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In this study, BG microspheres, based on 58S (60 mol.% SiO2, 35 mol.% CaO, and 5 mol.% P2O5), were synthesized using both spray drying and the spray granulation process. Firstly, spray-dried BG powders were fabricated, using tetraethyl orthosilicate (TEOS, >98.0 wt.%, Seedchem, Camberwell, Melbourne, Australia), calcium nitrate tetrahydrate (CaN, 98.5 wt.%, Showa, Gyoda, Saitama, Japan) and triethyl phosphate (TEP, 99.0 wt.%, Alfa Aesar, Haverhill, MA, USA) as the sources of SiO2, CaO and P2O5, and the precursor solutions were prepared by dissolving the above precursors (TEOS, CaN, and TEP) in 0.5M HCl and ethanol, based on a nominal ratio of 58S. Next, 1 L deionized water was added for dilution, and all precursor solutions were stirred at 25 °C for 4 h to achieve solution homogeneity. Following that, the solutions were disseminated into fine droplets using a high-speed spinning disc at 20,000 rpm. The fine droplets were then led into the spray dryer machine (SD D0-03, IDTA machinery, New Taipei City, Taiwan), wherein the chamber inlet/outlet temperature was set at 200/80 °C with atmospheric air, and a precursor flow rate of 20 mL/min was set to form the spray-dried powders. The resulting powders were obtained in an attached collection tube and were then calcined at 600 °C for 1 h to obtain the preliminary 58S powder.

For the fabrication of macroporous BG microspheres, the precursor solutions were prepared by adding 20 wt.% spray dried BG powder, 1 wt.% poly (N-vivylactamide) ((C4H7NO)n, Showa, Gyoda, Saitama, Japan) as a dispersant, and various concentrations (0, 5, 10 and 20 wt.%) of PMMA as a hard template [33,34,35] into 40 mL deionized water and stirred at 25 °C for 4 h. Meanwhile, the binder solutions were prepared by dissolving 5 wt.% PVA ((C2H4O)n, ACROS) and 0.25 wt.% emulsified polyacrylic resin (Sun-Yarak technology) into 60 mL deionized water and stirred at 25 °C for 18 h. Next, by mixing both precursor and binder solutions, the mixtures were stirred at 25 °C for an additional 18 h. Finally, the macroporous BG microspheres were prepared following the spray drying procedure, as described above. The resulting powders were calcined at 800 °C for another 6 h to remove binders, dispersants and structural templates to avoid the influence of additives on bioactivity.

Finally, a photosensitive drug, tetracycline hydrochloride (TC, C22H24N2O8∙HCl, Biosynth), was employed for the preparation of drug carriers. First, by dissolving TC into ethanol based on a concentration of 0.3 mg/mL, the macroporous BG microspheres were immersed into the TC solution with a solid to liquid ratio of 10 mg/mL. Next, the solution was removed, and the specimens were dried at 70 °C in an oven for 12 h to complete the loading process. Furthermore, the additional process was carried out by immersing the specimens into a gelatin solution (C102H151O39N31, Sigma-Aldrich, St. Louis, MO, USA) and drying at 70 °C for 6 h to form the gelatin-capsulated BG microspheres for controlled drug release.

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