Collagen in Connective Tissues

Collagen is the main structural protein in the extracellular matrix found in the body's various connective tissues. As the main component of connective tissue, it is the most abundant protein in mammals, making up from 25% to 35% of the whole-body protein content. Collagen consists of amino acids bound together to form a triple helix of elongated fibril known as a collagen helix.  It is mostly found in connective tissue such as cartilage, bones, tendons, ligaments, and skin.

Depending upon the degree of mineralization, collagen tissues may be rigid (bone) or compliant (tendon) or have a gradient from rigid to compliant (cartilage). Collagen is also abundant in corneas, blood vessels, the gut, intervertebral discs, and the dentin in teeth.  In muscle tissue, it serves as a major component of the endomysium.  Collagen constitutes one to two percent of muscle tissue and accounts for 6% of the weight of strong, tendinous muscles.  The fibroblast is the most common cell that creates collagen.  Gelatin, which is used in food and industry, is collagen that has been irreversibly hydrolyzed.  Collagen has many medical uses in treating complications of the bones and skin.

The name collagen comes from the Greek κόλλα (kólla), meaning "glue", and suffix -γέν, -gen, denoting "producing".  This refers to the compound's early use in the process of creating glue from boiling the skin and tendons of horses and other animals.

Uses of Collagen

Collagen has a wide variety of applications, from food to medical. For instance, it is used in cosmetic surgery and burn surgery.  It is widely used in the form of collagen casings for sausages.

If collagen is subject to sufficient denaturation, e.g. by heating, the three tropocollagen strands separate partially or completely into globular domains, containing a different secondary structure to the normal collagen polyproline II (PPII), e.g. random coils.  This process describes the formation of gelatin, which is used in many foods, including flavored gelatin desserts.  Besides food, gelatin has been used in pharmaceutical, cosmetic, and photography industries. It is also used as a dietary supplement.

Collagen adhesive was used by Egyptians about 4,000 years ago, and Native Americans used it in bows about 1,500 years ago. The oldest glue in the world, carbon-dated as more than 8,000 years old, was found to be collagen – used as a protective lining on rope baskets and embroidered fabrics, to hold utensils together, and in crisscross decorations on human skulls.  Collagen normally converts to gelatin, but survived due to dry conditions. Animal glues are thermoplastic, softening again upon reheating, so they are still used in making musical instruments such as fine violins and guitars, which may have to be reopened for repairs – an application incompatible with tough, synthetic plastic adhesives, which are permanent.  Animal sinews and skins, including leather, have been used to make useful articles for millennia.

Gelatin-resorcinol-formaldehyde glue (and with formaldehyde replaced by less-toxic pentanedial and ethanedial) has been used to repair experimental incisions in rabbit lungs.

                https://en.wikipedia.org/wiki/Collagen#Uses