the negative environmental effects of microplastics. [ 281 ] Illinois was the first US state to ban cosmetics containing microplastics. [ 145 ] At the federal level, the Microbead-Free Waters Act 2015 was enacted after being signed by President Barack Obama on 28 December 2015. The law bans "rinse-off" cosmetic products that perform an exfoliating function, such as toothpaste or face wash. It does not apply to other products such as household cleaners. The act took effect on 1 July 2017, with respect to manufacturing, and 1 July 2018, with respect to introduction or delivery for introduction into interstate commerce. [ 282 ] On 16 June 2020, California adopted a definition of 'microplastics in drinking water', setting the foundation for a long-term approach to studying their contamination and human health effects. [ 283 ]
On 25 July 2018, a microplastic reduction amendment was passed by the U.S. House of Representatives. [ 284 ] The legislation, as part of the Save Our Seas Act designed to combat marine pollution, aims to support the NOAA 's Marine Debris Program. In particular, the amendment is geared towards promoting NOAA's Great Lakes Land-Based Marine Debris Action Plan to increase testing, cleanup, and education around plastic pollution in the Great Lakes. [ 284 ] President Donald Trump signed the re-authorization and amendment bill into effect on 11 October 2018.
On 15 June 2018, the Japanese government passed a bill with the goal of reducing microplastic production and pollution, especially in aquatic environments. [ 285 ] Proposed by the Environment Ministry and passed unanimously by the Upper House, this is also the first bill to pass in Japan that is specifically targeted at reducing microplastic production, specifically in the personal care industry with products such as face wash and toothpaste. [ 285 ] This law is revised from previous legislation, which focused on removing plastic marine debris . It also focuses on increasing education and public awareness surrounding recycling and plastic waste. [ 285 ] The Environment Ministry has also proposed a number of recommendations for methods to monitor microplastic quantities in the ocean (Recommendations, 2018). [ 286 ] However, the legislation does not specify any penalties for those who continue manufacturing products with microplastics. [ 285 ]
The European Commission has noted the increased concern about the impact of microplastics on the environment. [ 287 ] In April 2018, the European Commission's Group of Chief Scientific Advisors commissioned a comprehensive review of the scientific evidence on microplastic pollution through the EU 's Scientific Advice Mechanism . [ 287 ] The evidence review was conducted by a working group nominated by European academies and delivered in January 2019. [ 288 ] A Scientific Opinion based on the SAPEA report was presented to the Commission in 2019, on the basis of which the commission will consider whether policy changes should be proposed at a European level to curb microplastic pollution. [ 289 ]
In January 2019, the European Chemicals Agency (ECHA) proposed to restrict intentionally added microplastics. [ 290 ]
The European Union participates with 10% of the global total, around 150 000 tonnes of microplastics each year. This is 200 grams per person per year, with significant regional variance in per-capita microplastic creation. [ 172 ] [ 291 ]
The European Commission's Circular Economy Action Plan sets out mandatory requirements for the recycling and waste reduction of key products e.g. plastic packaging. The plan starts the process to restrict addition of microplastics in products. It mandates measures for capturing more microplastics at all stages of the lifecycle of a product. E.g. the plan would examine different policies which aim to reduce release of secondary microplastics from tires and textiles. [ 292 ] The European Commission plans to update the Urban Waste Water Treatment Directive to further address microplastic waste and other pollution. They aim to protect the environment from industrial and urban waste water discharge. A revision to the EU Drinking Water Directive was provisionally approved to ensure microplastics are regularly monitored in drinking water. It would require countries must propose solutions if a problem is found. [ 9 ]
The REACH restriction on synthetic polymer microparticles entered into force on 17 October 2023. [ 293 ] [ 294 ]
The Environmental Protection (Microbeads) (England) Regulations 2017 ban the production of any rinse-off personal care products (such as exfoliants) containing microbeads. [ 295 ] This particular law denotes specific penalties when it is not obeyed. Those who do not comply are required to pay a fine. In the event that a fine is not paid, product manufacturers may receive a stop notice, which prevents the manufacturer from continuing production until they have followed regulation preventing the use of microbeads. Criminal proceedings may occur if the stop notice is ignored. [ 295 ]
Haiti has no collective system for waste collection and treatment, [ 296 ] and thus plastic is often disposed of in urban water evacuation canals, which then degrade to form microplastics. Due to tropical temperatures and average daily duration of 12 hours, [ clarify ] the plastics present in urban waterways could degrade more rapidly. Their discharge into Port-au-Prince Bay exposes this ecosystem to a number of environmental hazards pollutants contained in the waste, and to climatic hazards, particularly ocean acidification. [ 297 ]
On August 9, 2012, the Haitian government published a decree prohibiting the production, importation, marketing and use, of polyethylene bags and expanded polystyrene objects for foodstuffs. However, 14 Caribbean countries (more than a third) have banned single-use plastic bags and/or polystyrene containers.
On July 10, 2013, a second decree was published to once again prohibit "the importation, production or sale of expanded polystyrene articles for food use". In support of the second decree, the ministries of the Environment, Justice and Public Security, Trade and Industry as well as the Economy and Finance announced in a note published in January 2018 that specialists from the brigade will be deployed on the territory to force the application of the said decree. [ 297 ] | https://en.wikipedia.org/wiki/Microplastics |
The effects of microplastics on human health are a growing concern and an actively increasing area of research. Tiny particles known as microplastics , have been found in various environmental and biological matrices, including air, water, food, and human tissues. Microplastics, defined as plastic fragments smaller than 5 millimeters (mm), and even smaller particles such as nanoplastics, particles smaller than 1000 nanometers (nm) (0.001 mm or 1 micrometer [μm]), have raised concerns impacting human health. [ 1 ] [ 2 ] The pervasive presence of plastics in our environment has raised concerns about their long-term impacts on human health. While visible pollution caused by larger plastic items is well-documented, the hidden threat posed by nanoplastics remains underexplored. These particles originate from the degradation of larger plastics and are now found in various environmental matrices, including water, soil, and air. Given their minute size, nanoplastics can penetrate biological barriers and accumulate in human tissues, potentially leading to adverse health effects. [ 3 ] [ 4 ]
Plastics continue to accumulate in landfills and oceans, leading to pollution that negatively affects both human and animal health. Notably, microplastics and nanoplastics are now ubiquitous, infiltrating our food chain and water supplies. Studies indicate that humans ingest significant amounts of microplastics daily through food, especially seafood [ 5 ] and inhalation, with estimates ranging from 39,000 to 52,000 particles per person annually. [ 6 ] Additionally, the presence of MPs in human feces suggests widespread exposure and absorption. [ 7 ]
Understanding the sources and health effects of nanoplastics is crucial for developing effective public health policies. As plastics are an integral part of modern life, balancing their benefits with the associated health risks is essential. This research aims to provide evidence-based recommendations to mitigate the adverse health effects of nanoplastics, thereby informing future regulatory and policy decisions. The increasing presence of nanoplastics in the environment has raised concerns about their potential impacts on human health. Research has shown that nanoplastics can penetrate biological barriers, induce toxicity, and accumulate in organs, leading to various health issues. [ 8 ] NPs have been found in drinking water, food, and air, making human exposure ubiquitous. [ 9 ]
The major pathways of human exposure to micro- and nanoplastics (MNPs) are ingestion, inhalation, and dermal contact, with bioaccumulation varying based on particle size, composition, and physicochemical characteristics. Research suggests that MNPs above 150 μm typically remain confined to tissues and do not enter systemic circulation, whereas particles below 200 nm can breach cellular and tissue barriers, potentially reaching the bloodstream and other organs. [ 10 ] [ 11 ] [ 12 ] [ 13 ] This diversity in bioaccumulation pathways underscores the widespread yet nuanced risks of MNP exposure to human health.
Plastics are extensively used in the construction and renovation industry. [ 14 ] Airborne microplastic dust is produced during renovation , building, bridge and road reconstruction projects [ 15 ] and the use of power tools . [ 16 ]
Airborne MNPs originate from urban dust , synthetic fibers from textiles, rubber tires, and household plastic items. [ 17 ] [ 10 ] These airborne particles may become suspended in the air due to wave action in aquatic environments or the spread of wastewater treatment sludge on agricultural fields. [ 13 ] Once inhaled, these particles may lodge in the lungs or, through mucociliary clearance, be ingested and enter the digestive system. [ 18 ] [ 19 ] [ 20 ] [ 21 ] Airborne microplastics have been detected in urban atmospheres, with reports showing a fallout of 29–280 particles per square meter per day on an urban rooftop, underscoring the potential for routine exposure. [ 4 ] Annual inhalation exposure rates are estimated at around 39,000–52,000 microplastic particles, with studies highlighting the significant contributions from synthetic textiles and urban dust sources. [ 6 ]
These findings collectively suggest that MNPs may accumulate in multiple organ systems depending on the exposure route, potentially leading to long-term health consequences as their presence in human tissues becomes more pervasive over time.
Ingestion is one of the primary pathways of MNP exposure due to the omnipresence of these particles in food, beverages, and drinking water. Studies show that MNPs are detected in a variety of consumables, including drinking water, [ 22 ] [ 23 ] beer, [ 24 ] honey, sugar, [ 25 ] table salt, [ 26 ] [ 27 ] and even airborne particles that settle on food. [ 19 ] [ 20 ] [ 28 ] [ 13 ] Indirect ingestion includes toothpaste, face wash, scrubs, [ 29 ] [ 30 ] and soap. [ 31 ] [ 32 ]
Marine products are particularly concerning sources of ingestion-related exposure due to the accumulation of MNPs in aquatic environments. Fish, bivalves, and other seafood are frequently contaminated with MNPs ingested through water and food, and humans consuming these animals are thus directly exposed to microplastics embedded in tissue. The entire soft tissue of bivalves, for instance, is eaten by humans, which increases the direct transfer of MNPs. In a study along the Mediterranean coast of Turkey, 1822 microplastics were extracted from the stomachs and intestines of 1337 fish specimens, with fibers accounting for 70% of these particles. [ 13 ]
Contamination is further compounded by plastic packaging and storage materials, which can leach MNPs over time, leading to additional ingestion from common foods and drinks. [ 10 ] [ 33 ] Fecal sample analyses estimate a daily intake of approximately 203–332 MNPs, translating to an annual ingestion rate of around 39,000–52,000 particles. [ 6 ] [ 34 ] This suggests that daily MNP exposure from food and drink may be substantial, with significant implications for gastrointestinal and systemic health. Estimates of annual MNPs ingested and inhaled range from 74,000-121,000, which varies based on age, sex, and location. [ 6 ] If an individual ingests their required daily intake of water using only plastic-bottled water, then they would be ingesting an extra 90,000 MNPs. [ 6 ]
Recent studies have shown the presence of microplastics in breast milk, often leading to exposures in very young children. While it has already been established that chemicals [ 35 ] such as flame retardants [ 36 ] [ 37 ] [ 38 ] and pesticides [ 39 ] have been detected in breast milk, knowledge about microplastics is limited in comparison. A 2022 study [ 40 ] detected microplastics smaller than 5 mm in 75% of analyzed breast milk samples, raising concerns about infant exposure during critical developmental windows. [ 41 ] [ 42 ]
Exposure during developmental stages can lead to long lasting developmental defects or other issues later in life. While these detected levels were not above the currently established thresholds for unsafe levels, they show another possible route for microplastic ingestion. For some native populations in North Canada and people who live near industrial factories, pediatricians sometimes suggest that mothers not nurse their children [ 43 ] over fear of ingestion of microplastics and other potentially harmful chemicals. It has also been suggested that mothers should directly breastfeed their children instead of from a bottle. Studies have shown that pumping milk, freezing it in plastic bags, then subsequently heating it up will increase the contamination of microplastics in the milk. [ 44 ] Similar results have been seen from heating plastic reusable food containers in a microwave, showing the release of both micro- and nanoplastics. [ 45 ] It has been suggested that mothers try to avoid ingesting microplastics themselves, to try and avoid passing them onto their children through breastfeeding. Studies have shown that drinking water from plastic bottles has significantly greater detectable plastic content than tap water. [ 46 ]
These findings suggest that breastfeeding may inadvertently expose infants to endocrine-disrupting plastics, which could have lasting effects on growth and development. To mitigate these risks, pediatricians recommend reducing the use of plastic bottles and avoiding the heating or freezing of breast milk in plastic containers, as temperature fluctuations can increase MNP leaching.
Dermal exposure to MNPs occurs through contact with contaminated media like soil, water, and personal care products, including facial and body scrubs containing MNPs as exfoliants. [ 47 ] [ 48 ] [ 13 ] Although the skin generally acts as a barrier, conditions such as skin lesions or high exposure environments may allow for enhanced absorption of MNPs, particularly nanoplastics, which can penetrate the stratum corneum . Furthermore, workers handling production of textiles, garments, fabric, and other fiber products are constantly exposed through inhalation and direct dermal contact. [ 49 ] This highlights the need for further research into the effects MNPs have on human health, especially on industrial workers who have higher rates of exposure.
Studies on dermal exposure highlight the potential for these particles to enter systemic circulation, especially if the skin barrier is disrupted by wounds or conditions that increase permeability, like pores such as sweat glands and hair follicles. [ 10 ]
Incidental generation of MNPs is mechanical or environmental degradation or industrial processes such as plastic manufacturing (heating and chemical condensation) and intentional generation of MNPs occur during 3D printing .
The main route of workplace exposure is acute inhalation. [ 21 ] Workplace exposure can be high concentration and lasting the duration of a shift and thus short-term whereas exposure outside of work is at low concentration and long-term. [ 50 ] The concentration of worker exposure is orders of magnitude higher than the general population (e.g., 4×10 10 particles per cubic meter [m 3 ] from extrusion 3D printers [ 51 ] versus 50 particles per m 3 in the general environment [ 52 ] ).
High chronic exposure to aerosolized MNPs occur in the synthetic textile industry, the flocking industry, and the plastics industry, especially in vinyl chloride and polyvinyl chloride manufacturers. [ 53 ]
The potential health impacts of MPs vary based on factors, such as their particle sizes, shape, exposure time, chemical composition (enriched with heavy metals , polycyclic aromatic hydrocarbons [PAHs], etc.), surface properties, and associated contaminants. [ 80 ] [ 81 ]
Experimental and observational studies in mammals have shown that MPs and NPs exposure have the following adverse effects:
Despite growing concern and evidence, most epidemiologic studies have focused on characterizing exposures. Epidemiological studies directly linking MPs to adverse health effects in humans remain yet limited and research is ongoing to determine the full extent of potential harm caused by MPs and their long-term impact on human health. [ 95 ] [ 96 ]
MPs have been found in blood. [ 97 ]
As of April 2024, there is no established NIOSH Recommended Exposure Limit (REL) for MNPs due to limited data on exposure levels to adverse health effects, the absence of standardization to characterize the heterogeneity of MNPs by chemical composition and morphology, and difficulty in measuring airborne MNPs. [ 98 ] [ 99 ] Thus, safety measures focus on the hierarchy of controls for nanomaterials with good industrial hygiene to implement source emission control with local exhaust ventilation , air filtration, and non-ventilating engineering controls such as substitution with less hazardous materials, administrative controls , Personal Protective Equipment (PPE) for skin, and respiratory protection. [ 100 ]
Research from the U.S. National Institute of Occupational Safety and Health (NIOSH) Nanotechnology Research Center (NTRC) show local exhaust ventilation and High Efficiency Particulate Air (HEPA) filtration to be effective mitigation to theoretically filter 99.97% of nanoparticles down to 0.3 microns. [ 100 ] | https://en.wikipedia.org/wiki/Microplastics_and_human_health |
Microplastics are "synthetic solid particles or polymeric matrices, with regular or irregular shape and with size ranging from 1 μm to 5 mm, of either primary or secondary manufacturing origin, which are insoluble in water." [ 1 ] Microplastics are dangerous to human health [ citation needed ] and the environment because they contain harmful chemicals which leak into the air, water, and food.
Microplastics cause pollution by entering natural ecosystems from a variety of sources, including cosmetics , clothing , construction , renovation , food packaging , and industrial processes.
The term microplastics is used to differentiate from larger, non-microscopic plastic waste . Two classifications of microplastics are currently recognized. Primary microplastics include any plastic fragments or particles that are already 5.0 mm in size or less before entering the environment . These include microfibers from clothing, microbeads , plastic glitter [ 2 ] and plastic pellets (also known as nurdles). [ 3 ] [ 4 ] [ 5 ] Secondary microplastics arise from the degradation (breakdown) of larger plastic products through natural weathering processes after entering the environment. Such sources of secondary microplastics include water and soda bottles, fishing nets, plastic bags, microwave containers , tea bags and tire wear. [ 6 ] [ 5 ] [ 7 ] [ 8 ]
Both types are recognized to persist in the environment at high levels, particularly in aquatic and marine ecosystems , where they cause water pollution . [ 9 ]
Approximately 35% of all ocean microplastics come from textiles/clothing, primarily due to the erosion of polyester , acrylic , or nylon -based clothing, often during the washing process. [ 10 ] Microplastics also accumulate in the air and terrestrial ecosystems . Airborne microplastics have been detected in the atmosphere, as well as indoors and outdoors.
Because plastics degrade slowly (often over hundreds to thousands of years), [ 11 ] [ 12 ] microplastics have a high probability of ingestion, incorporation into, and accumulation in the bodies and tissues of many organisms. The toxic chemicals that come from both the ocean and runoff can also biomagnify up the food chain. [ 13 ] [ 14 ] In terrestrial ecosystems, microplastics have been demonstrated to reduce the viability of soil ecosystems. [ 15 ] [ 16 ] As of 2023, the cycle and movement of microplastics in the environment was not fully known. Microplastics in surface sample ocean surveys might have been underestimated as deep layer ocean sediment surveys in China found that plastics are present in deposition layers far older than the invention of plastics.
