Tracking the transformations of mesoporous microspheres of calcium silicate hydrate at the nanoscale upon ibuprofen release: a XANES and STXM study

Drug release and the accompanying biomineralization of the drug carrier, mesoporous calcium silicate hydrate (CSH) microspheres, are monitored with X-ray absorption near edge structures and scanning transmission X-ray microscopy (STXM). The in vitro biomineralization of hydroxyapatite (HAp) on CSH microspheres is investigated by tracking specimens soaked in simulated body fluid (SBF) for various time periods; the study is complemented with X-ray powder diffraction. We clarified the presence of amorphous CaCO3 at the early stage of biomineralization with solid evidence, which is still controversial from previous studies. More importantly, the observations from the STXM images and microscopy spectra directly demonstrated that amorphous SiO2 from the hydrolysis of silicate ions provide the preferential sites for the aggregation of HAp. These results demonstrate that XANES and STXM are sensitive techniques which can be used to analyze various bioceramics for medical applications.