Deeper Insights into a Bioactive Glass Nanoparticle Synthesis Protocol To Control Its Morphology, Dispersibility, and...

The aim of this study was to investigate the effect of three synthesis parameters on the morphology and composition of nanosized binary bioactive glass particles (nBGPs) obtained through a modified Stöber process. Syntheses were conducted by varying only one parameter at a time while keeping the other parameters constant. As already mentioned in the literature, the ammonium hydroxide volume conditioned the size of the nanoparticles. Nonagglomerated monodispersed spherical particles with a diameter between 70 and 452 nm were produced. The quantity of calcium nitrate and the moment it was introduced in the sol had a tremendous impact on the quantity of calcium inserted and on the particle morphology and aggregation state. High Ca-content particles were obtained when the calcium precursor addition time was 1 h or less after the beginning of the sol-gel reaction but at the cost of a strong aggregation. A better control on the morphology, polydispersity and dispersibility of the nBGPs was achieved when the Ca(NO₃)₂ addition time was increased up to 6 h. However, a significant decrease of the quantity of Ca²⁺ inserted was also noticed. Using an intermediate (3 h) addition time, the quantity of calcium nitrate has been optimized to maximize the insertion of Ca²⁺ ions inside the silica particles. Finally, an optimum initial Ca/Si atomic ratio of 2, maximizing Ca insertion while limiting the salt quantity used, was found. It led to the synthesis of particles with a molar composition of 0.9SiO₂-0.1CaO without any side effect on the particle stability and morphological characteristics.