Borate bioactive glass powders: Sol–gel synthesis via metathesis reaction and evaluation of dissolution in simulated body fluid

The readily available and cheap alkaline-earth-metal nitrates are attractive alternatives to the costly corresponding alkoxides used in the conventional sol–gel syntheses of borate bioactive glasses (BBGs). However, the calcination required to decompose these nitrates causes undesired crystallization. To address this problem, we synthesized BBG powders (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%) using a metathesis-based sol–gel method. Filtration-based nitrate removal as NaNO 3 and KNO 3 precipitates and the concomitant in situ formation of alkaline-earth-metal alkoxides eliminated the need for chelating agents and prevented contamination by carbon. Consequently, amorphous 13-93B3 powders with low nitrate and carbon contents were obtained by calcination at 450–550 °C. Fourier transform infrared spectroscopy, scanning electron microscopy, and nitrogen sorption isotherm (Brunauer−Emmett−Teller and Barrett−Joyner−Halenda methods) analyses revealed that the hydroxyl content, pore size/volume, and specific surface area were highest for the sample calcined at 450 °C and decreased with the increase in calcination temperature. Dissolution in simulated body fluid was assessed using tris(hydroxymethyl)aminomethane–HCl and increased with the decrease in calcination temperature. This work provides a versatile and practical method of producing BBGs with tunable structures, textures, and dissolution, offering new opportunities for designing bioactive glasses tailored to specific biomedical applications.