Sequential Angiogenic–Osteogenic Coupling via a Spatiotemporally Graded Hydrogel Enables Vascularized Bone Organoids for Critical-Sized Calvarial Defect Reconstruction

This study presents a silk fibroin methacryloyl (SiIMA)–based spatiotemporally graded hydrogel integrating dimethyloxalylglycine (DMOG) and nano-hydroxyapatite (nHAP) microspheres to enable sequential angiogenic–osteogenic coupling for vascularized bone organoid (BO) formation. The biphasic system coordinates early vascular network formation via DMOG release and later osteogenic differentiation through silk fibroin degradation, enabling bone–vascular synchronization in vitro and in vivo. The hydrogel constructs promoted vascularized bone matrix deposition within 21 days, leading to complete calvarial defect bridging in mice. This modular approach demonstrates controllable spatial and temporal signaling for bone organoid assembly and repair.