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 1000oC 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.