Deposition of Ti based coatings with different surface structure and chemistry for medical devices

Titanium alloys with small amounts of Aluminium and Vanadium are by now the favourite base materials for orthopaedic implants for their good biocompatibility, but stainless steel is wider in use because of its lower material costs and easier handling. By Metal Plasma Immersion Ion Implantation and Deposition (MPIIID) coatings of Ti, TiN, TixAl1-x, and TixAl1-xN layers were deposited on mirror polished stainless steel with a different process parameters, i.e. the bias voltage was changed systematically.
Coatings produced with a bias voltage of -2000 V had a roughness up to 70 nm, whereas those with zero bias voltage were much smoother (6 nm). In coatings with higher voltage the ration Ti : Al shifted to Ti. Rat one marrow cells were seeded out on these surfaces in a serum free medium. After 5h cell spreading and organisation of the cytoskeleton was best on the smoother samples with best spreading on Ti and TixAl1-xN with 0 bias voltage. There was no significant necrosis as measured by lactate dehydrogenase release within 5 h, but up to 25% pyknotic and fragmented cell nuclei as signs of apoptosis. This behaviour was different for the different samples, but there was no correlation with the surface roughness or chemistry. The effect of the medium, direct induction of apoptosis by the coating or apoptotic cell death due to inhibited adhesion by roughness or surface chemistry will be discussed.