Abstract

Tendon plays a fundamental role in locomotion, facilitating energy efficient movement. However, not all tendons perform the same function, and the roles of our different tendons vary significantly. Energy storing tendons such as the Achilles must be highly extensible and elastic, to help us move efficiently, and to provide energy to help with locomotion. Such a function is not necessary in positional tendons, such as the digital extensor tendons of the hand. Here, accurate and careful positioning of the fingers is required, with a tendon that provides some dampening and can modulate muscle contraction (1).

All tendons are composed of the same hierarchical collagen arrangement, so to meet these disparate functional requirements, structural and compositional optimisation is required. Research in our group has focused on characterising the mechanisms by which different types of tendon function to transfer load, looking for mechanistic differences between tendons. Our data indicate that tendon extension and recoil relies on a series of hierarchical extension mechanisms all working together, with sliding between adjacent collagen units and rotation of helically arranged fascicles. However, we have evidence that different types of tendons utilise these mechanisms differently. More highly loaded energy storing tendons showing less sliding between structural units and behave more like springs. By contrast, positional tendons, which are more viscoelastic in nature, relying more heavily on sliding between fibres and fibrils for extension (2).

With a prevalence of tendinopathy in energy storing tendons, we are now interested to establish if the tendency towards damage is associated with the degree of specialisation. We are also looking to understand the cell environment within these different tendons, to see if mechanotransduction cues differ. Long term, we hope these data will provide insights into functional specialisation across a range of aligned fibrous tissues, subsequently guiding efforts towards repair and regeneration. We have recently developed a novel fibre composite material for tendon mechanobiology research, able to apply specific and controllable levels of shear and tension to tenocytes. Our preliminary data indicates that a shear environment modulates the mechanotransduction response of the cells, potentially providing us with insights into how cells may control the homeostasis of different types of tendon (3).

(1) Birch HL Int J Exp Pathol 2007, 88; 241-8

(2) Thorpe CT et al J Roy Soc Int 2012

(3) Screen et al Adv Funct Mat 2010, 20; 1-20