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<title>Efficiency-COU</title>
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<h2 id="context-of-use-cou">Context of Use (COU)</h2>
<p>The extraction efficiency module of the CHemical RISk calculator
(CHRIS) allows the user to compare the theoretical impact of extraction
conditions, sample geometry and material properties on extraction
efficiency and extraction solvent concentration. These assessments can
assist device manufacturers and test laboratories by providing immediate
feedback on “worst-case” device geometries and extraction conditions
based on the endpoint of interest. This information can support reducing
the number of configurations that need to be tested for a device product
line to support biocompatibility evaluation of a medical device.
Further, the tool can potentially be used to guide the development of
alternative extraction test protocols.</p>
<p>The CHRIS - extraction efficiency module outputs a predicted
extraction efficiency (mass of extractable released over the initial
mass in the test article) and relative extract solvent concentration
(concentration in the solvent over the initial concentration in the test
article) based a non-steady state mass transfer model. The model
requires eight (8) input fields that describe the extraction conditions,
test article geometry, and test material system, including the mass,
density and surface area of the test article, extraction solvent volume,
extraction time, number of iterations, and the diffusion and partition
coefficients that describe the system of interest. For additional
details on the model please see this <a
href="https://www.sciencedirect.com/science/article/pii/S0273230023000739">article</a>.</p>
<p>The tool is limited by the assumptions upon which the model is based.
The salient limitations are enumerated below:</p>
<ol type="1">
<li>The extractable is macroscopically homogeneous within the matrix.
Therefore, the output is only applicable to compounds that are
introduced either intentionally or unintentionally during synthesis
(e.g., residual monomers and oligomers, catalysts, initiators) or
compounding (e.g., stabilizers, antioxidants, plasticizers). The model
is not appropriate for surface residuals from processing, cleaning, and
sterilization.</li>
<li>The solvent is “perfectly mixed”. This should be a reasonable
assumption provided the samples are adequately agitated over the
timeframe of the testing. However, this assumption may not be
appropriate if sufficient agitation is not applied and a signficant
boundary layer develops that slows the release rate or if the extraction
is conducted under flow conditions.</li>
<li>Possible chemical reactions are not considered. Therefore, if the
polymer matrix undergoes substantive degradation during the extraction
test, the predictions may not be relevant. Further, the model does not
consider the potential for individual extractable compounds to degrade
over the selected timeframe.</li>
<li>The test article is comprised of a single polymer matrix. In
practice, complex devices may be comprised of multiple components and/or
polymer matrices. In these scenarios, careful consideration of the
potential contributions of each material constituent of the test article
to the extractables profile is critical when attempting to leverage the
model predictions.</li>
</ol>
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