Modeling shear behavior of the annulus fibrosus

Area of Science:

• Biomechanics
• Biomaterials Science
• Tissue Engineering

Background:

• The annulus fibrosus exhibits complex, anisotropic, and nonlinear mechanical properties.
• Previous models often neglected shear data, potentially limiting understanding of tissue behavior and damage.

Purpose of the Study:

• To compare four hyperelastic constitutive models for the annulus fibrosus.
• To evaluate the impact of including shear data in model fitting.
• To assess model predictive capabilities for unseen deformations.

Main Methods:

• Fitted four hyperelastic models to uniaxial tension, biaxial tension, confined compression, and shear experimental data.
• Models were based on Spencer's formulation or represented transversely isotropic materials.
• Investigated fiber restrictions (tensile loads only) and analyzed strain energy contributions.

Main Results:

• Models incorporating shear data showed improved performance, particularly Spencer-based formulations.
• All models fit well without shear data, but predictive accuracy decreased for unseen deformations.
• Restricting fibers to tension had a minor effect on model fit but altered strain energy distribution.

Conclusions:

• A single hyperelastic model can potentially describe annulus fibrosus anisotropic behavior across multiple loading conditions, including shear.
• Care is needed when extrapolating models to deformations outside the fitted dataset.