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 (H;PO,) 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 degreesC showed the highest pull-out test value of 20.6 MPa and good biocompatibility. (C) 2002 Elsevier Science B.V. All rights reserved.