Session: 05-01-02: Injury and Damage Biomechanics: Brain Response at the Cellular Level

Paper Number: 97059

97059 - Hyper-Viscoelastic 3D Response of Axons Subjected to Repeated Tensile Loads in Brain White Matter 

Traumatic brain injury (TBI) have emerged as a leading cause of death and disability among children and young adults in the United States. Brainstem and corpus callosum are often subjected to high strains and this makes them susceptible to severe axonal damage. The external mechanical forces that may result in temporary or permanent impairment could be impulsive or repetitive nature. Many athletes experience repeated head concussions during their playing career and succumb to chronic brain ailments. Finite element methods (FEM) have emerged as a promising tool to model, characterize stress-strain response of the brain tissue and predict response to such singular and repeated traumatic load events. In this paper, a novel FEM has been developed to study mechanical response of axons embedded in extra cellular matrix (ECM) when subjected to repeated tensile loads/ uniaxial stretch under purely non-affine kinematic boundary conditions. To closely depict time dependent repeated loading driven strain accumulation, a hybrid material modelling technique is required. Novel Material modeling approach fusing hyper-elastic (such as Ogden model) and time/frequency domain viscoelastic constitutive models are experimented to evaluate impact of parametrically varying oligodendrocyte-axon tethering under repeated tensile loads. Such a hybrid Hyper-Viscoelastic (HVE) material model helped analyzed influence of repeated impact loading on stress propagation and damage accumulation in white matter.

In proposed FEM, oligodendrocyte connections to axons are depicted via linear spring-dashpot model. Such tethering technique facilitates contact definition at various locations, parameterize connection points and vary stiffness of connection hubs. In the current study, proposed FEM analyzes oligodendrocyte tethering by simulating an ensemble of connection scenarios in two FE submodels configurations: 1) in the multi-OL FE setup, multiple oligodendrocytes arbitrarily tethered to the nearest axons, and 2) single-OL FEM, a single oligodendrocyte stationed centrally tethered to all axons at various locations. Root mean square deviation (RMSD) were computed between stress-strain plots to quantitatively evaluate mechanical response increase due to cumulative strains. Explicit FE analysis in Abaqus revealed that time-dependent viscoelastic material parameters (Prony series) embedded in the HVE material definition are needed to simulate stress characteristics under cumulative strains unlike frequency domain viscoelastic constituent. Amplified stress-strain response noted in repeated load FEM when compared against a simpler uniaxial tensile stretch FEM. Thus, indicating a simple damage accumulation scenario. Axonal stiffness improved with increasing tethering, emphasizing role of oligodendrocytes in stress redistribution under repeated concussions. Representative von-Mises stress plot indicated that undulated axons experience bending stresses along their tortuous path. These bending stresses appear to undergo cyclic reversal from tension to compression at each inflection point along the length of axon due to inbuilt tortuosity. Greater bending stresses in repeated load FEM versus uniaxial FE setup for both submodels. Thus, axons are rendered more prone to localized bending stresses and expedited fatigue failure risks under cumulative strains.

Presenting Author: Assimina Pelegri Rutgers, The State University of New Jersey

Presenting Author Biography: Assimina Pelegri is a Professor and the Executive Officer/Undergraduate Director of Mechanical and Aerospace Engineering at Rutgers, The State University of New Jersey. Her research interests include composite materials design, experimental and computational interfacial mechanics. She has developed CNN multiscale material models for characterization of aerospace composites and ballistic materials. Her models have also found applications in biological fibrous tissues in the fields of traumatic brain injury and degenerative diseases. Her research is funded by several agencies including NSF, AFOSR, ONR, PEO Soldier, NASA, NJCBIR, NJCHE, and DARPA. Pelegri is a fellow of ASME, an Associate Fellow of AIAA. She held the M. W. Railser Distinguished Teaching Chair (2010-2013) at Rutgers University. She has served as an Associate Editor for the American Institute of Aeronautics and Astronautics Journal (AIAAJ) and the Journal of Engineering Materials and Technology (JEMT). She is the recipient of the ASME Gold Medal and an inducted member of Georgia Tech’s Council of Outstanding Young Engineering Alumni. Pelegri has been heavily involved in ASME and AIAA organization of symposia, minority committees, and technical committees. Currently she the Chair of the Engineering Sciences Segment and she is an active member of the Inter-Sector Committee on Federal Research and Development task force of the ASME Government Relations Board. In 2016, Professor Pelegri was selected as the Career Mentor of the Year at Rutgers University and the SOE Outstanding Faculty. Currently, she is serving as an associate editor on the editorial board of Journal of Engg and Science in Medical Diagnostics and Therapeutics

Authors:

Mohit Agarwal Rutgers, The State University of New Jersey
Assimina Pelegri Rutgers, The State University of New Jersey