Orthophosphate nanostructures in SiO2–P2O5–CaO–Na2O–MgO bioactive glasses

Vibrational spectroscopy, 29Si and 31P magic-angle spinning nuclear magnetic resonance spectroscopy and high resolution transmission electron microscopy were used to investigate structural aspects of SiO2–P2O5–CaO–Na2O–MgO glasses. The experimental results show that for the two compositions, 25.3SiO2–10.9P2O5–32.6CaO–31.2MgO and 33.6SiO2–6.40P2O5–19.0CaO–41.0MgO, phosphorous is present in a nano-crystalline form with interplanar distances in the 0.21–0.26 nm range. The two glasses develop a surface CaP-rich layer and the presence of any intermediate silica-rich layer was not detected. It was suggested that the phosphate nano-regions may play a key role in the initial stages of the bioactive process, acting as nucleation sites for the calcium phosphate-rich layer.