Formation of hydroxyapatite on CaSiO₃ powders in simulated body fluid

CaSiO₃ powders were prepared from ethanol solutions of Ca(NO₃)₂·4H₂O and Si(OC₂H₅)₄ using NaOH as a precipitant. The resultant powders were heated at three different temperature regimes, (1) 500°C, (2) 500 and 1000°C and (3) 500 and 1400°C, to obtain the amorphous phase (amorphous-CS), low temperature phase (β-CS), and high temperature phase (α-CS) of CaSiO₃, respectively. The different amorphous and crystalline phases exhibited different microtextures and specific surface areas of the powders. The rough, porous particles of amorphous-CS and β-CS have higher specific surface areas than the smooth, dense particles of α-CS. These CaSiO₃ powders were soaked in a simulated body fluid (SBF) at 36.5°C for 2 h to 30 days. Formation of hydroxyapatite (HAp) was observed on the surfaces of all samples, but the formation behavior and microstructures were different, resulting the differences in microstructure and crystal structure of the starting powders as well as particle size and specific surface area. The HAp formed on the amorphous-CS was a loose porous layer consisting of uniformly-sized tiny ball-like agglomerated particles, while that formed on the β-CS and α-CS was a dense layer consisting of larger ball-like agglomerated particles.