Is it ensure, insure, or assure?
collagen col·la·gen (kŏl'ə-jən)
The fibrous protein constituent of bone, cartilage, tendon, and other connective tissue that converts into gelatin by boiling.
Any of various tough, fibrous proteins found in bone, cartilage, skin, and other connective tissue. Collagens have great tensile strength, and provide these body structures with the ability to withstand forces that stretch them. Collagens consist of three polypeptide chains arranged in a triple helix, and are bundled together in fibers. When boiled in water, collagen is converted into gelatin.