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Ground Substance

Tendon acquires much of its viscoelastic properties from the extracellular matrix, or ground substance, surrounding the collagen fibers. Human tendons contain limited amounts of ground substance by total dry weight (~1%). The ground substance is rich with (GAGs) linked to proteoglycans at the molecular level.

These GAGs are long, unbranched, polysaccharide chains of repeating disaccharide units that are covalently linked to the proteoglycan core as side chains. Currently, researchers hypothesize that these molecules are critical for stabilizing the collagen fiber arrangement in tendons—in effect, acting as an extracellular cytoskeleton.

The proteoglycans have a high affinity for water, imparting a gellike consistency to the extracellular matrix. The high viscosity that this provides is important for reducing shear and compressive forces in areas of mechanical stress.

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