Self-assembly of dual drug-delivery coating for synergistic bone regeneration

Bone regeneration for the treatment of bone diseases represents a major clinical need. Introducing recombinant human bone morphogenetic protein-2 (rhBMP-2) into biomaterials is an extensively used approach to induce osteogenic differentiation and accelerate bone regeneration. However, serious adverse events can occur in the event of an overdose of rhBMP-2. Dexamethasone (DEX) is a synthetic hydrophobic glucocorticoid, which can enhance rhBMP-2-induced osteogenic differentiation by binding to a glucocorticoid receptor intracellularly. In this study, we have developed a multilayered composite coating made of poly(l-lactide-co-glycolide) (PLGA) nanoparticles, heparin and chitosan to deliver DEX and rhBMP-2 dually. The coating can reserve DEX and rhBMP-2 using the building blocks of the PLGA nanoparticles and heparin. Sustained release of DEX and rhBMP-2 by this coating was achieved. Moreover, a flow cytometry assay suggests that the PLGA nanoparticles could be transported across the cell membrane and presumably could improve the intracellular delivery of DEX via cell internalization. The in vitro osteogenesis studies reveal that the dual drug-loaded coating has a synergistic osteogenic differentiation effect on C2C12 myoblasts, as indicated by the upregulation of the alkaline phosphatise activity and osteo-related gene expression. In addition, μCT and histological analysis of the in vivo experiments demonstrate that the dual drug-loaded coating induced more ectopic bone formation than the individual drug-loaded coating. Therefore, this study demonstrates that our coating system can reserve these two drugs and deliver them locally to cells with the ability to induce rapid osteogenic differentiation and bone regeneration synergistically. Compared to other reported DEX/rhBMP-2 delivery systems, our coating system represents a simple, safe and effective dual drug delivery alternative. Moreover, since a layer-by-layer strategy is easily applied onto varying substrates, our coating system can be combined with many commercially available or existing biomaterials to improve their osteogenetic performance.