Intrafibrillar silicified collagen scaffold promotes in-situ bone regeneration by activating the monocyte p38 signaling pathway

Intrafibrillar silicified collagen scaffold (SCS) is a promising biomaterial for bone regeneration because it promotes cell homing and angiogenesis in bone defects via monocyte modulation. In the present study, a rat femoral defect model was used to examine the contribution of monocyte signaling pathways to SCS modulation. Activation of the monocyte p38 signaling pathway by SCS resulted in monocyte differentiation into TRAP-positive mononuclear cells. These cells demonstrated increased secretion of SDF-1α VEGFa and PDGF-BB, which, in turn, promoted homing of bone marrow stromal cells (BMSCs) and endothelial progenitor cells (EPCs), as well as local vascularization. Monocyte differentiation and secretion were blocked after inhibition of the p38 pathway, which resulted in reduction in cell homing and angiogenesis. Taken together, these novel findings indicate that the p38 signaling pathway is crucial in SCS-modulated monocyte differentiation and secretion, which has a direct impact on SCS-induced bone regeneration. Statement of significance: Intrafibrillar silicified collagen scaffold (SCS) is a promising biomaterial for bone regeneration. The present work demonstrates that SCS possesses favorable bone regeneration potential in a rat femoral defect model. The degrading scaffold modulates monocyte differentiation and release of certain cytokines to recruit MSCs and EPCs, as well as enhances local vascularization by activating the p38 MAPK signaling pathway. These findings indicate that SCS contributes to bone defect regeneration by stimulating host cell homing and promoting local angiogenesis and osteogenesis without the need for loading cytokines or xenogenous stem cells.