The three-stage in vitro degradation behavior of mesoporous silica in simulated body fluid

A previously unexpected three-stage degradation behavior of surfactant-extracted MCM-41-type mesoporous silica (MS) in simulated body fluid (SBF) on two time-scales, involving an extraordinarily fast bulk degradation stage on hour-scale and a decelerated degradation stage blocked by the formation of calcium/magnesium silicate layer followed by a maintained slow diffusion stage on day-scale, has been revealed. The great effect of the initial concentration and specific surface area of MS on its three-stage degradation behavior has been investigated and well-understood by kinetic simulation and calculation in combination with experimental data. The results indicate that both low specific surface areas and high concentrations will result in the reduction of the degradation percentage and the prolongation of the degradation. MS can almost degraded thoroughly after 15-day immersion at 0.5 mg mL^-1 in SBF. The degradation behaviors of calcined MS and conventional non-mesoporous amorphous silica have been compared with that of extracted MS.