Apatite-Forming Ability of Alkali-Treated Ti Metal in Body Environment

Abstract

The essential requirement for an artificial material to bond to living bone is the formation of bonelike apatite layer on its surface in the living body. This apatite layer can be reproduced on its surface even in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. In the present study, Ti metal was treated with various NaOH aqueous solutions, and apatite formation on the resultant metals were examined in SBF. A sodium titanate hydrogel layer was formed on the surface of Ti metal, when it was treated with NaOH solutions with concentrations higher than 0.5M at 60°C for periods longer than 24h. Thus treated metals exchanged Na⁺ ion in the surface layer for H₃O⁺ ion in SBF to produce a hydrated titania on their surfaces and to increase the degree of supersaturation with respect to the apatite of SBF. The hydrated titania induced the apatite nucleation and the increased supersaturation accelerated the apatite nucleation. Thus formed apatite nuclei spontaneously grow by consuming calcium and phosphate ions from SBF. These results indicate that bioactive metal can be obtained by a simple alkali treatment.