Microplastics are likely to degrade into smaller nanoplastics through chemical weathering processes, mechanical breakdown, and even through the digestive processes of animals. Nanoplastics are a subset of microplastics and they are smaller than 1 μm (1 micrometer or 1000 nm). Nanoplastics cannot be seen by the human eye. [ 17 ]
The term "microplastics" was introduced in 2004 by Professor Richard Thompson , a marine biologist at the University of Plymouth in the United Kingdom. [ 18 ] [ 19 ] [ 20 ] [ 21 ]
Microplastics are common in our world today. In 2014, it was estimated that there are between 15 and 51 trillion individual pieces of microplastic in the world's oceans, which was estimated to weigh between 93,000 and 236,000 metric tons. [ 22 ] [ 23 ] [ 24 ] Under the influence of sunlight, wind , waves and other factors, plastic degrades into small fragments known as microplastics, or even nanoplastics. [ 25 ]
Primary microplastics are small pieces of plastic that are purposefully manufactured. [ 26 ] They are usually used in facial cleansers and cosmetics , or in air blasting technology. In some cases, their use in medicine as vectors for drugs was reported. [ 27 ] Microplastic "scrubbers", used in exfoliating hand cleansers and facial scrubs, have replaced traditionally used natural ingredients , including ground almond shells, oatmeal , and pumice . Primary microplastics have also been produced for use in air-blasting technology. This process involves blasting acrylic , melamine , or polyester microplastic scrubbers at machinery, engines, and boat hulls to remove rust and paint. As these scrubbers are used repeatedly until they diminish in size and their cutting power is lost, they often become contaminated with heavy metals such as cadmium , chromium , and lead . [ 28 ] Although many companies have committed to reducing the production of microbeads , [ 29 ] there are still many bioplastic microbeads that also have a long degradation life cycle, for example in cosmetics. [ 30 ]
Secondary microplastics are small pieces of plastic derived from the physical breakdown and mechanical degradation of larger plastic debris, both at sea and on land. Over time, a culmination of physical, biological, and photochemical degradation, including photo-oxidation caused by sunlight exposure, can reduce the structural integrity of plastic debris to a size that is eventually undetectable to the naked eye. [ 31 ] This process of breaking down large plastic material into much smaller pieces is known as fragmentation. [ 28 ] It is considered that microplastics might further degrade to be smaller in size, although the smallest microplastic reportedly detected in the oceans in 2017 was 1.6 micrometres (6.3×10 −5 in) in diameter. [ 32 ] The prevalence of microplastics with uneven shapes suggests that fragmentation is a key source. [ 13 ] One study suggested that more microplastics might be formed from biodegradable polymer than from non-biodegradable polymer in both seawater and fresh water. [ 33 ] [ 34 ] [ additional citation(s) needed ]
"It's actually classified as a very high priority high contaminant by the EPA... when they litter or put something in a landfill, the plastic will break down into smaller and smaller particles. And eventually, they become microplastics... They're in the air, they're in the water, they're in the soil." – University of Tennessee professor Mike McKinney. [ 35 ]
Microplastic fibers enter the environment as a by-product during wear and tear and from the washing of synthetic clothing . [ 36 ] [ 7 ] Tires, composed partly of synthetic styrene-butadiene rubber, erode into tiny plastic and rubber particles as they are used and become dust particles. 2.0-5.0 mm plastic pellets, used to create other plastic products, enter ecosystems due to spillages and other accidents . [ 5 ]
A 2015 Norwegian Environment Agency review report about microplastics stated it would be beneficial to classify these sources as primary, as long as microplastics from these sources are added from human society since the "start of the pipe", and their emissions are inherently a result of human material and product use and not secondary to fragmentation in the nature. [ 37 ] [ incomplete short citation ]
Depending on the definition used, nanoplastics are less than 1 μm (i.e. 1000 nm) or less than 100 nm in size. [ 38 ] [ 39 ] Speculations over nanoplastics in the environment range from it being a temporary byproduct during the fragmentation of microplastics to it being an invisible environmental threat at potentially high and continuously rising concentrations. [ 40 ] The presence of nanoplastics in the North Atlantic Subtropical Gyre has been confirmed [ 41 ] and recent developments in Raman spectroscopy coupled with optical tweezers (Raman Tweezers) [ 42 ] as well as nano-fourier-transform infrared spectroscopy (nano- FTIR ) or atomic force infrared ( AFM-IR ) are promising answers in the near future regarding the nanoplastic quantity in the environment. Fluorescence could represent a unique tool for the identification and quantification of nanoplastics, since it allows the development of fast, easy, cheap, and sensitive methods. [ 43 ] However, the nanoplastic problem is complex and nanoscale properties as well as interaction with biomolecules need to be explored at the fundamental level with high spatial and temporal resolution. [ 44 ]
Nanoplastics are thought to be a risk to environmental and human health. [ 38 ] [ 45 ] Due to their small size, nanoplastics can cross cellular membranes and affect the functioning of cells. Nanoplastics are lipophilic and models show that polyethylene nanoplastics can be incorporated into the hydrophobic core of lipid bilayers. [ 46 ] Nanoplastics are also shown to cross the epithelial membrane of fish accumulating in various organs including the gallbladder, pancreas, and the brain. [ 47 ] [ 48 ] Nanoplastics are believed to cause interruptions in bone cell activities, causing improper bone formation. [ 49 ] [ 50 ] Little is known on adverse health effects of nanoplastics in organisms including humans. In zebrafish ( Danio rerio ), polystyrene nanoplastics can induce a stress response pathway altering glucose and cortisol levels, which is potentially tied to behavioral changes in stress phases. [ 51 ] In Daphnia , polystyrene nanoplastic can be ingested by the freshwater cladoceran Daphnia pulex and affect its growth and reproduction as well as induce stress defense, including the ROS production and MAPK-HIF-1/NF-κB-mediated antioxidant system. [ 52 ] [ 53 ] [ 54 ] Nanoplastics can also adsorb toxic chemical pollutants, such as antibiotics, which enable the selective association with antibiotic-resistant bacteria, resulting in the dissemination of nanoplastics and antibiotic-resistant bacteria by bacterivorous nematode Caenorhabditis elegans across the soil. [ 55 ]
The existence of microplastics in the environment is often established through aquatic studies. These include taking plankton samples, analyzing sandy and muddy sediments , observing vertebrate and invertebrate consumption, and evaluating chemical pollutant interactions. [ 56 ] Through such methods, it has been shown that there are microplastics from multiple sources in the environment. [ citation needed ]
Textiles, tires, and urban dust [ 57 ] account for over 80% of all microplastics in the seas and the environment. [ 9 ] Microplastic is also a type of airborne particulates and is found to prevail in air. [ 58 ] [ 59 ] [ 60 ] Paint appears as the largest source of microplastic leakage into the ocean and waterways (1.9 Mt/year), outweighing all other sources of microplastic leakage. [ 61 ] Microplastics could contribute up to 30% of the Great Pacific Garbage Patch polluting the world's oceans and, in many developed countries, are a bigger source of marine plastic pollution than the visible larger pieces of marine litter, according to a 2017 IUCN report. [ 5 ] Oceanic microplastics are a common source of heavy metals [ 62 ] due to the inclusion of coloring compounds containing chromium, manganese, cobalt, copper, zinc, zirconium, molybdenum, silver, tin, praseodymium, neodymium, erbium, tungsten, iridium, gold, lead, or uranium. [ 63 ]
Oral intake is the main pathway of human exposure to microplastics. [ 64 ] Microplastics exist in our daily necessities like drinking water, bottled water, seafood, salt, sugar, tea bags, milk, and so on. [ 65 ]
65 million microplastics are released into water sources everyday. [ 66 ] In 2017, more than eight million tons of plastics entered the oceans, greater than 33 times as much as that of the total plastics accumulated in the oceans by 2015. [ 67 ] One consequence of this is marine life consumption of microplastics. It is estimated that Europeans are exposed to about 11,000 particles/person/year of microplastics due to shellfish consumption. [ 68 ]
Microplastics may enter drinking-water sources in a number of ways: from surface run-off (e.g. after a rain event), to wastewater effluent (both treated and untreated), combined sewer overflows, industrial effluent, degraded plastic waste, and atmospheric deposition. [ 69 ] Surface run-off and wastewater effluent are recognized as the two main sources, but better data are required to quantify the sources and associate them with more specific plastic waste streams. Plastic bottles and caps that are used in bottled water may also be sources of microplastics in drinking-water. [ 69 ]
Microplastics may also have been widely distributed in soil, especially in agricultural systems. [ 70 ] They (especially with negative charge) can get into the water transport system of plants, and then move to the roots, stems, leaves, and fruits. [ 71 ] Once microplastics enter agricultural systems through sewage sludge, compost, and plastic mulching, they will cause food pollution, which may increase the risk of human exposure. [ 72 ]
Studies have shown that many synthetic fibers , such as polyester, nylon, acrylics, and spandex , can be shed from clothing and persist in the environment. [ 73 ] [ 74 ] [ 75 ] Each garment in a load of laundry can shed more than 1900 fibers of microplastics, with fleeces releasing the highest percentage of fibers, over 170% more than other garments. [ 76 ] [ 77 ] For an average wash load of 6 kilograms (13 lb), over 700,000 fibers could be released per wash. [ 78 ]
Washing machine manufacturers have also reviewed research into whether washing machine filters can reduce the amount of microfiber fibers that need to be treated by sewage treatment facilities. [ 79 ]
These microfibers have been found to persist throughout the food chain from zooplankton to larger animals such as whales. [ 5 ] The primary fiber that persists throughout the textile industry is polyester which is a cheap cotton alternative that can be easily manufactured. However, these types of fibers contribute greatly to the persistence to microplastics in terrestrial, aerial, and marine ecosystems. The process of washing clothes causes garments to lose an average of over 100 fibers per liter of water. [ 77 ] This has been linked with health effects possibly caused by the release of monomers , dispersive dyes, mordants , and plasticizers from manufacturing. The occurrence of these types of fibers in households has been shown to represent 33% of all fibers in indoor environments. [ 77 ]
Textile fibers have been studied in both indoor and outdoor environments to determine the average human exposure. The indoor concentration was found to be 1.0–60.0 fibers/m 3 , whereas the outdoor concentration was much lower at 0.3–1.5 fibers/m 3 . [ 80 ] The deposition rate indoors was 1586–11,130 fibers per day/m 3 which accumulates to around 190-670 fibers/mg of dust. [ 80 ] The largest concern with these concentrations is that it increases exposure to children and the elderly, which can cause adverse health effects. [ citation needed ]
Plastic containers can shed microplastics and nanoparticles into foods and beverages. [ 81 ]
In one study, 93% of the bottled water from 11 different brands showed microplastic contamination. Per liter, researchers found an average of 325 microplastic particles. [ 82 ] Of the tested brands, Nestlé Pure Life and Gerolsteiner bottles contained the most microplastic with 930 and 807 microplastic particles per liter (MPP/L), respectively. [ 82 ] San Pellegrino products showed the least quantity of microplastic densities. Compared to water from taps, water from plastic bottles contained twice as much microplastic. [ 82 ] Another study capable of detecting nanoplastics found 240,000 fragments per liter: 10% between 5 mm and 1 μm and 90% under 1 μm in diameter. [ 83 ] [ 84 ]
Some of the contamination likely comes from the process of bottling and packaging the water, [ 82 ] and possibly from filters used to purify the water. [ 83 ]
In 2020 researchers reported that polypropylene infant feeding bottles with contemporary preparation procedures were found to cause microplastics exposure to infants ranging from 14,600 to 4,550,000 particles per capita per day in 48 regions. Microplastics release is higher with warmer liquids and similar with other polypropylene products such as lunchboxes. [ 85 ] [ 86 ] [ 87 ] Unexpectedly, silicone rubber baby bottle nipples degrade over time from repeated steam sterilization, shedding micro- and nano-sized particles of silicone rubber, researchers found in 2021. They estimated that, using such heat-degraded nipples for a year, a baby will ingest more than 660,000 particles. [ 88 ] [ 89 ]
Common single-use plastic products, such as plastic cups, or even paper coffee cups that are lined with a thin plastic film inside, release trillions of microplastic- nanoparticles per liter into water during normal use. [ 91 ] [ 92 ] [ 93 ] Single-use plastic products enter aquatic environments [ 94 ] and "[l]ocal and statewide policies that reduce single-use plastics were identified as effective legislative actions that
communities can take to address plastic pollution". [ 95 ] [ 96 ]
Plastics are extensively used in the construction and renovation industry. [ 97 ] Airborne microplastic dust is produced during renovation , building, bridge and road reconstruction projects [ 98 ] and the use of power tools . [ 99 ]
Materials containing polyvinyl chloride (PVC), polycarbonate , polypropylene , and acrylic , can degrade overtime releasing microplastics. [ 97 ] During the construction process single use plastic containers and wrappers are discarded adding to plastic waste . [ 100 ] These plastics are difficult to recycle and end up in landfills where they break down over a long period of time causing potential leaching into the soil and the release of airborne microplastics. [ 101 ] [ 102 ] Airborne microplastic dust is also generated by deterioration of building materials [ 60 ]
Due to the environmental impact from plastic waste creation in the construction and renovation sectors waste management practices that address this issue are required. [ 103 ] [ 104 ] [ 105 ] Although many researchers have investigated the use of wastes, such as plastic, in the construction process in an effort to reduce waste and increase sustainability, construction is not an environmentally-friendly activity by nature. Efforts have been made to reduce plastic waste by adding it to concrete as agglomerates. However, one solution for resolving the problem from the large amount of plastic wastes generated could bring another serious problem of leaching of microplastics. The unknown part of this area is huge and needs prompt investigation. [ 104 ]
Around twenty percent of all plastics and seventy percent of all polyvinyl chloride (PVC) produced in the world each year are used by the construction industry. [ 106 ] [ 107 ] It is predicted that much more will be produced and used in the future. [ 106 ] "In Europe, approximately 20% of all plastics produced are used in the construction sector including different classes of plastics, waste and nanomaterials." [ 107 ]
Common types: [ 107 ]
Indirect use (packaging of construction materials) examples: [ 107 ]
Direct use (construction materials containing plastics) examples: [ 107 ]
Some companies have replaced natural exfoliating ingredients with microplastics, usually in the form of " microbeads " or "micro-exfoliates". These products are typically composed of polyethylene , a common component of plastics, but they can also be manufactured from polypropylene , polyethylene terephthalate (PET), and nylon . [ 108 ] They are often found in face washes, hand soaps , and other personal care products; the beads are usually washed into the sewage system immediately after use. Their small size prevents them from fully being retained by preliminary treatment screens at wastewater plants, thereby allowing some to enter rivers and oceans. [ 109 ] Wastewater treatment plants only remove an average of 95–99.9% of microbeads because of their small design. This leaves an average of 0–7 microbeads per litre being discharged. [ 110 ] Considering that the treatment plants of the world discharge 160 trillion liters of water per day, around 8 trillion microbeads are released into waterways every day. This number does not account for the sewage sludge that is reused as fertilizer after the waste water treatment that has been known to still contain these microbeads. [ 111 ]
Although many companies have committed to phasing out the use of microbeads in their products, there are at least 80 different facial scrub products that are still being sold with microbeads as a main component. [ 110 ] [ failed verification ] This contributes to the 80 metric tons of microbead discharge per year by the United Kingdom alone, which not only has a negative impact upon the wildlife and food chain, but also upon levels of toxicity, as microbeads have been proven to absorb dangerous chemicals such as pesticides and polycyclic aromatic hydrocarbons . [ 110 ] The restriction proposal by the European Chemicals Agency (ECHA) and reports by the United Nations Environment Programme ( UNEP ) and TAUW suggest that there are more than 500 microplastic ingredients that are widely used in cosmetics and personal care products. [ 112 ]
Even when microbeads are removed from cosmetic products, there are still harmful products being sold with plastics in them. For example, acrylate copolymers cause toxic effects for waterways and animals if they are polluted. [ 113 ] Acrylate copolymers also can emit styrene monomers when used in body products which increases a person's chances of cancer. [ 114 ] Countries like New Zealand which have banned microbeads often pass over other polymers such as acrylate copolymers, which can be just as toxic to people and the environment. [ 115 ]
After the Microbead-Free Waters Act of 2015 , the use of microbeads in toothpaste and other rinse-off cosmetic products has been discontinued in the US, [ 116 ] however since 2015 many industries have instead shifted toward using FDA -approved "rinse-off" metallized-plastic glitter as their primary abrasive agent . [ 117 ] [ 118 ] [ 119 ]
Recreational and commercial fishing , marine vessels , and marine industries are all sources of plastic that can directly enter the marine environment, posing a risk to biota both as macroplastics, and as secondary microplastics following long-term degradation. Marine debris observed on beaches also arises from beaching of materials carried on inshore and ocean currents. Fishing gear is a form of plastic debris with a marine source. Discarded or lost fishing gear, including plastic monofilament line and nylon netting (sometimes called ghost nets ), is typically neutrally buoyant and can, therefore, drift at variable depths within the oceans. Various countries have reported that microplastics from the industry and other sources have been accumulating in different types of seafood. In Indonesia, 55% of all fish species had evidence of manufactured debris similar to America which reported 67%. [ 120 ] However, the majority of debris in Indonesia was plastic, while in North America the majority was synthetic fibers found in clothing and some types of nets. The implication from the fact that fish are being contaminated with microplastic is that those plastics and their chemicals will bioaccumulate in the food chain. [ 121 ]
One study analyzed the plastic-derived chemical called polybrominated diphenyl ethers (PBDEs) in the stomachs of short-tailed shearwaters . It found that one-fourth of the birds had higher-brominated congeners that are not naturally found in their prey. However, the PBDE got into the birds' systems through plastic that was found in the stomachs of the birds. It is therefore not just the plastics that are being transferred through the food chain but the chemicals from the plastics as well. [ 122 ]
The manufacture of plastic products uses granules and small resin pellets as their raw material. In the United States, production increased from 2.9 million pellets in 1960 to 21.7 million pellets in 1987. [ 123 ] In 2019, plastic world production was 368 million tonnes; 51% were produced in Asia. China, the world's largest producer, created 31% of the world total. [ 124 ] Through accidental spillage during land or sea transport, inappropriate use as packing materials , and direct outflow from processing plants, these raw materials can enter aquatic ecosystems . In an assessment of Swedish waters using an 80 μm mesh, KIMO Sweden found typical microplastic concentrations of 150–2,400 microplastics per m 3 ; in a harbor adjacent to a plastic production facility, the concentration was 102,000 per m 3 . [ 28 ]
Many industrial sites in which convenient raw plastics are frequently used are located near bodies of water. If spilled during production, these materials may enter the surrounding environment, polluting waterways. [ 37 ] "More recently, Operation Cleansweep, a joint initiative of the American Chemistry Council and Society of the Plastics Industry , is aiming for industries to commit to zero pellet loss during their operations". [ 28 ] Overall, there is a significant lack of research aimed at specific industries and companies that contribute to microplastics pollution.
