Mineralized Collagen Regulates Macrophage Polarization During Bone Regeneration

The host immune response to bone biomaterials is vital in determining the fate of scaffolds and also the outcomes of bone regeneration. Mineralized collagen is an ideal tissue-engineering scaffold for bone repair; however, little is known about its immunomodulatory properties after implantation. In this study, extrafibrillarly-mineralized collagen (EMC) and intrafibrillarly-mineralized collagen (IMC) scaffolds with different nanostructures were fabricated and their immunomodulatory properties via macrophage polarization during bone regeneration were investigated. Micro-CT findings showed that the IMC scaffold yielded more new bone formation than the EMC scaffold. In the defect area, more CD68+ CD163+ M2-like macrophages were observed in the IMC group, while M1-like macrophages positive for CD68 and inducible nitric oxide synthase (iNOS) increased dramatically in the EMC group. We further demonstrated, from the protein and RNA levels, that M2-associated anti-inflammatory cytokines interleukin (IL)-10 and arginase-1 were highly expressed in the macrophages seeded on the IMC scaffold, while those seeded on the EMC scaffold expressed more M1-related genes iNOS and IL-6. Moreover, the macrophage polarization in response to the nanostructure of mineralized collagen scaffolds influenced the osteogenesis of human bone marrow stromal cells. These findings suggest that the nanostructure of mineralized collagen scaffolds affects macrophage functional polarization during bone regeneration. The immunomodulatory properties of biomaterial scaffolds can be a dictator of bone regeneration outcomes.