11 - Collagen-based tissue repair composite

Summary

Introduction

The most abundant proteins in the extracellular matrix are members of the collagen family. Collagen is composed largely of the amino acids glycine, proline, and hydroxyproline, which are often present as Gly–X–Y repeats (where X and Y are either proline or hydroxyproline). Tropocollagen is the subunit of collagen fibrils formed of three polypeptide strands (each offset by one amino acid), approximately 300 nm long and 1.5 nm in diameter. Each of the three parallel polypeptide strands is in a left-handed helical polyproline II-type coil with three residues to form a right-handed triple helix. The tropocollagen units assemble in a parallel, quarter-staggered arrangement. There is a 40-nm gap, also called the “hole zone,” between the ends of each of these units, with 27 nm of overlap between adjacent units. The chemistry underlying the formation of these tissues is all quite similar; the fundamental differences depend on their hierarchical fibrillar architectures. More than 20 human collagens have been reported, many of which display a 67-nm periodicity, due to the axial packing of the individual collagen molecules [1, 2].

Collagens constitute an important family of proteins in the vertebrate body and serve as extracellular matrix molecules for many soft and hard connective tissues, including cornea, skin, tendon, cartilage, and bone [1, 3]. Collogen provides cellular recognition for regulating cell attachment and functions. Collagen favors cell adhesion that is normally found in joint tissues and those exogenous cells embedded in a collagen delivery device. Almost all of the connective tissues with collagen fibrils as the basic building blocks have remarkably similar chemistry at the macromolecular and fibrillar levels of structure. However, differentiation in the hierarchical structure takes place as these fibrils are arranged in the specific architecture required for the construction of special tissues each with unique functions, which is generally considered the function of other, non-collagen, molecules.