The effect of synthesis route and magnesium addition on structure and bioactivity of sol–gel derived calcium-silicate glasses

Three silicate systems, i.e. pure SiO2, SiO2–CaO and SiO2–CaO–MgO, were prepared via sol–gel method in two different ways: (i) following the acid catalysed route (noted A), and (ii) the quick alkali mediated route (noted Q). The thermal behaviour was investigated for the as-prepared matrices and, according to differential thermal analysis (DTA) and thermogravimetric (TGA) analyses, the calcination temperature was establish at 600 °C in order to remove the synthesis residues and to stabilise the structure. Structural, textural and morphological investigations on the heat treated samples were performed before and after immersion in simulated body fluid (SBF) by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), N2-adsorption and scanning electron microscopy (SEM). After 600 °C thermal treatment the samples remain mainly amorphous, only the CaO containing samples prepared by A route evidence an incipient Ca2SiO4 crystalline phase. The N2-adsorption results showed that the specific surface area and the pore volume of the samples synthesised by Q route have higher values comparing with their counterparts prepared following the A route. Bioactivity tests carried out in SBF proved that the magnesium addition to the matrix obtained by Q route favours the hydroxyapatite (HA) self-assembly on the glass surface, and inhibits HA formation when it is added to the matrix obtained by A route. These results are supported by both FTIR and SEM analyses.