Effect of processing parameters on textural and bioactive properties of sol–gel-derived borate glasses

A compositional range of recently developed bioactive sol–gel-derived borate glasses (SGBGs) have demonstrated remarkably rapid rates of conversion to hydroxy-carbonated apatite (HCA) in simulated body fluid (SBF). Although the composition of SGBGs did not greatly impact HCA conversion rates, it is still unknown how the sol–gel processing parameters affect the textural properties and thus bioactivity of the glass. In this study, a borate-substituted Bioglass® “45S5” formulation [(46.1)B2O3-(26.9)CaO-(24.4)Na2O-(2.6)P2O5; mol%] was fabricated using different sol–gel processing parameters including precursor materials, ageing time and temperature, along with calcination rate and temperature. It was found that a higher calcination temperature led to a partially crystallized glass with almost a magnitude decrease in specific surface area relative to the other glasses. All processing routes resulted in highly bioactive glasses according to Fourier transform infrared spectroscopy, X-ray diffraction, and scanning electron microscopy, which confirmed HCA formation in SBF in as little as 2 h. The majority of ion-exchange occurred within 30 min, facilitating this rapid conversion to bone-like HCA. Interestingly, the partially crystallized glasses (i.e., glass–ceramics) also underwent full conversion to HCA in SBF. Furthermore, ageing time and temperature did not affect the bioactive properties of these glasses, which allow for significantly reduced processing times. In summary, this study demonstrates that SGBGs can be tailored for targeted tissue engineering applications by varying the sol–gel processing parameters.