Mild traumatic brain injury (mTBI), often referred to as concussion, has become increasingly recognized as a serious health issue in the general population. The prevalence of mTBI in athletes, particularly repeated injuries in young athletes, is of great concern as injuries to the developing brain can have long-term detrimental effects. In this study we used a novel awake closed-head injury (ACHI) model in rodents to examine repeated mTBI (rmTBI), to determine if repeated injuries produced the neurological and molecular changes evident with human concussion. Animals were administered 4, 8, and 16 rmTBIs and acute neurological assessments were performed after the injuries. Changes in glial fibrillary acidic protein (GFAP) and ionized calcium-binding adapter molecule 1 (Iba-1) levels were assessed using Western blot analysis at one day following rmTBI in the ipsilateral dentate gyrus (DG) and the cornu ammonis (CA) regions of the hippocampus and the cortex (CX) indicative of astrocyte and microglial cell reactivity. Results indicated that the ACHI model produces neurological deficits immediately after the injuries, with the most deficits arising in the rmTBI16 group. Despite deficits in all injury groups, histological staining with cresyl violet revealed no significant morphological tissue damage to the brain. Western blot analysis, however, showed a significant increase in DG and CX GFAP expression in the rmTBI16 group with no changes in Iba-1 levels. This suggests an acute activation of astrocytes in response to injury, with a delay or absence of microglial activation. Our findings show that with repetitive concussions, we are able to detect acute neurological and molecular changes in the juvenile female brain. However, further investigation is necessary to determine if these are transient changes. / Graduate

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In Operations Enduring Freedom and Iraqi Freedom, explosions accounted for 81% of all injuries; this is a higher casualty percentage than in any previous wars. Blast wave overpressure has recently been associated with varying levels of traumatic brain injury in soldiers exposed to blast loading. Presently, the injury mechanism behind primary blast brain injury is not well understood due to the complex interactions between the blast wave and the human body. Despite these limitations in the understanding of head injury thresholds, head kinematics are often used to predict the overall potential for head injury. The purpose of this study was to investigate head kinematics, and predict injury from a range of simulated blast loads at varying standoff distances and differing heights of bursts. The validated Generator of body data multi-body human surrogate model allows for numerical kinematic data simulation in explicit finite element method fluid structure interaction blast modeling. Two finite element methods were investigated to simulate blast interaction with humans, an enhanced blast uncoupled method, and an Arbitrary Lagrangian Eularian fully coupled method. The enhanced blast method defines an air blast function through the application of a blast pressure wave, including ground reflections, based on the explosives relative location to a target; the pressures curves are based on the Convention Weapons databases. LBE model is efficient for parametric numerical studies of blast interaction where the target response is the only necessary result. The ALE model, unlike classical Lagrangian methods, has a fixed finite element mesh that allows material to flow through it; this enables simulation of large deformation problems such as blast in an air medium and its subsequent interaction with structures. The ALE model should be used when research into a specific blast scenario is of interest, since this method is more computationally expensive. The ALE method can evaluate a blast scenario in more detail including: explosive detonation, blast wave development and propagation, near-field fireball effects, blast wave reflection, as well as 3D blast wave interaction, reflection and refraction with a target. Both approaches were validated against experimental blast tests performed by Defense Research and Development Valcartier and ConWep databases for peak pressure, arrival time, impulse, and curve shape. The models were in good agreement with one another and follow the experimental data trend showing an exponential reduction in peak acceleration with increasing standoff distance until the Mach stem effect reached head height. The Mach stem phenomenon is a shock front formed by the merging of the incident and reflected shock waves; it increases the applied peak pressure and duration of a blast wave thus expanding the potential head injury zone surrounding a raised explosive. The enhanced blast model was in good agreement with experimental data in the near-field, and mid-field; however, overestimated the peak acceleration, and head injury criteria values in the far-field due to an over predicted pressure impulse force. The ALE model also over predicted the response based on the head injury criteria at an increased standoff distance due to smearing of the blast wave over several finite elements leading to an increased duration loading. According to the Abbreviated Injury Scale, the models predicted a maximal level 6 injury for all explosive sizes in the near-field, with a rapid acceleration of the head over approximately 1 ms. There is a drastic exponential reduction in the insult force and potential injury received with increasing standoff distance outside of the near-field region of an explosive charge.

