Influence of strontium on structure, sintering and biodegradation behaviour of CaO–MgO–SrO–SiO2–P2O5–CaF2 glasses

The present study investigates the influence of SrO on structure, apatite-forming ability, physico-chemical degradation and sintering behaviour of melt-quenched bioactive glasses with the composition (mol.%): (36.07 − x) CaO–xSrO–19.24MgO–5.61P2O5–38.49SiO2–0.59CaF2, where x varies between 0 and 10. The detailed structural analysis of the glasses is made by infrared spectroscopy and magic angle spinning–nuclear magnetic resonance spectroscopy. Silicon is predominantly present as Q2 (Si) species, while phosphorus is found as orthophosphate in all the investigated glasses. The apatite-forming ability of glasses is investigated by immersion of glass powders in simulated body fluid for time durations varying between 1 h and 7 days. While increasing the Sr2+/Ca2+ ratio in the glasses does not affect their structure significantly, their apatite-forming ability is decreased considerably. Further, physico-chemical degradation of glasses is studied in accordance with ISO 10993-14 “Biological evaluation of medical devices – Part 14: Identification and quantification of degradation products from ceramics” in Tris–HCl and citric acid buffer, and the possible implications of the ion release profiles from the glasses in different solutions are discussed. The addition of strontium to the glasses leads to a sevenfold decrease in chemical degradation of glasses in Tris–HCl. The sintering of glass powders renders glass ceramics (GCs) with varying degrees of crystallinity and good flexural strength (98–131 MPa), where the mechanical properties depend on the nature and amount of crystalline phases present in the GCs.