Facile route to obtain a highly bioactive SiO2–CaO–Na2O–P2O5 crystalline powder

This work describes a facile method to obtain highly bioactive crystalline powders of the SiO2–CaO–Na2O–P2O5 system using a simple route: solid state reaction. Success in obtaining the highly bioactive crystal phase of interest (sodium calcium silicate Na2Ca2Si3O9 containing phosphorus) involves heating the starting reactant powder mixture under an oxidizing atmosphere for 480 min in the temperature range 950–1000 °C. Despite a significant loss of phosphorus at heat treatment temperatures above 950 °C, the resulting Na2Ca2Si3O9 crystal phase is thermally stable up to 1100 °C. Longer treatment times favor the formation of a secondary phase (sodium calcium phosphate NaCaPO4), which, according to recent studies, further increases the bioactivity of a similar material. Finally, in vitro bioactivity tests in acellular simulated body fluid (SBF) of a powder containing only the Na2Ca2Si3O9 phase has shown behavior similar to that of Biosilicate® — an ~ 99.5% crystalline glass–ceramic whose outstanding characteristics of interaction with living tissue have already been reported in the literature.