A methodology for examining the plausibility of accelerated aging protocols for UHMWPE components

In light of the time-intensive nature of using real-time shelf-aged specimens in research into property changes of ultra-high-molecular-weight polyethylene (UHMWPE), accelerated thermal diffusion oxidative aging (usually referred to as accelerated aging) is frequently resorted to. A number of such aging protocols have been reported in the literature, with various claims for their producing changes in the properties of the polymer being the same as or similar to those seen in real-time shelf-aged samples. The thrust of the present work is the presentation of a methodology for examining such claims. The methodology is applied to six properties (% crystallinity, melting temperature, oxidation index, ultimate tensile strength, ultimate tensile elongation, and tensile toughness) of 4150HP UHMWPE grade, sterilized using six different methods, prior to and following the use of a specific accelerated aging protocol (oxygen gas at 70 degrees C and 507 kPa pressure; 14 d.). These six properties have been identified in the literature as being strongly correlated with the clinical wear of UHMWPE articular components. It is shown that the claim for the protocol used in the present work (in terms of the simulated equivalent shelf aging time) is plausible. It needs to be emphasized, however, that this conclusion is tentative given the paucity of the relevant literature results that are currently available and which are vital to the application of the methodology.