Since the emergence of the COVID-19 pandemic , the usage of medical face masks has sharply increased to reach approximately 89 million masks each. [ 125 ] Single use face masks are made from polymers, such as polypropylene , polyurethane , polyacrylonitrile , polystyrene , polycarbonate , polyethylene , or polyester . The increase in production, consumption, and littering of face masks was added to the list of environmental challenges, due to the addition of plastic particles waste in the environment. After degrading, disposable face masks could break down into smaller size particles (under 5mm) emerging a new source of microplastic. [ 126 ] A single surgical weathered face mask may release up to 173,000 fibers/ day. [ 125 ]
A report made in February 2020 by Oceans Asia, an organization committed to advocacy and research on marine pollution, confirms "the presence of face masks of different types and colors in an ocean in Hong Kong". [ 126 ]
Sewage treatment plants, also known as wastewater treatment plants (WWTPs), remove contaminants from wastewater, primarily from household sewage, using various physical, chemical, and biological processes. [ 127 ] Most plants in developed countries have both primary and secondary treatment stages. In the primary stage of treatment, physical processes are employed to remove oils, sand, and other large solids using conventional filters, clarifiers , and settling tanks. [ 128 ] Secondary treatment uses biological processes involving bacteria and protozoa to break down organic matter. Common secondary technologies are activated sludge systems, trickling filters , and constructed wetlands . [ 128 ] The optional tertiary treatment stage may include processes for nutrient removal ( nitrogen and phosphorus ) and disinfection . [ 128 ]
Microplastics have been detected in both the primary and secondary treatment stages of the plants. A groundbreaking 1998 study suggested that microplastic fibers would be a persistent indicator of sewage sludges and wastewater treatment plant outfalls. [ 129 ] A study estimated that about one particle per liter of microplastics are being released back into the environment, with a removal efficiency of about 99.9%. [ 127 ] [ 130 ] [ 131 ] A 2016 study showed that most microplastics are actually removed during the primary treatment stage where solid skimming and sludge settling are used. [ 127 ] When these treatment facilities are functioning properly, the contribution of microplastics into oceans and surface water environments from WWTPs is not disproportionately large. [ 127 ] [ 132 ] Many studies show that while wastewater treatment plants certainly reduce the microplastic load on waterways, with current technological developments they are not able to clean the waters fully of this pollutant. [ 133 ] [ 134 ]
Sewage sludge is used for soil fertilizer in some countries, which exposes plastics in the sludge to the weather, sunlight, and other biological factors, causing fragmentation. As a result, microplastics from these biosolids often end up in storm drains and eventually into bodies of water. [ 135 ] In addition, some studies show that microplastics do pass through filtration processes at some WWTPs. [ 28 ] According to a study from the UK, samples taken from sewage sludge disposal sites on the coasts of six continents contained an average one particle of microplastic per liter. A significant amount of these particles was of clothing fibers from washing machine effluent. [ 77 ]
Wear and tear from tires significantly contributes to the flow of (micro-)plastics into the environment. Estimates of emissions of microplastics to the environment in Denmark are between 5,500 and 14,000 tonnes (6,100 and 15,400 tons) per year. Secondary microplastics (e.g. from car and truck tires or footwear) are more important than primary microplastics by two orders of magnitude. The formation of microplastics from the degradation of larger plastics in the environment is not accounted for in the study. [ 136 ]
The estimated per capita emission ranges from 0.23 to 4.7 kg/year, with a global average of 0.81 kg/year. The emissions from car tires (wear reaching 100%) are substantially higher than those of other sources of microplastics, e.g., airplane tires (2%), artificial turf (wear 12–50%), brakes (wear 8%), and road markings (wear 5%). In the case of road markings, recent field study indicated that they were protected by a layer of glass beads and their contribution was only between 0.1 and 4.3 g/person/year, [ 137 ] which would constitute approximately 0.7% of all of the secondary microplastics emissions; this value agrees with some emissions estimates. [ 138 ] [ 139 ] Emissions and pathways depend on local factors like road type or sewage systems. The relative contribution of tire wear and tear to the total global amount of plastics ending up in our oceans is estimated to be 5–10%. In air, 3–7% of the particulate matter (PM 2.5 ) is estimated to consist of tire wear and tear, indicating that it may contribute to the global health burden of air pollution which has been projected by the World Health Organization at 3 million deaths in 2012. Pollution from tire wear and tear also enters the food chain, but further research is needed to assess human health risks. [ 140 ]
Shipping has significantly contributed to marine pollution . Some statistics indicate that in 1970, commercial shipping fleets around the world dumped over 23,000 tons of plastic waste into the marine environment. In 1988, an international agreement ( MARPOL 73/78 , Annex V) prohibited the dumping of waste from ships into the marine environment. In the United States, the Marine Plastic Pollution Research and Control Act of 1987 prohibits discharge of plastics in the sea, including from naval vessels. [ 141 ] [ 142 ] However, shipping remains a dominant source of plastic pollution , having contributed around 6.5 million tons of plastic in the early 1990s. [ 143 ] [ 144 ] Research has shown that approximately 10% of the plastic found on the beaches in Hawaii are nurdles. [ 145 ] In one incident on 24 July 2012, 150 tonnes of nurdles and other raw plastic material spilled from a shipping vessel off the coast near Hong Kong after a major storm. This waste from the Chinese company Sinopec was reported to have piled up in large quantities on beaches. [ 37 ] While this is a large incident of spillage, researchers speculate that smaller accidents also occur and further contribute to marine microplastic pollution. [ 37 ]
Airborne microplastics have been detected in the atmosphere , as well as indoors and outdoors. Microplastic can be atmospherically transported to remote areas by the wind. [ 146 ] A 2017 study found indoor airborne microfiber concentrations between 1.0 and 60.0 microfibers per cubic meter (33% of which were found to be microplastics). [ 147 ] Another study looked at microplastic in the street dust of Tehran and found 2,649 particles of microplastic within 10 samples of street dust, with ranging samples concentrations from 83 particle – 605 particles (±10) per 30.0 g of street dust. [ 148 ] Microplastics and microfibers were also found in snow samples, [ 149 ] and high up in "clean" air in high mountains at vast distances from their source. [ 150 ] [ 151 ] Much like freshwater ecosystems and soil, more studies are needed to understand the full impact and significance of airborne microplastics. [ 152 ]
A growing concern regarding plastic pollution in the marine ecosystem is the use of microplastics. Microplastics are beads of plastic less than 5 millimeters wide, [ 153 ] and they are commonly found in hand soaps, face cleansers, and other exfoliators. When these products are used, the microplastics go through the water filtration system and into the ocean, but because of their small size they are likely to escape capture by the preliminary treatment screens on wastewater plants. [ 154 ] These beads are harmful to the organisms in the ocean, especially filter feeders, because they can easily ingest the plastic and become sick. The microplastics are such a concern because it is difficult to clean them up due to their size, so humans can try to avoid using these harmful plastics by purchasing products that use environmentally safe exfoliates.
Plastic pollution has previously been recorded in Antarctic surface waters and sediments as well as in the Arctic sea ice , [ 157 ] but in 2009, for the first time, plastic was found in Antarctic sea ice, with 96 microplastic particles from 14 different types of polymers in an ice core sampled from east Antarctica . [ 158 ] Relatively large particle sizes in Antarctic sea ice suggest local pollution sources.
Microplastics have been widely detected in the world's aquatic environments. [ 159 ] [ 160 ] The first study on microplastics in freshwater ecosystems was published in 2011 that found an average of 37.8 fragments per square meter of Lake Huron sediment samples. Additionally, studies have found MP (microplastic) to be present in all of the Great Lakes with an average concentration of 43,000 MP particle km −2 . [ 161 ] Microplastics have also been detected in freshwater ecosystems outside of the United States, for example in 2019 study conducted in Poland showed that microplastic was present in all 30 studied lakes of the Masurian Lakeland with density from 0.27 to 1.57 particles per liter. [ 162 ] In Canada, a three-year study found a mean microplastic concentration of 193,420 particles km −2 in Lake Winnipeg . None of the microplastics detected were micro-pellets or beads and most were fibers resulting from the breakdown of larger particles, synthetic textiles, or atmospheric fallout. [ 163 ] The highest concentration of microplastic ever discovered in a studied freshwater ecosystem was recorded in the Rhine river at 4000 MP particles kg −1 . [ 164 ]
Researchers from Western Carolina University, Highlands Biological Station, and Virginia Tech found microplastics in Richland Creek watershed in Western North Carolina. 90% of the microplastics were fibers, largely attributed to clothing, city runoff, and atmospheric deposition. [ 165 ] [ 166 ] [ 167 ]
A substantial portion of microplastics are expected to end up in the world's soil , yet very little research has been conducted on microplastics in soil outside of aquatic environments. [ 168 ] In wetland environments microplastic concentrations have been found to exhibit a negative correlation with vegetation cover and stem density. [ 159 ] There exists some speculation that fibrous secondary microplastics from washing machines could end up in soil through the failure of water treatment plants to completely filter out all of the microplastic fibers. Furthermore, geophagous soil fauna, such as earthworms, mites, and collembolans could contribute to the amount of secondary microplastic present in soil by converting consumed plastic debris into microplastic via digestive processes. Further research, however, is needed. There is concrete data linking the use of organic waste materials to synthetic fibers being found in the soil; but most studies on plastics in soil merely report its presence and do not mention origin or quantity. [ 5 ] [ 169 ] Controlled studies on fiber-containing land-applied wastewater sludges (biosolids) applied to soil reported semiquantitative [ clarification needed ] recoveries of the fibers a number of years after application. [ 170 ]
A 2015 review of 15 brands of table salts commercially available in China found microplastics were much more prevalent in sea salts compared to lake, rock, or well salts, attributing this to sea salts being contaminated by ocean water pollution while the rock/well salts were more likely contaminated during the production stages of collecting, wind drying, and packaging. [ 171 ] According to a 2017 estimate, a person who consumes seafood will ingest 11,000 bits of microplastics per year. A 2019 study found a kilo of sugar had 440 microplastic particles, a kilo of salt contained 110 particles, and a litre of bottled water contained 94 particles. [ 172 ] [ 173 ] [ 174 ]
The composition of microplastics are complex. A study in 2023 tested some fish species and found that "about 80% of the MPs detected were fibrous in shape and were made of polyethylene (25%), polyester (20%), and polyamide (10%). Most microplastic particles observed were black (61%) or blue (27%) in color." [ 175 ]
Microplastics contain two different types of chemicals. The first are additives and polymeric raw materials such as monomers or oligomers. Additives are chemicals intentionally added during plastic production to give plastic qualities like color and transparency and to enhance the performance of plastic products to improve both the resistance to degradation by ozone, temperature, light radiation, mold, bacteria and humidity, and mechanical, thermal and electrical resistance. Examples of additives in microplastics are inert or reinforcing fillers, plasticizers, antioxidants, UV stabilizers, lubricants, dyes and flame-retardants [ 176 ] The second type of chemicals are ones absorbed from the surrounding environment.
In 2008, an International Research Workshop at the University of Washington at Tacoma concluded that microplastics were a problem in the marine environment, based on their documented occurrence, the long residence times of these particles, their likely buildup in the future, and their demonstrated ingestion by marine organisms . [ 177 ]
According to a comprehensive review of scientific evidence published by the European Union 's Scientific Advice Mechanism in 2019, microplastics were present in every part of the environment. While there was no evidence of widespread ecological risk from microplastic pollution yet, risks were likely to become widespread within a century if pollution continued at its current rate. [ 152 ]
As of 2020 microplastics had been detected in freshwater systems including marshes, streams, ponds, lakes, and rivers in Europe, North America, South America, Asia, and Australia. [ 159 ] [ 178 ] Samples collected across 29 Great Lakes tributaries from six states in the United States were found to contain plastic particles, 98% of which were microplastics ranging in size from 0.355mm to 4.75mm. [ 179 ] Likewise, they have been found in high mountains, at great distances from their source. [ 150 ]
Deep layer ocean sediment surveys in China (2020) show the presence of plastics in deposition layers far older than the invention of plastics, leading to suspected underestimation of microplastics in surface sample ocean surveys. [ 180 ]
In September 2021 Hurricane Larry deposited, during the storm peak, 113,000 particles/m 2 /day as it passed over Newfoundland , Canada. Back-trajectory modelling and polymer type analysis indicated that those microplastics may have been ocean-sourced as the hurricane traversed the North Atlantic garbage patch of the North Atlantic Gyre . [ 181 ]
As of 2023 there was rapid growth of microplastic pollution research, with marine and estuarine environments most frequently studied. Researchers have called for better sharing of research data that might lead to effective solutions. [ 182 ]
A 2023 study formally identified plasticosis as a fibrotic disease caused by plastic ingestion, distinguishing it from general physical damage by detailing the chronic tissue remodeling and inflammation it induces in seabird digestive systems. [ 183 ]
Consequences of plastic degradation and pollution release over long term have mostly been overlooked. The large amounts of plastic in the environment, exposed to degradation, with years of decay and release of toxic compounds to follow was referred to as toxicity debt . [ 40 ]
Microplastics are inconspicuous, being less than 5 mm. Particles of this size are available to every species, enter the food chain at the bottom, and become embedded in animal tissue.
Micro- and nanoplastics can become embedded in animals' tissue through ingestion or respiration. The initial demonstration of bioaccumulation of these particles in animals was conducted under controlled conditions by exposing them to high concentrations of microplastics over extended periods, accumulating these particles in their gut and gills due to ingestion and respiration, respectively. Various annelid species, such as deposit-feeding lugworms ( Arenicola marina ), have been shown to accumulate microplastics embedded in their gastrointestinal tract . Similarly, many crustaceans , like the shore crab Carcinus maenas , have been seen to integrate microplastics into both their respiratory and digestive tracts. [ 74 ] [ 184 ] [ 185 ] Plastic particles are often mistaken by fish for food, which can block their digestive tracts, sending incorrect feeding signals to the brains of the animals. [ 9 ] However, research in 2021 revealed that fish ingest microplastics inadvertently rather than intentionally. [ 186 ] The first occurrence of bioaccumulation of micro and nanoplastics in wild animals was documented in the skin mucosa of salmon, and it was attributed to the resemblance between nanoplastics and the outer shell of the viruses that the mucosa traps. [ 187 ] This discovery was entirely serendipitous, as the research team had developed a detailed molecular separation process for the components of fish skin with the primary objective of isolating chitin from a vertebrate for the first time. [ 188 ]
A study done at the Argentinean coastline of the Rio de la Plata estuary , found the presence of microplastics in the guts of 11 species of coastal freshwater fish. These 11 species of fish represented four different feeding habits: detritivore , planktivore , omnivore and ichthyophagous . [ 189 ] This study is one of the few so far to show the ingestion of microplastics by freshwater organisms.
