Preparation of bioactive spherical particles in the CaO–SiO2 system through sol–gel processing under coexistence of poly(ethylene glycol)

Glasses in CaO–SiO2 system provide bioactive materials that achieve direct bonding to living bone. In the development of bioactive organic–inorganic composites, CaO–SiO2 particles with controlled size and morphology are expected to be useful as inorganic fillers. Our previous study showed that sol–gel processing of tetraethoxysilane (TEOS) and calcium nitrate tetrahydrate (CNT, Ca(NO3)2·4H2O) in the presence of poly(ethylene glycol) (PEG) can produce bioactive CaO–SiO2 spherical particles. However, the detailed conditions for preparing the particles with controlled morphology have not been revealed. In the present study, we investigated relationships between starting composition, specifically the weight ratios of TEOS, CNT and PEG, and morphology of the obtained gels. Aggregation of spherical particles was obtained when PEG was added, and the size of particles decreased from micro- to nano-sized with increasing amounts of PEG. Within 1 day of soaking in a simulated body fluid (SBF) a bone-like apatite layer was formed on the surface of all gels starting from the molar ratio of CNT/TEOS = 3/7 (which is assumed to be 30CaO·70SiO2), followed by heat treatment at 600 °C.