The wear resistance of diamond-like carbon coated and uncoated Co28Cr6Mo knee prostheses

Diamond-like carbon (DLC) coatings were deposited on medical grade Co28Cr6Mo femoral segments for knee joint prostheses by plasma decomposition of the gaseous hydrocarbon methane. In dependence on the DLC-coating thickness (0.8, 2.7 and 4.5 μm), the wear of the polymeric UHMW-PE (UHMW-PE: ultra high molecular weight polyethylene) counter face was increasing. In comparison with an uncoated Co28Cr6Mo femur, the surface modification with 0.8 and 2.7 μm thick DLCs resulted in improved wear resistance. A 4.5 μm thick DLC coating led to a strong decrease of the wear resistance of the UHMW-PE counter face. A possible reason for this phenomenon may be changes in the heat transfer. The heat transfer may be reduced due to lower fraction of defects, like pinholes, in thicker DLC coatings. Starting from a certain temperature level at the surface of the polymeric inlays, structural changes could be expected, causing a higher materials loss. Furthermore, in comparison with the uncoated Co28Cr6Mo femoral components, the release of metallic wear products is reduced due to the coverage of the metallic alloy with the DLCs. Hereby, an improved biocompatibility is expected.