Bioactivity and Cell Compatibility of β-Wollastonite Derived from Rice Husk Ash and Limestone.

The aim of this study was to prepare β-wollastonite using a green synthesis method (autoclaving technique) without organic solvents and to study its bioactivity. To prepare β-wollastonite, the precursor ratio of CaO:SiO₂ was set at 55:45. This mixture was autoclaved for 8 h and later sintered at 950 °C for 2 h. The chemical composition of the precursors was studied using X-ray fluorescence (XRF), in which rice husk ash consists of 89.5 wt % of SiO₂ in a cristobalite phase and calcined limestone contains 97.2 wt % of CaO. The X-ray diffraction (XRD) patterns after sintering showed that only β-wollastonite was detected as the single phase. To study its bioactivity and degradation properties, β-wollastonite samples were immersed in simulated body fluid (SBF) for various periods of time. Throughout the soaking period, the molar ratio of Ca/P obtained was in the range of 1.19 to 2.24, and the phase detected was amorphous calcium phosphate, which was confirmed by scanning electron microscope with energy dispersive X-ray analysis (SEM/EDX) and XRD. Fourier-transform infrared spectroscopy (FTIR) analysis indicated that the peaks of the calcium and phosphate ions increased when an amorphous calcium phosphate layer was formed on the surface of the β-wollastonite sample. A cell viability and proliferation assay test was performed on the rice husk ash, calcined limestone, and β-wollastonite samples by scanning electron microscope. For heavy metal element evaluation, a metal panel that included As, Cd, Pb, and Hg was selected, and both precursor and β-wollastonite fulfilled the requirement of an American Society for Testing and Materials (ASTM F1538-03) standard specification. Apart from that, a degradation test showed that the loss of mass increased incrementally as a function of soaking period. These results showed that the β-wollastonite materials produced from rice husk ash and limestone possessed good bioactivity, offering potential for biomedical applications.