Development and bioactivity evaluation of bioglasses with low Na2O content based on the system Na2O–CaO–MgO–P2O5–SiO2

Osteoconductive bioglasses, free of K2O and Al2O3 and with content of Na2O lower than 10 mol%, were designed based on the ratio (SiO2 + MgO)/(P2O5 + CaO + Na2O) in the system Na2O–CaO–MgO–P2O5–SiO2. The developed glasses have shown a strong potential for the formation of hydroxycarbonated apatite (HCA) in vitro. The particles of HCA aggregates tend to be of finer size with increasing the ratio of (SiO2 + MgO)/(CaO + P2O5 + Na2O) in the glass chemical composition indicating significant bioactivity. Critical size bone defects created in the femurs of albino adult female rats, and grafted with the glass particles for 12 weeks post implantation, were completely healed by filling with mineralized bone matrix without infection showing a strong potential for new bone formation in vivo. Osteoblasts and osteocytes were observed close to the surface of the granular implants with active areas of bone deposition, resorption and remodelling. The bioglass with lowest (SiO2 + MgO)/(CaO + P2O5 + Na2O) ratio has shown the highest bioactivity while the bioglass with the highest (SiO2 + MgO)/(CaO + P2O5 + Na2O) has shown the lowest bioactivity. The newly formed bone in vivo has shown a similar structure to that of the original bone as indicated by the histology and microstructural results. In addition, Ca/P molar ratio of the newly formed bone was found to be (~1.67), which is similar to that of the original bone.