Improvement of bone regeneration by a synergistic combination of octacalcium phosphate and water glass

• We developed a new type of synthetic bone graft by adding water glass to OCP (W-OCP). • In a rabbit calvarial defect model, W-OCP increased the bone area by 22.4%. • In clinical trials, the new bone formation rate was 49.5%. • Microarray analysis showed osteogenesis-related gene expression changes in MG-63. • W-OCP boosts bone growth during early implantation stages. Octacalcium phosphate (OCP) is a precursor of biological apatite minerals that can be used in synthetic bone grafts. In this work, a new type of synthetic bone grafts was developed by adding water glass to OCP (W-OCP). The OCP phase is generally known to be thermodynamically unstable and rapidly hydrolyzes to apatite. However, X-ray diffraction confirmed that OCP can remain stable even in the presence of water glass. In a rabbit calvarial defect model, W-OCP increased the bone area by 22.4 %, which was significantly higher than that of defects only at week 4 (p < 0.05). In clinical trials, the new bone formation rate was 49.5 %, confirming that W-OCP had an extremely high application potential as a new bone graft material. After treating MG-63 cells with a W-OCP elution medium, changes in gene expression levels that promoted bone formation were verified via microarray analysis. From the results, W-OCP can be inferred that sodium and silicate ions in water glass play an important role in the recruitment of osteoblasts, significantly increasing the bone growth rate at the early implantation stages. The obtained results suggest that W-OCP can be potentially applied as a new type of synthetic bone materials.