The Effect of Protein Adsorption on the Friction Behavior of Ultra-High Molecular Weight Polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) is a popular choice for the liner material of the acetabular cup and forms one of the articulating surfaces in total joint replacements (TJRs). Evaluating the tribological characteristics of UHMWPE on immediate contact with the physiological fluid is essential to understand pathways and mechanisms of eventual failure. In this study, the friction response and interfacial shear strength of a UHMWPE-ceramic interface was quantified using atomic force microscopy (AFM) before and after exposure to bovine serum albumin (BSA) solution. A 10% protein solution concentration was used to closely mimic protein levels in human physiological fluid. Medical grade UHMWPE samples with two different surface finishing treatments, milling and melting/reforming were used in the experiments. Friction response as a function of normal load was monitored on a particular area on each sample. Fluorescence microscopy was used to assess the protein adsorption on the test area. The interfacial shear strength of the interface was calculated from the friction data using contact mechanics. Contact angle measurements were also performed on the surfaces to evaluate the surface energies before and after protein adsorption. Correlations between the friction behavior and surface energy of the surfaces are discussed.