Hydroxyapatite Coating on Titanium Substrate by the Sol-Gel Process

Hydroxyapatite coatings on titanium were attempted by a sol‐gel process combined with conventional heat treatment and with UV irradiation at ambient temperature after dipping/ withdrawing a substrate into/from the sol. X‐ray diffraction data showed that a coating film prepared by heat treatment was amorphous and crystallized in Ca5(PO4)3(OH) at a temperature of 773–973 K. The infrared spectra for coating films that have been prepared by heat treatment at a temperature of 573–873 K were in fair agreement with those for a coating film prepared by UV irradiation. After ethylene oxide sterilization, the cytotoxicity of coating film decreased with increasing irradiation time in UV irradiation, whereas it decreased with increasing temperature in conventional heat treatment. In comparisons between ethylene oxide sterilization and autoclave sterilization, the coating film sterilized by autoclave had much lower cytotoxicity than that sterilized by ethylene oxide. Furthermore, an animal test in the transfemoral drill hole on a rat for 4 weeks was examined using an implant prepared by heat treatment and autoclave sterilization. The sol‐gel‐coated titanium had slightly higher bone apposition than uncoated titanium as a control material.