THE INFLUENCE OF ANISOTROPY AND HETEROGENEITY ON THE MECHANICS OF MILD TRAUMATIC BRAIN INJURY

Embargo until
2020-05-01
Date
2018-12-11
Journal Title
Journal ISSN
Volume Title
Publisher
Johns Hopkins University
Abstract
Traumatic Brain Injury (TBI) has been intensively studied for several decades. Much attention has been directed towards mild TBI (mTBI) due to the increased rates of occurrence compared to other types of TBI especially in military and sports. There are two general approaches to study mTBI: computational and experimental, and each approach complements the other. The experimental direction provides observations of injury as well as the necessary material behavior for the computational models, while the computational models can simulate injury-inducing events which cannot be performed experimentally (in humans). In this work, we use the computational approach to examine how heterogeneities in the human brain affect the mechanical response and/or the deformation of the brain tissue in mTBI. We focus on white matter, the vasculature network and gray matter. Constitutive models for white matter have evolved from linear elastic to isotropic hyperelastic and finally to transversely isotropic hyperelastic material. Although experimental evidence points to anisotropy of white matter in both tension and shear, prior models have accounted for anisotropy in tension but not in shear. We investigate the effects of shear anisotropy in mTBI by comparing two models: one that captures anisotropy in both tension and shear to another model that captures only tension anisotropy. With respect to vasculature, there is very limited literature that studies the effects of the vasculature on the mechanics of mTBI. In this work, we build two models (with and without vasculature) to investigate vasculature effects on the likelihood of injury. Finally, we investigate the effects of gray matter heterogeneity by building two models, one with homogeneous gray matter and another with heterogeneous gray matter. To our knowledge, the effect of gray matter heterogeneity has not been investigated in computational models although recent experiments provide evidence of heterogeneity in gray matter. Since the most commonly used injury criteria in recent literature are strain-based, we compare the strains predicted by the two models to address the main questions we raised about heterogeneity (how white matter shear anisotropy, vasculature network and gray matter heterogeneity affect the mechanics of mTBI). Our results show that two heterogeneity sources, white matter shear anisotropy and the vasculature, significantly influence the brain deformation and subsequently the predicted injury.
Description
Keywords
Biomechanics, TBI, Brain, Injury, Anisotropy, Heterogeneity, Cerebral Vasculature, White Matter, Gray Matter
Citation