Bidirectional hyperelastic characterization of brain white matter tissue

Area of Science:

• Biomechanics
• Materials Science
• Neuroscience

Background:

• Understanding brain white matter's mechanical properties is crucial for studying injuries.
• Direct measurement of axonal fibers and extracellular matrix is challenging.
• Existing models lack detailed hyperelastic characterization of white matter components.

Purpose of the Study:

• To develop a theoretical framework for bidirectional hyperelastic characterization of brain white matter.
• To model white matter as a composite material using Ogden hyperelasticity.
• To determine the mechanical contributions of axonal fibers and the extracellular matrix.

Main Methods:

• Utilized homogenization theory and microstructural composite modeling.
• Formulated Cauchy stresses for Ogden hyperelastic materials.
• Employed multi-parametric optimization and response surface methodology.
• Developed a micromechanical finite element model.

Main Results:

• Obtained direction-dependent hyperelastic constants for white matter tissue.
• Validated model predictions against experimental data with high accuracy.
• Demonstrated that stiffer axonal fibers dominate tissue reinforcement.
• Predicted tissue responses under various non-equibiaxial loadings.

Conclusions:

• The developed theoretical framework accurately characterizes white matter's hyperelastic behavior.
• Axonal fibers play a critical role in the directional mechanical reinforcement of brain tissue.
• This approach provides a foundation for predicting brain injury biomechanics.