Surface morphology and wear mechanisms of four clinically relevant biomaterials after hip simulator testing

The surfaces of worn components hold clues to the underlying wear mechanism s. Previous evidence suggested that the absolute wear rates of acetabular c omponents in a hip simulator were related to mechanical behavior; we hypoth esized that the surface morphology of the liners might also be sensitive to mechanical properties. A noncontact, three-dimensional surface topography measurement system based on white light interferometry was used to quantify the surface morphology of ultra-high molecular weight polyethylene, polyte trafluoroethylene, high-density polyethylene, and polyacetal liners, and th eir corresponding femoral heads, after 3 million cycles in a multi-directio nal hip simulator. Comparisons were made with the fatigue soaked and contro l (as machined) components. Statistically significant power law relationshi ps were observed between the arithmetic mean surface roughness (R-a) of the worn acetabular liners and the volumetric wear rate in the hip simulator ( p < 0.01, r(2) = 0.52). Significant relationships were also observed betwee n R-a and the elastic and large deformation mechanical behavior of the line r materials, measured directly from the wear-tested liners using the small punch test (p < 0.01, r(2) = 0.54-0.81). The results support the hypothesis that wear mechanisms of acetabular liners during hip simulator testing are related to surface morphology in conjunction with the mechanical behavior of the polymeric materials. (C) 2000 John Wiley & Sons, Inc.