Nanocrystalline homometallic (same as the substrate and without interface) coatings will be developed to reduce wear of ultra-high molecular weight polyethylene (UHMWPE) in orthopedic prostheses. UHMWPE wear is a primary cause of prosthesis failure, and roughness of the mating Co-Cr surface has been identified as a major contributing factor to UHMWPE wear. Third-body wear particles, such as bone cement constituents, scratch the articulating surface, roughening it and accelerating UHMWPE wear. Attempts to apply conventional hard ceramic coatings to the metallic surfaces have not been successful because of difficulties in achieving adequate adhesion due to dissimilarity of coating and substrate materials and thermal and lattice mismatches. We have demonstrated, for the first time, that nanocrystalline (3-40 nm grains) Co-Or deposited onto Co-Cr-Mo substrates possesses hardness close to that of some ceramics (18-26 GPa, 400% increase), without the associated problems with adhesion to metallic substrates. (Similar results have also been obtained for Ti and stainless steel). In post Phase I work, we have demonstrated uniform deposition of superhard homometallic coatings onto Co-Cr femoral hip heads. Ongoing hip simulation tests have demonstrated up to 75% reduction in UHWMPE wear against homometallic Co-Or femoral heads vs. uncoated Co-Cr. Additionally, atomic force microscopy shows that the homometallic coatings retain the same low surface roughness as the original, highly polished Co-Cr. These results clearly demonstrate feasibility of the proposed technology. Phase 2 will optimize the processes involved in deposition of homometallic coatings and evaluate them in Hip Simulation tests, which will be done by Stephen Li at the Medical Device Testing and Innovation and a major Orthopedic Company.
