2.15 Collagen: Materials Analysis and Implant Uses ☆

Collagen is the oldest extracellular matrix component in the animal kingdom. Currently, 29 homo- and hetero-trimmers have been identified, all of which have in common the amino acid repeat [Gly-X-Y]n that distinguishes their primary structure from other proteins and enables the signature quaternary structure, the triple helix. Depending on the aggregate structure, collagens have been classified as fibrous, non-fibrous, filamentous and fibril associated collagens with interrupted triple-helices. Among them, collagen type I is the most abundant collagen in mammalian tissues (70–90% of the collagen found in the body). Collagen type I fibrils are the primary structural elements of all connective tissues, providing a structural scaffold for other components primarily due to native cross-linking pathway of lysyl oxidase. Collagen type I is also associated with cell interaction, migration, attachment, differentiation and organisation. For these reasons, collagen type I is extensively used for tissue engineering applications. Mammalian extracted collagen (acid or pepsin derived) is almost exclusively used for industrial applications in leather, food, biomaterial, cosmetic and pharmaceutical industry. Fear, however, of interspecies transmission of disease has encouraged the development of synthetic and recombinant collagen technologies, which may hold the future in biomaterials applications. Numerous fabrication, stabilisation and functionalisation strategies have been developed over the years in order to produce tissue facsimiles that will promote functional regeneration. A number of collagen-specific assays have also been developed to ensure reproducibility and full characterisation of collagen preparations and collagen-based devices.