It can take up to 14 days for microplastics to pass through an animal (as compared to a normal digestion period of 2 days), but enmeshment of the particles in animals' gills can prevent elimination entirely. [ 184 ] When microplastic-laden animals are consumed by predators, the microplastics are then incorporated into the bodies of higher trophic-level feeders. For example, scientists have reported plastic accumulation in the stomachs of lantern fish which are small filter feeders and are the main prey for commercial fish like tuna and swordfish . [ 190 ] [ 191 ] Microplastics also absorb chemical pollutants that can be transferred into the organism's tissues. [ 192 ] Small animals are at risk of reduced food intake due to false satiation and resulting starvation or other physical harm from the microplastics. [ citation needed ]
Zooplankton ingest microplastics beads (1.7–30.6 μm) and excrete fecal matter contaminated with microplastics. Along with ingestion, the microplastics stick to the appendages and exoskeleton of the zooplankton. [ 3 ] Zooplankton, among other marine organisms, consume microplastics because they emit similar infochemicals, notably dimethyl sulfide , just as phytoplankton do. [ 193 ] [ verification needed ] [ 194 ] Plastics such as high-density polyethylene (HDPE), low-density polyethylene (LDPE), and polypropylene (PP) produce dimethyl sulfide odors. [ 193 ] These types of plastics are commonly found in plastic bags, food storage containers, and bottle caps. [ 195 ] Green and red filaments of plastics are found in the planktonic organisms and in seaweeds. [ 196 ]
Bottom feeders , such as benthic sea cucumbers , who are non-selective scavengers that feed on debris on the ocean floor , ingest large amounts of sediment. It has been shown that four species of sea cucumber ( Thyonella gemmate , Holothuria floridana , H. grisea and Cucumaria frondosa ) ingested between 2- and 20-fold more PVC fragments and between 2- and 138-fold more nylon line fragments (as much as 517 fibers per organism) based on plastic-to-sand grain ratios from each sediment treatment. These results suggest that individuals may be selectively ingesting plastic particles. This contradicts the accepted indiscriminate feeding strategy of sea cucumbers, and may occur in all presumed non-selective feeders when presented with microplastics. [ 197 ]
Bivalves , important aquatic filter feeders, have also been shown to ingest microplastics and nanoplastics. [ 198 ] Upon exposure to microplastics, bivalve filtration ability decreases. [ 199 ] Multiple cascading effects occur as a result, such as immunotoxicity and neurotoxicity . [ 200 ] [ 201 ] [ 202 ] Decreased immune function occurs due to reduced phagocytosis and NF-κB gene activity. [ 200 ] [ 202 ] Impaired neurological function is a result of the inhibition of ChE and suppression of neurotransmitter regulatory enzymes. [ 202 ] When exposed to microplastics, bivalves also experience oxidative stress , indicating an impaired ability to detoxify compounds within the body, which can ultimately damage DNA. [ 201 ] Bivalve gametes and larvae are also impaired when exposed to microplastics. Rates of developmental arrest, and developmental malformities increase, while rates of fertilization decrease. [ 198 ] [ 203 ] When bivalves have been exposed to microplastics as well as other pollutants such as POPs , mercury or hydrocarbons in lab settings, toxic effects were shown to be aggravated. [ 199 ] [ 200 ] [ 201 ]
Not only fish and free-living organisms can ingest microplastics. Some corals such as Pocillopora verrucosa have also been found to ingest microplastics. [ 204 ] Scleractinian corals , which are primary reef-builders, have been shown to ingest microplastics under laboratory conditions. [ 205 ] Researchers from Japan and Thailand investigating microplastics in coral have found that all three parts of the coral anatomy (surface mucus, tissue, and skeleton) contain microplastics. [ 206 ] According to recent study, mall-polyp corals (P. cf. damicornis and P. lutea) demonstrated a higher degree of MP accumulation than the large-polyp corals. [ 207 ] The interplay of precipitation, wind patterns, and ocean currents considerably influences MP abundance in corals by increasing the exposure of corals to elevated MP concentrations. Additionally, since the reef site was situated near a large rock formation, it experienced strong water movements due to constant wave action. MPs deposited in skeletons are likely to be preserved on a millennium timescale, even if the corals die. Thus, given the extensive presence of coral reefs worldwide, corals can accumulate a considerable number of MPs, thereby acting as a sink for ocean plastics. [ 208 ]
While the effects of ingestion on these corals has not been studied, corals can easily become stressed and bleach. Microplastics have been shown to stick to the exterior of the corals after exposure in the laboratory. [ 205 ] The adherence to the outside of corals can potentially be harmful, because corals cannot handle sediment or any particulate matter on their exterior and slough it off by secreting mucus, expending energy in the process, increasing the likelihood of mortality. [ 209 ] The thermodynamic properties, development, and nutrition of corals are thought to be negatively impacted by the engaged consumption and detached exterior bond strength of MPs. This could result in decreased feed intake, decreased photosynthetic efficiency, altered metabolic rates, decreased bone calcification, and even skin chlorination and necrotizing. [ 210 ]
Marine biologists in 2017 discovered that three-quarters of the underwater seagrass in the Turneffe Atoll off the coast of Belize had microplastic fibers, shards, and beads stuck to it. The plastic pieces had been overgrown by epibionts (organisms that naturally stick themselves to seagrass). Seagrass is part of the barrier reef ecosystem and is fed on by parrotfish , which in turn are eaten by humans. These findings, published in Marine Pollution Bulletin, may be "the first discovery of microplastics on aquatic vascular plants... [and] only the second discovery of microplastics on marine plant life anywhere in the world." [ 211 ]
Research published in 2023 demonstrated that microplastic exposure impaired the cognitive performance of hermit crabs, which could potentially impact their survivability. [ 212 ]
Microplastics can affect the soil ecosystem and stunt the growth of terrestrial plants due to the increased uptake of toxic metals such as cadmium. [ 213 ] [ 214 ] [ 215 ] [ 216 ] Microplastics can reduce weight of earthworms . [ 217 ]
Microbes also live on the surface of microplastics, and can form a biofilm which, according to a 2019 study, [ 218 ] has a unique structure and possesses a special risk, because microplastic biofilms have been proven to provide a novel habitat for colonization that increases overlap between different species, thus spreading pathogens and antibiotic resistant genes [ 219 ] through horizontal gene transfer . Then, due to rapid movement through waterways, these pathogens can be moved from their origin to another location where a specific pathogen may not be naturally present, spreading potential disease. [ 218 ] There is concern microplastic pollutants may act as a vector for antibiotic resistant genes and bacteria. [ 220 ] Clinically important bacterial genus like Eggerthella were more than three times enriched on riverine microplastics compared to water. [ 219 ]
In 2019, the first European records of microplastic items in amphibians' stomach content was reported in specimens of the common European newt ( Triturus carnifex ) . This also represented the first evidence for Caudata worldwide, highlighting that the emerging issue of plastics is a threat even in remote high-altitude environments. [ 221 ] The microplastic has also been found in common blackbirds ( Turdus merula ) and song thrushes ( Turdus philomelos ) which shows a ubiquity of microplastics in terrestrial environments. [ 222 ]
In 2023, plasticosis , a new disease caused solely by plastics, was discovered in seabirds who had scarred digestive tracts from ingesting plastic waste. [ 223 ] "When birds ingest small pieces of plastic, [...]it inflames the digestive tract. Over time, the persistent inflammation causes tissues to become scarred and disfigured, affecting digestion, growth and survival." [ 224 ]
Plastic particles may highly concentrate and transport synthetic organic compounds (e.g. persistent organic pollutants and emerging organic contaminants), commonly present in the environment and ambient seawater, on their surface through adsorption . [ 225 ] Microplastics can act as carriers for the transfer of POPs from the environment to organisms, also termed as the Trojan Horse effect . [ 226 ] [ 143 ] [ 144 ] Recent articles have also shown that microplastics can sorb emerging organic chemicals such as pharmaceuticals and personal care products. [ 227 ] [ 228 ] The sorption potential is affected by water matrix, pH, ionic strength and aging of microparticles. [ 227 ]
Additives added to plastics during manufacture may leach out upon ingestion, potentially causing serious harm to the organism. Endocrine disruption by plastic additives may affect the reproductive health of humans and wildlife alike. [ 144 ]
Microplastics can increase the stability of breaking waves or sea foam , potentially affecting sea albedo or atmosphere-ocean gas exchange. [ 229 ] Microplastics in the ocean may re-enter the atmosphere via sea spray . [ 230 ]
Although the impacts of microplastics on human health are still being tested, their possible effects can be studied through human absorption models of nanomaterials that are produced by various industrial production processes. [ 231 ] Several in vitro and in vivo studies have shown that micro- and nanoplastics were able to cause serious impacts on the human body, including physical stress and damage, apoptosis, necrosis, inflammation, oxidative stress and immune responses. [ 232 ] Microplastic pollution has been associated with various adverse human health conditions, including respiratory disease and inflammation , but it was not known whether this was a causative effect. [ 233 ]
Microplastics often contain chemical additives like phthalates and bisphenol A (BPA), which are known endocrine-disrupting chemicals. Microplastics and their additives can disrupt the hypothalamic-pituitary-gonadal (HPG) axis, a critical regulator of male reproductive function [ 234 ]
A study from Harvard found that microplastics have been linked to "inflammation, cell death, lung and liver effects, changes in the gut microbiome, and altered lipid and hormone metabolism." [ 235 ]
A number of studies have concluded that microplastics create inflammatory effects in the human body. An in vitro study found that ultrafine particles composed of low-toxicity material, such as polystyrene, have proinflammatory activity as a consequence of their large surface area. [ 236 ] Another study found pro-inflammatory factors and debris in human joints from polyethylene components used as prostheses, for example knee and hip replacements. [ 237 ]
In vitro studies have also shown that different polystyrene nanoparticles can induce oxidative stress, apoptosis and autophagic cell death in cell context-dependent manner. [ 238 ] Despite these toxic effects, no obvious severe toxicity was observed in liver, duodenum, ileum, jejunum, large intestine, testes, lungs, heart, spleen, and kidneys of mice following oral exposure of a mixture of microplastics. [ 239 ]
Recent studies have revealed that microplastics and nanoplastics can impair cellular metabolism in both in vitro and in vivo models. [ 238 ] After exposure to negatively charged carboxylated polystyrene nanoparticles measuring 20 nm, basolateral K+ ion channels were found to be activated in human lung cells. The nanoplastic particles caused persistent and concentration-dependent increases in short-circuit currents by the activation of the ion channels and the stimulation of Cl− and HCO3− ion efflux. [ 240 ] Furthermore, 30 nm polystyrene nanoparticles induced large vesicle-like structures in the endocytic route in macrophages and human cancer cell lines A549, HepG-2, and HCT116. As a result, vesicle transport and the distribution of proteins involved in cytokinesis are blocked, thus stimulating the formation of binucleated cells. [ 241 ]
Some of the suggested dust control measures include "lining cutting areas with tarps, cutting inside a protective tent, and using vacuum bags on power tool" when cutting materials like Trex and Azek . The cost of these measures is low." [ 99 ] Street sweeping may also inhibited the spread of pollutants by gathering significant amounts of dirty materials from the extensive construction, renovation and reconstruction projects of road tunnels, bridges, roads and buildings. [ 104 ]
Some researchers have proposed incinerating plastics to use as energy, which is known as energy recovery. As opposed to losing the energy from plastics into the atmosphere in landfills , this process turns some of the plastics back into energy that can be used. However, as opposed to recycling, this method does not diminish the amount of plastic material that is produced. Therefore, recycling plastics is considered a more efficient solution. [ 145 ]
Biodegradation is another possible solution to large amounts of microplastic waste. In this process, microorganisms consume and decompose synthetic polymers by means of enzymes. [ 242 ] These plastics can then be used in the form of energy and as a source of carbon once broken down. The microbes could potentially be used to treat sewage wastewater, which would decrease the amount of microplastics that pass through into the surrounding environments. [ 242 ]
Efficient removal of microplastics via waste water treatment plants is critical to prevent the transfer of microplastics from society to natural water systems. The captured microplastics in the treatment plants become part of the sludge produced by the plants. The problem is that this sludge is often used as farm fertilizer meaning the plastics enter waterways through runoff. [ 9 ]
Fionn Ferreira , winner of the 2019 Google Science Fair , is developing a device for the removal of microplastic particles from water using a ferrofluid . [ 243 ]
The Ocean Cleanup , a Dutch foundation, has developed various proposals, with the stated aim of "clearing 90% of the ocean's microplastics". [ 244 ] [ 245 ] [ 246 ] The project has been met with widespread criticism from oceanographers and plastic pollution experts, despite positive news articles. [ 247 ] [ 248 ] [ 249 ] It has been dismissed by almost all microplastics experts as unlikely to have any impact on the microplastics issue. Some of the reasons for this are it only targets plastics larger than 2 cm (this is larger than the criteria for a microplastic), is infeasible from an engineering standpoint and likely to fail rapidly, and it only captures plastic from the top 3m of depth (most plastic circulates much deeper than this. [ 247 ]
In addition, some bacteria have adapted to eat plastic, and some bacteria species have been genetically modified to eat (certain types of) plastics. [ 250 ] Other than degrading microplastics, microbes had been engineered in a novel way to capture microplastics in their biofilm matrix from polluted samples for easier removal of such pollutants. [ 251 ] The microplastics in the biofilms can then be released with an engineered 'release' mechanism via biofilm dispersal to facilitate with microplastics recovery. [ 252 ]
Absorption devices include sponges made of cotton and squid bones, which may be scalable for water remediation projects. [ 253 ]
Increasing education through recycling campaigns is another proposed solution for microplastic contamination. While this would be a smaller-scale solution, education has been shown to reduce littering, especially in urban environments where there are often large concentrations of plastic waste. [ 145 ] If recycling efforts are increased, a cycle of plastic use and reuse would be created to decrease our waste output and production of new raw materials. In order to achieve this, states would need to employ stronger infrastructure and investment around recycling. [ 254 ] Some advocate for improving recycling technology to be able to recycle smaller plastics to reduce the need for production of new plastics. [ 145 ]
In April 2013, Italian artist Maria Cristina Finucci founded The Garbage Patch State in order to create awareness, [ 255 ] under the patronage of UNESCO and the Italian Ministry of the Environment. [ 256 ]
In February 2013 the U.S. Environmental Protection Agency (EPA) launched its "Trash-Free Waters" initiative to prevent single-use plastic wastes from ending up in waterways and ultimately the ocean. [ 257 ] As of 2018, EPA collaborated with the United Nations Environment Programme –Caribbean Environment Programme (UNEP-CEP) and the Peace Corps to reduce and remove trash in the Caribbean Sea . [ 258 ] EPA also funded various projects in the San Francisco Bay Area including one that is aimed at reducing the use of single-use plastics such as disposable cups , spoons and straws, from three University of California campuses. [ 259 ]
The Florida Microplastic Awareness Project (FMAP), a group of volunteers who search for microplastics in coastal water samples Many organizations advocate action to counter microplastic, spreading microplastic awareness. [ 260 ] Global advocacy aimed at achieving the target of the United Nations Sustainable Development Goal 14 hopes to prevent and significantly reduce all forms of marine pollution by 2025. [ 261 ]
The Clean Oceans Initiative is a project launched in 2018 by the public institutions European Investment Bank , Agence Française de Développement and KfW Entwicklungsbank . Their goal was to provide up to €2 billion in lending, grants and technical assistance until 2023 to develop projects that removed pollution from waterways (with a focus on macroplastics and microplastics) before it reached the oceans. [ 9 ] The effort focuses on initiatives that demonstrate efficient methods of minimising plastic waste and microplastics output, emphasising on riverine and coastal areas. [ 262 ] Cassa Depositi e Prestiti (CDP), the Italian national promotional institution and financial institution for development cooperation, and the Instituto de Crédito Oficial (ICO), the Spanish promotional bank, became new partners in October 2020. [ 263 ] [ 264 ] [ 265 ] As of December 2023, The Clean Oceans Initiative had funded almost €3.2 billion, exceeding 80% of its €4 billion objective. Over 20 million people were supposed to benefit from the signed project proposals, which include better wastewater treatment in Sri Lanka, China, Egypt, and South Africa, solid waste management in Togo and Senegal, and stormwater management and flood protection in Benin, Morocco, and Ecuador. [ 266 ] [ 267 ]
In February 2022, the initiative stated that it would increase its financing aim to €4 billion by the end of 2025. At the same time, the European Bank for Reconstruction and Development (EBRD) became the Clean Oceans Initiative's sixth member. [ 262 ] By February 2023, the program had met 65% of its goal, with €2.6 billion spent in 60 projects benefiting more than 20 million people across Africa, Asia, Latin America , and Europe. [ 263 ] [ 268 ] By the beginning of 2022, more than 80% of this target was achieved, with €1.6 billion being used in long-term financing for public and private sector initiatives that minimise the discharge of plastics, microplastics, and other pollutants through enhanced solid waste, wastewater, and storm water management. [ 262 ]
In January 2021, the European Investment Bank and the Asian Development Bank had formed the Clean and Sustainable Ocean Partnership to promote cooperative projects for a clean and sustainable ocean and blue economy in the Asia-Pacific region. [ 269 ] [ 270 ]
With increasing awareness of the detrimental effects of microplastics on the environment, groups are now advocating for the removal and ban of microplastics from various products. [ 271 ] One such campaign is "Beat the Microbead", which focuses on removing plastics from personal care products. [ 108 ] The Adventurers and Scientists for Conservation run the Global Microplastics Initiative, a project to collect water samples to provide scientists with better data about microplastic dispersion in the environment. [ 272 ] UNESCO has sponsored research and global assessment programs due to the trans-boundary issue that microplastic pollution constitutes. [ 273 ] These environmental groups will keep pressuring companies to remove plastics from their products in order to maintain healthy ecosystems. [ 274 ]
In 2018, China banned the import of recyclables from other countries, forcing those other countries to re-examine their recycling schemes. [ 275 ] The Yangtze River in China contributes 55% of all plastic waste going to the seas. Including microplastics, the Yangtze bears an average of 500,000 pieces of plastic per square kilometer. [ 276 ] Scientific American reported that China dumps 30% of all plastics in the ocean. [ 277 ]
In 2024, the Hong Kong government implemented the first phase of its plastic restriction regulation. Promotional videos have also been produced to encourage citizens to bring their own utensils when dining out, to refrain from using disposable utensils, and to bring their own shopping bags when shopping. Merchants are prohibited from providing related plastic products to customers. [ 278 ] [ 279 ] [ 280 ]
In the US, some states have taken action to mitigate the negative environmental effects of microplastics. [ 281 ] Illinois was the first US state to ban cosmetics containing microplastics. [ 145 ] At the federal level, the Microbead-Free Waters Act 2015 was enacted after being signed by President Barack Obama on 28 December 2015. The law bans "rinse-off" cosmetic products that perform an exfoliating function, such as toothpaste or face wash. It does not apply to other products such as household cleaners. The act took effect on 1 July 2017, with respect to manufacturing, and 1 July 2018, with respect to introduction or delivery for introduction into interstate commerce. [ 282 ] On 16 June 2020, California adopted a definition of 'microplastics in drinking water', setting the foundation for a long-term approach to studying their contamination and human health effects. [ 283 ]
On 25 July 2018, a microplastic reduction amendment was passed by the U.S. House of Representatives. [ 284 ] The legislation, as part of the Save Our Seas Act designed to combat marine pollution, aims to support the NOAA 's Marine Debris Program. In particular, the amendment is geared towards promoting NOAA's Great Lakes Land-Based Marine Debris Action Plan to increase testing, cleanup, and education around plastic pollution in the Great Lakes. [ 284 ] President Donald Trump signed the re-authorization and amendment bill into effect on 11 October 2018.
