Clinical meaning
Wound healing at the molecular level is orchestrated by a cascade of growth factors, cytokines, and extracellular matrix (ECM) components that regulate each healing phase. During hemostasis, platelet degranulation releases platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), and epidermal growth factor (EGF) from alpha granules, initiating chemotaxis of neutrophils, macrophages, and fibroblasts. In the inflammatory phase, macrophages are the master regulators — M1 macrophages release pro-inflammatory cytokines (TNF-α, IL-1β, IL-6) for pathogen clearance, then polarize to M2 macrophages that secrete anti-inflammatory cytokines (IL-10, TGF-β) and growth factors (VEGF, PDGF, FGF) to drive the transition to proliferation. Vascular endothelial growth factor (VEGF) is the primary driver of angiogenesis, binding to VEGFR-2 receptors on endothelial cells to stimulate proliferation, migration, and tube formation of new capillaries. Fibroblast growth factor (FGF) promotes fibroblast proliferation and ECM deposition. TGF-β stimulates collagen synthesis by fibroblasts and regulates myofibroblast differentiation for wound contraction. Matrix metalloproteinases (MMPs) remodel the ECM during healing, but excessive MMP activity (as seen in chronic wounds) leads to growth factor degradation and stalled healing. In chronic wounds, the molecular environment is characterized by elevated pro-inflammatory cytokines, excessive MMP activity (MMP-2, MMP-9), reduced tissue inhibitors of metalloproteinases (TIMPs), growth factor deficiency, and senescent fibroblasts — understanding these molecular deficits guides advanced NP-level interventions including growth factor therapy, bioengineered skin substitutes, and targeted wound bed preparation.