Surface treatment on an implant cobalt alloy for high biocompatibility and wear resistance

Total hip prostheses are implanted to younger and more active patients, so the open problem is to create implants which will enhance the implant survivorship and will offer greater longevity. From this point of view, metal-on-metal arthroprostheses are well performing. The volume of periprosthetic inflammatory tissues appears to be less than with metal-on-UHMPWE, however osteolysis often occurs and it is known that the levels of metal ions in the blood and urine are elevated in patients with metal-on-metal bearing. The aim of this research activity was the synthesis and characterization of surface modified cobalt alloys, in order to obtain a biocompatible material presenting at the same time good wear performances, low metal ion release and low toxicity. The surface chemical composition of an implant cobalt alloy (Biodur) was modified, producing relevant tantalum enrichment. Tantalum was chosen because of its low toxicity and high corrosion resistance. The chemical composition, morphology, roughness, crystallographic structure and wettability of the surface, as well as the interface of the modified layer with the substrate, were characterized. The mechanical behavior of the modified materials was investigated by scratch and pin-on-disc wear tests. The metal ion release of the modified surfaces was measured by in vitro experiments after wear tests.