Sol–gel preparation of bioactive apatite films

The surface of biomedical metallic implants covered by a bioactive apatite film can create bioactivity of the implant and shorten healing time. In this work, apatite films on Ti6Al4V were prepared by sol–gel route using Ca(NO3)2, P2O5 and HPF6 as the precursors, in vitro evaluations of the resulting hydroxyapatite (HA) and fluorapatite/hydroxyapatite solid solution (FHA) films were done in Kokuboʹs simulated body fluid and citric acid modified phosphate buffer solution (CPBS). HPF6 showed a good reagent for the incorporation of fluorine into apatite films. The FHA film demonstrated to have good bioactivity, and to have better stability in CPBS and higher adhesion strength than the HA film. When fluorine is incorporated into the film, an increase in crystallinity of the apatite film and a decrease in intrinsic solubility of the FHA film could make significant contributions to the improvement in the stability; the thermal expansion coefficient of the FHA film getting closer to that of Ti6Al4V could be responsible for the increase in adhesion strength.