3,296 research outputs found

    THE MECHANICS OF INTRACRANIAL LOADING DURING BLAST AND BLUNT IMPACTS – EXPERIMENTAL AND NUMERICAL STUDIES

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    Head injuries in an explosion occur as a result of a sudden pressure changes (e.g. shock-blast) in the atmosphere (primary injury), high velocity impacts of debris (secondary injury) and people being thrown against the solid objects (tertiary injury) in the field. In this thesis, experimental and numerical approaches are used to delineate the intracranial loading mechanics of both primary (blast) and tertiary injuries (blunt). The blast induced head injuries are simulated using a fluid-filled cylinder. This simplified model represents the head-brain complex and the model is subjected to a blast with the Friedlander waveform type of loading. We measured the temporal variations in surface pressure and strain in the cylinder and corresponding fluid pressure. Based on these data, the loading pathways from the external blast to the pressure field in the fluid are identified. The results indicate that the net loading at a given point in the fluid comprises direct transmissive loads and deflection-induced indirect loads. The study also shows that the fluid pressure (analogue of intracranial pressure) increases linearly with increase in reflected blast overpressures (ROP) for a given shell thickness. When the ROP is kept constant, fluid pressure increases linearly with the decrease in shell thickness. For understanding the blunt induced head injuries, the complaint (acrylic gel complex) and rigid (aluminum body) head surrogates with an identical mass are impacted on target surfaces of different stiffnesses. The study indicates that the acceleration field in the gel-filled head surrogate varies from coup to counter-coup region, whereas the field is uniform in the rigid surrogate. The variation in the acceleration field is influenced by the shell deformation that in turn depends on the stiffness of the target surface. Impact studies on the helmet padding currently being used by the US Army are also carried out at different loading conditions. Our results indicate that for a fixed thickness of a foam pad, an increase in the stiffness of the pad will result in the increased absorption of the impact energy. Advisor: Namas Chandr

    Neuroimaging of structural pathology and connectomics in traumatic brain injury: Toward personalized outcome prediction.

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    Recent contributions to the body of knowledge on traumatic brain injury (TBI) favor the view that multimodal neuroimaging using structural and functional magnetic resonance imaging (MRI and fMRI, respectively) as well as diffusion tensor imaging (DTI) has excellent potential to identify novel biomarkers and predictors of TBI outcome. This is particularly the case when such methods are appropriately combined with volumetric/morphometric analysis of brain structures and with the exploration of TBI-related changes in brain network properties at the level of the connectome. In this context, our present review summarizes recent developments on the roles of these two techniques in the search for novel structural neuroimaging biomarkers that have TBI outcome prognostication value. The themes being explored cover notable trends in this area of research, including (1) the role of advanced MRI processing methods in the analysis of structural pathology, (2) the use of brain connectomics and network analysis to identify outcome biomarkers, and (3) the application of multivariate statistics to predict outcome using neuroimaging metrics. The goal of the review is to draw the community's attention to these recent advances on TBI outcome prediction methods and to encourage the development of new methodologies whereby structural neuroimaging can be used to identify biomarkers of TBI outcome

    Mild Traumatic Brain Injury: Combined in Silico and in Vitro Studies

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    Mild traumatic brain injury (TBI) is a significant public health concern worldwide and has attracted significant attention due to high-impact sport as well as improvised explosive devices used in military conflicts. The earliest sign of mild TBI is associated with cognitive, behavioral and physical/somatic changes, which are commonly invisible to existing medical techniques. Thus it is essential to target mechanisms of mild TBI and its associated damage measures for earlier diagnosis/treatment and enhanced protection strategies. In this work, the mechanism of blast-induced mild TBI was inspected through integrated in silico and in vitro models. A three-dimensional (3D) human head model with anatomical details was reconstructed from high-resolution medical images, and positioned in three different directions with respect to the blast wave. The effects of head orientations as well as cerebral blood vessel network in brain mechanics were investigated. The dynamic responses of the brain were monitored by the maximum principal strain (MPS), shear strain (SS), and intracranial pressure (ICP). The developed numerical model was validated by the shock tube experiment using a surrogate head, i.e., water-filled polycarbonate shell. Results demonstrated that the ICP alternations in the brain was initially dominated by the direct blast wave propagation and the skull flexure took effect at a later time. It is worth noting that cerebral blood vessel network induced larger MPS and SS in the brain, which were influenced by vessel diameter and density. Moreover, the contour of the head and its orientation significantly altered the flow dynamics around the head, resulting in different spatial and temporal distributions of brain mechanics. Excessive mechanical stain sensed by brain cells, especially abundant cortical astrocytes, could be a potential index factor for the brain injury. An in vitro injury model for primary cortical astrocytes was developed to identify the injury threshold. Rat cortical astrocytes cultured on silicone membrane were subjected to equibiaxial pulse stretch. The blast pressure profile on the membrane was monitored and the membrane deformations were captured through the high-speed imaging system. The simulated membrane strain, validated by experimental measures, was used to construct an exposure-response curve. It was observed that live cells declined sharply in the strain range from 18% to 35%, which was identified as the injury threshold of cortical astrocytes. The obtained damage threshold of rat cortical astrocytes could be inferred about the level of brain injury in a rat. A 3D rat head model was constructed with an impactor mimicking the loading conditions of contact sports. Results revealed that impact depth and impactor shape were the two leading factors affecting brain dynamics. The influence of impactor diameter was region-specific and an increase in impactor diameter could substantially increase brain strains in the region which located directly beneath the impactor. The lateral impact could induce higher strains in the brain than the central impact. Results suggested that indentation depth instead of impact depth would be appropriate to characterize the influence of a softer impactor. Advisor: Linxia G

