Effect of hydrothermal temperature on phase transformation and mechanical property of non-sintered hydroxyapatite and its in vitro solubility

Sintered Hydroxyapatite (HA) has been used as bone graft for years. Nevertheless, its slow resorbability is the main drawbacks. This study aims to evaluate the effect of temperature on phase transformation and mechanical property of non-sintered HA obtained from gypsum block under hydrothermal and its solubility compared to commercially available sintered HA. HA block was fabricated from gypsum block in Na₃PO₄.12H₂O solution at 100 °C, 140 °C, and 180 °C for 24 h under hydrothermal. It was found that pure HA block could be obtained at 180 °C. The diametral tensile strength (DTS) of the obtained HA block decreased considerably compared to set gypsum block. The obtained HA has higher solubility in acetate buffer compared to commercial sintered HA, which predicts its higher osteoclastic resorption. In Tris–HCl buffer, the obtained HA has lower solubility compared to the commercial sintered HA. In conclusion, non-sintered HA block could be obtained via hydrothermal at 180 °C for 24 h. The DTS values of the obtained blocks decreased with the increase of hydrothermal temperature. The current non-sintered HA block showed better solubility in acetate buffer compared to sintered HA, which simulated its resorbability in osteoclastic environment.