Nonlinear model for viscoelastic behavior of Achilles tendon

Area of Science:

• Biomechanics
• Materials Science
• Computational Modeling

Background:

• Tendon and ligament mechanical properties are well-researched, but unified models for diverse loading scenarios are scarce.
• Existing models often fail to capture the full range of tendon responses to complex mechanical solicitations.
• Understanding tendon mechanics is crucial for injury prevention and rehabilitation strategies.

Purpose of the Study:

• To propose a novel mechanical model capable of describing tendon responses to various loading conditions, including cyclic loading and relaxation.
• To develop a unified formulation that accounts for the complex, time-dependent behavior of tendons.
• To provide a computational tool for predicting tendon mechanical behavior under physiological and pathological conditions.

Main Methods:

• Experimental testing of white New Zealand rabbit Achilles tendons under cyclic loading/reloading and relaxation sequences.
• Development of a local thermodynamic formulation based on the concept of relaxed stress.
• Application of the model at a representative element volume scale to capture macroscopic behavior.

Main Results:

• The proposed thermodynamic model demonstrated a good correlation with experimental data from rabbit Achilles tendons.
• The model successfully described tendon responses to cycles of loading, unloading, reloading, and successive relaxations.
• Validation of the model's ability to predict macroscopic tendon behavior based on microphysical mechanisms.

Conclusions:

• Tendon mechanical properties are complex, arising from microphysical mechanisms like collagen fiber recruitment and microstructural rearrangement.
• The developed model provides a robust framework for understanding and predicting tendon behavior under diverse mechanical loads.
• Further research can refine the model by incorporating more detailed microphysical interactions and validating it across different tendon types and species.