A 3D-printed composite scaffold with sequential release of graphene oxide/hydroxyapatite synergistically enhances angiogenesis-osteogenesis for bone defect repair

• Engineered PH/GO scaffold enables sequential release of GO for angiogenesis and HAp for osteogenesis. • Rapid Gel degradation releases GO to enhance endothelial migration/vascularization. • Slow PCL degradation sustains HAp release to promote osteoblast mineralization/osteogenic protein expression. • PH/GO-1 scaffold upregulates early angiogenesis and significantly accelerates new bone formation in vivo . Angiogenic and osteogenic factors coordinate bone repair through time-dependent regulation of cellular responses, ensuring synchronized neovascularization and osteogenesis. Therefore, we designed a framework using polycaprolactone (PCL) and hydroxyapatite (HAp), which was then filled with a gelatin (GEL) matrix containing graphene oxide (GO) (PH/GO scaffold). The GEL matrix rapidly degrades in the early stage, releasing GO to enhance the migration of vascular endothelial cells and promote the expression of angiogenic factors to stimulate early angiogenesis. The continuous release of HAp from the PCL framework promotes osteoblast differentiation by enhancing expression of bone-specific proteins and matrix mineralization. In vivo studies confirmed that PH/GO-1 (1%GO) significantly elevates the expression of early angiogenic factors and accelerates new bone formation during defect healing. This scaffold synergistically enhances angiogenesis and osteogenesis via spatiotemporal release, demonstrating superior regenerative capacity. It enables sustained delivery of key bioactive molecules, offering a promising biomaterial strategy for critical-sized bone defect repair.