Filling the Void: Rapid Revascularization via Vasculogenic Assembly in Semi-synthetic Granular Hydrogel Grafts

Rapid revascularization is critical to tissue graft survival, as delayed reperfusion drives tissue ischemia and compromises cell viability and graft function. Although bulk hydrogels have been explored for promoting vessel formation, vascularization remains too slow to prevent ischemic injury to grafted tissues, highlighting the need for biomaterial platforms that accelerate graft revascularization and reperfusion. In this study, we present granular hydrogel composites (GHCs), where interstitial space is filled with fibrin and collagen to provide a vasculogenic matrix environment. GHCs supported the assembly of embedded endothelial cells into interconnected, lumenized networks in vitro which anastomosed with host vasculature and were systemically perfused 7 days after implantation. Careful optimization studies revealed that GHCs formed from covalently interlinked, RGD-functionalized microgels of 115 μm diameter best supported vascular network formation in vitro and intravascular blood perfusion in vivo. To test the utility of GHCs for the vascular integration of a demanding and therapeutically relevant parenchymal tissue, GHC-based ovarian tissue grafts were implanted in a murine xenograft model and successfully connected to host vasculature, restoring blood flow to embedded human ovarian tissues within 10 days post-implantation. Notably, endothelial cells seeded within GHCs formed viable vasculature without pre-culture. This work establishes GHCs as a biomaterial platform to rapidly connect parenchymal tissues to host vasculature, with broad translational potential across engineered tissue grafting applications.