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A new route for preparing hydroxyapatite (Ca10(PO4)6(OH)2) bioceramic has been described. An amorphous, nanosized, and carbonate‐containing calcium phosphate powder that had a Ca:P ratio of 1.67 was synthesized from calcium diethoxide and phosphoric acid in ethanol via a sol‐gel method. The powder was pressed at 98 MPa into green specimens and then heated to a temperature range of 500°‐1300°C. At 600°C, the powder crystallized to a carbonated hydroxyapatite and a trace of ß‐tricalcium phosphate before converting to hydroxyapatite at 900°C. The thermal crystallization was associated with grain growth, shrinkage, and active surface diffusion. The activation energy of grain growth was 37 ± 2 kJ/mol. After sintering at 1100°C, the decomposition of carbonated hydroxyapatite generated a microporous ceramic with an average pore size of 0.2 µm and an open porosity of 15.5%. This microporous bioceramic can be used as a bone filler.

Although hydroxyapatite (HAP) and tricalcium phosphate (TCP) are currently used as bone graft substitutes or coatings on metallic prostheses because of their excellent biocompatibility and osteoconductivity, they do not stimulate bone formation or inhibit bone resorption. Zinc, an essential trace element in many animals, has a direct specific proliferative effect on osteoblastic cells and has a potent and selective inhibitory effect on osteoclastic bone resorption in vitro. Therefore, zinc-containing beta-tricalcium phosphate (ZnTCP) ceramics and composite ceramics of ZnTCP and HAP (ZnTCP/HAP) were implanted in the femora of New Zealand White rabbits for 4 weeks to promote bone formation. The implants were sintered ceramics with zinc contents of 0 (control), 0.063, 0.316 and 0.633 wt %. Histological and histomorphometrical investigation of the undecalcified sections revealed an increase by 51% (p =.0509) in the area of newly formed bone around the ZnTCP/HAP implants of 0. 316 Zn wt % compared with the control. Plasma zinc concentration was unchanged. An increased bone resorption on the endosteal surface was observed when ZnTCP and ZnTCP/HAP of 0.633 Zn wt % were implanted. To promote bone formation, the optimum zinc content of the calcium phosphate ceramics was therefore 0.316 wt %.