Cells and Materials


Screw implants of commercially pure titanium and titanium alloy together with rods of slip-cast dense hydroxyapatite were implanted transfemorally in young adult rats. The femora were harvested after fixation and freeze-fractured in liquid nitrogen to create two tissue fragments of each specimen. The first contained the implant while the second enabled examination of the tissue immediately adjacent to the implant. In all cases, the tissue abutting the implant was a cement line-like layer which separated the implant from the surrounding bone proper. Greater adherence of this interfacial tissue was demonstrated to hydroxyapatite samples compared with the titanium screws, while no adherence was demonstrated to the titanium alloy implants. The differences in adhesion of interfacial tissue to titanium and titanium alloy were attributed, in some areas, to localized increase in surface roughness, and in others to subtle chemical differences between the oxide-covered metal surfaces. The cement line-like layer was composed of globular accretions which were clearly visible on the apparently smooth grain surfaces of the retrieved hydroxyapatite rods. However, modification of the ceramic, during the implantation period, to produce a micropitted surface, also suggested that microtopographical features were implicated in interfacial tissue adhesion.