Session: 05-02-02: Injury and Damage Biomechanics II

Paper Number: 73376

Start Time: Wednesday, 01:10 PM

73376 - Oligodendrocyte Tethering Effect on Hyperelastic 3D Response of Injured Axons in Brain White Matter 

Numerical modeling of traumatic brain injury (TBI) and central nervous system (CNS) extremities intrigues researchers to depict and analyze the impact of axonal injuries deterministically. Finite element simulations leveraging nonlinear, hyperelastic material models have emerged as prospective solutions to characterize stress-states and investigate structural stiffness changes.  Few of these models approximate connections between oligodendrocytes and axons in an extracellular matrix (ECM) corresponding to parametrically varying oligodendrocyte-axon connections. In this paper, a finite element model (FEM) examines the mechanical response of axons embedded in ECM when subjected to tensile loads under purely non-affine kinematic boundary conditions. The axons and the ECM material characterizations are described by Ogden hyperelastic material model. While expanding on previously published results [1], the current work investigates additional tethering scenarios between axons and oligodendrocytes using finite element modeling and evaluates the effect of axon aging on stress propagation.  

Here, oligodendrocyte connections to axons use a spring-dashpot model approximation as deployed in our predicate study.  The tethering technique allows oligodendrocytes to wrap around the outer diameter of the axons at various locations, facilitates parameterization of connections (one to five connection per axon), distance between connection points, and vary stiffness of the connection hubs. The deployed connection model mimics the tethering between oligodendrocytes and axons, enabling inter-axonal bonding and creating a myelin sheath, which insulates and supports axons in the brainstem. At first, 1) multiple oligodendrocytes arbitrarily tethered to the nearest axons FEM was analyzed for varying stiffnesses, and 2) a single oligodendrocyte tethered to all the axons at various locations FEM was improved by adding two and four nodal oligodendrocyte connections per axons scenarios to complete the ensemble.  Results yielded from both sub-models encompass all parametrically varying scenarios and enabled comprehensive comparative analysis.  Next, stress states and stiffness variations for both sub-models were also analyzed by incorporating injured tissue characteristics, for instance, softening of the brain, in the axon FEM model.  Root mean square deviation (RMSD) was computed between stress-strain response plots for varying connections in the ensemble to depict trends in mechanical response and bending stresses. It is noted that axonal stiffness rises with increasing connections, indicating oligodendrocytes' role in stress redistribution and enhanced mechanical response.  In the second sub-model, for same number of connections per axons, RMSD values increased as "k" (oligodendrocyte stiffness) values were set higher. RMSD calculations reveal that for a "k" value, sub-model 2 yielded slightly stiffer models compared to sub-model 1. Appearance of cyclic bending stresses in both sub-models suggests risk of axonal damage accumulation and fatigue failure. Finally, stress state results incorporating aging axon material properties, with varying stiffnesses and number of connections in the FEM ensemble have also been discussed.

Presenting Author: Mohit Agarwal Rutgers, State University of New Jersey

Authors:

Mohit Agarwal Rutgers, State University of New Jersey
Parameshwaran Pasupathy Rutgers, State University of New Jersey
Robert Desimone Marotta Controls
Assimina A. Pelegri Rutgers, State University of New Jersey