Negative Poisson's ratios in tendons: An unexpected mechanical response

Area of Science:

• Biomechanics
• Materials Science
• Orthopedics

Background:

• Tendons are crucial for force transfer and movement, but are susceptible to debilitating injuries like Achilles tendinopathies.
• Assessing tendon health is challenging, particularly for athletes experiencing common injuries.

Purpose of the Study:

• To investigate the mechanical properties of healthy tendons, specifically their response to stretching.
• To explore the potential of these properties as diagnostic markers for tendon health.

Main Methods:

• In vivo and ex vivo testing of human, sheep, and pig tendons.
• Analysis of tendon behavior under tensile strain within normal physiological ranges.

Main Results:

• Healthy tendons demonstrate a negative Poisson's ratio (auxeticity), expanding laterally when stretched longitudinally.
• This auxetic behavior occurs within the typical range of motion experienced during daily activities.
• The Poisson's ratio is sensitive to microstructural changes, suggesting its utility in health assessment.

Conclusions:

• Human and animal tendons exhibit auxeticity, a counterintuitive mechanical property where they widen upon stretching.
• This finding provides a basis for developing novel diagnostic tests for tendon health.
• The understanding of tendon auxeticity can inform the design of advanced tendon prostheses.