Computation of history-dependent mechanical damage of axonal fiber tracts in the brain: towards tracking sub-concussive and occupational damage to the brain

Abstract

Finite element models are frequently used to simulate traumatic brain injuries. However, current models are unable to capture the progressive damage caused by repeated head trauma. In this work, we propose a method for computing the history-dependent mechanical damage of axonal fiber bundle tracts in the brain. Through the introduction of multiple damage models, we provide the ability to link consecutive head impact simulations, so that potential injury to the brain can be tracked over time. In addition, internal damage variables are used to degrade the mechanical response of each axonal fiber bundle element. As a result, the stiffness of the aggregate tissue decreases as damage evolves. To counteract this degenerative process, we have also introduced a preliminary healing model that reverses the accumulated damage, based on a user-specified healing duration. Using two detailed examples, we demonstrate that damage produces a significant decrease in fiber stress, which ultimately propagates to the tissue level and produces a measurable decrease in overall stiffness. These results suggest that damage modeling has the potential to enhance current brain simulation techniques and lead to new insights, especially in the study of repetitive head injuries. KEYWORDSaxonal injury, diffusion tensor imaging, traumatic brain injury, damage mechanics, finite element analysis, composites, embedded element method, occupational brain injury, sub-concussive brain injury INTRODUCTIONTraumatic brain injury (TBI) is a significant cause of death and long-term disability [1]. In the United States, there were 2.8 million TBI-related emergency department visits, hospitalizations, and deaths in 2013 [2]. The structure of the brain can be divided into the gray and white matter regions. In general, gray matter tissue forms the outer layer of the brain and contains the neuron cell bodies, while white matter tissue forms the central region of the brain and contains neuron cell extensions, known as axons. These tightly bundled axons form a dense communication network that transmits signals between the neuron cell bodies. While axons account for the majority of white matter tissue, they are surrounded by a mixture of other components, such as glial cells and the extracellular matrix (ECM). However, this surrounding host material is much softer than the axons [3] [4]. As a result, white matter tissue is commonly treated as a fiber-reinforced composite in mechanical simulations [5] [6] [7] [8]. During severe head impacts, brain deformations can result in the widespread stretching and shearing of axons. This kind of TBI is classified as diffuse axonal injury (DAI) and is typically associated with motor vehicle crashes, sports injuries, and military blast trauma [9] [10]. DAI is the primary injury mechanism in more than 40% of all hospitalized TBIs [11] and can result in both physical and cognitive impairments, which may be temporary or permanent [12].In an effort to design safer products and study the underlying mechanisms of brain injury, there h...

Use of Brain Biomechanical Models for Monitoring Impact Exposure in Contact Sports

“…Note that while wearable kinematic sensors may have the ability to measure repeated sub-concussive impacts with accuracy, there are currently no widely accepted methods for quantifying the history-dependent tissue damage that results from repeated loading. 41,53 Applying boundary conditions is another numerical aspect needing attention. Conceptually, an impact transfers force to the head via contact with the helmet or ground.…”

“…Note that while wearable kinematic sensors may have the ability to measure repeated sub-concussive impacts with accuracy, there are currently no widely accepted methods for quantifying the history-dependent tissue damage that results from repeated loading. 41 , 53 …”