On 15 June 2018, the Japanese government passed a bill with the goal of reducing microplastic production and pollution, especially in aquatic environments. [ 285 ] Proposed by the Environment Ministry and passed unanimously by the Upper House, this is also the first bill to pass in Japan that is specifically targeted at reducing microplastic production, specifically in the personal care industry with products such as face wash and toothpaste. [ 285 ] This law is revised from previous legislation, which focused on removing plastic marine debris . It also focuses on increasing education and public awareness surrounding recycling and plastic waste. [ 285 ] The Environment Ministry has also proposed a number of recommendations for methods to monitor microplastic quantities in the ocean (Recommendations, 2018). [ 286 ] However, the legislation does not specify any penalties for those who continue manufacturing products with microplastics. [ 285 ]
The European Commission has noted the increased concern about the impact of microplastics on the environment. [ 287 ] In April 2018, the European Commission's Group of Chief Scientific Advisors commissioned a comprehensive review of the scientific evidence on microplastic pollution through the EU 's Scientific Advice Mechanism . [ 287 ] The evidence review was conducted by a working group nominated by European academies and delivered in January 2019. [ 288 ] A Scientific Opinion based on the SAPEA report was presented to the Commission in 2019, on the basis of which the commission will consider whether policy changes should be proposed at a European level to curb microplastic pollution. [ 289 ]
In January 2019, the European Chemicals Agency (ECHA) proposed to restrict intentionally added microplastics. [ 290 ]
The European Union participates with 10% of the global total, around 150 000 tonnes of microplastics each year. This is 200 grams per person per year, with significant regional variance in per-capita microplastic creation. [ 172 ] [ 291 ]
The European Commission's Circular Economy Action Plan sets out mandatory requirements for the recycling and waste reduction of key products e.g. plastic packaging. The plan starts the process to restrict addition of microplastics in products. It mandates measures for capturing more microplastics at all stages of the lifecycle of a product. E.g. the plan would examine different policies which aim to reduce release of secondary microplastics from tires and textiles. [ 292 ] The European Commission plans to update the Urban Waste Water Treatment Directive to further address microplastic waste and other pollution. They aim to protect the environment from industrial and urban waste water discharge. A revision to the EU Drinking Water Directive was provisionally approved to ensure microplastics are regularly monitored in drinking water. It would require countries must propose solutions if a problem is found. [ 9 ]
The REACH restriction on synthetic polymer microparticles entered into force on 17 October 2023. [ 293 ] [ 294 ]
The Environmental Protection (Microbeads) (England) Regulations 2017 ban the production of any rinse-off personal care products (such as exfoliants) containing microbeads. [ 295 ] This particular law denotes specific penalties when it is not obeyed. Those who do not comply are required to pay a fine. In the event that a fine is not paid, product manufacturers may receive a stop notice, which prevents the manufacturer from continuing production until they have followed regulation preventing the use of microbeads. Criminal proceedings may occur if the stop notice is ignored. [ 295 ]
Haiti has no collective system for waste collection and treatment, [ 296 ] and thus plastic is often disposed of in urban water evacuation canals, which then degrade to form microplastics. Due to tropical temperatures and average daily duration of 12 hours, [ clarify ] the plastics present in urban waterways could degrade more rapidly. Their discharge into Port-au-Prince Bay exposes this ecosystem to a number of environmental hazards pollutants contained in the waste, and to climatic hazards, particularly ocean acidification. [ 297 ]
On August 9, 2012, the Haitian government published a decree prohibiting the production, importation, marketing and use, of polyethylene bags and expanded polystyrene objects for foodstuffs. However, 14 Caribbean countries (more than a third) have banned single-use plastic bags and/or polystyrene containers.
On July 10, 2013, a second decree was published to once again prohibit "the importation, production or sale of expanded polystyrene articles for food use". In support of the second decree, the ministries of the Environment, Justice and Public Security, Trade and Industry as well as the Economy and Finance announced in a note published in January 2018 that specialists from the brigade will be deployed on the territory to force the application of the said decree. [ 297 ] | https://en.wikipedia.org/wiki/Microplastics_in_Haiti |
Micropollutants are substances that even at very low concentrations have adverse effects on different environmental matrices. They are an inhomogeneous group of atroprogenic chemical compounds that is discharged by human to the environment. Commonly known micropollutants that might pose possible threats to ecological environments are, to name just a few:
To date, most of the scientists have identified wastewater treatment plants as the main source of micropollutants to aquatic ecosystems and/or adversely affect the extraction of potable water from raw water. [ 1 ] [ 2 ] Due to in many places drinking water is also extracted from surface waters , or the substances also reach the groundwater via the water, they are also found in raw water and must be laboriously removed by drinking water treatment. In addition, some of the substances are bioaccumulative , which means that they accumulate in animals or plants and thus also in the human food chain .
It is estimated that there are currently around 235,000 individual chemical substances registered worldwide. [ 3 ] A large number of these are released into wastewater by humans. If these are persistent, they remain during clarification in the wastewater and enter the environment. Some of them have ecotoxic relevant properties. In some cases, the chemical itself is not a concern, but its degradation products are.
This has been known for a longer time. As early as 1976, a study was published in which salicylic acid and clofibric acid were detected in the effluent of a sewage treatment plant in Kansas City. [ 4 ] We currently know that there are well over 1,000 substances in wastewater that pose a risk. Many others have not yet been sufficiently researched in this regard. [ 3 ]
In current studies of water quality in European rivers by the Helmholtz Centre for Environmental Research, 610 chemicals whose occurrence or problematic effects are known were examined in more detail and analyzed to determine whether and, if so, in what concentrations they occur in Europe's flowing waters. The evaluation of 445 samples from a total of 22 rivers showed that the researchers were able to detect a total of 504 of the 610 chemicals. In total, they found 229 pesticides and biocides , 175 pharmaceutical chemicals as well as surfactants , plastic and rubber additives, per- and polyfluoroalkyl substances (PFAS) and corrosion inhibitors . In 40 percent of the samples they detected up to 50 chemical substances, in another 41 percent between 51 and 100 chemicals. In 4 samples they were even able to detect more than 200 organic micropollutants. With 241 chemicals, they detected the most substances in a water sample from the Danube . [ 5 ]
The influences of micropollutants are varied. The best known are those of hormones that enter the water through the contraceptive pill . Several studies have shown that feminization occurs in an unusually high number of fish below discharges from sewage treatment plants, which has a negative impact on the population. One in five male smallmouth bass in U.S. rivers has developed female sexual characteristics. [ 6 ] Estrogen-like artificial compounds such as the plasticizer bisphenol A also have this effect. There is evidence that this also applies to humans. Such substances are called endocrine disruptors . Other substances, such as benzotriazole , which is added to dishwasher detergent as corrosion protection for silver cutlery, are suspected of being carcinogenic in addition to acting as an endocrine disruptor in the concentrations found. [ 7 ]
Another relevant factor is the danger posed by the spread of multi-resistant bacteria. There are two possible ways in which this can happen through wastewater. Firstly, by transporting already resistant strains into the receiving water due to inadequate treatment technology. The other possibility is the development of resistant cultures in the environment by introducing antibiotics into the water body. Preventing the entry of bacteria has long been used as a form of hygienic treatment using UV light or ozone, especially if the water is to be reused. Membrane systems such as membrane bioreactors or downstream ultrafiltration also serve this purpose. [ 8 ] Depending on the intensity and technology, some micropollutants are also removed in addition to the bacteria. The extent to which membrane technologies with low energy consumption are able to deplete trace substances is being investigated.
Techniques for elimination of micropollutants via a so called fourth treatment stage during sewage treatment are implemented in Germany, Switzerland, Sweden and the Netherlands and tests are ongoing in several other countries. [ 9 ] In Switzerland it has been enshrined in law since 2016. [ 10 ]
Since 1 January 2025, there has been a recast of the Urban Waste Water Treatment Directive in the European Union, which requires the removal of a large proportion of micropollutants from wastewater. Due to the large number of amendments that have now been made, the directive was rewritten on November 27, 2024 as Directive (EU) 2024/3019, published in the EU Official Journal on December 12, and entered into force on January 1, 2025. The member states now have 31 months, i.e. until July 31, 2027, to adapt their national legislation to the new directive ("implementation of the directive").
The implementation of the framework guidelines is staggered until 2045, depending on the size of the sewage treatment plant and its population equivalents (PE). Sewage treatment plants with over 150,000 PE have priority and should be adapted immediately, as a significant proportion of the pollution comes from them followed by wastewater treatment plants with 10,000 to 150,000 PE that discharge into coastal waters or sensitive waters. The latter concerns waters with a low dilution ratio, waters from which drinking water is obtained and those that are coastal waters, or those used as bathing waters or used for mussel farming. Member States will be given the option not to apply fourth treatment in these areas if a risk assessment shows that there is no potential risk from micropollutants to human health and/or the environment. [ 11 ] [ 12 ]
Due to the large number of substances with very different chemical and physical properties, the removal of these substances is difficult.
Three techniques and cominationes of them have been established so far.
Two remove the contaminants with the help of activated carbon (PAC (Powdered Activated Carbon), GAC (Granulated Activated Carbon)) and one with ozone . [ 13 ] [ 14 ] [ 15 ]
In addition to that a large number of techniques are still in experimental stage. These include for example processes that work with plasma [ 16 ] or ultrasound , so-called AOP processes , applications with zeolites and cyclodextrins , membrane processes or photocatalysis . | https://en.wikipedia.org/wiki/Micropollutant |
A microporous material is a material containing pores with typical sizes less than 2 nm in diameter. Microporous materials, like mesoporous materials, are a subset of nanoporous materials. Examples of microporous materials include zeolites and metal-organic frameworks . [ 1 ]
Porous materials are classified into several kinds by their size. The recommendations of a panel convened by the International Union of Pure and Applied Chemistry (IUPAC) are: [ 2 ]
Micropores may be defined differently in other contexts. For example, in the context of porous aggregations such as soil, micropores are defined as cavities with sizes less than 30 μm. [ 3 ]
Microporous materials are often used in laboratory environments to facilitate contaminant-free exchange of gases. Mold spores, bacteria, and other airborne contaminants will become trapped, while gases are allowed to pass through the material. This allows for a sterile environment within the contained area.
Microporous media are used in large format printing applications, normally with a pigment based ink, to maintain colour balance and life expectancy of the resultant printed image.
Microporous materials are also used as high performance insulation in applications ranging from homes to metal furnaces requiring material that can withstand more than 1000 Celsius.
This article about materials science is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microporous_material |
Micropower describes the use of very small electric generators and prime movers or devices to convert heat or motion to electricity, for use close to the generator. [ 1 ] The generator is typically integrated with microelectronic devices and produces "several watts of power or less." [ 2 ] These devices offer the promise of a power source for portable electronic devices which is lighter weight and has a longer operating time than batteries.
The components of any turbine engine — the gas compressor , the combustion chamber , and the turbine rotor — are fabricated from etched silicon , much like integrated circuits . The technology holds the promise of ten times the operating time of a battery of the same weight as the micropower unit, and similar efficiency to large utility gas turbines . Researchers at Massachusetts Institute of Technology have thus far succeeded in fabricating the parts for such a micro turbine out of six etched and stacked silicon wafers, and are working toward combining them into a functioning engine about the size of a U.S. quarter coin. [ 3 ]
Researchers at Georgia Tech have built a micro generator 10 mm wide, which spins a magnet above an array of coils fabricated on a silicon chip. The device spins at 100,000 revolutions per minute, and produces 1.1 watts of electrical power , sufficient to operate a cell phone . Their goal is to produce 20 to 50 watts, sufficient to power a laptop computer. [ 4 ]
Scientists at Lehigh University are developing a hydrogen generator on a silicon chip that can convert methanol , diesel , or gasoline into fuel for a microengine or a miniature fuel cell. [ 5 ]
Professor Sanjeev Mukerjee of Northeastern University 's chemistry department is developing fuel cells for the military that will burn hydrogen to power portable electronic equipment, such as night vision goggles, computers, and communication equipment. In his system, a cartridge of methanol would be used to produce hydrogen to run a small fuel cell for up to 5,000 hours. It would be lighter than rechargeable batteries needed to provide the same power output, with a longer run time. Similar technology could be improved and expanded in future years to power automobiles. [ 6 ]
The National Academies ' National Research Council recommended in a 2004 report that the U.S. Army should investigate such micropower sources for powering electronic equipment to be carried by soldiers in the future, since batteries sufficient to power the computers, sensors, and communications devices would add considerable weight to the burden of infantry soldiers. [ 7 ]
The Future Warrior Concept of the U.S. Army envisions a 2- to 20-watt micro turbine fueled by a liquid hydrocarbon being used to power communications and wearable heating/cooling equipment for up to six days on 10 ounces of fuel. [ 8 ]
Professor Orest Symko of the University of Utah physics department and his students developed Thermal Acoustic Piezo Energy Conversion (TAPEC), devices of a cubic inch (16 cubic centimeters), or so, which convert waste heat into acoustic resonance and then into electricity. It would be used to power microelectromechanical systems, or MEMS. The research was funded by the U.S. Army. Symko was to present a paper at the Acoustical Society of America . [ 9 ] June 8, 2007. Researchers at MIT developed the first micro-scale piezoelectric energy harvester using thin film PZT in 2005. [ 10 ] Arman Hajati and Sang-Gook Kim invented the Ultra Wide-Bandwidth micro-scale piezoelectric energy harvesting device by exploiting the nonlinear stiffness of a doubly clamped microelectromechanical systems (MEMS) resonator. The stretching strain in a doubly clamped beam shows a nonlinear stiffness, which provides a passive feedback and results in amplitude-stiffened Duffing mode resonance. [ 11 ]
Professor Zhong Lin Wang of the Georgia Institute of Technology said his team of investigators had developed a "nanometer-scale generator ... based on arrays of vertically aligned zinc oxide nanowires that move inside a "zigzag" plate electrode ." Built into shoes, it could generate electricity from walking to power small electronic devices. It could also be powered by blood flow to power biomedical devices. [ 12 ] Per an account of the device which appeared in the journal Science , bending of the zinc oxide nanowire arrays produces an electric field by the piezoelectric properties of the material. The semiconductor properties of the device create a Schottky barrier with rectifying capabilities. The generator is estimated to be 17% to 30% efficient in converting mechanical motion into electricity. This could be used to power biomedical devices that have wireless transmission capabilities for data and control. [ 13 ] A later development was to grow hundreds of such nanowires on a substrate that functioned as an electrode. On top of this was placed a silicon electrode covered with a series of platinum ridges. Vibration of the top electrode caused the generation of direct current. [ 14 ] A report by Wang was to appear in the August 8, 2007 issue of the journal "Nano Letters," saying that such devices could power implantable biomedical devices. The device would be powered by flowing blood or a beating heart. It could function while immersed in body fluids, and would get its energy from ultrasonic vibrations. [ 15 ] Wang expects that an array of the devices could produce 4 watts per cubic centimeter. [ 16 ] Goals for further development are to increase the efficiency of the array of nanowires, and to increase the lifetime of the device, which as of April 2007 was only about one hour. [ 17 ] By November 2010 Wang and his team were able to produce 3 volts of potential and as much as 300 nanoamperes of current, an output level 100 times greater than was possible a year earlier, from an array measuring about 2 cm by 1.5 cm. [ 18 ]
The windbelt is a micropower technology invented by Shawn Frayne. It is essentially an aeolian harp , except that it exploits the motion of the string produced by aeroelastic flutter to create a physical oscillation that can be converted to electricity. It avoids the losses inherent in rotating wind powered generators. Prototypes have produced 40 milliwatts in a 16 km/h wind. Magnets on the vibrating membrane generate currents in stationary coils. [ 19 ] [ 20 ]
Piezoelectric nanofibers in clothing could generate enough electricity from the wearer's body movements to power small electronic devices, such as iPods or some of the electronic equipment used by soldiers on the battlefield, based on research by University of California, Berkeley Professor Liwei Lin and his team. One million such fibers could power an iPod, and would be altogether as large as a grain of sand. Researchers at Stanford University are developing "eTextiles" — batteries made of fabric — that might serve to store power generated by such technology. [ 21 ]
Thermal resonator technology allows generation of power from the daily change of temperature, even when there is no instantaneous temperature difference as needed for thermoelectric generation, and no sunlight as needed for photovoltaic generation. A phase change material such as octadecane is selected which can change from solid to liquid when the ambient temperature changes a few degrees celsius. In a small demonstration device created by chemical engineering professor Michael Strano and seven others at MIT , a 10 degree celsius daily change produced 350 millivolts and 1.3 milliwatts. The power levels envisioned could power sensors and communication devices. [ 22 ] [ 23 ] | https://en.wikipedia.org/wiki/Micropower |
A microprobe is an instrument that applies a stable and well-focused beam of charged particles ( electrons or ions ) to a sample.
When the primary beam consists of accelerated electrons, the probe is termed an electron microprobe , when the primary beam consists of accelerated ions, the term ion microprobe is used. The term microprobe may also be applied to optical analytical techniques, when the instrument is set up to analyse micro samples or micro areas of larger specimens. Such techniques include micro Raman spectroscopy , micro infrared spectroscopy and micro LIBS . All of these techniques involve modified optical microscopes to locate the area to be analysed, direct the probe beam and collect the analytical signal.
A laser microprobe is a mass spectrometer that uses ionization by a pulsed laser and subsequent mass analysis of the generated ions. [ 1 ] [ 2 ] [ 3 ]
Scientists use this beam of charged particles to determine the elemental composition of solid materials ( minerals , glasses , metals ). [ 4 ] The chemical composition of the target can be found from the elemental data extracted through emitted X-rays (in the case where the primary beam consists of charged electrons) or measurement of an emitted secondary beam of material sputtered from the target (in the case where the primary beam consists of charged ions).
When the ion energy is in the range of a few tens of keV (kilo-electronvolt) these microprobes are usually called FIB ( Focused ion beam ). An FIB makes a small portion of the material into a plasma; the analysis is done by the same basic techniques as the ones used in mass spectrometry .
When the ion energy is higher, hundreds of keV to a few MeV (mega-electronvolt) they are called nuclear microprobes. Nuclear microprobes are extremely powerful tools that utilize ion beam analysis techniques as microscopies with spot sizes in the micro-/nanometre range. These instruments are applied to solve scientific problems in a diverse range of fields, from microelectronics to biomedicine. In addition to the development of new ways to exploit these probes as analytical tools (this application area of the nuclear microprobes is called nuclear microscopy ), strong progress has been made in the area of materials modification recently (most of which can be described as PBW, proton beam writing ).
The nuclear microprobe's [ 5 ] beam is usually composed of protons and alpha particles . Some of the most advanced nuclear microprobes have beam energies in excess of 2 MeV. This gives the device very high sensitivity to minute concentrations of elements, around 1 ppm at beam sizes smaller than 1 micrometer . This elemental sensitivity exists because when the beam interacts with the a sample it gives off characteristic X-rays of each element present in the sample. This type of detection of radiation is called PIXE . Other analysis techniques are applied to nuclear microscopy including Rutherford backscattering (RBS), STIM , etc.
