The effects of vitamin E added to the ultrahigh molecular weight polyethylene (UHMWPE) on the frictional properties were examined in order to clarify the wear mechanism of vitamin E-containing UHMWPE in knee prostheses. The sample UHMWPE was slid against the surface of a Co-28Cr-6Mo alloy in bovine serum and in ultrapure water lubricants by using a pin-on-disk friction test apparatus. Fresh serum and post-friction (PF) serum and diluted-PF (DPF) serum were used in order to investigate the effects of friction-dependent conformational changes in serum proteins on the frictional properties. Vitamin E-containing UHMWPE showed a significantly higher friction force than that of virgin UHMWPE in fresh serum lubricant at 30 MPa loading, while there were little differences in ultrapure water, PF and DPF serum. These results suggest that the addition of vitamin E to UHMWPE can affect the boundary lubrication state in the presence of native conformation proteins.
