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1.1 This test method covers in vitro degradation of hydrolytically degradable polymers (HDP) intended for use in surgical implants. It provides a detailed methodology for conditioning samples and suggests quantitative techniques for evaluating changes in properties (for example, mass, molar mass, and mechanical strength) over time.

1.2 The requirements of this test method apply to HDPs in various forms:

1.3 This standard provides guidance for mechanical loading or fluid flow, or both, when relevant to the device being evaluated. The specifics of loading type, magnitude, and frequency for a given application are beyond the scope of this test method.

1.4 This standard is not applicable to conditioning of polymers that degrade primarily through mechanisms other than hydrolysis (for example, enzymatic or oxidative degradation). See X1.1.1 for more information.

1.5 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.

1.6 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.

1.7 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

5.1 This test method is intended to help assess the degradation rates (that is, the mass loss rate) and changes in material or structural properties, or both, of HDP materials used in surgical implants. Polymers that are known to degrade primarily by hydrolysis include but are not limited to homopolymers and copolymers of l-lactide, d-lactide, d,l-lactide glycolide, caprolactone, and p-dioxanone.7

5.2 This test method may not be appropriate for all types of implant applications or for all known absorbable polymers. The user is cautioned to consider the appropriateness of the test method in view of the materials being tested and their potential application (see X1.1.1).

5.3 Since it is well known that mechanical loading can increase the degradation rate of absorbable polymers, the presence and extent of such loading needs to be considered when comparing in vitro behavior with that expected or observed in vivo.

5.4 Absorbable devices subjected to flow conditions (for example, vascular stents, particularly those with a drug eluting component) may degrade more rapidly than the same device maintained under static degradation test conditions. When it is feasible to estimate the flow conditions that an implant will be subjected to in vivo and replicate them in vitro the degradation study should be conducted under flow conditions. However, details regarding appropriate flow modeling are beyond the scope of this test method.

5.5 Sterilization of HDP materials should be expected to cause changes in molar mass or structure, or both, of the polymers. This can affect the initial mechanical and physical properties of a material or device, as well as its subsequent rate of degradation. Therefore, if a test is intended to be representative of actual performance in vivo, specimens shall be packaged and sterilized in a manner consistent with that of the final device. Non-sterilized specimens may be included for comparative purposes.