Another use for microprobes is the production of micro and nano sized devices, as in microelectromechanical systems and nanoelectromechanical systems . [ 6 ] The advantage that microprobes have over other lithography processes is that a microprobe beam can be scanned or directed over any area of the sample. This scanning of the microprobe beam can be imagined to be like using a very fine tipped pencil to draw your design on a paper or in a drawing program. Traditional lithography processes use photons which cannot be scanned and therefore masks are needed to selectively expose your sample to radiation. It is the radiation that causes changes in the sample, which in turn allows scientists and engineers to develop tiny devices such as microprocessors, accelerometers (like in most car safety systems), etc. | https://en.wikipedia.org/wiki/Microprobe |
The microprocessor complex is a protein complex involved in the early stages of processing microRNA (miRNA) and RNA interference (RNAi) in animal cells. [ 2 ] [ 3 ] The complex is minimally composed of the ribonuclease enzyme Drosha and the dimeric RNA-binding protein DGCR8 (also known as Pasha in non-human animals), and cleaves primary miRNA substrates to pre-miRNA in the cell nucleus . [ 4 ] [ 5 ] [ 6 ] Microprocessor is also the smaller of the two multi-protein complexes that contain human Drosha . [ 7 ]
The microprocessor complex consists minimally of two proteins: Drosha , a ribonuclease III enzyme; and DGCR8 , a double-stranded RNA binding protein . [ 4 ] [ 5 ] [ 6 ] (DGCR8 is the name used in mammalian genetics, abbreviated from " DiGeorge syndrome critical region 8"; the homologous protein in model organisms such as flies and worms is called Pasha , for Pa rtner of Dro sha .) The stoichiometry of the minimal complex was at one point experimentally difficult to determine, but it has been demonstrated to be a heterotrimer of two DGCR8 proteins and one Drosha. [ 1 ] [ 8 ] [ 9 ] [ 10 ]
In addition to the minimal catalytically active microprocessor components, other cofactors such as DEAD box RNA helicases and heterogeneous nuclear ribonucleoproteins may be present in the complex to mediate the activity of Drosha . [ 4 ] Some miRNAs are processed by microprocessor only in the presence of specific cofactors. [ 11 ]
Located in the cell nucleus , the microprocessor complex cleaves primary miRNA (pri-miRNA) into precursor miRNA (pre-miRNA). [ 13 ] Its two subunits have been determined as necessary and sufficient for the mediation of the development of miRNAs from the pri-miRNAs. [ 7 ] These molecules of around 70 nucleotides contain a stem-loop or hairpin structure. Pri-miRNA substrates can be derived either from non-coding RNA genes or from introns . In the latter case, there is evidence that the microprocessor complex interacts with the spliceosome and that the pri-miRNA processing occurs prior to splicing . [ 5 ] [ 14 ]
Microprocessor cleavage of pri-miRNAs typically occurs co- transcriptionally and leaves a characteristic RNase III single-stranded overhang of 2-3 nucleotides, which serves as a recognition element for the transport protein exportin-5 . [ 15 ] Pre-miRNAs are exported from the nucleus to the cytoplasm in a RanGTP -dependent manner and are further processed, typically by the endoribonuclease enzyme Dicer . [ 4 ] [ 5 ] [ 6 ]
Hemin allows for the increased processing of pri-miRNAs through an induced conformational change of the DGCR8 subunit, and also enhances DGCR8's binding specificity for RNA. [ 16 ] DGCR8 recognizes the junctions between hairpin structures and single-stranded RNA and serves to orient Drosha to cleave around 11 nucleotides away from the junctions, and remains in contact with the pri-miRNAs following cleavage and dissociation of Drosha. [ 17 ]
Although the large majority of miRNAs undergo processing by microprocessor, a small number of exceptions called mirtrons have been described; these are very small introns which, after splicing, have the appropriate size and stem-loop structure to serve as a pre-miRNA. [ 18 ] The processing pathways for microRNA and for exogenously derived small interfering RNA converge at the point of Dicer processing and are largely identical downstream. Broadly defined, both pathways constitute RNAi . [ 5 ] [ 18 ] Microprocessor is also found to be involved in ribosomal biogenesis specifically in the removal of R-loops and activating transcription of ribosomal protein encoding genes. [ 19 ]
Gene regulation by miRNA is widespread across many genomes – by some estimates more than 60% of human protein-coding genes are likely to be regulated by miRNA, [ 20 ] though the quality of experimental evidence for miRNA-target interactions is often weak. [ 21 ] Because processing by microprocessor is a major determinant of miRNA abundance, microprocessor itself is then an important target of regulation.
Both Drosha and DGCR8 are subject to regulation by post-translational modifications modulating stability, intracellular localization, and activity levels. Activity against particular substrates may be regulated by additional protein cofactors interacting with the microprocessor complex. The loop region of the pri-miRNA stem-loop is also a recognition element for regulatory proteins, which may up- or down-regulate microprocessor processing of the specific miRNAs they target. [ 11 ]
Microprocessor itself is auto-regulated by negative feedback through association with a pri-miRNA-like hairpin structure found in the DGCR8 mRNA, which when cleaved reduces DGCR8 expression. The structure in this case is located in an exon and is unlikely to itself function as miRNA in its own right. [ 11 ]
Drosha shares striking structural similarity with the downstream ribonuclease Dicer , suggesting an evolutionary relationship, though Drosha and related enzymes are found only in animals while Dicer relatives are widely distributed, including among protozoans . [ 8 ] Both components of the microprocessor complex are conserved among the vast majority of metazoans with known genomes. Mnemiopsis leidyi , a ctenophore , lacks both Drosha and DGCR8 homologs, as well as recognizable miRNAs, and is the only known metazoan with no detectable genomic evidence of Drosha . [ 22 ] In plants, the miRNA biogenesis pathway is somewhat different; neither Drosha nor DGCR8 has a homolog in plant cells, where the first step in miRNA processing is usually executed by a different nuclear ribonuclease , DCL1 , a homolog of Dicer . [ 11 ] [ 23 ]
It has been suggested based on phylogenetic analysis that the key components of RNA interference based on exogenous substrates were present in the ancestral eukaryote , likely as an immune mechanism against viruses and transposable elements . Elaboration of this pathway for miRNA-mediated gene regulation is thought to have evolved later. [ 24 ]
The involvement of miRNAs in diseases has led scientists to become more interested in the role of additional protein complexes, like microprocessor, that have the ability to influence or modulate the function and expression of miRNAs. [ 25 ] Microprocessor complex component, DGCR8, is affected through the micro-deletion of 22q11.2 , a small portion of chromosome 22 . This deletion causes irregular processing of miRNAs which leads to DiGeorge Syndrome . [ 26 ] | https://en.wikipedia.org/wiki/Microprocessor_complex |
A microprocessor development board is a printed circuit board containing a microprocessor and the minimal support logic needed for an electronic engineer or any person who wants to become acquainted with the microprocessor on the board and to learn to program it. It also served users of the microprocessor as a method to prototype applications in products.
Unlike a general-purpose system such as a home computer , usually a development board contains little or no hardware dedicated to a user interface. It will have some provision to accept and run a user-supplied program, such as downloading a program through a serial port to flash memory , or some form of programmable memory in a socket in earlier systems.
The reason for the existence of a development board was solely to provide a system for learning to use a new microprocessor, not for entertainment, so everything superfluous was left out to keep costs down. Even an enclosure was not supplied, nor a power supply. This is because the board would only be used in a "laboratory" environment so it did not need an enclosure, and the board could be powered by a typical bench power supply already available to an electronic engineer.
Microprocessor training development kits were not always produced by microprocessor manufacturers. Many systems that can be classified as microprocessor development kits were produced by third parties, one example is the Sinclair MK14 , which was inspired by the official SC/MP development board from National Semiconductor , the "NS introkit". [ 1 ]
Although these development boards were not designed for hobbyists, they were often bought by them because they were the earliest cheap microcomputer devices available. They often added all kinds of expansions, such as more memory, a video interface etc. It was very popular to use (or write) an implementation of Tiny Basic . The most popular microprocessor board, the KIM-1 , received the most attention from the hobby community, because it was much cheaper than most other development boards, and more software was available for it (Tiny Basic, games, assemblers ), and cheap expansion cards to add more memory or other functionality. [ 2 ] More articles were published in magazines like " Kilobaud Microcomputing " that described home-brew software and hardware for the KIM-1 than for other development boards. [ 3 ]
Today some chip producers still release "test boards" to demonstrate their chips, and to use them as a " reference design ". Their significance these days is much smaller than it was in the days that such boards, (the KIM-1 being the canonical example) were the only low cost way to get "hands-on" acquainted with microprocessors..
The most important feature of the microprocessor development board was the ROM -based built-in machine language monitor , or "debugger" as it was also sometimes called. Often the name of the board was related to the name of this monitor program, for example the name of the monitor program of the KIM-1 was "Keyboard Input Monitor", because the ROM-based software allowed entry of programs without the rows of cumbersome toggle switches that older systems used. The popular Motorola 6800 -based systems often used a monitor with a name with the word "bug" for "debugger" in it, for example the popular " MIKBUG ". [ 4 ]
Input was normally done with a hexadecimal keyboard, using a machine language monitor program, and the display only consisted of a 7-segment display. Backup storage of written assembler programs was primitive: only a cassette type interface was typically provided, or the serial Teletype interface was used to read (or punch) a papertape . [ 5 ]
Often the board has some kind to expansion connector that brought out all the necessary CPU signals, so that an engineer could build and test an experimental interface or other electronic device.
External interfaces on the bare board were often limited to a single RS-232 or current loop serial port, so a terminal , printer, or Teletype could be connected.
A DSP evaluation board, sometimes also known as a DSP starter kit (DSK) or a DSP evaluation module, is an electronic board with a digital signal processor used for experiments, evaluation and development. [ 6 ] Applications are developed in DSP Starter Kits using software usually referred as an integrated development environment (IDE). [ 7 ] Texas Instruments and Spectrum Digital are two companies who produce these kits.
Two examples are the DSK 6416 by Texas Instruments, [ 8 ] based on the TMS320C6416 fixed point digital signal processor, a member of C6000 series of processors that is based on VelociTI.2 architecture, [ 9 ] and the DSK 6713 by Texas Instruments, which was developed in cooperation with Spectrum Digital, based on the TMS320C6713 32-bit floating point digital signal processor, [ 9 ] : 3 which allows for programming in C and assembly. | https://en.wikipedia.org/wiki/Microprocessor_development_board |
A microprotein (miP) is a small protein encoded from a small open reading frame (sORF), [ 1 ] also known as sORF-encoded protein ( SEP ). They are a class of protein with a single protein domain that are related to multidomain proteins. [ 2 ] Microproteins regulate larger multidomain proteins at the post-translational level. [ 3 ] Microproteins are analogous to microRNAs (miRNAs) and heterodimerize with their targets causing dominant and negative effects. [ 4 ] In animals and plants, microproteins have been found to greatly influence biological processes. [ 2 ] Because of microproteins' dominant effects on their targets, microproteins are currently being studied for potential applications in biotechnology. [ 2 ]
The first microprotein (miP) discovered was during a research in the early 1990s on genes for basic helix–loop–helix (bHLH) transcription factors from a murine erythroleukaemia cell cDNA library . [ 3 ] The protein was found to be an inhibitor of DNA binding (ID protein), and it negatively regulated the transcription factor complex. [ 3 ] The ID protein was 16 kDa and consisted of a helix-loop-helix (HLH) domain. [ 2 ] The microprotein formed bHLH/HLH heterodimers which disrupted the functional basic helix–loop–helix (bHLH) homodimers. [ 2 ]
The first microprotein discovered in plants was the LITTLE ZIPPER (ZPR) protein. [ 2 ] The LITTLE ZIPPER protein contains a leucine zipper domain but does not have the domains required for DNA binding and transcription activation. [ 2 ] Thus, LITTLE ZIPPER protein is analogous to the ID protein. [ 2 ] Despite not all proteins being small, in 2011, this class of protein was given the name microproteins because their negative regulatory actions are similar to those of miRNAs. [ 3 ]
Evolutionarily, the ID protein or proteins similar to ID found in all animals. [ 3 ] In plants, microproteins are only found in higher order. [ 3 ] However, the homeodomain transcription factors that belong to the three-amino-acid loop-extension (TALE) family are targets of microproteins, and these homeodomain proteins are conserved in animals, plants, and fungi. [ 3 ]
Microproteins are generally small proteins with a single protein domain. [ 2 ] [ 4 ] The active form of microproteins are translated from smORF. [ 1 ] The smORF codons which microproteins are translated from can be less than 100 codons. [ 1 ] However, not all microproteins are small, and the name was given because their actions are analogous to miRNAs. [ 3 ]
The function of microproteins is post-translational regulators . [ 3 ] Microproteins disrupt the formation of heterodimeric, homodimeric, or multimeric complexes. [ 4 ] Furthermore, microproteins can interact with any protein that require functional dimers to function normally. [ 3 ] The primary targets of microproteins are transcription factors that bind to DNA as dimers. [ 5 ] [ 3 ] Microproteins regulate these complexes by creating homotypic dimers with the targets and inhibit protein complex function. [ 3 ] There are two types of miP inhibitions: homotypic miP inhibition and heterotypic miP inhibition. [ 4 ] In homotypic miP inhibition, microproteins interact with proteins with similar protein-protein interaction (PPI) domain. [ 4 ] In heterotypic miP inhibition, microproteins interact with proteins with different but compatible PPI domain. [ 4 ] In both types of inhibition, microproteins interfere and prevent the PPI domains from interacting with their normal proteins. [ 4 ] | https://en.wikipedia.org/wiki/Microprotein |
Micropumps are devices that can control and manipulate small fluid volumes. [ 3 ] [ 4 ] Although any kind of small pump is often referred to as a micropump, a more accurate definition restricts this term to pumps with functional dimensions in the micrometer range. Such pumps are of special interest in microfluidic research, and have become available for industrial product integration in recent years. Their miniaturized overall size, potential cost and improved dosing accuracy compared to existing miniature pumps fuel the growing interest for this innovative kind of pump.
Note that the below text is very incomplete in terms of providing a good overview of the different micropump types and applications, and therefore please refer to good review articles on the topic. [ 3 ] [ 5 ] [ 6 ] [ 7 ]
First true micropumps were reported in the mid-1970s, [ 8 ] but attracted interest only in the 1980s, when Jan Smits and Harald Van Lintel developed MEMS micropumps. [ 9 ] Most of the fundamental MEMS micropump work was done in the 1990s. More recently, efforts have been made to design non-mechanical micropumps that are functional in remote locations due to their non-dependence on external power.
Within the microfluidic world, physical laws change their appearance. [ 10 ] As an example, volumetric forces, such as weight or inertia, often become negligible, whereas surface forces can dominate fluidical behaviour, [ 11 ] especially when gas inclusion in liquids is present. With only a few exceptions, micropumps rely on micro-actuation principles, which can reasonably be scaled up only to a certain size.
Micropumps can be grouped into mechanical and non-mechanical devices. [ 12 ] Mechanical systems contain moving parts, which are usually actuation and microvalve membranes or flaps. The driving force can be generated by utilizing piezoelectric , [ 13 ] electrostatic , thermo-pneumatic, pneumatic or magnetic effects. Non-mechanical pumps function with electro-hydrodynamic, electro-osmotic , electrochemical [ 14 ] or ultrasonic flow generation, just to name a few of the actuation mechanisms that are currently studied.
A diaphragm micropump uses the repeated actuation of a diaphragm to drive a fluid. The membrane is positioned above a main pump valve, which is centered between inlet and outlet microvalves . When the membrane is deflected upwards through some driving force, fluid is pulled into the inlet valve into the main pump valve. The membrane is then lowered, expelling the fluid through the outlet valve. This process is repeated to pump fluid continuously. [ 6 ]
Piezoelectric micropump is one of the most common type of displacement reciprocating diaphragm pumps. Piezoelectric driven micropumps rely on electromechanical property of piezo ceramic to deform in response to applied voltage. Piezoelectric disk attached to the membrane causes diaphragm deflection driven by the external axial electric field thus expanding and contracting the chamber of the micropump. [ 15 ] This mechanical strain results in pressure variation in the chamber, which causes inflow and outflow of the fluid. The flow rate is controlled by the polarization limit of the material and the voltage applied on the piezo. [ 16 ] In comparison with other actuation principles piezoelectric actuation enables high stroke volume, high actuation force and fast mechanical response, though requiring comparatively high actuation voltage and complex mounting procedure of the piezo ceramic. [ 9 ]
The smallest piezoelectric micropump with dimensions of 3.5x3.5x0.6 mm 3 was developed by Fraunhofer EMFT [ 17 ] the world-renowned research organization with focus on MEMS and Microsystem technologies . The micropump consists of three silicon layers, one of which as a pump diaphragm confines the pump chamber from above, while two others represent middle valve chip and bottom valve chip. Openings of the passive flap valves at the inlet and outlet are oriented according to the flow direction. The pump diaphragm expands with application of a negative voltage to the piezo thus creating negative pressure to suck the fluid into the pump chamber. While positive voltage vice versa drives the diaphragm down, which results in overpressure opening outlet valve and forcing the fluid out of the chamber.
Currently mechanical micropump technology extensively uses Silicon and Glass based micromachining processes for fabrication. Among the common microfabrication processes, the following techniques can be named: photolithography, anisotropic etching , surface micromachining and bulk micromachining of silicon. [ 16 ] Silicon micromachining has numerous advantages that facilitate the technology widespread in high performance applications as, for example, in drug delivery. [ 9 ] Thus, silicon micromachining allows high geometric precision and long-term stability, since mechanically moving parts, e.g. valve flaps, do not exhibit wear and fatigue. As an alternative to silicon polymer -based materials like PDMS , PMMA, PLLA, etc. can be used due to the superior strength, enhanced structural properties, stability and inexpensiveness. Silicon micropumps at Fraunhofer EMFT are manufactured by silicon micromachining technology. [ 18 ] Three monocrystalline silicon wafers (100 oriented) are structured by doublesided lithography and etched by silicon wet etching (using potassium hydroxide solution KOH). The connection between the structured wafer layers is realized by silicon fusion bond. This bonding technology needs very smooth surfaces (roughness lower than 0.3 nm) and very high temperatures (up to 1100 °C) to perform a direct silicon–silicon bond between the wafer layers. Absence of the bonding layer allows definition of the vertical pump design parameters. Additionally, the bonding layer might be affected by the pumped medium.
The compression ratio of the micropump as one of the critical performance indicator is defined as the ratio between the stroke volume, i.e. fluid volume displaced by the pump membrane over the course of the pump cycle, and the dead volume, i.e. the minimum fluid volume remaining in the pump chamber in pumping mode. [ 15 ]
ε =△ V / V 0 {\textstyle \varepsilon =\bigtriangleup V/V_{0}}
The compression ratio defines the bubble tolerance and the counter pressure capability of the micropumps. Gas bubbles within chamber hinder micropump operation as due to the damping properties of the gas bubbles the pressure peaks (∆P) in the pump chamber decreases, while due to the surface properties the critical pressure (∆P crit ) that opens passive valves increases. [ 19 ] The compression ratio of Fraunhofer EMFT micropumps reaches the value of 1, which implies self-priming capability and bubble tolerance even at challenging outlet pressure conditions. Large compression ratio is achieved thanks to special patented technique of piezo mounting, when electrical voltage is applied on the electrodes on the top and bottom of the piezoelectric ceramic during the curing process of the adhesive used for the piezo mounting. Considerable reduction of the dead volume resulted from predeflected actuators along with shallow fabricated pump chamber heights increases the compression ratio.
