Changes in the surface oxide composition of Co-Cr-Mo implant alloy by macrophage cells and their released reactive chemical species.

We hypothesized in this study that macrophage cells and their released reactive chemical species (RCS) alter the surface oxide composition of Co-Cr-Mo alloys in vitro. Alloys were prepared to simulate the clinical conditions and incubated for 3 days in cell culture medium, medium with macrophage cells and medium with activated macrophage cells. X-ray photoelectron spectroscopy was used to evaluate the elemental and chemical changes of the surface oxide compositions. The as-polished and passivated specimens exhibited typical Cr(2)O(3) rich surfaces. After 3 days in medium, the major metal peaks were masked by proteins from the culture medium, as indicated by the increase in N and C peaks. When cultured with cells, the Cr peaks reappeared and the O peak increased in intensity. These peak intensities increased further when the cells were activated to release NO and other RCS. We speculated that the cells reduced protein depositions and RCS may have enhanced alloy surface oxides through the oxidation and nitration reactions. These data have demonstrated that surface oxide composition varied with in vitro environments. Changes in the composition of the alloy surface oxides over time by cells are important to the understanding of host-material interactions and in the release of alloy corrosion products.