Alkali-free bioactive glasses for bone tissue engineering: a preliminary investigation

An alkali-free series of bioactive glasses has been designed and developed in the glass system CaO-MgO-SiO₂-P₂O₅-CaF₂ along the diopside (CaMgSi₂O₆)-fluorapatite (Ca₅(PO₄)₃F)-tricalcium phosphate (3CaO·P₂O₅) join. The silicate network in all the investigated glasses is predominantly coordinated in Q² (Si) units, while phosphorus tends to remain in an orthophosphate (Q⁰) environment. The in vitro bioactivity analysis of glasses has been made by immersion of glass powders in simulated body fluid (SBF) while chemical degradation has been studied in Tris-HCl in accordance with ISO-10993-14. Some of the investigated glasses exhibit hydroxyapatite formation on their surface within 1-12 h of their immersion in SBF solution. The sintering and crystallization kinetics of glasses has been investigated by differential thermal analysis and hot-stage microscopy, respectively while the crystalline phase evolution in resultant glass-ceramics has been studied in the temperature range of 800-900 °C using powder X-ray diffraction and scanning electron microscopy. The alkaline phosphatase activity and osteogenic differentiation for glasses have been studied in vitro on sintered glass powder compacts using rat bone marrow mesenchymal stem cells. The as-designed glasses are ideal candidates for their potential applications in bone tissue engineering in the form of bioactive glasses as well as glass/glass-ceramic scaffolds.