A comparative study on physico-mechanical and bioactivity properties of β-wollastonite derived from rice husk ash and calcined limestone drying through freeze-dried and incubator technique

Abstract

β-wollastonite powder was synthesized via a solid-state reaction using rice husk ash and calcined limestone as the precursors at a SiO2:CaO ratio of 45:55. The resulting mixture was autoclaved and sintered at 950 °C for 2 h to obtain the single-phase β-wollastonite. The β-wollastonite powder was mixed with a phosphate buffer at a liquid to powder ratio (L/P) of 0.5. The samples were dried using two different techniques: freeze-drying at −40 °C for 12 h and incubation in an incubator at body temperature (36.7 °C) for 48 h. The aim of this study was to determine the physico-mechanical properties, and in vitro bioactivity of the β-wollastonite was investigated by simulated body fluid (SBF) soaking experiment. The density increased from 3.02 to 3.12 gcm−3, but the porosity decreased from 63.9 to 56.1% for samples dried in an incubator and freeze-dried samples, respectively. The compressive strength for freeze-dried samples was higher (0.83 ± 0.05 MPa) compared to the incubated samples (0.69 ± 0.13 MPa). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) revealed the presence of hydroxyapatite-like microstructures for both samples. After 21 days of soaking, amorphous calcium phosphate (ACP) and calcium-deficient hydroxyapatite (CDHA) were formed, with the molar ratio of Ca/P ranging between 1.63 and 1.76 for both samples. Thus, freeze-dried β-wollastonite has shown good density and compressive strength but poor bioactivity properties.