Influence of polymer surface chemistry on frictional properties under protein-lubrication conditions: implications for hip-implant design

Wear processes in hip joints are believed to occur chiefly under boundary l ubrication conditions. We have shown that the efficiency of boundary lubric ation of the ultrahigh-molecular-weight polyethylene (UHWMPE)-alumina tribo pair in protein-containing solutions can be improved by modifying the surfa ce hydrophilicity of the UHMWPE. Our experiments show that an oxygen-plasma treatment of polyethylene, producing significantly greater hydrophilicity due to modified surface chemistry, leads to faster and modified protein ads orption. A denser boundary layer of human serum albumin (HSA) proteins on t he PE surface appears to enhance boundary lubrication, which leads to a 50% reduction of dynamic friction, as well as to a reduction of stiction, whic h is believed to be a key factor in wear mechanisms occurring in artificial hip joints. Following tribological testing in pure water, we observed the presence of a polyethylene transfer film on the alumina disc. This film was not formed after tribotesting either in protein or in Ringer's solution.