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Queen Mary University of LondonQueen Mary University of London
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School of Engineering and Materials Science
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PhD Thesis: The contribution of structural components to tendon mechanics.

Author: SCREEN, Hazel RC

Year: 2003

Supervisor(s): David Lee, Julia Shelton

This thesis presents the development of a series of techniques to examine the hypotheses that gross applied strain generates heterogeneous local strain fields within tendon fascicles, and that physiologically representative tenocyte strains are dependent on the extension mechanisms employed during tendon extension.

A model system involving rat-tail tendon fascicles was developed, enabling the micro analysis of local strain fields using the cell nuclei as strain markers. This system was used in conjunction with macro analysis techniques to examine fascicle extension and failure mechanisms. Under gross tensile strain, local strain fields within the fascicle matrix were consistently lower than the applied strain, with maximal values of approximately 2.5% local strain. Within the toe-in region, crimp straightening, fibre alignment and fascicle rotation were visualised, beyond which further fascicle extension was enabled by relative sliding of adjacent collagen fibres. Indeed, fascicle failure was demonstrated through the debonding and sliding of adjacent collagen fibres, initiated at strains of approximately 12-13%. These data indicate that tenocytes may experience significant shear or compressive forces during physiological loading.

Further studies utilised specific molecules to disrupt the composition of the non-collagenous matrix. Microanalysis revealed that these changes had significant effect on both local strain fields and primary extension mechanisms. For example, chondroitinase ABC treatment was observed to increase the degree of fibre sliding at the expense of fibre extension. These data demonstrate the importance of proteoglycan matrix in regulating tendon elongation mechanics, and highlight a plausible mechanism by which tendon can control it mechanical response, without altering inherent collagenous hierarchy. These findings are fundamental to the understanding of tendon structure-function mechanics and necessary for relevant analysis of the mechanotransduction pathways for tenocytes.