Biological Safety Evaluation and Surface Modification of Biocompatible Ti-15Zr-4Nb Alloy

We performed biological safety evaluation tests of three Ti-Zr alloys under accelerated extraction condition. We also conducted histopathological analysis of long-term implantation of pure V, Al, Ni, Zr, Nb, and Ta metals as well as Ni-Ti and high-V-containing Ti-15V-3Al-3Sn alloys in rats. The effect of the dental implant (screw) shape on morphometrical parameters was investigated using rabbits. Moreover, we examined the maximum pullout properties of grit-blasted Ti-Zr alloys after their implantation in rabbits. The biological safety evaluation tests of three Ti-Zr alloys (Ti-15Zr-4Nb, Ti-15Zr-4Nb-1Ta, and Ti-15Zr-4Nb-4Ta) showed no adverse (negative) effects of either normal or accelerated extraction. No bone was formed around the pure V and Ni implants. The Al, Zr, Nb, and Ni-Ti implants were surrounded by new bone. The new bone formed around Ti-Ni and high-V-containing Ti alloys tended to be thinner than that formed around Ti-Zr and Ti-6Al-4V alloys. The rate of bone formation on the threaded portion in the Ti-15Zr-4Nb-4Ta dental implant was the same as that on a smooth surface. The maximum pullout loads of the grit- and shot-blasted Ti-Zr alloys increased linearly with implantation period in rabbits. The pullout load of grit-blasted Ti-Zr alloy rods was higher than that of shot-blasted ones. The surface roughness (Ra) and area ratio of residual Al₂O₃ particles of the Ti-15Zr-4Nb alloy surface grit-blasted with Al₂O₃ particles were the same as those of the grit-blasted Alloclassic stem surface. It was clarified that the grit-blasted Ti-15Zr-4Nb alloy could be used for artificial hip joint stems.