The effect of α-tocopherol on the oxidation and free radical decay in irradiated UHMWPE

We developed a radiation cross-linked ultra-high molecular weight polyethylene (UHMWPE) stabilized with α-tocopherol (Vitamin E) as a bearing material in total joint replacements. The stabilizing effect of α-tocopherol on free radical reactions in UHMWPE is not well understood. We investigated the effect of α-tocopherol on the oxidation and transformation of residual free radicals during real-time aging of α-tocopherol-doped, irradiated UHMWPE (αTPE) and irradiated UHMWPE (control). Samples were aged at 22 °C (room temperature) in air, at 40 °C in air and at 40 °C in water for 7 months. During the first month, αTPE showed some oxidation at the surface, which stayed constant thereafter. Control exhibited substantial oxidation in the subsurface region, which increased with time. The alkyl/allyl free radicals transformed to oxygen centered ones in both materials; this transformation occurred faster in α-TPE. In summary, the real-time oxidation behavior of α-TPE was consistent with that observed using accelerated aging methods. This new UHMWPE is oxidation resistant and is expected to maintain its properties in the long term.