NB

For industrial purposes collagen is denatured by heating. This causes the three tropocollagen strands to separate partially or completely into globular domains, containing a different secondary structure to the normal collagen polyproline II (PPII), e.g. random coils. This is called formation of gelatin.
Gelatin is used in many foods, including flavored gelatin desserts. Besides food, gelatin has been used in pharmaceutical, cosmetic, and photography industries.
Collagen was originally used to produce glue. The word collagen is derived from the Greek for glue (''kolla''). Earlier the skin and sinews of horses and other animals were boiled to obtain glue. Collagen adhesive was used by Egyptians about 4,000 years ago, and Native Americans used it in bows about 1,500 years ago. 
Animal glues from collagen are thermoplastic, meaning they dry up and harden and soften on reheating. These are still used in making musical instruments such as fine violins and guitars. Animal sinews and skins, including leather, have been used to make useful articles since ages.