The primary cause of failure in hip and knee replacement implants is polymer debris produced by rubbing action of the metal Co-Cr-Mo alloy component against the polymer (UHMWPE) counter surface. This debris is largely caused by sharp carbide protrusions on the metal component that are present even when the surface is highly polished. The proposed Phase I project aims to demonstrate that improved smoothness and wear properties can be produced on Co-Cr-Mo orthopedic implants when processed with an energetic boron plasma (ionized vapor) source. The processing is expected to produce a thin (approximately 1 mu), smooth coating on the substrate, as well as an interlayer of boron reacted with the metal components of the alloy. The interlayer will assure a high level of adhesion, an effect already demonstrated on steel substrates. The boron top-coating is expected to smooth the protrusions and provide lubricity, which is a natural property of its surface oxide. Since particle debris from the plasma source can also adversely impact surface smoothness, a novel debris filter will be added to the source to produce near-debris-free boron plasma. Optimization of the source/filter system, together with the electrical biasing of the substrate, to get uniform, adherent and smooth coatings on flat Co-Cr-Mo sample will be a major part of the effort. The impact of the surface treatment on the surface morphology will be studied with a scanning emission spectroscopy (SEM) system, equipped with 3D imaging capability. The uniformity of film adhesion will be studied with a high-frequency scanning acoustic microscope capable of probing the subsurface interlayer. Other materials characterization will include Rutherford Backscattering Spectroscopy (RBS) to study the composition of the coating and the interlayer as a function of depth, as well as wear and friction characterization, with emphasis on mass loss from the UHMWPE counter surface in simulations of hip and knee joint replacements. Finally, a first stage biocompatibility screening test for the coatings material in included in the workplan. A successful project will lay the foundation for a technology for improved implants, substantially reducing the need for costly revision surgery, which is a major economic burden on society.
| Klepper, C C; Williams, J M; Truhan, J J et al. (2008) Tribo-mechanical properties of thin boron coatings deposited on polished cobalt alloy surfaces for orthopedic applications. Thin Solid Films 516:3070-3080 |
