New Mechanics of Traumatic Brain Injury

The prediction and prevention of traumatic brain injury is a very important aspect of preventive medical science. This paper proposes a new coupled loading-rate hypothesis for the traumatic brain injury (TBI), which states that the main cause of the TBI is an external Euclidean jolt, or SE(3)-jolt, an impulsive loading that strikes the head in several coupled degrees-of-freedom simultaneously. To show this, based on the previously defined covariant force law, we formulate the coupled Newton-Euler dynamics of brain's micro-motions within the cerebrospinal fluid and derive from it the coupled SE(3)-jolt dynamics. The SE(3)-jolt is a cause of the TBI in two forms of brain's rapid discontinuous deformations: translational dislocations and rotational disclinations. Brain's dislocations and disclinations, caused by the SE(3)-jolt, are described using the Cosserat multipolar viscoelastic continuum brain model. Keywords: Traumatic brain injuries, coupled loading-rate hypothesis, Euclidean jolt, coupled Newton-Euler dynamics, brain's dislocations and disclinationsComment: 18 pages, 1 figure, Late

Master of Science

thesisTraumatic brain injury (TBI) is a leading cause of death and disability in the U.S.A. In mild cases, common etiologies of TBI (i.e., hemorrhage or edema) are not readily apparent during medical examination. We propose that the pia-arachnoid complex (PAC) contributes to the brain's response in TBI. The PAC is the only layer of tissue between the brain and dura (a tough membrane tightly adhered to the skull), and acts as a mechanical tether between the brain and skull. If the fine structures of the PAC are damaged during TBI, they likely go undiagnosed due to their small size and difficulty to image. To better understand the mechanics of PAC injury, several experimental and computational studies were conducted. First, a novel application of optical coherence tomography (OCT) was utilized to acquire microscale images of the in-situ porcine PAC and measure the amount of arachnoid trabeculae (AT) present. Next, two parametric studies were conducted on a microscale model of the PAC which evaluated its sensitivity to variable substructure moduli and AT volume fraction (VF). Afterwards, the microscale PAC model was paired with a macroscale head model to determine the effect of a nonuniform AT VF on whole-head mechanics. Finally, an immature porcine model of mild TBI was used to investigate PAC damage following head rotation, and identify clinically relevant MRI biomarkers indicative of PAC damage. The OCT imaging of the PAC revealed high variability of VF within each head, but low variability between brain regions and between animals. The microscale parametric studies showed high sensitivity to changes in substructure moduli and VF. The macroscale model studies showed improvement of intracranial hemorrhage prediction when variable VF was introduced into the models. Clinically relevant biomarkers of PAC damage were not able to be confidently developed, but increased sample size and improved resolution may lead to innovative biomarkers for TBI. The work presented here addresses a significant lack of data on the PAC, and presents new insights into its anatomy and biomechanics. Many of the studies presented here are the first of their kind, opening up many new paths of TBI research opportunities

SIMBIO-M 2014, SIMulation technologies in the fields of BIO-Sciences and Multiphysics: BioMechanics, BioMaterials and BioMedicine, Marseille, France, june 2014

Proceedings de la 3ème édition de la conférence internationale Simbio-M (2014). Organisée conjointement par l'IFSTTAR, Aix-Marseille Université, l'université de Coventry et CADLM, cette conférence se concentre sur les progrès des technologies de simulation dans les domaines des sciences du vivant et multiphysiques: Biomécanique, Biomatériaux et Biomédical. L'objectif de cette conférence est de partager et d'explorer les résultats dans les techniques d'analyse numérique et les outils de modélisation mathématique. Cette approche numérique permet des études prévisionnelles ou exploratoires dans les différents domaines des biosciences

Numerical Simulation of Blast Interaction with the Human Body: Primary Blast Brain Injury Prediction

