Migration stability of α-tocopherol in irradiated UHMWPE

The oxidation resistance of irradiated ultra-high molecular weight polyethylene (UHMWPE) components used in total joint arthroplasty can be improved by adding α-tocopherol (vitamin E) through diffusion. To ensure long-term oxidative stability, a minimum α-tocopherol concentration needs to be maintained throughout these components. Migration of α-tocopherol out of the components is one mechanism that could compromise long-term oxidative stability. We hypothesized that α-tocopherol could elute out during standard implant fabrication steps such as cleaning as well as during in vivo use. We doped 85 kGy irradiated UHMWPE with α-tocopherol at 120 °C and homogenized at 120 °C. We determined the extent of elution of α-tocopherol or its effect on oxidative stability following cleaning in isopropyl alcohol (IPA) and following 5 million cycles (MC) of simulated normal gait in bovine serum. There was no significant elution of α-tocopherol in repeated and prolonged cleaning in IPA as measured by average surface and bulk α-tocopherol concentrations. There was no change in the oxidative stability following 5 MC of hip simulator testing, indicating minimal elution during simulated normal gait.