Direct Observation of Low Strain, High Rate Deformation of Cultured Brain Tissue During Primary Blast

Effect of blast orientation, multi-point blasts, and repetitive blasts on brain injury

Explosions in the battlefield can result in brain damage. Research on the effects of shock waves on brain tissue mainly focuses on the effects of single-orientation blast waves, while there have been few studies on the dynamic response of the human brain to directional explosions in different planes, multi-point explosions and repetitive explosions. Therefore, the brain tissue response and the intracranial pressure (ICP) caused by different blast loadings were numerically simulated using the CONWEP method. In the study of the blast in different directions, the lateral explosion blast wave was found to cause greater ICP than did blasts from other directions. When multi-point explosions occurred in the sagittal plane simultaneously, the ICP in the temporal lobe increased by 37.8 % and the ICP in the parietal lobe decreased by 17.6 %. When multi-point explosions occurred in the horizontal plane, the ICP in the frontal lobe increased by 61.8 % and the ICP in the temporal lobe increased by 12.2 %. In a study of repetitive explosions, the maximum ICP of the second blast increased by 40.6 % over that of the first blast, and that of the third blast increased by 61.2 % over that of the second blast. The ICP on the brain tissue from repetitive blasts can exceed 200 % of that of a single explosion blast wave.

Partial Depletion of Microglia Attenuates Long-Term Potentiation Deficits following Repeated Blast Traumatic Brain Injury in Organotypic Hippocampal Slice Cultures

Blast-induced traumatic brain injury (bTBI) has been a health concern in both military and civilian populations due to recent military and geopolitical conflicts. Military service members are frequently exposed to repeated bTBI throughout their training and deployment. Our group has previously reported compounding functional deficits as a result of increased number of blast exposures. In this study, we further characterized the decrease in long-term potentiation (LTP) by varying the blast injury severity and the inter-blast interval between two blast exposures. LTP deficits were attenuated with increasing inter-blast intervals. We also investigated changes in microglial activation; expression of CD68 was increased and expression of CD206 was decreased after multiple blast exposures. Expression of macrophage inflammatory protein (MIP)-1α, interleukin (IL)-1β, monocyte chemoattractant protein (MCP)-1, interferon gamma-inducible protein (IP)-10, and regulated on activation, normal T cell expressed and secreted (RANTES) increased, while expression of IL-10 decreased in the acute period after both single and repeated bTBI. By partially depleting microglia prior to injury, LTP deficits after injury were significantly reduced. Treatment with the novel drug, MW-189, prevented LTP deficits when administered immediately following a repeated bTBI and even when administered only for an acute period (24 h) between two blast injuries. These findings could inform the development of therapeutic strategies to treat the neurological deficits of repeated bTBI suggesting that microglia play a major role in functional neuronal deficits and may be a viable therapeutic target to lessen the neurophysiological deficits after bTBI.

Protective Performance of Helmets and Goggles in Mitigating Brain Biomechanical Response to Primary Blast Exposure

The current combat helmets are primarily designed to mitigate blunt impacts and ballistic loadings. Their protection against primary blast wave is not well studied. In this paper, we comprehensively assessed the protective capabilities of the advanced combat helmet and goggles against blast waves with different intensity and directions. Using a high-fidelity human head model, we compared the intracranial pressure (ICP), cerebrospinal fluid (CSF) cavitation, and brain strain and strain rate predicted from bare head, helmet-head and helmet-goggles-head simulations. The helmet was found to be effective in mitigating the positive ICP (24–57%) and strain rate (5–34%) in all blast scenarios. Goggles were found to be effective in mitigating the positive ICP in frontal (6–16%) and lateral (5–7%) blast exposures. However, the helmet and goggles had minimal effects on mitigating CSF cavitation and even increased brain strain. Further investigation showed that wearing a helmet leads to higher risk of cavitation. In addition, their presence increased the head kinetic energy, leading to larger strains in the brain. Our findings can improve our understanding of the protective effects of helmets and goggles and guide the design of helmet pads to mitigate brain responses to blast.

