Microstructure evolution in Stober-type silica nanoparticles and their in vitro apatite deposition

Prepared via Stober-type sol-gel routes were three types of silica particles of < 1 mu m in size: pure silica, Ca-involving silica, and chitosan/alginate-coated silica with a polymershell-silica core structure. Calcium ions were impregnated in the organic layers of the polymer-coated silica particle. The sol-gel procedure was applied to tetraethoxysilane dissolved in an ethanol/water mixture, while Ca-silica was derived from CaCl2-containing ethanol/water solutions. Scanning and transmission electron micrograph analyses indicated that those silica particles consisted of similar to 10 nm primary particles, the Ca-silica particles (similar to 500 nm) were larger than the Ca-free ones (similar to 200 nm) and that their size increased with the Ca concentration in the precursor solutions. From H-1- and Si-29- magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectra and Si-29 cross-polarization NMR spectra, the mechanism of primary particle agglomeration and degradation of the secondary particles in saline were discussed in terms of the content of H2O molecules and > Si-OH as well as hydrogen bonding interactions among them. In addition, the Ca-silica and core-shell silica deposited apatite in Kokubo's simulated body fluid. Thus, the present Ca-silica and polymer-coated silica particles were suggested to be applicable to injectable bone fillers for bone generation.