קולגנים הם החלבונים המבניים העיקריים של ECM

Collagens are one of the most commonly found proteins in mammals. They are known for their high tensile strength and provide excellent resistance to pulling forces. Collagens are basically fibrous proteins exclusively found in the extracellular matrix.

They are primarily produced by fibroblasts and in smaller quantities by smooth muscle cells and epithelial cells.

Collagen molecules are trimers consisting of three polypeptide chains, called alpha chains. These chains are rich in glycine, proline and hydroxyproline, necessary for structural stability and triple-stranded helix formation. 

In the case of fibrillar collagen, these trimers or protocollagens first assemble into collagen fibrils. Then, these fibrils assemble into collagen fibers, forming tendons that attach muscle to bone, rendering a stable framework for tissues.

Conversely, non-fibrillar collagens, such as type IV collagen, do not form fibrils. They are an important component of basal lamina, which separates cells from other cells and from connective tissue.