Viscoelastic damage evaluation of the axon

Area of Science:

• Neuroscience
• Biophysics
• Materials Science

Background:

• Axonal cytoskeleton comprises microtubules (MT), Tau proteins (Tau), neurofilaments (NF), and microfilaments (MF).
• MT provide rigidity, while Tau contributes viscoelasticity; NF and MF have minimal elastic impact.
• The cross-linked network topology of MT and Tau is crucial for axonal mechanical response.

Purpose of the Study:

• To develop a computational model of axonal microstructure mechanics.
• To evaluate the mechanical responses and failure mechanisms of axons under varying conditions.
• To establish a link between microstructural properties and macroscale brain tissue behavior.

Main Methods:

• Developed a hexagonal Representative Volume Element (RVE) modeling MT and Tau as cross-linked fibers.
• Incorporated NF and MF effects into the RVE matrix.
• Performed finite element analysis with varied MT/Tau properties and strain rates.
• Quantified 3D viscoelastic relaxation and failure behavior.

Main Results:

• Axonal failure occurs when Tau reaches its 40% failure strain, prior to MT reaching 50% failure strain.
• Axonal failure strain and stress range from 6-11% and 5-19.8 MPa, respectively.
• Viscoelastic relaxation was characterized using Prony series fitting.

Conclusions:

• The MT-Tau cross-linked network is critical for axonal mechanical integrity.
• The developed RVE model accurately predicts axonal mechanical response and failure.
• This model can inform macroscale modeling of white matter brain tissue.