Ti based coatings on stainless steel for bone integrated implants

Various titanium based coatings have been produced by metal plasma immersion ion implantation assisted deposition (PIIIAD) technique on stainless steel. TiN coatings with some Al substitution for Ti exhibit good mechanical properties and their use for implant coating is considered. Therefore the adherence of rat bone marrow cells as osteoblast progenitor cells to these coatings was investigated in correlation with deposition parameters and surface morphology. For comparison of the above coating's performance with other coat-ings (Ti, TiAl), all these coatings were developed using PIIIAD technique on stainless steel with the bias voltages 0 kV, -1 kV, -2 kV. Apart from increasing the bonding strength between the coating and the stainless steel substrate, the bias can also be used to manipulate the surface roughness of the coatings (10 - 80 nm). Rat bone marrow cells at the first passage were seeded out on the samples in medium with or without serum, allowed to adhere for 6 hours, fixed with paraformaldehyde, fluorescent stained for the adhesion protein vinculin, the cytoskeleton protein actin, the nuclei were couterstained. No difference in cell behaviour in the different surfaces was seen in medium with serum, indicating that adsorbed serum pro-teins equalise differences between surfaces. In the serum free medium there was a general trend of a bet-ter adherence of the cells and better organisation of the cytoskeleton on coatings produced at 0 kV bias voltage compared to those with -1 kV or -2 kV bias voltage. There have been no signs of necrotic cell death but a high rate (5 to 25%) of pyknotic, fragmented nuclei has been found as hint for apoptotic cell death in serum free medium. This rate has been different for the different substrates, but there was no correlation to surface chemistry or surface roughness. As a reason an effect of the serum free medium, direct effect of the coating or inhibition of the adherence cells to the coating are discussed. For further research and possible applications gradient layers produced from -2 kV at the substrate to 0 kV at the top are suggested.