Computational modeling investigation of pulsed high peak power microwaves and the potential for traumatic brain injury

When considering safety standards for human exposure to radiofrequency (RF) and microwave energy, the dominant concerns pertain to a thermal effect. However, in the case of high-power pulsed RF/microwave energy, a rapid thermal expansion can lead to stress waves within the body. In this study, a computational model is used to estimate the temperature profile in the human brain resulting from exposure to various RF/microwave incident field parameters. The temperatures are subsequently used to simulate the resulting mechanical response of the brain. Our simulations show that, for certain extremely high-power microwave exposures (permissible by current safety standards), very high stresses may occur within the brain that may have implications for neuropathological effects. Although the required power densities are orders of magnitude larger than most real-world exposure conditions, they can be achieved with devices meant to emit high-power electromagnetic pulses in military and research applications.

Investigation of the Compressive Viscoelastic Properties of Brain Tissue Under Time and Frequency Dependent Loading Conditions

The mechanical characterization of brain tissue has been generally analyzed in the frequency and time domain. It is crucial to understand the mechanics of the brain under realistic, dynamic conditions and convert it to enable mathematical modelling in a time domain. In this study, the compressive viscoelastic properties of brain tissue were investigated under time and frequency domains with the same physical conditions and the theory of viscoelasticity was applied to estimate the prediction of viscoelastic response in the time domain based on frequency-dependent mechanical moduli through Finite Element models. Storage and loss modulus were obtained from white and grey matter, of bovine brains, using dynamic mechanical analysis and time domain material functions were derived based on a Prony series representation. The material models were evaluated using brain testing data from stress relaxation and hysteresis in the time dependent analysis. The Finite Element models were able to represent the trend of viscoelastic characterization of brain tissue under both testing domains. The outcomes of this study contribute to a better understanding of brain tissue mechanical behaviour and demonstrate the feasibility of deriving time-domain viscoelastic parameters from frequency-dependent compressive data for biological tissue, as validated by comparing experimental tests with computational simulations.

Craniocerebral Dynamic Response and Cumulative Effect of Damage Under Repetitive Blast

Soldiers suffer from multiple explosions in complex battlefield environment resulting in aggravated brain injuries. At present, researches mostly focus on the damage to human body caused by single explosion. In the repetitive impact study, small animals are mainly used for related experiments to study brain nerve damage. No in-depth research has been conducted on the dynamic response and damage of human brain under repetitive explosion shock waves. Therefore, this study use the Euler-Lagrange coupling method to construct an explosion shock wave-head fluid-structure coupling model, and numerically simulated the brain dynamic response subjected to single and repetitive blast waves, obtained flow field pressure, skull stress, skull displacement, intracranial pressure to analyze the brain damage. The simulation results of 100 g equivalent of TNT exploding at 1 m in front of the craniocerebral show that repetitive blast increase skull stress, intracranial pressure, skull displacement, and the damage of brain tissue changes from moderate to severe. Repetitive blasts show a certain cumulative damage effect, the severity of damage caused by double blast is 122.5% of single shock, and the severity of damage caused by triple blast is 105.9% of double blast and 131.5% of single blast. The data above shows that it is necessary to reduce soldiers' exposure from repetitive blast waves.

Efficacy of Body Armor in Protection Against Blast Injuries Using a Swine Model in a Confined Space with a Blast Tube

The purpose of this study was to clarify whether or not body armor would protect the body of a swine model using a blast tube built at National Defense Medical College, which is the first such blast tube in Japan. Seventeen pigs were divided into two groups: the body armor group and the non-body armor group. Under intravenous anesthesia, the pigs were tightly fixed in the left lateral position on a table and exposed from the back neck to the upper lumbar back to the blast wave and wind with or without body armor, with the driving pressure of the blast tube set to 3.0 MPa. When the surviving and dead pigs were compared, blood gas analyses revealed significant differences in PaO2, PaCO2, and pH in the super-early phase. All pigs injured by the blast wave and wind had lung hemorrhage. All 6 animals in the body armor group and 6 of the 11 animals in the control group survived for 3 hours after injury. Respiratory arrest immediately after exposure to the blast wave was considered to influence the mortality in our pig model. Body armor may have a beneficial effect in protecting against respiratory arrest immediately after an explosion.