Investigation of Protein Adsorption Mechanism and Biotribological Properties at Simulated Stem-Cement Interface

Debonding of the stem-cement interface occurs inevitably for almost all stem designs under physiological loading, and the wear debris generated at this interface is showing an increasing significance in contributing to the mechanical failure of cemented total hip replacements. However, the influence of protein adsorption onto the femoral stem and the bone cement surfaces has not been well taken into consideration across previous in vitro wear simulations. In the present study, the protein adsorption mechanism and biotribological properties at the stem-cement interface were investigated through a series of frictional tests using bone cements and femoral stems with two kinds of surface finishes, lubricated by calf serum at body temperature. The friction coefficient was dependent on the surface finish of the samples, with an initial much lower value obtained for the polished contacting pairs followed by a sudden increase in the friction coefficient with regard to the tests performed at higher frequencies. The friction coefficient did not change much during the tests for the glass-bead blasted contacting pairs. In addition, proteins from the calf serum were found to adsorb onto both the femoral stem and the bone cement surfaces, and the thickness of the physically adsorbed proteins on the polished metallic samples was more than 10 mu m, which was measured using an optical interferometer and validated through a vertical scanning methodology based on Raman spectroscopy. An initial protein adsorption mechanism and biotribological properties at the stem-cement interface were examined in this study, and it suggested that wear at the stem-cement interface may be postponed or reduced by tailoring physicochemical properties of the femoral components to promote protein adsorption.