    Finite Element Simulation of Skull Fracture Evoked by Fall Injuries

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    This study presents novel predictive equations for von Mises stresses and deflection of bones in the frontal and lateral regions of the skull. The equations were developed based on results of a finite element model developed here. The model was validated for frontal and lateral loading conditions with input values mimetic to fall scenarios. Using neural network processing of the information derived from the model achieved R2 values of 0.9990 for both the stress and deflection. Based on the outcome of the fall victims, a threshold von Mises stress of 40.9 to 46.6 MPa was found to indicate skull fracture given a maximum input force of 26 kN and a load rate of 40 kN/ms

    Development of a Reverse Engineered, Parameterized, and Structurally Validated Computational Model to Identify Design Parameters that Influence American Football Faceguard Performance

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    Traumatic brain injury (TBI) continues to have the greatest incidence among athletes participating in American football. The headgear design research community has focused on developing accurate computational and experimental analysis techniques to better assess the ability of headgear technology to attenuate impacts and protect athletes from TBI. Despite efforts to innovate the headgear system, minimal progress has been made to innovate the faceguard. Although the faceguard is not the primary component of the headgear system that contributes to impact attenuation, faceguard performance metrics, such as weight, structural stiffness, and visual field occlusions, have been linked to athlete safety. To improve upon the understanding of the discrepancies in faceguard performance metrics, this research developed reverse engineered, structurally validated, and parameterized finite element (FE) simulations of common American football faceguards. The reverse engineered, FE simulation validation, and parametric analysis process was repeated for a total of nine common American football faceguards spanning four style categories, four helmet-compatible series, and three equipment manufacturers. The results comparing the faceguard models indicated measured responses—mass and stiffness—varied across faceguard styles and helmet-compatible series. Additionally, this work developed the Central Visual Field – Occlusion (CVF-O) metric and the Peripheral Visual Field – Occlusion (PVF-O) metric which quantified the amount of occlusion from each faceguard in each of the hypothesized segments of the visual field. The comparison of the nine faceguards modeled indicated a large difference in faceguard styles and helmet-compatible series; however, the results were not correlated to faceguard style, mass, or structural stiffness. Leveraging the results from the parametric analysis, an “overbuilt” faceguard was reverse engineered and modeled. The metal wire cross-sections were parameterized as an ellipse, and the mass of the overbuilt faceguard was minimized subject to stress and stiffness constraints. When comparing the models of the original manufacturer’s designs with two materials, the masses and structural stiffnesses were directly proportional to the densities and elastic moduli of the two materials. Both innovating the metal wire cross section and changing material properties have demonstrated the potential to improve upon faceguard performance metrics

    Effect of full helmet systems on human head responses under blast loading

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    This paper focuses on helmet design for head protection under blast threats. It is presented a numerical investigation of the head response accruing to blast loads on helmet protective systems. Various combinations of the helmet, visor and mandible guard were numerically analyzed for a given mass of TNT at a distance to the target representing an anti-vehicle buried mine threat. Limited published articles on the subject are available in the scientific literature. In this paper, a 3D head helmet numerical model for blast analyses is developed in the finite element code ABAQUS/Explicit. The results showed that individual protective systems are not effective enough to mitigate the damage caused by blast loading. The complete protective equipment reduces the pressures on the brain by up to 5 times and ensures that no fracture in the skull appears. This numerical study aims to provide helmet manufacturers and users with some insight in what possible brain injuries are to be expected in various blast scenarios so as to help in better diagnosis of unsuspected brain injury.The Ministry of Economy and Competitiveness of Spain and FEDER program under the Project RTC-2015-3887-8 for the financial support of the work
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