Improved oxidation and wear resistance of ultrahigh molecular weight polyethylene using cross-linked powder reinforcement.

Abstract

Radiation crosslinking decreases the wear of ultrahigh molecular weight polyethylene (UHMWPE) used in total joint implants and creates residual free radicals, which are the precursors of oxidative degradation. It is desirable to obtain a simultaneously wear- and oxidation-resistant UHMWPE in order to prolong the longevity of implants. In this study, we hypothesized that the oxidative stability of a vitamin E-containing, wear resistant UHMWPE can be improved by limiting the exposure of the antioxidant to radiation to maximize its activity. We blended UHMWPE powder with 0.1 wt % vitamin-E and irradiated these powder blends (XPE). We further blended and consolidated uncrosslinked 0.1 wt % vitamin E-blended UHMWPE with XPE and assessed the effects of radiation dose used for XPE and XPE content in the formulation on pin-on-disk wear resistance, static mechanical properties, and squalene-initiated accelerated thermal aging. The wear rate decreased significantly with increasing XPE content in UHMWPE/XPE and increasing radiation dose used in the XPE preparation. The UHMWPE/XPE blends displayed improved oxidation resistance in the presence of the pro-oxidant squalene compared to vitamin E-blended UHMWPE irradiated to 125 kGy after consolidation. Strength and toughness of the UHMWPE/XPE blends decreased with increasing radiation dose and increasing XPE content; and these were comparable to those measured with the consolidated and irradiated vitamin E-blended UHMWPE. Blending UHMWPE with XPE is a feasible approach to create a wear resistant UHMWPE with more active vitamin E available for long-term oxidative protection of the polymer as the radiation exposure of the vitamin-E in the vitamin E-blended UHMWPE matrix is minimized. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater 107B: 716-723, 2019.