The effect of pre-irradiation vacuum storage on the oxidation and wear of radiation sterilized UHMWPE

The adverse biological response to ultra-high molecular weight polyethylene (UHMWPE) wear debris in total joint replacement warrants the need for the material's improved wear resistance. The reaction of oxygen with radiation-induced free radicals within UHMWPE leads to oxidative degradation of the material. This work examines the effect of storing UHMWPE in vacuum at an elevated temperature (70 °C) prior to gamma irradiation in an attempt to remove pre-existing free oxygen from within the material and hence reduce oxidation that occurs during the irradiation process. UHMWPE specimens both with and without pre-irradiation vacuum were gamma irradiated to either 4 or 10 Mrad and then artificially aged to simulate the material's long-term oxidative behavior. Oxidation, degree of crosslinking, and wear resistance were measured. The benefit of pre-irradiation vacuum in terms of reduced oxidation, higher degree of crosslinking, and improved wear resistance measured after aging was observed for both 4 and 10 Mrad irradiation doses.