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

This study used citric acid (CA)-assisted sol–gel process to synthesize 13–93B3 (54.6B₂O₃–22.1CaO–7.7MgO–6.0Na₂O–7.9K₂O–1.7P₂O₅ 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 P₂O₅ 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.