Incorporation of Nb and Ta into Calcium Borate Sol−Gel Glasses and Their Impact on the Structure and Properties

The effects of incorporating Nb2O5 or Ta2O5, both intermediate oxides, on the structure and ion release behavior of calcium borate-based sol−gel glasses [(70 − x)B2O3-30CaO-xM2O5, x = 0, 2.5, 5, and 7.5 (mol%), and M = Nb or Ta] were investigated. The glasses were prepared by dissolving niobium (V) ethoxide or tantalum (V) ethoxide in methanol, followed by the addition of boric acid and calcium lactate pentahydrate, stirring, drying, and calcination. Nb2O5 incorporation was accompanied by FT-IR spectral changes consistent with a transition from pyroborate to metaborate, and sustained release of B and Ca for up to 24 h. These observations suggest an increase in bridging oxygens, which could be associated with enhanced structural stability. Conversely, Ta2O5 incorporation resulted in concentration-dependent changes in density-related structural parameters. These structural changes may have contributed to the plateau in ion dissolution from 6 h onward. The specific surface area remained nearly unchanged with Nb2O5 incorporation but increased with Ta2O5 incorporation; however, no clear correlation was observed between specific surface area and ion release behavior. Cell culture tests using mouse-derived osteoblast-like cells demonstrated cell proliferation in the glass extracts, and by day 3 of cultivation, the number of viable cells was comparable to that of the control sample, indicating cytocompatibility. Therefore, the glasses are promising candidates as suppliers of therapeutic ions for biomaterial applications.