Fig. 1
Adapted with permission from [21]
The bone repair process involves four phases: a inflammatory phase, b soft callus formation, c hard callus formation and d bone remodeling. Different growth factors and cytokines are secreted during each phase. SDF-1, stromal cell-derive factor 1; RANKL, receptor activator of nuclear factor κB ligand; VEGF, vascular endothelial growth factor; M-CSF, macrophage colony-stimulating factor; PlGF, placental growth factor; GDF-5, growth/differentiation factor 5; OPG, osteoprotegerin; BMP, bone morphogenetic protein; TNF-α, tumor necrosis factor α; PTH, parathyroid hormone; PDGF, platelet-derived growth factor; FGF, fibroblast growth factor.