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

Abstract

Wear processes in hip joints are believed to occur chiefly under boundary lubrication conditions. We have shown that the efficiency of boundary lubrication of the ultrahigh-molecular-weight polyethylene (UHWMPE)–alumina tribopair in protein-containing solutions can be improved by modifying the surface 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 adsorption. A denser boundary layer of human serum albumin (HSA) proteins on the PE surface appears to enhance boundary lubrication, which leads to a 50% reduction of dynamic friction, as well as to a reduction of stiction, which 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.