An insight into the thermal processability of highly bioactive borosilicate glasses through kinetic approach

Abstract

The paucity of crystallization resistant bioactive glasses with desired biological functions stands as a bottleneck toward the fabrication of various biomedical constructs such as amorphous coatings, scaffolds, and fibers for advanced tissue engineering applications. In this context, a series of borosilicate-based bioactive glasses with a range of compositions: (53.88 − x)SiO₂–21.7Na₂O–21.7CaO–1.7P₂O₅–xB₂O₃ (mol%) where x = 0, 13.47, 22.45, 31.43, and 40.41 were prepared to address such limitation. The glasses were primarily investigated for their potential to be processed into amorphous scaffolds through evaluation of crystallization kinetics, sintering behavior, and viscosity–temperature dependence. The inclusion of B₂O₃ gradually reduces the activation energy of crystallization (E_a), according to the prediction from different kinetic models, whereas Friedman's model-free method unraveled the variation in E_a as crystallization progresses. The crystallization event is further elucidated by obtaining the Avrami parameter (n) and dimensionality (m) through Matusita–Sakka equation. The optimization of the sintering schedule for amorphous scaffold preparation was accomplished by exploiting isothermal prediction from Avrami–Erofeev model. Moreover, viscosity–temperature relationship for the studied glasses was established to identify the processing window for drawing and sintering. This study proposes a comprehensive approach adopting theoretical models to elucidate suitable high-temperature process parameters of bioactive glasses avoiding devitrification.