Paper TF+EM-MoM10
Titanium-doped Carbon-based Nanocomposite Coatings, Mechanical and Tribological Properties, Biocompatibility and Cell-Attachment Properties: Implications in Orthopedic Implants

Monday, October 18, 2010, 11:20 am, Room Ruidoso

Stress shielding due to uneven load distributions at the bone–prosthesis interface affect joint prostheses and can lead to wear and loosening. Commonly used cobalt–chromium–molybdenum alloys can degrade during wear at an average rate of 0.02–0.06 mm/year. Other alloys such as titanium–aluminium–vanadium although biocompatible and highly corrosion resistant, exhibit relatively low mechanical properties and poor wear resistance. Nanocomposite nanocrystalline (nc-) Ti(N,C)/ amorphous diamond-like-carbon (a-C:H) coatings exhibit high hardness (H), low friction coefficients, high wear resistance and resilience to substrate deformation thus making them promising candidates for prosthetic implant applications. In this work we investigate the influence of the microstructure of nc-Ti(N,C)/a-C:H coatings on the mechanical, tribological and biological properties with the aim of using such materials not only as wear resistant films in biomedical implants, but also as a bioactive surface that can promote bone ingrowth at areas of medical implants, such as the femoral stem or the acetabular cell in hip replacement joints, that are in direct contact with bone. Approximately 2 μm thick, nc-Ti(N,C)/ a-C:H coatings were deposited on Si wafer and implant alloy coupons using low temperature (~ 200 ^oC) DC reactive magnetron sputtering. The carbon content was varied from 41 to 57 at % and the obtained a-C:H phase ranged from 31 – 47 at. % in order to form the desired nanocomposite structure of 2-4 nm wide Ti(N,C) with 1 to 2 monolayer coverage of a-C:H. An increase in the amorphous phase results in a decrease in mechanical and a decline in tribological performance, however the change in structure and surface morphology at increased carbon content favours the bioactivity of the films. Coating chemical composition and microstructure was investigated by means of x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical and tribological properties of the films where determined using nanoindentation and nanotriboscope methods. In order to assess the biocompatibility of nc-Ti(N,C)/a-C:H coatings and investigate their osteoblast - attachment properties and thus determine their efficacy as implant coatings, the osteoblastogenic osteosarcoma immortalised cell lines Saos-2 and Hos were seeded and allowed to grow on the coating surface. Cell attachment properties were assessed in terms of viability of seeded cells. Viable attached cells were quantified by a mitochondrial enzymatic activity-based colorimetric assay against cultures seeded on conventional tissue-culture treated plastic surface.