Parallel collagen fibers such as ligaments and tendons are composed of fiber bundles, or fascicles, enclosed in a sheath of reticular membrane. In the Achilles tendon, these fascicles can be long, extending from the gastro-soleus unit to the calcaneal insertion site (Fig. 1). Although the overall functional behavior of the whole tendon is well established[1], there is little information detailing properties of individual fascicles or their interactions. Knowledge of the structural and biomechanical properties at the “mesostructural” scale (i.e. fascicle-scale) is critical to understanding tissue pathologies; in particular the processes involved in injury and healing, and the development of improved computational models and functional tissue engineered constructs.
