Characterization and canine bone tissue reaction of hydroxyapatite-coated titanium using thermal decomposition method

Hydroxyapatite (HA)-coating by plasma spraying technique, which has been the common method used for HA coating, is not useful for coating the surfaces of porous metal implants because of difficulty in producing a homogeneous HA coating layer less than 30 micrometers. A new coating method, thermal decomposition, has been developed to obtain a dense coating layer with a thickness of 5 micrometer. In this study, the phase composition, surface morphology and adhesive strength between the coating layer and titanium substrate were evaluated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and tear-off testing, respectively. The biocompatibility of the implant prepared using this coating technique was compared with that of implants obtained using the plasma spraying technique or uncoated titanium following implantation into canine femurs. Bonding strength between the bone and implant was evaluated by pull-out testing. New bone formation was observed by light microscopy and SEM. The dense coating layer obtained by thermal decomposition ,method was found to be composed of well-crystallized HA on XRD and SEM, and exhibited high adhesive strength. The biocompatibility of the samples obtained using this coating method was superior to that of the uncoated titanium implants and comparable to that obtained using the plasma spraying technique. The thin coating layer obtained using the thermal decomposition method should be useful for coating porous implants.