The Influence of Phase Separation on Bioactivity of Spray Pyrolyzed Bioactive Glass.

In this study, bioactive glass (BG) particles were synthesized directly using spray pyrolysis (SP). Since the bioactivity of glass particles is well correlated with their chemical composition, how to obtain homogenous bioactive glass becomes an important issue. For SP, the main reason for chemical inhomogeneity was considered to be caused by the difference in the precipitation speed of each precursor. So, two Si-containing precursors of BG, namely tetraethyl orthosilicate (TEOS) and silicon acetate (SiA), have been applied to prepare BG particles. The bioglasses were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy to examine their phase composition, and surface structures, inner morphologies and chemical compositions. It was observed that, under the calcination temperature of 700 degrees C, TEOS-derived powder contained Si-rich nanoparticles and Si-deficit submicron particles as inhomogeneity, whereas the SiA-derived powder was homogenous. The reason of inhomogeneity is that TEOS dissolves in "volatile" ethanol more readily than in water via the SP mechanism of "gas-to-particle-conversion" to form Si-rich nanoparticles. The presence of Si-rich nanoparticles causes Si-deficit "wollastonite submicron particles" to form, which impairs the bioactivity. Finally, BG particle formation mechanisms from different precursors have been proposed.