Zinc- and fluoride-containing bioactive glass enhances angiogenesis-mediated bone regeneration via M2d macrophage...

Angiogenesis is crucial for bone regeneration because it supplies oxygen and nutrients to developing tissues. Immune cells, particularly macrophages, play an important role in regulating vascularization. The M2d macrophage subtype, which is phenotypically similar to tumor-associated macrophages, is characterized by high vascular endothelial growth factor (VEGF) expression; however, its role in regenerative angiogenesis and bone regeneration remains unclear. In this study, we developed a zinc- and fluoride-containing phosphate-based bioactive glass (ZFBG) by incorporating ZnO, CaF₂, and Al₂O₃ into a phosphate glass network. Compared with conventional silicate-based bioactive glass (BG45S5), ZFBG exhibited superior ion release and solubility under physiological conditions. In vitro, ZFBG polarized macrophages toward the VEGF-producing M2d phenotype, and conditioned media from these macrophages significantly enhanced endothelial cell migration. In a mouse calvarial defect model, ZFBG increased M2d macrophage accumulation, CD31⁺ neovascularization, bone volume, and bone mineral density relative to BG45S5. ZFBG showed minimal direct effects on human umbilical vein endothelial cells, suggesting that its proangiogenic effects are primarily macrophage mediated. Collectively, these findings suggest that ZFBG is associated with enhanced angiogenesis-related bone regeneration, potentially through modulation of VEGF-producing macrophages, and highlight the promise of ion-releasing bioactive glasses for immune-mediated bone repair.