Abstract Title

Association Between Collagen Crimp and Mechanical Properties in Developing Tendons

Additional Funding Sources

The project described was supported by an Institutional Development Award (IDeA) from the National Institute of General Medical Sciences of the National Institutes of Health under Grant No. P20GM103408. The project described was supported by the Arnold and Mabel Beckman Foundation through a Beckman Scholars Program award to the University of Idaho.

Abstract

Tendons are soft collagenous tissues that transfer mechanical forces between muscle and bone. Tendons are highly susceptible to injury and have a poor healing capacity leading to long-term functional deficiencies. A challenge for regenerative tendon therapies is a limited understanding of the mechanisms governing tendon formation. Development of weight-bearing locomotion exposes tendons to mechanical loading and temporally coincides with significant changes in the mechanical properties of neonatal tendons, but the mechanisms are unknown. Accordingly, we hypothesized that development of tendon mechanical properties is associated with maturation of the underlying collagen structure. We assessed the mechanical properties of weight-bearing Achilles tendons (AT) and non-weight-bearing tail tendons (TT) in postnatal day (P)1-P20 rats. To visualize and quantify the underlying collagen crimp structure (the wavy appearance of collagen fibers) of developing tendons, we used second harmonic generation (SHG) microscopy and image analysis tools (ImageJ). AT material properties (stress, strain, elastic modulus) were not affected by age, however stiffness increased (p < 0.05). TT elastic modulus peaked at P10, and cross-sectional area increased from P5 to P20 (p < 0.05), but stiffness was maintained. AT collagen crimp distance peaked at P15, but TT crimp distance continued to increase (p < 0.0001). AT and TT maximum force correlated with crimp distance. AT stiffness correlated with crimp distance, but TT stiffness did not. Results suggest that AT and TT develop differently, and that collagen crimp development is associated with some structural mechanical properties. Other possible mechanisms regulating tendon formation will be identified in future studies.

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Association Between Collagen Crimp and Mechanical Properties in Developing Tendons

Tendons are soft collagenous tissues that transfer mechanical forces between muscle and bone. Tendons are highly susceptible to injury and have a poor healing capacity leading to long-term functional deficiencies. A challenge for regenerative tendon therapies is a limited understanding of the mechanisms governing tendon formation. Development of weight-bearing locomotion exposes tendons to mechanical loading and temporally coincides with significant changes in the mechanical properties of neonatal tendons, but the mechanisms are unknown. Accordingly, we hypothesized that development of tendon mechanical properties is associated with maturation of the underlying collagen structure. We assessed the mechanical properties of weight-bearing Achilles tendons (AT) and non-weight-bearing tail tendons (TT) in postnatal day (P)1-P20 rats. To visualize and quantify the underlying collagen crimp structure (the wavy appearance of collagen fibers) of developing tendons, we used second harmonic generation (SHG) microscopy and image analysis tools (ImageJ). AT material properties (stress, strain, elastic modulus) were not affected by age, however stiffness increased (p < 0.05). TT elastic modulus peaked at P10, and cross-sectional area increased from P5 to P20 (p < 0.05), but stiffness was maintained. AT collagen crimp distance peaked at P15, but TT crimp distance continued to increase (p < 0.0001). AT and TT maximum force correlated with crimp distance. AT stiffness correlated with crimp distance, but TT stiffness did not. Results suggest that AT and TT develop differently, and that collagen crimp development is associated with some structural mechanical properties. Other possible mechanisms regulating tendon formation will be identified in future studies.