Figure 1.

Tendon hierarchical structure (adapted from Kastelic et al. (1978)). Collagen molecules are organized into extracellular structures called fibrils, which are the primary tensile load bearing elements in tendon. The fibrils are highly aligned and tightly packed into fascicles, which are the final macroscopic subunits in tendon. Within each fascicle are cells and an interfibrillar matrix surrounding the fibrils containing proteoglycans, elastin, and other macromolecules.