Definition
The extracellular matrix is the non-cellular scaffold that surrounds and supports cells in tissues. Its main components are fibrous proteins such as collagens, elastin, fibronectin and laminins, together with proteoglycans and glycosaminoglycans like hyaluronic acid that retain water and resist compression. Beyond mechanical support, the matrix binds growth factors and signals to cells through integrin receptors, influencing migration, proliferation and differentiation. It is continuously remodelled by matrix metalloproteinases and their inhibitors. Collagen is the most abundant protein in mammals. In peptide research, the copper peptide GHK-Cu has been studied in cell culture for effects on collagen and glycosaminoglycan synthesis, and matrix-derived fragments can themselves act as signals.