Effect of the continuous solution exchange on the in vitro reactivity of a CaO-SiO(2) sol-gel glass

The in vitro reactivity of a sol-gel glass with a composition in mol % of 80% SiO(2)-20% CaO (80S20C) was studied by soaking in a simulated body fluid (SBF). To model the continuous flow of body fluids, in this article a protocol for in vitro tests with continuous exchange of the assay solution (continuous) is proposed. The in vitro behavior of 80S20C in continuous is compared with that without SBF exchange (static). In static, remarkable variations in ionic concentration and pH of solution were detected after a few minutes of soaking. However, exchange of solution with 1 mL/min flow allowed us to maintain SBF ionic concentration and pH almost constant and close to plasma. Glass surface before and after soaking was studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and electron diffraction (ED). After soaking, a calcium phosphate layer formed in both cases on the glass surface. However, some differences were observed as a function of the in vitro protocol used. In static, faster formation of the phosphate layer was detected in the first 6 h by FTIR, but for higher soaking times the situation was equivalent in both cases. After 7-day assay in continuous, XRD, SEM, TEM, and ED studies showed larger crystalline aggregates and apatite crystals on the newly formed layer. The use of a continuous protocol allowed us to perform complete in vitro studies with an ionic concentration and pH in solution almost identical to physiological fluids.