Effects of catalysts on polymerization and microstructure of sol-gel derived bioglasses

This work investigates the effects of the type and concentration of acid catalysts on the microstructural features of silica-rich bioactive glasses (75Si–16Ca–5Na–4P, in mol%) synthesized from acetate and nitrate precursor salts, using an innovative rapid sol-gel method, followed by thermal stabilization at 550°C. The results of XRD, SEM, Fourier Transform Infrared Spectrometer (FTIR) and solid state MAS NMR analysis revealed that the lower degrees of polymerization and network connectivity were found for bioglass powders obtained in the presence of high acid concentrations. A low amount of citric acid gave a polymerization degree similar to that obtained in the absence of any catalyst, but the synthesis time was as short as that found for high acid concentrations. The XRD and FTIR results demonstrated amorphous glass powders free of any nitrate by-products. The microstructure and degree of polymerization could be modified by changing the type and concentration of acid catalyst, enabling one to tailor the bioactivity of glasses even without changing the starting composition.