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

Biomechanics of Head Impacts in an Unhelmeted Sport

Concussion in sport is very common and often the injury is undetectable using CT and MRI scans. In addition, approximately 50% of concussions areunreported.The project initially investigated the suitability of a skin patch sensor and a head-band sensorfor the measurement of head impacts in unhelmeted sports. It was found that both were unsuitable due to large angular accelerationerrors. Thestudy then collaborated withCAMLab at Stanford University and 25 Mixed Martial Arts (MMA) athletes were fitted CAMLab’s validated instrumented mouthguard. 451 video confirmed impacts were recorded at 19 sparring and 11 competitive MMA events. Five concussions were diagnosed during the competitive events. The most severe impacts were simulated using the Global Human Body Model Consortium head model. The average resultant linear acceleration of the impacts that resulted in a concussion was approximately 20% lower than concussive studies of US football while the resultant average angular acceleration was 34% higher. It ishypothesised that these differences are due to the high energy frontal impacts in US football as opposed to the ‘hook’ style punches in MMA.Large strains in the mid-brain occurred from frontal impacts whereas lateralimpacts resultedin large strains in the corpus callosum. It was found that the average strain in the corpus callosum of the concussed athletes was 0.27 which was 88% higher than that in uninjured fighters. In collaboration with the Genetics department in Trinity College Dublin it was found that the maximum principal strain correlated (R2=0.84) with the volume fraction of blood brain barrierdisruptionpost-fight. In conjunction with Stanford University,it was found that the spectral density of MMA impacts was higher than that in US football.This study is the first known study to measure in vivohead impacts in unhelmeted athletes that have suffered a concussion

Head Acceleration in Men’s University Rugby Union and the Effect of Neck Strength Training

There is increasing concern regarding concussion and exposure to repeated head impacts in rugby union due to the associated long-term health consequences. To date, measurement systems associated with a high degree of measurement error have been utilised to research head impacts. Moreover, increases in neck strength have been shown to reduce the risk of concussion risk. The aim of this thesis was to investigate the relationship between neck strength and head acceleration in Rugby Union players. Maximum isometric strength data were collected from 27 male university rugby players at the start of the competitive season and following neck-specific resistance training completed throughout the season. The training programme was completed two times per week and consisted of deep neck stabiliser exercises, weighted isometric training, and dynamic resistance training. The bespoke isometric apparatus utilised four, 150 kg load cells, measuring neck strength in flexion, extension, and left and right lateral flexion. Linear and rotational head acceleration data were recorded throughout the season using mouthguards that were instrumented with a nine-axis inertial motion unit and an additional triaxial accelerometer. The neck strength training programme resulted in improvements in all outcome parameters (5.5 – 18.8%), with significant improvements for all, except extension (p < 0.05). A median (IQR) of 13 g (11 - 18 g) and 849 rad•s-2 (642 - 1,115 rad•s-2) were observed for peak linear and rotational acceleration, respectively. Results revealed that participants with greater neck strength experienced lower head acceleration values throughout the season (p <0.05). The neck-specific training programme was effective in increasing isometric neck strength. The head acceleration values recorded in the current thesis were substantially lower than those previously recorded. Findings indicate that increasing neck strength may be effective in reducing head inertial load experienced during rugby matches

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

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

Head impact effects in Small Remotely Piloted Aircraft System (sRPAS) collisions: Gender specific risks and vulnerable population protection

This study focuses on supporting the development of safety regulations for vulnerable populations during drone to head impacts. First, the small female head and neck model was compared to cadaveric data. Then, combined with lab’s previous work, gender-based disparities in head impact responses were highlighted, with small females experiencing higher injury risk metrics, despite lower skull von Mises stress. Beyond small females, children of various ages and their head responses during impacts were also analyzed. In addition to the previously developed quadcopter drone model, a new Mavic Pro drone model was developed, and this model was integrated with human head models during comparison against cadaveric data. The Mavic Pro, despite its lower weight, demonstrated higher injury risks compared to the previously studied Phantom 3. Overall, in this study head kinematics, head injury criteria (HIC), rotational velocities, and brain strains were analyzed, indicating potential risks for vulnerable populations. These findings underscore the need for tailored safety measures, regulatory guidelines, and comprehensive injury prevention strategies in the field of drone operations