Traumatic brain injury (TBI) is a worldwide public health problem. It is often caused by impacts to the head, which can cause translational and rotational motions. During impacts to the head, the neck serves as one of the boundary conditions for determining its kinematic response. In today’s helmet assessment standards, the dynamics of the neck are not included, and in most standards only translational accelerations are examined within a short time interval around 20- 30 ms. However, to understand the risk of brain injury, it is also important to account for the rotational motions and the influence of the neck on head kinematics.  In this thesis the influence of the neck on head kinematics was investigated by comparing 5 different finite element (FE) models of the human. By using finite element analysis, simulations of four different accident scenarios were conducted. Most models are produced for the automotive industry and are not validated in vertical impacts with forces acting on the head. The accident scenarios included vertical and horizontal impacts to the head with different striking objects. The models included two anthropomorphic test devices (ATD) and three human body models (HBM). Furthermore, an isolated head was also used. The models were equipped with an industrial safety helmet, with and without a low friction layer (LFL). Additionally, the helmet versions were used to investigate how the various FE models predict the difference in rotational kinematics.  The head kinematics showed considerable disparities between the ATDs and the HBMs. The ATDs mostly showed a stiffer, spring-like behavior with higher translational accelerations and lesser rotational motions. Furthermore, the HBMs showed responses that were assumed to have been in better proximity to biofidelic responses. The incorporation of the LFL led to a reduction in peak resultant rotational velocity (PRV) in most models and accident scenarios. Furthermore, the results were highly influenced by the choice of duration. It was seen that the differences between the models increased over time, as the boundary effects could influence the kinematics to a larger extent. Hence, the neck had more influence on head kinematics at longer time durations.  This thesis contributes to a comparison of different FE models and how various boundary conditions affect the kinematics of the head. The Hybrid III should only be used in cases involving pure flexion-extension. The attachment of the KTH neck to the Hybrid III torso led to large differences in kinematic responses to the other models, and therefore it should not be used in virtual testing. Due to the resemblance between head-only and the HBMs, as well as the short duration in bicycle helmet assessment, the use of only a headform is probably a better approximation as the ATD necks that could be used are not good representations of biofidelity. Before implementing surrogate necks in helmet assessment, more investigations on the influence of the neck on head kinematics are necessary as well as the development of neck models with high biofidelity. / Traumatiska hjärnskador är ett globalt folkhälsoproblem. Traumatiska hjärnskador orsakas ofta av slag mot huvudet, vilket kan orsaka både translations- och rotationsrörelser av hjärnan. Vid slag mot huvudet verkar halsen som ett av randvillkoren som styr kinematiken av huvudet. I dagens hjälmstandarder är halsens dynamik inte inkluderad och i majoriteten av standarder är det endast translationsaccelerationer som undersöks samt inom en kort tidsram, runt 20-30 ms. För att förstå risken för hjärnskador behöver man även beakta rotationsrörelser och då blir halsens inflytande på huvudets kinematik av vikt, liksom att utvärdera kinematiken under en längre tid.  I detta examensarbete studeras halsens inverkan på huvudets kinematik genom att jämföra fem olika finita element (FE) modeller av människan. Genom att använda finita elementmetoden, genomfördes simuleringar av 4 olika olycksscenarior. Olycksscenariorna inkluderade vertikala och horisontella islag med olika objekt. De modeller som användes var två krockdockor och tre humanmodeller samt ett isolerat huvud. De flesta modeller är framtagna för bilindustrin vilket påverkar dess användningsområde genom begränsade valideringar av vertikala slag med krafter som verkar direkt på huvudet. Alla modeller var utrustade med en industrihjälmsmodell, med respektive utan ett lågfriktionslager. Dessutom användes hjälmmodellerna till att undersöka hur de olika FE modellerna förutspådde skillnader i rotationskinematik.  Kinematiken av huvudet visade på signifikanta skillnader mellan krockdockorna och humanmodellerna. Krockdockorna hade generellt ett stelare, fjäderliknande beteende med högre translationsacceleration och mindre rotationsrörelse. Vidare hade humanmodellerna ett beteende som var mer likt den förväntade mänskliga responsen. Användandet av lågfriktionslagret ledde till reduktion i resulterande peak rotationshastighet bland de flesta modeller och olycksscenarior. Resultatet påverkades nämnvärt av valet av tidsintervall. Vid längre tidsintervall var skillnaderna i beteende större mellan modellerna. Därför hade halsen större inverkan på huvudets kinematik vid längre durationer.  Detta examensarbete bidrar till en jämförelse av olika FE modeller och förståelse för hur olika randvillkor påverkar huvudets kinematik. Hybrid III borde endast användas för horisontella islag med enbart flexion-extensions rörelser. Infästningen av KTH halsen till Hybrid III gav stora skillnader i kinematiken jämfört med de andra modellerna, och därför ska den inte användas vid virtuella tester. På grund av de likheter som sågs mellan enbart huvud och humanmodellerna samt på grund av de korta islagen vid cykelhjälmsbedömningar, är troligtvis användandet av ett isolerat huvud en bättre approximation än användandet av de tillgängliga krockdockornas halsar. Innan man använder halsmodeller vid hjälmbedömningar, krävs fler studier på halsens inverkan på kinematiken samt framtagande av halsmodeller med mer människoliknande respons.