Structure of Na2O-CaO-P2O5-SiO2 Glass-Ceramics with Multimodal Porosity

We have investigated the evolution of the structure of nano-macro porous CaO-Na2O-P2O5-SiO2 bioactive glass-ceramics by Fourier transform infrared (FTIR) and Raman spectroscopies, and X-ray diffraction (XRD). A controlled devitrification, followed by a chemical leaching treatment is used to produce a multimodal distribution of nano/macro pores that are expected to improve cell attachment. Data show that the leaching process removes the sodium- and calcium-containing crystalline phases that are formed during the ceramming heat treatment. The primary Si-O peaks in the infrared spectra blue shift with leaching, indicating that the sample becomes SiO2 rich. In parallel, the fraction of nonbridging oxygen decreases. These results suggest a restructuring of the glass network far below the glass transition temperature. The stresses from leaching, capillary forces, and subsequent restructuring develop and grow, eventually producing cracks in the sample.