Titanium and its alloys have been employed in bone plates/screws, and these are often designed to be removed after recovery. Bone is known to bond to the surface of Ti alloys. This can lead to re-fracture of newly repaired bone during operations to remove the implants, however bone does not bond to Zr-based alloys. The inhibition of bone conduction on the surface of Zr-based alloys is thought to be due to the presence of a thin layer of zirconia (ZrO2) on the surface. The purpose of the present study was to synthesize bioinert films, including ZrO2 on pure Ti surfaces. In vitro apatite (HAp) formation and in vivo bone conduction in the tibiae of rats on the films were also investigated.
Commercial purity Ti was chemically treated with aqueous H2O2/HNO3 at 353 K for 20 min. The disks were hydrothermally treated with aqueous ZrOCl2/NH3/C6H8O7 (citric acid) in an autoclave at 453 K for 12 h. Simulated body fluid (SBF) immersion test and implantation into tibiae of rats were carried out.
In the hydrothermal treatment with aqueous ZrOCl2/NH3, the surface product was anatase-type TiO2. On the other hand, when citric acid was added the surface of Ti was covered homogeneously with a TiO2–ZrO2 composite film though the amount of ZrO2 was very small. HAp began to form on the non-modified Ti and TiO2 surfaces after 6 days and 4 days immersion in Hank’s solution, respectively. On the surfaces of TiO2–ZrO2, the presence of precipitates was confirmed after 6-8 days. The HAp formation was suppressed on the surfaces of TiO2–ZrO2.The present TiO2-ZrO2 surface also showed significantly lower bone-implant contact ratio in cortical bone compared with TiO2.