NB

Collagen is a structural protein that is naturally produced in the body’s connective tissues. It is the most abundant protein in our bodies, making up between 25% and 35%.^[1] It is found in the bones, muscles, skin and tendons. In the majority of collagens, the molecules are packed together to form very similar long thin fibrils. According to MediLexicon, collagen comprises a family of genetically distinct molecules, all of which have a unique triple helix configuration of three polypeptide subunits known as alpha-chains. Each chain contains around 1,000 amino acids, and usually features an amino acid sequence consisting of glycine, proline and hydroxyproline. There are kinds types of collagen, 28 types of collagen have been identified and described, ^[2]  but the main type is types I, II and III which are contain 80%-90% . Specially, type I collagen fibrils are particularly tensile and over 90% of the collagen in the human body is Type I ^[3]

References:

 ^[1] Sherman, Vincent R. (2015). "The materials science of collagen".Journal of the Mechanical Behavior of Biomedical Materials. 52: 22–50.doi:10.1016/j.jmbbm.2015.05.023.

 ^[2]  Sherman, Vincent R. (2015). "The materials science of collagen".Journal of the Mechanical Behavior of Biomedical Materials. 52: 22–50.doi:10.1016/j.jmbbm.2015.05.023.

 ^[3] Sabiston textbook of surgery board review, 7th edition. Chapter 5 wound healing, question 14