Synthesis and Characterization of Sol-Gel-Derived SiO2-CaO Particles: Size Impact on Glass (Bio)Properties

Four highly bioactive glasses in a binary SiO2-CaO system are prepared following a sol-gel method using Ca(OH)(2) as a calcium precursor. In the synthesis of glass according to the modified Stober method, Ca(OH)(2) suspended in polyethylene glycol allows the elimination of the presence of calcite and the increase of ammonia concentration causes formation of spherical particles with different sizes in the range of 26-266 nm. The relation among the size and properties, including bioactivity, of the glass particles is evaluated. New glasses that vary in composition (10-25 wt% CaO), porosity (15-113 m(2) g(-1)), and hydroxyl groups content greatly enhance the formation process of hydroxyapatite (HA) in simulated physiological fluids. For all glasses, superior apatite-mineralization ability in time as short as 2 h in the physiological-like buffer is achieved, thus exceeding the bioactivity of the known bioactive glasses, including 45S5 glass (Bioglass). The assessment of the safety and toxicity profile of the obtained glasses is verified in a wide range of concentrations (1-1000 mu g mL(-1)) against human dermal fibroblasts and MC3T3 mouse osteoblast precursors, but also to human erythrocytes by determining hemocompatibility. Two glasses of different sizes, 73 and 266 nm, are promising and warrant further research.