Significance and Use
4.1 This practice summarizes two methods that may be used to precondition UHMWPE by the absorption of lipids to differentiate the simulated in vitro oxidative stability of UHMWPEs, after lipid exposure.
4.1.1 Procedure A, High Squalene Absorption—This method of preconditioning with lipids may be used for comparative oxidative stability testing to screen different materials under aggressive conditions.
4.1.2 Procedure B, Mixed Lipid Absorption—This method of preconditioning may be used for comparative oxidative stability testing under mild conditions that more closely simulate in-vivo conditions.
4.2 This practice may be used to accelerate the oxidation of UHMWPE components when using elevated temperature and elevated oxygen pressure according to the methods of Practice F2003. Under real-time conditions such as implantation, oxidative changes to UHMWPE formulations may take months or years to produce changes that may result in deleterious mechanical performance. The method outlined in this practice permits the preparation of UHMWPE for evaluation of oxidative stability in a relatively short period of time (for example, weeks).
4.3 This practice may also be used to precondition UHMWPE test specimens prior to characterization of their physical and chemical properties. In particular, this practice may be used for preconditioning with lipids prior to oxidation induction time (OIT) testing as outlined in Test Method D3895.
Scope
1.1 It is the intent of this practice to permit an investigator to incorporate lipids found in the synovial environment into polymeric specimens. This can be used as a preconditioning step to evaluate the oxidative stability of ultra-high-molecular-weight polyethylene (UHMWPE) materials. This practice describes a laboratory procedure for preconditioning of UHMWPE specimens.
1.2 The preconditioned UHMWPE can be aged at elevated temperature and at elevated oxygen pressure following methods of accelerated aging described in Practice F2003, to accelerate oxidation of the material and thereby allow for the evaluation of its long-term chemical stability.
1.3 The preconditioned UHMWPE can be tested without further aging using a method to evaluate oxidative stability such as oxidation induction time as described in Test Method D3895.
1.4 The methods of this practice may be used on any type of UHMWPE material intended for use in total joint arthroplasty in a synovial joint (for example, conventional, cross-linked, antioxidant stabilized, etc.). See Appendix X1.
1.5 Although the preconditioning method followed by accelerated aging described by this practice will permit an investigator to compare the oxidative stability of different UHMWPE materials, it is recognized that this method is not known to simulate the degradative mechanisms for an implant during real-time shelf aging or in vivo. The described methods have not been evaluated for mechanical testing under cyclic loading.
1.6 The preconditioning and accelerated aging methods specified herein are intended to rank the resistance to oxidation of materials as a result of the absorption of lipids, which may occur in UHMWPE following implantation, and to determine susceptibility to oxidative changes. The methods have not been evaluated for use in preconditioning of UHMWPE components for subsequent testing of mechanical or wear properties. Procedure A should not be used for preconditioning of UHMWPE components for subsequent testing of mechanical or wear properties.
1.7 The values stated in SI units are to be regarded as standard. The values given in parentheses are mathematical conversions to inch-pound units that are for information only and are not considered standard.
1.8 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.
1.9 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.