Assessment of head injury risk caused by impact using finite element models

[ES] Las cargas de impacto son la fuente primaria de lesiones en la cabeza y pueden resultar en un rango de traumatismo desde leve hasta severo. Debido a la existencia de múltiples entornos en los que se pueden desencadenar lesiones por impacto (accidentes automovilísticos, deportes, caídas accidentales, violencia), éstas pueden afectar potencialmente a toda la población independientemente de su estado de salud. Pese al creciente esfuerzo en investigación para comprender la biomecánica de las lesiones por traumatismo en la cabeza, todavía no es del todo posible realizar predicciones precisas ni prevenir estos eventos. En esta Tesis, se han estudiado algunos aspectos del comportamiento ante impacto de los diferentes tejidos biológicos involucrados mediante el desarrollo de un modelo numérico de cabeza humana a partir de imágenes de tomografía computerizada (TAC). Se han realizado simulaciones en elementos finitos (EF) de ensayos experimentales de la literatura con el fin de validar el modelo numérico desarrollado, estableciendo unas propiedades mecánicas adecuadas para cada uno de sus constituyentes. De esta manera se puede adquirir una predicción adecuada del riesgo de sufrir daños. Parte de esta Tesis se centra en el entorno balístico, específicamente en cascos de combate antibalas, los cuales son susceptibles de causar traumatismo craneoencefálico debido a la elevada deformación que sufren durante el impacto. Previamente al estudio de estos fenómenos de alta velocidad, se han realizado ensayos experimentales y numéricos para caracterizar la respuesta mecánica de algunos materiales compuestos ante impacto de baja velocidad. Al principio de esta Tesis se ha realizado una revisión del estado del arte acerca de los criterios existentes para cuantificar el trauma craneoencefálico.Este es un aspecto clave para las simulaciones numéricas, ya que la idoneidad de algunos de estos criterios para la predicción de lesiones cerebrales todavía es un debate abierto. Mediante EF se han realizado simulaciones de impactos balísticos en una cabeza protegida con un casco de combate. Mediante la posterior aplicación de diferentes criterios de daño sobre los resultados obtenidos se ha evaluado el nivel de protección que aseguran los protocolos de aceptación de cascos de combate, así como las estrategias para determinar su tallaje. Se ha demostrado que las normativas existentes para cascos de combate son capaces de mitigar algunos mecanismos de trauma pero no logran prevenir otros como los gradientes de presión intracraneales. Además, se ha demostrado que algunas de las estrategias de tallaje más comúnmente adoptadas por los fabricantes, como producir un solo tamaño de calota, deberían ser reconsideradas ya que existe un mayor riesgo de traumatismo cuando la distancia entre la cabeza y la calota del casco no es suficiente. Siguiendo la línea de protecciones personales, algunos de los materiales compuestos comúnmente empleados en la industria armamentística se han combinado para crear distintas configuraciones de calota para optimizar la relación entre peso del casco y protección para la cabeza. Materiales ligeros como el UHMWPE han resultado en un comportamiento menos eficiente que el de los apilados de tejido de aramida a la hora de limitar la BFD (deformación máxima en la calota del casco en la zona de impacto). Hacia el final de la Tesis se presenta un modelo numérico de cabeza humana detallado, que incluye treinta y tres de las estructuras anatómicas principales. Dicho modelo se ha desarrollado para la simulación de un accidente ecuestre en el que aparecen múltiples lesiones craneoencefálicas. Principalmente, se pretende establecer un criterio mecánico para predecir el hematoma subdural (HS) basado en la ruptura de los vasos sanguíneos intracraneales. Se ha propuesto un valor umbral de ruptura en tensiones de 3.5 MPa, pero tanto este límite como la localización del vaso dañado son altamen[CA] Les càrregues d'impacte son la font primària de lesions al cap i poden resultar en un rang de severitat des de lleu a greu. Degut als múltiples entorns en que poden desencadenar-se lesions per impacte (accidents automobilístics, esports, caigudes accidentals, violència), aquestes poden afectar potencialment a tota la població independentment del seu estat de salut. Malgrat el creixent esforç en investigació per comprendre la biomecànica de les lesions per traumatisme al cap, encara no és del tot possible realitzar prediccions precises ni prevenir aquestos esdeveniments. En aquesta Tesi, s'han estudiat alguns aspectes del comportament a impacte dels diferents teixits biològics involucrats mitjançant el desenvolupament d'un model numèric de cap humà a partir d'imatges de tomografia computeritzada (TAC). S'han realitzat simulacions en elements finits (EF) d'assajos experimentals de la literatura amb la finalitat de validar el model numèric desenvolupat, establint unes propietats mecàniques adequades per a cadascun dels seus constituents. D'aquesta manera es pot aconseguir una predicció del risc de sofrir danys traumàtics. Part d'aquesta Tesi es centra en l'entorn balístic, específicament en cascs de combat antibales, els quals són susceptibles de causar traumatisme degut a l'elevada deformació que sofrixen durant l'impacte. Previament a l'estudi d'aquests fenòmens d'alta velocitat, s'han realitzat assajos experimentals i numèrics per a caracteritzar la resposta mecànica d'alguns materials compostos en condicions d'impacte a baixa velocitat. Al començament d'aquesta Tesi s'ha realitzat una revisió de l'estat de l'art sobre els criteris existents per quantificar el trauma cranioencefàlic. Aquest és un aspecte clau per a les simulacions numèriques, ja que l'utilitat d'alguns d'aquestos criteris per a la predicció de lesions cerebrals és encara un debat obert. Mitjançant EF s'han realitzat simulacions numèriques d'impactes balístics en un