Injectable sericin based nanocomposite hydrogel for multi-modal imaging-guided immunomodulatory bone regeneration

Irregular bone defects, where the inflammation and immune microenvironment confronted with implanted biomaterials, remain a prominent challenge for bone regeneration. In this study, we fabricated an injectable alginate/sericin/graphene oxide (Alg/Ser/GO) hydrogel based on the Alg–Tyramine framework with HRP/H2O2 enzymatic crosslinking. This hydrogel exhibited bioimaging property and controlled degradation behavior upon releasing sericin and GO. Importantly, synergistic effects on bone regeneration between sericin and GO were demonstrated. GO significantly enhanced the spreading, osteogenic differentiation, and mineralization of encapsulated rat BMSCs, whereas the released sericin promoted M2 polarization and migration via the NF-κB and MAPK pathways. The M2 polarization of macrophages induced osteogenic differentiation of BMSCs via several secreted cytokines. Both in vivo and in vitro experiments showed that the Alg/Ser/GO hydrogel induced macrophage infiltration into the surrounding tissues and inhibited inflammation and fibrous capsule thickening. Last, the injected Alg/Ser/GO hydrogels with BMSCs promptly repaired established distal femoral defects in rats. Therefore, the fabricated Alg/Ser/GO hydrogel, along with macrophages and BMSCs, is a promising biomaterial for bone healing, especially the irregular bone defects.