DIAMOND, DIAMOND-LIKE AND TITANIUM NITRIDE BIOCOMPATIBLE COATINGS FOR HUMAN-BODY PARTS

A new approach is proposed for fabricating human body parts that last longer and are more biocompatible than those presently available. In this approach, bulk material is chosen that has desirable mechanical properties (low modulus, high strength, high ductility and high fatigue strength) and then this material is coated with highly corrosion- and erosion-resistant and totally biocompatible layers. As an example, we have investigated diamond, TiN, diamond/diamond-like, and diamond/TiN coatings on Ti-6wt.%Al-4wt.%V alloy used for hip prosthesis. This alloy has desirable mechanical properties but the toxicity of vanadium and the neurological disorders associated with aluminum have raised some concerns. To overcome this problem, we have developed a laser physical vapor deposition method to form TiN and diamond-like coatings, and a hot-filament-assisted chemical vapor deposition method to form diamond layers. Cementless diamond-coated hip prostheses of titanium alloys are expected to last approximately ten times longer or more compared with the polymethylmethacrylate-cement-coated Co-Cr prostheses used at present. The microstructure of diamond films can be controlled by substrate and deposition variables. The microstructures of these films have been investigated using optical and scanning electron microscopy, chemical composition by Auger electron spectroscopy, structure by X-ray diffraction, and atomic arrangements (lattice vibration) characteristics by Raman spectroscopy. The average grain size of diamond films varied from 0.5 to 2.0 mum, and the diamond-like films were amorphous. The average grain size of TiN films was found to vary from 10 to 20 nm. The diamond films showed characteristic Raman peak at 1332 cm-1 (sp3 bonding), and diamond-like films contained 1350 and 1580 cm- 1 Raman peaks (a mixture of sp2 and sp3 bonding). The mechanical properties and adhesion characteristics of these films together with biocompatibility issues are discussed for titanium alloy hip prosthesis.