Beyond Linear Elastic Modulus: Viscoelastic Models for Brain and Brain Mimetic Hydrogels.

Area of Science:

• Biomedical Engineering
• Neuroscience
• Materials Science

Background:

• In vitro models complement in vivo studies for disease research, especially for the brain.
• Current brain mimetic models may not replicate the in vivo mechanical environment, affecting cell behavior.
• Linear elastic modulus, often used for brain tissue, assumes rate-independent stiffness, which is inaccurate.

Purpose of the Study:

• To characterize the viscoelastic properties of porcine brain tissue.
• To evaluate the suitability of the linear elastic model versus viscoelastic models for describing brain mechanics.
• To assess factors influencing brain mechanical properties and inform the design of better brain mimetic models.

Main Methods:

• Porcine brain tissue was characterized using a modified stress relaxation test.
• Viscoelastic models, including the Maxwell model, were fitted to experimental data.
• Mechanical responses were analyzed using both Maxwell and linear elastic models under varying conditions.

Main Results:

• Brain tissue stiffness is dependent on the loading rate, invalidating the linear elastic modulus as a sole descriptor.
• The Maxwell model demonstrated a superior fit (R² = 0.99 ± 0.0006) and captured viscoelasticity.
• Linear elastic modulus was consistently lower than Maxwell elastic modulus, and the Maxwell model showed sensitivity to viscosity and elasticity changes.

Conclusions:

• Linear elastic modulus is insufficient for characterizing brain mimetic materials due to its rate-independent assumption.
• The Maxwell model provides a more accurate representation of native brain's mechanical behavior.
• Quantitative insights are provided for designing advanced brain mimetic materials with improved mechanical fidelity.