Studies on the thermal spraying of apatite bioceramics

Hydroxylapatite (HA) coatings on metal substrates have been investigated for many years. These coatings have proved to be compatible with bone. The degree of crystallinity of HA changed, and sometimes dissociation was observed with respect to the plasma spray process. However, the plasma spray process hardly altered the crystallographic structure, with only line broadening visible. Thein vitro solubility is dependent on the degree of crystallinity of the coating. Tensile strength measurements on the strength of the coating-substrate interface using various adhesives revealed a significant difference between epoxy resin and methacrylate. The failure mode of this tensile test was dependent on the coating thickness and surface texture (polished versus nonpolished). In animal studies, the fixation of hydroxylapatite plasma- spray coated cylinders as well as noncoated Ti- 6A1- 4V cylinders (Ti) in cortical bone was evaluated using pushout tests. It appeared that HA- coated implants showed higher push- out strengths in the first months than the titanium implants, because of the earlier bone formation against the HA coating.