Functionally graded coatings of HA–G–Ti composites and their in vivo studies

Hydroxyapatite (HA) was synthesized by the wet chemical method using phosphoric acid (H3PO4) and calcium hydroxide Ca(OH)2 aqueous solutions. The prepared HA powders were fired at various temperatures ranging from 200 to 1200 °C for 2 h to obtain different degrees of crystallinity. The HA powders having different crystallinities were mixed with glass (G) in different weight percentages to form HA–G ceramics. The properties of the HA–G ceramics and the reaction of glass with HA were investigated by X-ray diffraction (XRD), differential scanning calorimetry (DSC) and Fourier transform infra-red spectrometry (FTIR). HA fired at higher temperature showed higher crystallinity and lower solubility. HA slightly reacted with glass and formed a small amount boron containing apatite. HA–G ceramic powders were coated on pure titanium substrate to obtain functionally graded layers of HA–G ceramics. The hydroxyapatite–glass–titanium (HA–G–Ti) composites consisting of HA fired at 400, 800 and 1200 °C were implanted in the femur bone of dog to examine the in vivo behavior of the implant. The pull-out strength between the HA–G–Ti composite and the bone demonstrated that the composite using HA fired at 1200 °C showed the highest pull-out test value of 20.6 MPa and good biocompatibility.