Influence of the cooling regime of bioactive glass on the formation of crystalline phases in a physiological environment

Advancements in bioglass production enable the creation of materials with optimized properties for applications in implantology, orthopedics, and dentistry. This study aimed to investigate the effect of the cooling method on the phase composition and biological activity of bioglass. Bioglass samples were produced by melting a batch of identical composition in corundum crucibles (50 mL) at 13500C, followed by cooling using three different methods: casting the melt onto a stainless heat-resistant plate, quenching in distilled water, and allowing gradual cooling within the crucible inside the furnace. The results revealed that when small volumes are processed in corundum crucibles, the Al2O3 content in bioglass can reach up to 1.1 wt.% with rapid quenching in distilled water and up to 2.6 wt.% when the glass sample undergoes slow cooling within the crucible over 12 hours. Bioglass cooled on a plate or in distilled water remains a purely amorphous phase, whereas slow cooling in the crucible leads to the formation of a crystalline phase – combeite. Rapidly cooled bioglass samples exhibit active dissolution in a physiological environment and promote hydroxyapatite formation, whereas prolonged cooling in the crucible, due to the presence of the combeite phase, results in reduced solubility and significantly slower hydroxyapatite formation. The practical application of a specific cooling method depends on the intended use of the bioglass: for bioactive materials requiring rapid solubility and enhanced hydroxyapatite formation, rapid quenching in distilled water is recommended; for more inert bioglasses with superior mechanical strength, slow cooling is preferable, provided that ion exchange processes between the melt and the crucible are carefully controlled.