Dual Structural Role of Niobium in Bioactive Borate Glasses Modulates Bioactivity, Cytocompatibility, and Hemostatic Potential

Designing bioactive glasses with tunable biological responses requires a precise understanding of how network modifiers influence structure-property relationships. This work investigates the effect of incorporating niobium pentoxide (Nb₂O₅) into melt-derived borate glasses, aiming to uncover how Nb affects the glass structure and its multifunctional biological performance. Glasses with nominal compositions: 60B₂O₃-(19-<i>x</i>/2)CaO-(19-<i>x</i>/2)Na₂O-2P₂O₅-<i>x</i>Nb₂O₅ (<i>x</i> = 0, 2.5, 5, 7.5, and 10 wt %) were synthesized and comprehensively characterized. A key finding is the dual structural role of Nb: it predominantly acts as a network former at ≤5 wt % and as a network modifier at higher contents. This transition directly influences the glass network connectivity, as supported by physical, thermal, and vibrational techniques, and reflected a conversion from BO₄ to BO₃ units with an increase in Nb content, correlating with a modification in hardness and elastic modulus. Structural changes also suppressed surface reactivity and ion release, leading to a modulation in hydroxycarbonate apatite formation in simulated body fluid. On the other hand, glasses containing Nb maintained or enhanced cytocompatibility with human adipose mesenchymal stem cells. In contrast, Nb-containing glasses demonstrated reduced hemostatic potential, likely due to Nb forming niobate complexes that may influence ion exchange and clotting pathways. Overall, these findings shed light on the potential of Nb incorporation as a strategy to tailor the multifunctional properties of bioactive borate glasses for targeted biomedical applications and offer a fresh perspective on how the dual structural role of niobium contributes to their overall performance within the context of biomaterials.