And different tissues have different composition of their extracellular matrix. So the extracellular matrix or ECM, is a collection of all the molecules and fibers that are found outside the cells, that hold the individual cells together to form our tissues. And there are three major molecules that constitute our ECM or extracellular matrix. So we have structural proteins, we have Adhesive proteins and proteoglycans. So structural proteins are basically those proteins that give our extracellular matrix the tissue its tensile as well as compressive strength. So the most common type of structural protein in the human body is collagen.