A new approach is proposed for fabricating human body parts that last
longer and are more biocompatible than those presently available. In t
his approach, bulk material is chosen that has desirable mechanical pr
operties (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 allo
y 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 a
re expected to last approximately ten times longer or more compared wi
th the polymethylmethacrylate-cement-coated Co-Cr prostheses used at p
resent. The microstructure of diamond films can be controlled by subst
rate and deposition variables. The microstructures of these films have
been investigated using optical and scanning electron microscopy, che
mical composition by Auger electron spectroscopy, structure by X-ray d
iffraction, and atomic arrangements (lattice vibration) characteristic
s by Raman spectroscopy. The average grain size of diamond films varie
d 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. Th
e diamond films showed characteristic Raman peak at 1332 cm-1 (sp3 bon
ding), and diamond-like films contained 1350 and 1580 cm- 1 Raman peak
s (a mixture of sp2 and sp3 bonding). The mechanical properties and ad
hesion characteristics of these films together with biocompatibility i
ssues are discussed for titanium alloy hip prosthesis.