New PVD silver bearing coatings may protect against post-operative infection, and also provide a barrier to minimise metal ion release. Optimised coatings reduced the release of one important metal ion (Cobalt), implicated in chronic tissue inflammation, by 99%. These inherently wear resistance, anti-leaching and anti-microbial benefits have the potential to substantially reduce the lifetime cost of hip replacement implants to the NHS and health organisations worldwide, while providing a much improved patient experience.
Overall the SMART-HIP project demonstrated the potential of the new family of coatings to reduce initial post-operative implant wear by a factor of four and eventually to double implant service life.
The Chromium Nitride (CrN) coatings reduce induced wear to negligible levels. The incorporation of silver in the outer layer of the coatings provided the planned and self-sustaining release of beneficial silver anti-microbial particles. This gives both self-lubrication of the bearing surfaces and short and long term protection against post-operative infections.
The bioactive silver particles are generated in the normal wear process and have been shown to have effective anti-microbial properties. This controlled and engineered aspect of the wear process creates a benign environment around the implant reducing the post-operative chance of infection. Optimised coating formulations were shown to virtually eliminate cobalt ion leaching, achieving a reduction of 99% in treated components compared with untreated components.
Funded by the government-backed Technology Strategy Board, the Engineering and Physical Sciences Research Council (EPSRC) and the industrial partners, the £1.6 million SMART-HIP project included teams from the Research Centre in Surface Engineering at the University of Sheffield, Queen Mary College, University of London (QMUL), Imperial College London and Charing Cross Hospital. The coatings and other elements of the research are protected by international patents and relevant patent applications.
SMART-HIP is the first major research project to approach biomedical coating design and development in a multi-disciplinary, integrated way, and recognised that a successful outcome of the project would depend on an effective cross-disciplinary approach to the technical challenges. Indeed a substantial part of the successful innovation was the direct result of the interdisciplinary nature of the group. An important feature of the project was parallel evaluation of the toxicology and immunology as the coating formulation and orthopaedic work progressed. In particular, many of the immunological tests in this project had never previously been applied to the coating processes before. The work is particularly timely with the current concerns reported about Metal-on-Metal (MoM) total hip prosthesis implant designs and the potential impact of trunnion wear rates on large diameter bearings.