Collagen Mechanics.

The collagen superfamily has evolved over nearly a billion years to produce a set of at least 28 proteins that are present in all vertebrates. Of these, the fibrillar collagens (Types I-III, V, XI, XIV, and XVII) comprise a diverse, fibrous structural polymer system that extensively invests and mechanically supports connective tissue. The chemistry, structure, and mechanics of single collagen molecules will be reviewed to provide insight into why collagen's triple helical motif is such an effective, efficient, and versatile structural building block. Review of the integration of molecular collagen into each successive length scale: fibrils, fibers, and tissues will show how the mechanical signature of each level in the hierarchy reflects the mechanical behavior of the smaller length scales from which it is composed. The remarkable structural and mechanical versatility of multiple whole connective tissues with completely different structural roles will demonstrate how each of them relies on collagen to perform their diverse mechanical functions. Finally, multiple themes that address more transcendent phenomena such as fibril diameter modulation, crosslinking, fatigue, and collagen mechanochemistry will be examined to provide a broader view of the field and open new directions for research.