Titanium-zirconium (Ti-Zr) binary alloy has better corrosion resistance and mechanical properties than commercially pure Ti. The present study was designed to determine the biocompatibility of Ti-Zr alloy by an implantation test in animal bodies in comparison with pure Ti, Zr, and chromium (Cr) implants. Sample specimens were placed in a subcutaneous position in rats for 8 months. No significant decreases in body weight, the weight of any organ, or the weight of any organ relative to body weight were found in the implant groups compared to a no-implant control group. On hematological examination, small differences in several parameters were found in some groups, but these changes were not attributable to the materials implanted. Mitogen-induced blastogenesis was observed in similar degrees among all implant groups. These results suggest that the implantation of test samples did not cause systemic toxicity or a decrease in immune activity. The fibrous capsule membranes around the Ti and Ti-Zr alloy implants were thinner than those around Cr implants. The numbers of macrophages, inflammatory cells, and other cells involved in immune responses in and around the fibrous capsules of the Cr- and Ti-implant groups were higher than those of the Ti-Zr alloy- and Zr-implant groups. The Ti-Zr alloy had the lowest total score of tissue responses among the materials tested. None of the animals from the Ti-, Zr-, and Ti-Zr alloy-implant groups exhibited a skin reaction following exposure to Ti or Zr salt solutions. These results indicate the Ti-Zr alloy has better biocompatibility than Ti for use as an artificial surgical implant.
