Characterization of Sol-Gel Derived Zinc-Containing Hydroxyapatite Composites

Objectives: Hydroxyapatite (HA) ceramics are are currently used as bone graft substitutes and surface-coating materials of total-joint prostheses because of its osteoconductivity. Zinc improves quantity and quality of osteoblast cells and acts as a stimulator on bone growth. We are to synthesize HA via sol-gel route, followed by adding zinc oxide to form a composite material. Methods: The precurors in sol-gel method are calcium nitrate and triethyl phosphate, serving ammonium as pH adjusting agent. After aging and drying, the sol-gel powders without and with ZnO were heat-trated at different temperatures. The phase, microstructure and diametral tensile strength (DTS) of various samples were measured. One-way ANOVA statistical analysis was used to evaluate the statistical significance of the tensile strength data. Results: The XRD patterns show that HA phases can be obtained at 500oC for pH 0 condition, but for pH 9 at lower temperature of 300oC. It can be seen the appearance of extra CaO phase at temperature more than 500oC. The lower pH value used for preparation of the sol-gel derived powder, the higher crystallinity was. Scanning electron microscope observation indicated that the porrous structure of the composites was independent on the experimental conditions. Concerning tensile strength, the value (5.3 MPa) of monolithic HA derived from the sol-gel processing at pH 9 was five times higher than that (1.0 MPa) at pH 0. There was no significant effect of ZnO addition on DTS value (p > 0.05) in the present study, however, enhancing an oriented growth of the HA phase on the (002) plane. Conclusion: The pH value was an important factor controling characteristics of sol-gel derived hydroxyapatite. A small amount of added ZnO did not affect the diametral tensile strength and microstructure of HA/ZnO composites with an exception of phase composition. Supported by Taiwan grant NSC 94-2320-B-040-013. sjding@csmu.edu.tw