Supercritical CO2 foamed composite scaffolds incorporating bioactive lipids promote vascularized bone regeneration via Hif-1α upregulation and enhanced type H vessel formation

Bone tissue engineering has substantial potential for the treatment of massive bone defects; however, efficient vascularization coupled with bone regeneration still remains a challenge in this field. In the current study, supercritical carbon dioxide (scCO2) foaming technique was adopted to fabricate mesoporous bioactive glasses (MBGs) particle-poly (lactic-co-glycolic acid) (PLGA) composite scaffolds with appropriate mechanical and degradation properties as well as in vitro bioactivity. The MBG-PLGA scaffolds incorporating the bioactive lipid FTY720 (designated as FTY/MBG-PLGA) exhibited simultaneously sustained release of the bioactive lipid and ions. In addition to providing a favorable microenvironment for cellular adhesion and proliferation, FTY/MBG-PLGA scaffolds significantly facilitated the in vitro osteogenic differentiation of rBMSCs and also markedly stimulated the upregulation of Hif-1α expression via the activation of the Erk1/2 pathway, which mediated the osteogenic and pro-angiogenic effects on rBMSCs. Furthermore, FTY/MBG-PLGA extracts induced superior in vitro angiogenic performance of HUVECs. In vivo evaluation of critical-sized rat calvarial bone defects indicated that FTY/MBG-PLGA scaffolds potently promoted vascularized bone regeneration. Notably, the significantly enhanced formation of type H vessels (CD31hiEmcnhi neo-vessels) was observed in newly formed bone tissue in FTY/MBG-PLGA group, strongly suggesting that FTY720 and therapeutic ions released from the scaffolds synergistically induced more type H vessel formation, which indicated the coupling of angiogenesis and osteogenesis to achieve efficiently vascularized bone regeneration. Overall, the results indicated that the foamed porous MBG-PLGA scaffolds incorporating bioactive lipids achieved desirable vascularization-coupled bone formation and could be a promising strategy for bone regenerative medicine. Efficacious coupling of vascularization and bone formation is critical for the restoration of large bone defects. A novel technique was used to fabricate composite scaffolds incorporating bioactive lipids which possessed synergistic cues of bioactive lipids and therapeutic ions to potently promote bone regeneration as well as vascularization. The underlying molecular mechanism for the osteogenic and pro-angiogenic effects of the composite scaffolds was unveiled. Interestingly, the scaffolds were further found to enhance the formation of type H capillaries within the bone healing microenvironment to couple angiogenesis to osteogenesis to achieve satisfying vascularized bone regeneration. These findings provide a novel strategy to develop efficiently vascularized engineering constructs to treat massive bone defects.