Biomimetic porous hydrogel scaffolds enabled vascular ingrowth and osteogenic differentiation for vascularized tissue-engineered bone regeneration

The construction of vascularized tissue-engineered bone (VTEB) has been a promising alternative for bone defect repair but remains a remarkable challenge. To date, there have been very limited breakthroughs in VTEB regeneration based on hydrogel scaffolds due to nutrient exchange obstacle caused by a dense hydrogel network, as well as the lack of an osteogenic microenvironment and vascularized pipeline. Here, we developed a novel strategy to prepare porous hydrogel scaffolds with bone biomimetic microenvironments to promote vascular ingrowth and osteogenic differentiation for VTEB regeneration. Based on the phase-separation void-formation technology, porous hydrogel scaffolds with satisfactory mass transport capability were conveniently prepared using gelatin methacryloyl (GelMA) and poly (ethylene oxide) (PEO) emulsified two-phase aqueous solutions. By further combining the osteogenic ingredient, decalcified bone matrix (DBM) particles, and poly (lactic-co-glycolic acid)-encapsulated angiogenic vascular endothelial growth factor (PLGA/VEGF) microspheres, the porous hydrogel scaffolds with biomimetic osteogenic/angiogenic microenvironments were successfully constructed. Moreover, the osteogenic/angiogenic designs based on the DBM particles, porous structure, and VEGF-released microspheres efficiently enhanced the survival, spreading, migration, and osteogenic differentiation of BMSCs in the hydrogels in vitro, and significantly prompted bone regeneration of BMSC-laden hydrogels in vivo. More importantly, in situ bone defects in a rabbit skull model were successfully repaired with VTEB regenerated by BMSC-laden biomimetic porous hydrogels. This study developed a novel bone-biomimetic porous hydrogel scaffold, which provided promising strategies for ectopic VTEB regeneration and in situ bone defect repair.