Fabrication of apatite-coated gypsum granules and histological evaluation using rabbits

Calcium sulfate dihydrate (CSD) has been used as a material for bone augmentation for many years. However, rapid resorption of CSD sometimes results in insufficient formation of new bone. In the present study, the feasibility of fabricating apatite-coated CSD (Ap/CSD) was studied, with the hypothesis that the apatite coating would reduce the rate of CSD resorption and enhance the osteoconductivity. To prepare Ap/CSD granules, 300–400 µm CSD granules were immersed in Na₂HPO₄ solution at 20 °C or 60 °C, resulting in granules coated with apatitic precipitates. Granules were analyzed by microscopy and x-ray diffraction, and the dissolution rate into pH 7.5 Tris-HCl buffer solution was measured. Osteoconductivity was assessed by the release of calcium ions, and their ability to stimulate new bone formation was examined through reconstruction of rabbit distal femur bone defects. It was found that the apatite coating resulted in increased osteoconduction and a decreased dissolution rate compared with bare CSD granules. When rabbit distal femur bone defect was reconstructed with Ap/CSD, CSD and sintered hydroxyapatite (s-HAp), all samples demonstrated an excellent tissue response. Four weeks after surgery, a higher radio opacity was obtained for Ap/CSD when compared with CSD, indicating new bone formation. The s-HAp granules remained and thus, new bone formation was smallest even though s-HAp granules bonded with the bone. Ap/CSD that was fabricated at 60 °C induced greater bone formation than CSD. It is therefore concluded that Ap/CSD has good potential value as a bone augmentation material.