Synergistic regulation of osteoimmune microenvironment by IL-4 and RGD to accelerate osteogenesis

The control of early inflammatory reactions and recruitment of progenitor cells are critical for subsequent tissue repair and regeneration after biomaterial implantation. The aim of this study was to design a multi-functional biomaterial with a controlled drug delivery system to create an optimal local environment for early osteogenesis. Here, the anti-inflammatory cytokine IL-4 and pro-osteogenic RGD peptide were assembled layer-by-layer on TiO₂ nanotubes. A poly(dopamine) (DOP) coating was employed onto TiO₂ nanotubes (T/DOP) to functionalized with IL-4 (T/DOP-IL4). Then, a carboxymethyl chitosan hydrogel layer (CG) was generated on T/DOP-IL4 to control IL-4 release and RGD peptide immobilization. Cell co-culture models were applied to study macrophage polarization on various material surfaces and the regulation of mesenchymal stromal cell (MSC) osteogenic differentiation. Our data suggest that T/DOP-IL4/CG-RGD surfaces developed in this study are multi-functional, and can not only drive phenotypic changes in macrophages (switching to anti-inflammatory M2 phenotype), resulting in the production of reparative cytokines such as IL-10, but also enhance MSC differentiation related to the activation of BMP/SMAD/RUNX2 signaling. This study further confirmed that the introduction of anti-inflammatory cytokine (IL-4) and cell adhesive motif (RGD) onto Ti substrate can work synergistically to generate a more favorable early-stage osteo-immune environment with superior osteogenic properties, thus representing a potential ideal surface for the generation of bone biomaterials.