Comparative oxidative stability of α-tocopherol blended and diffused UHMWPEs at 3 years of real-time aging

Vitamin E (α-tocopherol) is a free-radical stabilizing antioxidant used to maintain oxidative stability in radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) used in total joint replacements. We investigated the oxidative resistance of vitamin E-stabilized UHMWPE in (i) postirradiation vitamin E-diffused UHMWPE, (ii) vitamin E blended and irradiated UHMWPE, and (iii) unstabilized, irradiated UHMWPE after accelerated aging and real-time aging in an aqueous environment at 40°C for 36 months. Unstabilized samples exhibited substantial oxidation throughout the surface and bulk with both types of aging. While vitamin E-stabilized, radiation cross-linked UHMWPEs were all superior to unstabilized samples, irradiated blends showed surface oxidation and subsurface oxidation potential beginning at ten months in real-time aging. In contrast, postirradiation vitamin E-diffused UHMWPEs showed no detectable oxidation and no increase in oxidation potential despite elution of some vitamin E. We also showed that current thermal accelerated aging methods were unable to differentiate among the oxidative stability of vitamin E-stabilized, radiation cross-linked UHMWPEs prepared by different processes.