What is extracellular matrix?
Water, ground substance, fibers...
Extracellular matrix is made of extracellular material, it is the "stuff" that surrounds the tissue cells themselves.
Extra cellular matrix is made of ground substance. Ground substance can be a fluid or gel-like substance in softer tissues or a hard substance like in bone ( this is actually the gel-like substance made firm by calcification ) that has a high water content with a lot of proteoglycans, hyaluronic acid, and GAGs.
Proteoglycans are macromolecules ( really big mollecules ) made of a protein core with glycosaminoglycans ( GAGs ) extending out radially from a core protein in different directions.
Glycosaminoglacans ( GAGs ) are long-chained polysacharides that attach to a core protein. They are anionc, negatively charged and hydrophilic, attract water.
The proteoglycans ( GAGs around a core protein ) are attached to hyaluronic acid, an even bigger mollecule, several of them on an acid, sort of like rows of bottle brushes attached to the acid.
All of this is negatively charged and attracts water, and ground substance is made mostly of proteoglycans and water.
Extracellular matrix also has protein fibers running through it, callogen, reticular, or elastic fibers.