cap protegit amb un casc de combat. Gràcies a la posterior aplicació de diferents criteris de dany sobre els resultats obtinguts s'ha evaluat el nivell de protecció que asseguren els protocols d'acceptació de cascs de combat, així com les estratègies per a determinar les seues talles. S'ha demostrat que les normatives existents són capaces de mitigar alguns mecanismes de trauma però no aconseguixen prevenir altres com els gradients de pressions intracranials. A més, s'ha demostrat que algunes estratègies per determinar les talles més comunament adoptades pels fabricants (com produir només un tamany de calota i adaptar el gruix de les escumes interiors a les diferents dimensions dels subjectes) haurien de ser reconsiderades ja que existeix un major risc de traumatisme quan la distància entre el cap i la calota del casc no és suficient. Seguint la línia de proteccions personals, alguns dels materials compostos comunament utilitzats en la indústria de l'armament s'han combinat per a crear distintes possibles configuracions de calota amb la finalitat d'optimitzar la relació entre pes i protecció. Materials lleugers com l'UHMWPE han resultat en un comportament menys eficient que el d'apilats de teixit d'aramida a l'hora de limitar la BFD (deformació màxima a la calota del casc a la zona d'impacte). Cap al final de la Tesi es presenta un model numèric detallat de cap humà, que inclou trenta-tres de les estructures anatòmiques principals. Aquest model s'ha desenvolupat per a la simulació d'un accident eqüestre en el qual apareixen múltiples lesions cranioencefàliques. Principalment, es pretén establir un criteri mecànic per a la predicció de l'hematoma subdural (HS) basat en la ruptura dels vasos sanguinis intracranials. S'ha proposat un valor umbral de ruptura en tensions de 3.5 MPa, pero tant aquest límit com la ubicació del vas danyat són altament dependents de l'anatomia específica de cada subjecte.[EN] Impact loading is the primary source of head injuries and can result in a range of trauma from mild to severe. Because of the multiple environments in which impact-related injuries can take place (automotive accidents, sports, accidental falls, violence), they can potentially affect the entire population regardless of their health conditions. Despite the increasing research effort on the understanding of head impact biomechanics, accurate prediction and prevention of traumatic injuries has not been completely achieved. In this Thesis, some aspects of the impact behaviour of the different biological tissues involved have been analysed through the development of a numerical human head model from Computed Tomography (CT) images. FE simulations of experimental tests from the literature have been performed and enhanced the validation of the head model through the establishment of proper material laws for its constituents, which enable adequate prediction of injury risks. Part of this Thesis focuses on the ballistic environment, especifically in bulletproof composite helmets, which are susceptible to cause blunt injuries to the head because of their large deformation during impact. Prior to the study of these high-speed impacts, experimental tests and finite element (FE) models have been performed to characterise the mechanical response of composite materials subjected to low velocity impact. The implementation of a continuum damage mechanics approach coupled to a Hashin failure criterion and surface-to-surface cohesive relations to the numerical model provided a good matching with the impact behaviour obtained experimentally, capturing the principal damage mechanisms. A review of the head injury criteria currently available in the literature has been performed at the beginning of this Thesis. This is a key issue for the numerical simulations, as the suitability of some criteria to predict head injuries is still an open question. Numerical simulation of ballistic impacts on a human head protected with a combat helmet has been conducted employing explicit FE analysis. The level of protection ensured by helmet acceptance protocols as well as their sizing strategies have been studied and discussed by means of the application of different mechanical-based head injury criteria. It has been demonstrated that current helmet testing standards do mitigate some specific forms of head trauma but fail to prevent other injury mechanisms such as the intracranial pressure gradients within the skull. Furthermore, it has been demonstrated that some well-established helmet sizing policies like manufacturing one single composite shell and adapting the thickness of the interior pads to the different head dimensions should be reconsidered, as there is a great risk of head injury when the distance between the head and the helmet shell (stand-off distance) is not sufficient. Following the line of personal protections, some composite materials commonly employed in the soft body armour industry have been combined into different helmet shells configurations to optimise the ratio of weight-to-head protection. Light materials like UHMWPE appear to be less efficient than integral woven-aramid lay-ups in the limitation of the backface deformation (BFD), the maximum deformation sustained by the helmet at the impact site. A detailed head numerical model including thirty-three of its main anatomical structures has been developed for the simulation of an equestrian accident that resulted in many head injuries. Above all, the establishment of a mechanical criterion for the prediction of subdural hematona (SDH) based on the rupture of the head blood vessels is intended. A stress threshold for vein rupture has been set on 3.5 MPa, but both this limit and the location of vessel failure are highly dependent on the specific anatomy of the subject's vascularity.Palomar Toledano, M. (2019). Assessment of head injury risk caused by impact using finite element models [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/135254TESI