Bioglass® synthesis, heat treatment and characterization

The 45S5 Bioglass^® used in this research was prepared and donated by Dr. Robert Hill from the Queen Mary University of London. In short, calculated amounts of high-purity precursors were mixed and then melted in a platinum/rhodium crucible at 1380 °C for 1 h using an electric furnace. The resulting melt was then rapidly quenched in deionized water at room temperature. Next, the glass frit was dried and melted again for 30 min. followed by a grinding process using a vibratory mill [19, 29, 31].

To eliminate any internal stress created during the grinding process, the as-received Bioglass^® was annealed at 460 °C for 8 h under ambient atmosphere. X-ray diffraction (XRD; PANalytical X'Pert Pro) using Cu Kα radiation (10° < 2θ < 90°) was used to confirm that the amorphous nature of the material was completely retained.

In order to prepare the 45S5 bioglass-ceramic containing combeite, the as-received 45S5 Bioglass^® was heat treated through a controlled process [29] to induce 74% crystallinity in its structure which was previously reported to be the optimum crystallinity, leading to the highest mechanical performance when incorporated into GICs [19]. The heat treatment profiles used to obtain various degrees of combeite crystallinity in 45S5 Bioglass^® are explained in detail in our previous study [29]. In brief, the heat treatment procedure to obtain 45S5 bioglass-ceramic with 74% crystallinity included a nucleation process at 550 °C for 6 h (dwell time) followed by a growth process at 680 °C for 5 min. (dwell time) [29]. The degree of crystallinity of the resulting heat-treated powder was calculated using its XRD pattern and the intensity of its different characteristic peaks, as explained in detail in reference [29]. The heat-treated glass-ceramic was then lightly ground using an agate mortar and pestle. The particle size distribution of the as-received glass and heat-treated glass-ceramic was measured via laser light scattering particle size distribution analysis (PSA; Horiba LA-920) using isopropyl alcohol as a dispersant and after 5 minutes in an ultrasonic bath. Note that the refractive indices of 1.55 and 1.08 were respectively used for the 45S5 Bioglass^® and isopropyl alcohol. Also, the morphology of the as-received glass and heat-treated glass-ceramic particles was examined using a scanning electron microscope (SEM; HITACHI, S-3400N).