A peristaltic micropump is a micropump composed of at least three microvalves in series. These three valves are opened and closed sequentially in order to pull fluid from the inlet to the outlet in a process known as peristalsis. [ 20 ]
Static valves are defined as valves which have fixed geometry without any moving parts. These valves provide flow rectification through addition of energy (active) or inducing desired flow behavior by fluid inertia (passive). Two most common types of static geometry passive valves are Diffuser-Nozzle Elements [ 21 ] [ 22 ] and Tesla valves. Micropumps having nozzle-diffuser elements as flow rectification device are commonly known as Valveless Micropumps.
In microfluidics, capillary pumping plays an important role because the pumping action does not require external actuation power. Glass capillaries and porous media, including nitrocellulose paper and synthetic paper, [ 23 ] can be integrated into microfluidic chips. Capillary pumping is widely used in lateral flow testing. Recently, novel capillary pumps, with a constant pumping flow rate independent of the liquid viscosity and surface energy, [ 24 ] [ 25 ] [ 26 ] [ 27 ] were developed, which have a significant advantage over the traditional capillary pump (of which the flow behaviour is Washburn behaviour, namely the flow rate is not constant) because their performance does not depend on the sample viscosity.
Chemically powered non-mechanical pumps have been fabricated by affixing nanomotors to surfaces, driving fluid flow through chemical reactions. A wide variety of pumping systems exist including biological enzyme based pumps, [ 28 ] [ 29 ] [ 30 ] [ 31 ] [ 32 ] [ 33 ] organic photocatalyst pumps, [ 34 ] and metal catalyst pumps. [ 31 ] [ 35 ] These pumps generate flow through a number of different mechanisms including self-diffusiophoresis, electrophoresis, bubble propulsion and the generation of density gradients. [ 29 ] [ 32 ] [ 36 ] Moreover, these chemically powered micropumps can be used as sensors for the detection of toxic agents. [ 30 ] [ 37 ] Recently, a combination of enzyme-based pumps has been used to enhance, suppress, and change the directionality of fluid flow. [ 38 ]
Another class of non-mechanical pumping is light-powered pumping. [ 39 ] [ 40 ] Certain nanoparticles are able to convert light from a UV source to heat which generates convective pumping. These kinds of pumps are possible with titanium dioxide nanoparticles and the speed of pumping can be controlled by both the intensity of the light source and the concentration of particles. [ 41 ]
Micropumps have potential industrial applications, such as delivery of small amounts of glue during manufacturing processes, and biomedical applications, including portable or implanted drug delivery devices. Bio-inspired applications include a flexible electromagnetic micropump using magnetorheological elastomer to replace lymphatic vessels . [ 42 ] Chemically powered micropumps also demonstrate potential for applications in chemical sensing in terms of detecting chemical warfare agents and environmental hazards, such as mercury and cyanide. [ 30 ]
Considering contemporary state of air pollution one of the most promising applications for micropump lies in enhancement of gas and particulate matter sensors for monitoring personal air quality. Thanks to MEMS fabrication technology, gas sensors based on MOS , NDIR , electrochemical principles could be miniaturized to fit portable devices as well as smartphones and wearables. Application of the Fraunhofer EMFT piezoelectric micropump reduces reaction time of the sensor up to 2 seconds through fast sampling of the ambient air. [ 43 ] This is explained by the fast convection that takes place when micropump drives the air towards the sensor, while in absence of the micropump due to slow diffusion sensor response is delayed for several minutes. The current alternative to the micropump – the fan – has numerous drawbacks. Unable to achieve substantial negative pressure fan cannot overcome pressure drop at the filter diaphragm. Further, the gas molecules and particles can easily re-adhere to the sensor surface and its housing, which in time results in sensor drift.
Additionally inbuilt micropump facilitates sensor regeneration and thus resolves saturation issues by expelling gas molecules out of the sensor surface. Breath analysis is related field of use for the gas sensor that is empowered by micropump. Micropump can advance remote diagnostic and monitoring of gastrointestinal tract and pulmonary diseases, diabetes, cancer etc. by means of portable devices within telemedicine programs.
The promising application for MEMS micropumps lies in drug delivery systems for diabetes-, tumor-, hormone-, pain and ocular therapy in forms of ultra-thin patches, targeted delivery within implantable systems or intelligent pills . Piezoelectric MEMS micropumps can replace traditional peristaltic or syringe pumps for intravenous , subcutaneous , arterial, ocular drug injection. Drug delivery application does not require high flow rates, however, the micropumps are supposed to be precise in delivering small doses and demonstrate back pressure independent flow. [ 16 ] Due to biocompatibility and miniature size, silicon piezoelectric micropump can be implanted on the eyeball to treat glaucoma or phthisis . Since under these conditions the eye loses its ability to ensure outflow or production of aqueous humour, the implanted micropump developed by Fraunhofer EMFT with the flow rate of 30 μL/s facilitates proper flow of the fluid without restricting or creating any inconvenience to the patient. [ 44 ] Another health issue to be solved by micropump is bladder incontinence . Artificial sphincter technology based on the titanium micropump ensures continence by automatically adjusting the pressure during laughter or coughing. The urethra is opened and closed by means of a fluid-filled sleeve that is regulated by the micropump. [ 45 ]
Micropump can facilitate scent scenario for consumer, medical, defense, first responder applications etc. to enhance the effect of with ubiquitous picture scenarios (movies) and sound scenarios (music). Microdosing device with several scent reservoirs that are mounted near the nose can release 15 different scent impressions in 1 min. [ 18 ] Advantage of the micropump lies in the possibility to smell sequence of scents without different odors being mixed. The system ensures an appropriate dose of the scent to be detected by the user only as soon as scent molecules are delivered. Numerous applications are possible with micropump for scent-dosing: tasters training (wine, food), learning programs, psychotherapy, anosmia treatment, first responder training etc. to facilitate full immersion in the desired environment.
Within analytical systems, the micropump can be for lab-on-chip applications, HPLC and Gas Chromatography systems etc. For the latter micropumps are required to ensure accurate delivery and flow of gases. Since the compressibility of the gases is challenging, the micropump must possess high compression ratio. [ 16 ]
Among other applications, the following fields can be named: dosage systems for small quantity of lubricants, fuel dosing systems, micro pneumatics, micro hydraulic systems and dosage systems in production processes, liquid handling (cushion pipettes, microliter plates). [ 46 ] | https://en.wikipedia.org/wiki/Micropump |
A micropyle is a pore in the membrane covering the ovum , through which a sperm enters.
Micropyles are also found in sporozoites of some digenetic microorganisms such as Plasmodium at the anterior part of the cell that ultimately leads towards the apical cap. Examples of other organisms that have micropyles are the Bombyx mandarina [ 1 ] and the Ceratitis capitata .
This animal anatomy –related article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Micropyle_(zoology) |
A Microraft ( Isoraft ) is an arrays of microwells for cell sorting , isolating cells , analyzing cells over time, and generating clonal populations . [ 1 ] This platform provides biomedical scientists with access to diverse cell culture surfaces with integrated, easy-to-use cell separating capabilities at low cost.
The microrafts have bases composed of detachable concave elements fabricated by a dip-coating process using a polydimethylsiloxane mold as the template and the array substrate. This manufacturing approach allows the microrafts to possess low autofluorescence and can therefore be utilized for fluorescence-based identification of cells. Cells plated on the microarray settle and attach at the center of the wells due to the microrafts’ concavity. Individual microrafts are dislodged using a needle inserted through the compliant polymer substrate. The hard polymer material of the microrafts protect the cells from damage by the needle. Cell analysis and isolation can be carried out using a standard inverted microscope . Released cells/microrafts can be collected, cultured and clonally expanded. [ 2 ] [ 3 ]
Using this system, extremely high single-cell cloning rates of greater than 95% have been achieved. [ citation needed ]
This system is ideal for both adherent and non-adherent cell types. | https://en.wikipedia.org/wiki/Microraft |
A microreactor or microstructured reactor or microchannel reactor is a device in which chemical reactions take place in a confinement with typical lateral dimensions below 1 mm;
the most typical form of such confinement are microchannels . [ 1 ] [ 2 ] Microreactors are studied in the field of micro process engineering , together with other devices (such as micro heat exchangers ) in which physical processes occur. The microreactor is usually a continuous flow reactor (contrast with/to a batch reactor ). Microreactors can offer many advantages over conventional scale reactors, including improvements in energy efficiency , reaction speed and yield, safety, reliability, scalability, on-site/on-demand production, and a much finer degree of process control .
Gas-phase microreactors have a long history but those involving liquids started to appear in the late 1990s. [ 1 ] One of the first microreactors with embedded high performance heat exchangers were made in the early 1990s by the Central Experimentation Department ( Hauptabteilung Versuchstechnik , HVT ) of Forschungszentrum Karlsruhe [ 3 ] in Germany, using mechanical micromachining techniques that were a spinoff from the manufacture of separation nozzles for uranium enrichment . [ 3 ] As research on nuclear technology was drastically reduced in Germany, microstructured heat exchangers were investigated for their application in handling highly exothermic and dangerous chemical reactions. This new concept, known by names as microreaction technology or micro process engineering , was further developed by various research institutions. An early example from 1997 involved that of azo couplings in a pyrex reactor with channel dimensions 90 micrometres deep and 190 micrometres wide. [ 1 ]
Using microreactors is somewhat different from using a glass vessel. These reactors may be a valuable tool in the hands of an experienced chemist or reaction engineer:
One of the simplest forms of a microreactor is a 'T' reactor. A 'T' shape is etched into a plate with a depth that may be 40 micrometres and a width of 100 micrometres: the etched path is turned into a tube by sealing a flat plate over the top of the etched groove. The cover plate has three holes that align to the top-left, top-right, and bottom of the 'T' so that fluids can be added and removed. A solution of reagent 'A' is pumped into the top left of the 'T' and solution 'B' is pumped into the top right of the 'T'. If the pumping rate is the same, the components meet at the top of the vertical part of the 'T' and begin to mix and react as they go down the trunk of the 'T'. A solution of product is removed at the base of the 'T'.
Microreactors can be used to synthesise material more effectively than current batch techniques allow. The benefits here are primarily enabled by the mass transfer , thermodynamics , and high surface area to volume ratio environment as well as engineering advantages in handling unstable intermediates. Microreactors are applied in combination with photochemistry , electrosynthesis , multicomponent reactions and polymerization (for example that of butyl acrylate ). It can involve liquid-liquid systems but also solid-liquid systems with for example the channel walls coated with a heterogeneous catalyst . Synthesis is also combined with online purification of the product. [ 1 ] Following green chemistry principles, microreactors can be used to synthesize and purify extremely reactive Organometallic Compounds for ALD and CVD applications, with improved safety in operations and higher purity products. [ 11 ] [ 12 ]
In microreactor studies a Knoevenagel condensation [ 13 ] was performed with the channel coated with a zeolite catalyst layer which also serves to remove water generated in the reaction. The same reaction was performed in a microreactor covered by polymer brushes. [ 14 ]
A Suzuki reaction was examined in another study [ 15 ] with a palladium catalyst confined in a polymer network of polyacrylamide and a triarylphosphine formed by interfacial polymerization :
The combustion of propane was demonstrated to occur at temperatures as low as 300 °C in a microchannel setup filled up with an aluminum oxide lattice coated with a platinum / molybdenum catalyst: [ 16 ]
Enzymes immobilized on solid supports are increasingly used for greener, more sustainable chemical transformation processes. > enabled to perform heterogeneous reactions in continuous mode, in organic media, and at elevated temperatures. Using microreactors, enabled faster polymerization and higher molecular mass compared to using batch reactors. It is evident that similar microreactor based platforms can readily be extended to other enzyme-based systems, for example, high-throughput screening of new enzymes and to precision measurements of new processes where continuous flow mode is preferred. This is the first reported demonstration of a solid supported enzyme-catalyzed polymerization reaction in continuous mode.
Microreactors can also enable experiments to be performed at a far lower scale and far higher experimental rates than currently possible in batch production, while not collecting the physical experimental output. The benefits here are primarily derived from the low operating scale, and the integration of the required sensor technologies to allow high quality understanding of an experiment. The integration of the required synthesis , purification and analytical capabilities is impractical when operating outside of a microfluidic context.
Researchers at the Radboud University Nijmegen and Twente University, the Netherlands, have developed a microfluidic high-resolution NMR flow probe. They have shown a model reaction being followed in real-time. The combination of the uncompromised (sub-Hz) resolution and a low sample volume can prove to be a valuable tool for flow chemistry. [ 17 ]
Mettler Toledo and Bruker Optics offer dedicated equipment for monitoring, with attenuated total reflectance spectrometry (ATR spectrometry) in microreaction setups. The former has been demonstrated for reaction monitoring. [ 18 ] The latter has been successfully used for reaction monitoring [ 19 ] and determining dispersion characteristics [ 20 ] of a microreactor.
Microreactors, and more generally, micro process engineering , are the subject of worldwide academic research. A prominent recurring conference is IMRET , the International Conference on Microreaction Technology. Microreactors and micro process engineering have also been featured in dedicated sessions of other conferences, such as the Annual Meeting of the American Institute of Chemical Engineers (AIChE), or the International Symposia on Chemical Reaction Engineering (ISCRE). Research is now also conducted at various academic institutions around the world, e.g. at the Massachusetts Institute of Technology (MIT) in Cambridge, Massachusetts, University of Illinois Urbana-Champaign , Oregon State University in Corvallis, Oregon, at University of California, Berkeley in Berkeley, California in the United States, at the EPFL in Lausanne, Switzerland, at Eindhoven University of Technology in Eindhoven, at Radboud University Nijmegen in Nijmegen, Netherlands and at the LIPHT of Université de Strasbourg in Strasbourg and LGPC of the University of Lyon , CPE Lyon , France and at KU Leuven , Belgium.
The market for microreactors can be segmented based on customer objectives, into turnkey, modular, and bespoke systems.
Turnkey (ready to run) systems are being used where the application environment stands to benefit from new chemical synthesis schemes, enhanced investigational throughput of up to approximately 10 - 100 experiments per day (depends on reaction time) and reaction subsystem, and actual synthesis conduct at scales ranging from 10 milligrams per experiment to triple digit tons per year (continuous operation of a reactor battery).
Modular (open) systems are serving the niche for investigations on continuous process engineering lay-outs, where a measurable process advantage over the use of standardized equipment is anticipated by chemical engineers. Multiple process lay-outs can be rapidly assembled and chemical process results obtained on a scale ranging from several grams per experiment up to approximately 100 kg at a moderate number of experiments per day (3-15). A secondary transfer of engineering findings in the context of a plant engineering exercise (scale-out) then provides target capacity of typically single product dedicated plants. This mimics the success of engineering contractors for the petro-chemical process industry.
With dedicated developments, manufacturers of microstructured components are mostly commercial development partners to scientists in search of novel synthesis technologies. Such development partners typically excel in the set-up of comprehensive investigation and supply schemes, to model a desired contacting pattern or spatial arrangement of matter. To do so they predominantly offer information from proprietary integrated modeling systems that combine computational fluid dynamics with thermokinetic modelling. Moreover, as a rule, such development partners establish the overall application analytics to the point where the critical initial hypothesis can be validated and further confined. | https://en.wikipedia.org/wiki/Microreactor |
A microsatellite is a tract of repetitive DNA in which certain DNA motifs (ranging in length from one to six or more base pairs ) are repeated, typically 5–50 times. [ 1 ] [ 2 ] Microsatellites occur at thousands of locations within an organism's genome . They have a higher mutation rate than other areas of DNA [ 3 ] leading to high genetic diversity . Microsatellites are often referred to as short tandem repeats ( STRs ) by forensic geneticists and in genetic genealogy , or as simple sequence repeats ( SSRs ) by plant geneticists. [ 4 ]
Microsatellites and their longer cousins, the minisatellites , together are classified as VNTR (variable number of tandem repeats ) DNA. The name "satellite" DNA refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying "satellite" layers of repetitive DNA. [ 5 ]
They are widely used for DNA profiling in cancer diagnosis , in kinship analysis (especially paternity testing ) and in forensic identification. They are also used in genetic linkage analysis to locate a gene or a mutation responsible for a given trait or disease. Microsatellites are also used in population genetics to measure levels of relatedness between subspecies, groups and individuals.
Although the first microsatellite was characterised in 1984 at the University of Leicester by Weller, Jeffreys and colleagues as a polymorphic GGAT repeat in the human myoglobin gene, the term "microsatellite" was introduced later, in 1989, by Litt and Luty. [ 1 ] The name "satellite" DNA refers to the early observation that centrifugation of genomic DNA in a test tube separates a prominent layer of bulk DNA from accompanying "satellite" layers of repetitive DNA. [ 5 ] The increasing availability of DNA amplification by PCR at the beginning of the 1990s triggered a large number of studies using the amplification of microsatellites as genetic markers for forensic medicine, for paternity testing, and for positional cloning to find the gene underlying a trait or disease. Prominent early applications include the identifications by microsatellite genotyping of the eight-year-old skeletal remains of a British murder victim ( Hagelberg et al. 1991), and of the Auschwitz concentration camp doctor Josef Mengele who escaped to South America following World War II ( Jeffreys et al. 1992). [ 1 ]
A microsatellite is a tract of tandemly repeated (i.e. adjacent) DNA motifs that range in length from one to six or up to ten nucleotides (the exact definition and delineation to the longer minisatellites varies from author to author), [ 1 ] [ 6 ] and are typically repeated 5–50 times. For example, the sequence TATATATATA is a dinucleotide microsatellite, and GTCGTCGTCGTCGTC is a trinucleotide microsatellite (with A being Adenine , G Guanine , C Cytosine , and T Thymine ). Repeat units of four and five nucleotides are referred to as tetra- and pentanucleotide motifs, respectively. Most eukaryotes have microsatellites, with the notable exception of some yeast species. Microsatellites are distributed throughout the genome. [ 7 ] [ 1 ] [ 8 ] The human genome for example contains 50,000–100,000 dinucleotide microsatellites, and lesser numbers of tri-, tetra- and pentanucleotide microsatellites. [ 9 ] Many are located in non-coding parts of the human genome and therefore do not produce proteins, but they can also be located in regulatory regions and coding regions .
