Accelerated Bone Regenerative Efficiency by Regulating Sequential Release of BMP-2 and VEGF and Synergism with Sulfated Chitosan.

Emerging evidence suggests that successful healing of bone substitutes depends on the osteogenesis-angiogenesis interplay. Bone morphogenetic protein-2 (BMP-2) and vascular endothelial growth factor (VEGF) have been identified as key regulators of osteogenesis and angiogenesis during bone regeneration. While the importance of growth factors is now widely accepted, the impact and mechanisms of different releasing sequences on bone repair have not been fully understood. Here, a composite vehicle (Gel/PMs), constructed with hydrogels and microspheres, was developed, which is capable of achieving two distinct releasing modes: BMP-2 first release followed by VEGF release (B/V) and VEGF first release followed by BMP-2 release (V/B). In our results, the B/V mode exhibited more extensive vascular network formation by up-regulating angiogenic genes during the bone remolding, thus facilitating rapid bone transformation which was confirmed by radiography. Further histological and immune-staining analysis revealed that fast release of BMP-2 made for rapidly initiating osteogenesis, while later VEGF release promoted persistent angiogenesis and mature bone formation. Moreover, interest arises from the introduction of 2-,6--sulfated chitosan (SCS), a sulfonated heparin-like polysaccharide. It has synergistic effects with both BMP-2 and VEGF, which can further accelerate bone healing by efficiently improving osteogenesis and angiogenesis. The results demonstrated that disparate releasing sequence of growth factors might influence regenerative efficiency. Such a strategy may provide insights toward designing bioactive materials and give promising application in tissue regeneration.