Effect of CaSO₄ dissolution-precipitation time on formation of porous carbonate apatite as bone replacement material

Introduction: Carbonate apatite type B (C-Ap) has been used as a bone replacement material because of its osteoconductive properties. Clinically, the pores formed in bone replacement material aid in cell mobility and nutrient supply, thereby increasing the bone regeneration ability. CO₃^2- ions found in this material are useful for maintaining a stable physiological environment in the bone in order for it to be easily absorbed by osteoclasts. Porous C-Ap type B is formed using the dissolution–precipitation method by immersing porous anhydrous CaSO₄ in a mixture of carbonate and phosphate solutions. Purpose: The present study aimed to investigate the effect of immersion time of CaSO4 using the dissolution–precipitation method on the formation of porous C-Ap type B with calcium sulfate hemihydrate as precursor. Method: Porous C-Ap type B was produced using a mixture of calcium sulfate hemihydrate precursors with 50 wt% polymethylmethacrylate(PMMA) porogen and distilled water. After hardening, the calcium sulfate dihydrate containing PMMA was burned in an oven at 700°C for 4 h to remove the PMMA. The specimen was immersed in a mixture of sodium phosphate (Na₃PO₄) and sodium carbonate (Na₂CO₃) for 6, 12, and 24 h. Phase testing through X-ray diffraction (XRD) using CuKα radiation at 40 kV and 40 mA was performed. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR, Thermo Fisher Scientific, Waltham, Massachusetts, USA) was used for detecting the functional groups of CO₃²and PO₄^2-. Results: XRD results showed the formation of C-Ap at 6 and 12 h, but the anhydrous CaSO4 phase remained; alternatively, this phase was absent after 24 h of immersion phase and FTIR showed the presence of the functional groups of CO₃^2- compounds. Conclusion: Porous C-Ap type B can be formed from CaSO4 precursors after 24 h of immersion using the dissolution–precipitation method.