Microsatellites in non-coding regions may not have any specific function, and therefore might not be selected against; this allows them to accumulate mutations unhindered over the generations and gives rise to variability that can be used for DNA fingerprinting and identification purposes. Other microsatellites are located in regulatory flanking or intronic regions of genes, or directly in codons of genes – microsatellite mutations in such cases can lead to phenotypic changes and diseases, notably in triplet expansion diseases such as fragile X syndrome and Huntington's disease . [ 10 ]
Telomeres are linear sequences of DNA that sit at the very ends of chromosomes and protect the integrity of genomic material (not unlike an aglet on the end of a shoelace) during successive rounds of cell division due to the "end replication problem". [ 6 ] In white blood cells, the gradual shortening of telomeric DNA has been shown to inversely correlate with ageing in several sample types. [ 11 ] Telomeres consist of repetitive DNA, with the hexanucleotide repeat motif TTAGGG in vertebrates. [ citation needed ] They are thus classified as minisatellites . Similarly, insects have shorter repeat motifs in their telomeres that could arguably be considered microsatellites. [ citation needed ]
Unlike point mutations , which affect only a single nucleotide, microsatellite mutations lead to the gain or loss of an entire repeat unit, and sometimes two or more repeats simultaneously. Thus, the mutation rate at microsatellite loci is expected to differ from other mutation rates, such as base substitution rates. [ 12 ] [ 13 ] The mutation rate at microsatellite loci depends on the repeat motif sequence, the number of repeated motif units and the purity of the canonical repeated sequence. [ 14 ] A variety of mechanisms for mutation of microsatellite loci have been reviewed, [ 14 ] [ 15 ] and their resulting polymorphic nature has been quantified. [ 16 ] The actual cause of mutations in microsatellites is debated.
One proposed cause of such length changes is replication slippage, caused by mismatches between DNA strands while being replicated during meiosis . [ 17 ] DNA polymerase , the enzyme responsible for reading DNA during replication, can slip while moving along the template strand and continue at the wrong nucleotide. DNA polymerase slippage is more likely to occur when a repetitive sequence (such as CGCGCG) is replicated. Because microsatellites consist of such repetitive sequences, DNA polymerase may make errors at a higher rate in these sequence regions. Several studies have found evidence that slippage is the cause of microsatellite mutations. [ 18 ] [ 19 ] Typically, slippage in each microsatellite occurs about once per 1,000 generations. [ 20 ] Thus, slippage changes in repetitive DNA are three orders of magnitude more common than point mutations in other parts of the genome. [ 21 ] Most slippage results in a change of just one repeat unit, and slippage rates vary for different allele lengths and repeat unit sizes, [ 3 ] and within different species. [ 22 ] [ 23 ] [ 24 ] If there is a large size difference between individual alleles, then there may be increased instability during recombination at meiosis. [ 21 ]
Another possible cause of microsatellite mutations are point mutations, where only one nucleotide is incorrectly copied during replication. A study comparing human and primate genomes found that most changes in repeat number in short microsatellites appear due to point mutations rather than slippage. [ 25 ]
Direct estimates of microsatellite mutation rates have been made in numerous organisms, from insects to humans. In the desert locust Schistocerca gregaria , the microsatellite mutation rate was estimated at 2.1 × 10 −4 per generation per locus. [ 26 ] The microsatellite mutation rate in human male germ lines is five to six times higher than in female germ lines and ranges from 0 to 7 × 10 −3 per locus per gamete per generation. [ 3 ] In the nematode Pristionchus pacificus , the estimated microsatellite mutation rate ranges from 8.9 × 10 −5 to 7.5 × 10 −4 per locus per generation. [ 27 ]
Microsatellite mutation rates vary with base position relative to the microsatellite, repeat type, and base identity. [ 25 ] Mutation rate rises specifically with repeat number, peaking around six to eight repeats and then decreasing again. [ 25 ] Increased heterozygosity in a population will also increase microsatellite mutation rates, [ 28 ] especially when there is a large length difference between alleles. This is likely due to homologous chromosomes with arms of unequal lengths causing instability during meiosis. [ 29 ]
Many microsatellites are located in non-coding DNA and are biologically silent. Others are located in regulatory or even coding DNA – microsatellite mutations in such cases can lead to phenotypic changes and diseases. A genome-wide study estimates that microsatellite variation contributes 10–15% of heritable gene expression variation in humans. [ 30 ] [ 16 ]
In mammals, 20–40% of proteins contain repeating sequences of amino acids encoded by short sequence repeats. [ 31 ] Most of the short sequence repeats within protein-coding portions of the genome have a repeating unit of three nucleotides, since that length will not cause frame-shifts when mutating. [ 32 ] Each trinucleotide repeating sequence is transcribed into a repeating series of the same amino acid. In yeasts, the most common repeated amino acids are glutamine, glutamic acid, asparagine, aspartic acid and serine.
Mutations in these repeating segments can affect the physical and chemical properties of proteins, with the potential for producing gradual and predictable changes in protein action. [ 33 ] For example, length changes in tandemly repeating regions in the Runx2 gene lead to differences in facial length in domesticated dogs ( Canis familiaris ), with an association between longer sequence lengths and longer faces. [ 34 ] This association also applies to a wider range of Carnivora species. [ 35 ] Length changes in polyalanine tracts within the HOXA13 gene are linked to hand-foot-genital syndrome , a developmental disorder in humans. [ 36 ] Length changes in other triplet repeats are linked to more than 40 neurological diseases in humans, notably trinucleotide repeat disorders such as fragile X syndrome and Huntington's disease . [ 10 ] Evolutionary changes from replication slippage also occur in simpler organisms. For example, microsatellite length changes are common within surface membrane proteins in yeast, providing rapid evolution in cell properties. [ 37 ] Specifically, length changes in the FLO1 gene control the level of adhesion to substrates. [ 38 ] Short sequence repeats also provide rapid evolutionary change to surface proteins in pathenogenic bacteria; this may allow them to keep up with immunological changes in their hosts. [ 39 ] Length changes in short sequence repeats in a fungus ( Neurospora crassa ) control the duration of its circadian clock cycles. [ 40 ]
Length changes of microsatellites within promoters and other cis-regulatory regions can change gene expression quickly, between generations. The human genome contains many (>16,000) short sequence repeats in regulatory regions, which provide 'tuning knobs' on the expression of many genes. [ 30 ] [ 41 ]
Length changes in bacterial SSRs can affect fimbriae formation in Haemophilus influenzae , by altering promoter spacing. [ 39 ] Dinucleotide microsatellites are linked to abundant variation in cis-regulatory control regions in the human genome. [ 41 ] Microsatellites in control regions of the Vasopressin 1a receptor gene in voles influence their social behavior, and level of monogamy. [ 42 ]
In Ewing sarcoma (a type of painful bone cancer in young humans), a point mutation has created an extended GGAA microsatellite which binds a transcription factor, which in turn activates the EGR2 gene which drives the cancer. [ 43 ] In addition, other GGAA microsatellites may influence the expression of genes that contribute to the clinical outcome of Ewing sarcoma patients. [ 44 ]
Microsatellites within introns also influence phenotype, through means that are not currently understood. For example, a GAA triplet expansion in the first intron of the X25 gene appears to interfere with transcription, and causes Friedreich's ataxia . [ 45 ] Tandem repeats in the first intron of the Asparagine synthetase gene are linked to acute lymphoblastic leukaemia. [ 46 ] A repeat polymorphism in the fourth intron of the NOS3 gene is linked to hypertension in a Tunisian population. [ 47 ] Reduced repeat lengths in the EGFR gene are linked with osteosarcomas. [ 48 ]
An archaic form of splicing preserved in zebrafish is known to use microsatellite sequences within intronic mRNA for the removal of introns in the absence of U2AF2 and other splicing machinery. It is theorized that these sequences form highly stable cloverleaf configurations that bring the 3' and 5' intron splice sites into close proximity, effectively replacing the spliceosome . This method of RNA splicing is believed to have diverged from human evolution at the formation of tetrapods and to represent an artifact of an RNA world . [ 49 ]
Almost 50% of the human genome is contained in various types of transposable elements (also called transposons, or 'jumping genes'), and many of them contain repetitive DNA. [ 50 ] It is probable that short sequence repeats in those locations are also involved in the regulation of gene expression. [ 51 ]
Microsatellites are used for assessing chromosomal DNA deletions in cancer diagnosis. Microsatellites are widely used for DNA profiling , also known as "genetic fingerprinting", of crime stains (in forensics) and of tissues (in transplant patients). They are also widely used in kinship analysis (most commonly in paternity testing). Also, microsatellites are used for mapping locations within the genome, specifically in genetic linkage analysis to locate a gene or a mutation responsible for a given trait or disease. As a special case of mapping, they can be used for studies of gene duplication or deletion . Researchers use microsatellites in population genetics and in species conservation projects. Plant geneticists have proposed the use of microsatellites for marker assisted selection of desirable traits in plant breeding.
In tumour cells, whose controls on replication are damaged, microsatellites may be gained or lost at an especially high frequency during each round of mitosis . Hence a tumour cell line might show a different genetic fingerprint from that of the host tissue, and, especially in colorectal cancer , might present with loss of heterozygosity . [ 52 ] [ 53 ] Microsatellites analyzed in primary tissue therefore been routinely used in cancer diagnosis to assess tumour progression. [ 54 ] [ 55 ] [ 56 ] Genome Wide Association Studies (GWAS) have been used to identify microsatellite biomarkers as a source of genetic predisposition in a variety of cancers. [ 57 ] [ 58 ] [ 59 ]
Microsatellite analysis became popular in the field of forensics in the 1990s. [ 60 ] It is used for the genetic fingerprinting of individuals where it permits forensic identification (typically matching a crime stain to a victim or perpetrator). It is also used to follow up bone marrow transplant patients. [ 61 ]
The microsatellites in use today for forensic analysis are all tetra- or penta-nucleotide repeats, as these give a high degree of error-free data while being short enough to survive degradation in non-ideal conditions. Even shorter repeat sequences would tend to suffer from artifacts such as PCR stutter and preferential amplification, while longer repeat sequences would suffer more highly from environmental degradation and would amplify less well by PCR . [ 62 ] Another forensic consideration is that the person's medical privacy must be respected, so that forensic STRs are chosen which are non-coding, do not influence gene regulation, and are not usually trinucleotide STRs which could be involved in triplet expansion diseases such as Huntington's disease . Forensic STR profiles are stored in DNA databanks such as the UK National DNA Database (NDNAD), the American CODIS or the Australian NCIDD.
Autosomal microsatellites are widely used for DNA profiling in kinship analysis (most commonly in paternity testing). [ 63 ] Paternally inherited Y-STRs (microsatellites on the Y chromosome ) are often used in genealogical DNA testing .
During the 1990s and the first several years of this millennium, microsatellites were the workhorse genetic markers for genome-wide scans to locate any gene responsible for a given phenotype or disease, using segregation observations across generations of a sampled pedigree. Although the rise of higher throughput and cost-effective single-nucleotide polymorphism (SNP) platforms led to the era of the SNP for genome scans, microsatellites remain highly informative measures of genomic variation for linkage and association studies. Their continued advantage lies in their greater allelic diversity than biallelic SNPs, thus microsatellites can differentiate alleles within a SNP-defined linkage disequilibrium block of interest. Thus, microsatellites have successfully led to discoveries of type 2 diabetes ( TCF7L2 ) and prostate cancer genes (the 8q21 region). [ 6 ] [ 64 ]
Microsatellites were popularized in population genetics during the 1990s because as PCR became ubiquitous in laboratories researchers were able to design primers and amplify sets of microsatellites at low cost. Their uses are wide-ranging. [ 66 ] A microsatellite with a neutral evolutionary history makes it applicable for measuring or inferring bottlenecks , [ 67 ] local adaptation , [ 68 ] the allelic fixation index (F ST ), [ 69 ] population size , [ 70 ] and gene flow . [ 71 ] As next generation sequencing becomes more affordable the use of microsatellites has decreased, however they remain a crucial tool in the field. [ 72 ]
Marker assisted selection or marker aided selection (MAS) is an indirect selection process where a trait of interest is selected based on a marker ( morphological , biochemical or DNA / RNA variation) linked to a trait of interest (e.g. productivity, disease resistance, stress tolerance, and quality), rather than on the trait itself. Microsatellites have been proposed to be used as such markers to assist plant breeding. [ 73 ]
Repetitive DNA is not easily analysed by next generation DNA sequencing methods, for some technologies struggle with homopolymeric tracts. A variety of software approaches have been created for the analysis or raw nextgen DNA sequencing reads to determine the genotype and variants at repetitive loci. [ 75 ] [ 76 ] Microsatellites can be analysed and verified by established PCR amplification and amplicon size determination, sometimes followed by Sanger DNA sequencing .
In forensics, the analysis is performed by extracting nuclear DNA from the cells of a sample of interest, then amplifying specific polymorphic regions of the extracted DNA by means of the polymerase chain reaction . Once these sequences have been amplified, they are resolved either through gel electrophoresis or capillary electrophoresis , which will allow the analyst to determine how many repeats of the microsatellites sequence in question there are. If the DNA was resolved by gel electrophoresis, the DNA can be visualized either by silver staining (low sensitivity, safe, inexpensive), or an intercalating dye such as ethidium bromide (fairly sensitive, moderate health risks, inexpensive), or as most modern forensics labs use, fluorescent dyes (highly sensitive, safe, expensive). [ 77 ] Instruments built to resolve microsatellite fragments by capillary electrophoresis also use fluorescent dyes. [ 77 ] Forensic profiles are stored in major databanks. The British data base for microsatellite loci identification was originally based on the British SGM+ system [ 78 ] [ 79 ] using 10 loci and a sex marker . The Americans [ 80 ] increased this number to 13 loci. [ 81 ] The Australian database is called the NCIDD, and since 2013 it has been using 18 core markers for DNA profiling. [ 60 ]
Microsatellites can be amplified for identification by the polymerase chain reaction (PCR) process, using the unique sequences of flanking regions as primers . DNA is repeatedly denatured at a high temperature to separate the double strand, then cooled to allow annealing of primers and the extension of nucleotide sequences through the microsatellite. This process results in production of enough DNA to be visible on agarose or polyacrylamide gels; only small amounts of DNA are needed for amplification because in this way thermocycling creates an exponential increase in the replicated segment. [ 82 ] With the abundance of PCR technology, primers that flank microsatellite loci are simple and quick to use, but the development of correctly functioning primers is often a tedious and costly process.
If searching for microsatellite markers in specific regions of a genome, for example within a particular intron , primers can be designed manually. This involves searching the genomic DNA sequence for microsatellite repeats, which can be done by eye or by using automated tools such as repeat masker . Once the potentially useful microsatellites are determined, the flanking sequences can be used to design oligonucleotide primers which will amplify the specific microsatellite repeat in a PCR reaction.
Random microsatellite primers can be developed by cloning random segments of DNA from the focal species. These random segments are inserted into a plasmid or bacteriophage vector , which is in turn implanted into Escherichia coli bacteria. Colonies are then developed, and screened with fluorescently–labelled oligonucleotide sequences that will hybridize to a microsatellite repeat, if present on the DNA segment. If positive clones can be obtained from this procedure, the DNA is sequenced and PCR primers are chosen from sequences flanking such regions to determine a specific locus . This process involves significant trial and error on the part of researchers, as microsatellite repeat sequences must be predicted and primers that are randomly isolated may not display significant polymorphism. [ 21 ] [ 83 ] Microsatellite loci are widely distributed throughout the genome and can be isolated from semi-degraded DNA of older specimens, as all that is needed is a suitable substrate for amplification through PCR.
More recent techniques involve using oligonucleotide sequences consisting of repeats complementary to repeats in the microsatellite to "enrich" the DNA extracted ( microsatellite enrichment ). The oligonucleotide probe hybridizes with the repeat in the microsatellite, and the probe/microsatellite complex is then pulled out of solution. The enriched DNA is then cloned as normal, but the proportion of successes will now be much higher, drastically reducing the time required to develop the regions for use. However, which probes to use can be a trial and error process in itself. [ 84 ]
ISSR (for inter-simple sequence repeat ) is a general term for a genome region between microsatellite loci. The complementary sequences to two neighboring microsatellites are used as PCR primers; the variable region between them gets amplified. The limited length of amplification cycles during PCR prevents excessive replication of overly long contiguous DNA sequences, so the result will be a mix of a variety of amplified DNA strands which are generally short but vary much in length.
Sequences amplified by ISSR-PCR can be used for DNA fingerprinting. Since an ISSR may be a conserved or nonconserved region, this technique is not useful for distinguishing individuals, but rather for phylogeography analyses or maybe delimiting species ; sequence diversity is lower than in SSR-PCR, but still higher than in actual gene sequences. In addition, microsatellite sequencing and ISSR sequencing are mutually assisting, as one produces primers for the other.
Repetitive DNA is not easily analysed by next generation DNA sequencing methods, which struggle with homopolymeric tracts. [ 85 ] Therefore, microsatellites are normally analysed by conventional PCR amplification and amplicon size determination. The use of PCR means that microsatellite length analysis is prone to PCR limitations like any other PCR-amplified DNA locus. A particular concern is the occurrence of ' null alleles ': | https://en.wikipedia.org/wiki/Microsatellite |
Microsatellite enrichment is a method in molecular biology used for enriching the amount of microsatellite sequences in a DNA sample. This can be achieved by designing oligonucleotide probes that hybridize with the repeats in the microsatellites and then pull out the probe/microsatellite complexes from the solution. [ 1 ] This has been shown to be a cost-effective method to sample the genetic diversity in non-model organisms. [ 2 ]
This molecular or cell biology article is a stub . You can help Wikipedia by expanding it . | https://en.wikipedia.org/wiki/Microsatellite_enrichment |
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