Citric acid-assisted sol–gel synthesis of highly reactive borate-based bioactive glass powders

• Synthesized 13–93B3 glass powders via a citric acid (CA)-assisted sol–gel method. • Sol pH and calcination temperature affected glass powder composition and phase. • Optimal 13–93B3 glass formed at pH 1 and a calcination temperature of 723 K. • CA-assisted sol-gel 13–93B3 glass showed high reactivity in simulated body fluids. This study used citric acid (CA)-assisted sol–gel process to synthesize 13–93B3 (54.6B 2 O 3 –22.1CaO–7.7MgO–6.0Na 2 O–7.9K 2 O–1.7P 2 O 5 mol%) borate bioactive glass (BBG) powders with nitrate precursors, thereby effectively suppressing crystallization. The effect of sol pH on the structure and composition of the powders is analyzed using Fourier transform infrared spectroscopy, X-ray diffraction, and inductively coupled plasma–atomic emission spectrometry. Amorphous powders are obtained at pH 1–9 and calcination temperatures below 923 K; however, pH 1 is required to achieve the 13–93B3 composition. At pH 3–9, compositional changes occur due to P 2 O 5 loss during drying at 323 K, attributed to the volatilization of unhydrolyzed triethyl phosphate. The sol–gel-derived powder at pH 1 is porous, with higher ion release and faster hydroxycarbonate apatite formation in a Tris–HCl solution compared with melt-quench-derived glass. These findings highlight the potential of CA-assisted sol–gel synthesis for producing highly reactive BBGs for bone tissue engineering.