Electronic Thesis and Dissertation Repository

Thesis Format

Integrated Article

Degree

Doctor of Philosophy

Program

Mechanical and Materials Engineering

Supervisor

Mao, Haojie

Abstract

Traumatic brain injury (TBI), including mild traumatic brain injury (mTBI) or concussion, is a severe health concern. Many symptoms, such as headache, dizziness, and working memory deficits, are reported to be related to the dysfunction of brain functional regions, but the underlying mechanism remains unknown. Hence, further developing tools and analyses to understand brain dysfunction for better TBI prevention are important. Additionally, such analyses should be conducted for both real-world TBI cases and laboratory studies, as TBI data can only be collected from the real world, and prevention measures, such as helmets, are developed and evaluated in the lab. Accordingly, this biomechanical study addressed four mTBI-related topics: 1) developing a novel pipeline that can segment the brain finite element (FE) into up to 1000 functional brain regions based on an advanced brain functional atlas; 2) using 39 national football legacy (NFL) kinematic curves (including 13 concussive impacts) which were collected and reconstructed from in-field mTBI impacts, the brain strain responses including strain of each functional region and strain-affected connections among brain functional regions were analyzed; 3) helmet protection mechanism was analyzed by investigating the characteristics of the helmet shell and foam under laboratory impacts; 4) effects of skull thickness change due to repeated mTBI impacts on head kinematics-based and brain strain-based responses were also investigated. This study found that: 1) certain brain functional regions consistently experienced high strain among mTBI impacts under various impacts, indicating their contribution to brain damage; 2) the brain strain could affect the functional connectivity of working memory tasks; 3) among the entire impact events, helmet outer shell absorbed the highest amount of strain energy, while helmet foam played an important role in brain strain responses based on factorial analysis; 4) the increase in skull thickness and the change in skull density had the small effect on head kinematics-based and brain strain responses. In brief, novel brain FE models with detailed function regions were developed. Using the new modeling technique, the potential effects of brain functional region strain under both real-world and laboratory settings, as well as repeated-mTBI-relevant skull changes, were analyzed.

Summary for Lay Audience

Traumatic brain injury (TBI) occurs when the head experiences external impacts or inertia effects. Many researchers demonstrated that the TBI symptoms, including working memory deficits, could be related to the dysfunction of brain functional regions or the change in brain functional connections, but the in-depth mechanism remains unclear. Biomechanical researchers found that brain strain could cause neuron cell death, which is related to brain dysfunction, but the brain strain responses of functional regions are still unclear because there lacks a finite element (FE) model with in-detailed brain functional regions. To overcome this challenge, this study developed a pipeline to segment the brain FE model into functional regions and used the FE model with functional regions to investigate the mechanism and prevention guidelines of TBI. By simulating 39 in-field National Football Legacy (NFL) impacts including 13 concussive impacts, the brain functional regions with high strain were identified. Furthermore, the brain strain-affected connection, which refers to more than one brain functional region exceeding the concussive strain threshold per every two brain functional regions, was analyzed, and compared to the healthy brain functional connectivity datasets of working memory. We found that the brain strain could affect the functional connectivity of the brain. The effects of the helmet outer shell and foam stiffness on the brain strain responses were investigated using laboratory impacts of TBI. The helmet outer shell absorbed the highest amount of energy, while the foam played an important role in brain strain responses. Moreover, based on the findings that the skull thickness increased under repeated mTBI impacts, this study investigated the effect of increased skull thickness on brain responses. As a result, the increase in skull thickness and density change played a small role in brain strain responses.

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