Standard Practice for Accelerated Aging of Ultra-High Molecular Weight Polyethylene after Gamma Irradiation in Air
This practice summarizes a method that may be used to accelerate the oxidation of UHMWPE components using elevated temperature and elevated oxygen pressure. Under real-time conditions, such as shelf aging and implantation, oxidative changes to UHMWPE after sterilization using high energy radiation may take months or years to produce changes that may result in deleterious mechanical performance. The method outlined in this practice permits the evaluation of oxidative stability in a relatively short period of time (for example, weeks).
This practice may also be used to oxidize UHMWPE test specimens and joint replacement components prior to characterization of their physical, chemical, and mechanical properties. In particular, this practice may be used for accelerated aging of UHMWPE components prior to evaluation in a hip or knee joint wear simulator as outlined in Guide F 1714 (hip wear), Guide F 1715 (knee wear), ISO 14242 (hip wear), or ISO 14243 (knee wear), or combination thereof.
1.1 It is the intent of this practice to permit an investigator to evaluate the oxidative stability of UHMWPE materials as a function of processing and sterilization method. This practice describes a laboratory procedure for accelerated aging of ultra-high molecular weight polyethylene (UHMWPE) specimens and components for total joint prostheses. The UHMWPE is aged at elevated temperature and at elevated oxygen pressure, to accelerate oxidation of the material and thereby allow for the evaluation of its long-term chemical and mechanical stability.
1.2 Although the accelerated-aging method described by this practice will permit an investigator to compare the oxidative stability of different UHMWPE materials, it is recognized that this method may not precisely simulate the degradative mechanisms for an implant during real-time shelf aging and implantation.
1.3 The accelerated aging method specified herein has been validated based on oxidation levels exhibited by certain shelf-aged UHMWPE components packaged in air and sterilized with gamma radiation. The method has not been shown to be representative of shelf aging when the UHMWPE is packaged in an environment other than air. For example, this practice has not been directly correlated with the shelf life of components that have been sealed in a low-oxygen package, such as nitrogen. This practice is not intended to simulate any change that may occur in UHMWPE following implantation.
1.4 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 and health practices and determine the applicability of regulatory limitations prior to use.
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