Silk fibroin/nano-hydroxyapatite scaffolds with graphene oxide induce macrophage M2 polarization and enhance angiogenesis to facilitate bone repair

Background : severe bone defects caused by trauma or tumor resection markedly reduce quality of life. Although autologous bone grafting remains the clinical gold standard, donor-site morbidity restricts its broader use. Silk fibroin/nano-hydroxyapatite (SF/nHA) composites are promising for bone tissue engineering, but poor mechanical strength and limited regulation of the immune microenvironment remain major barriers to application. Methods : a graphene oxide (GO)-modified SF/nHA scaffold was developed as a dual-delivery system for interleukin-4 (IL-4) and vascular endothelial growth factor (VEGF). In vitro , macrophages and endothelial progenitor cells (EPCs) were cultured separately with the scaffolds to assess immunomodulatory and angiogenic effects. In vivo , scaffold degradation and bone repair were examined in rat subcutaneous implantation and calvarial defect models. Results : the GO-SF/nHA scaffold showed improved compressive modulus and stable biphasic release behavior. In vitro , sustained IL-4 promoted macrophage polarization toward the M2 phenotype, whereas VEGF enhanced EPC angiogenic activity. In vivo , dual delivery was associated with faster scaffold degradation and increased early neovascularization after subcutaneous implantation. In the critical-sized calvarial defect model, the I + V scaffold promoted macrophage M2 polarization and angiogenesis in parallel. At 8 weeks, this response was accompanied by greater collagen deposition and bone formation, with nearly complete defect bridging. Conclusion : co-delivery of IL-4 and VEGF enabled the GO-modified SF/nHA scaffold to promote macrophage M2 polarization, angiogenesis, and subsequent bone formation. This strategy improved vascularized bone regeneration and supports the potential of this biomaterial platform for repair of complex bone defects. A GO-SF/nHA scaffold co-delivers IL-4 and VEGF through biphasic sustained release, synergistically inducing macrophage M2 polarization and EPC angiogenesis to promote vascularized bone regeneration.