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It is critical to understand the relationship between under-body blast (UBB) loading and occupant response to provide optimal protection to the warfighter from serious injuries, many of which affect the spine. Previous studies have examined component and whole body response to accelerative based UBB loading. While these studies both informed injury prediction efforts and examined the shortcomings of traditional anthropomorphic test devices in the evaluation of human injury, few studies provide response data against which future models could be compared and evaluated. The current study examines four different loading conditions on a seated occupant that demonstrate the effects of changes in the floor, seat, personal protective equipment (PPE), and reclined posture on whole body post-mortem human surrogate (PMHS) spinal response in a sub-injurious loading range. Twelve PMHS were tested across floor velocities and time-to-peak (TTP) that ranged from 4.0 to 8.0 m/s and 2 to 5 ms, respectively. To focus on sub-injurious response, seat velocities were kept at 4.0 m/s and TTP ranged from 5 to 35 ms. Results demonstrated that spine response is sensitive to changes in TTP and the presence of PPE. However, spine response is largely insensitive to changes in floor loading. Data from these experiments have also served to develop response corridors that can be used to assess the performance and predictive capability of new test models used as human surrogates in high-rate vertical loading experiments., (© 2020. Biomedical Engineering Society.)

Limited data exist on the injury tolerance and biomechanical response of humans to high-rate, under-body blast (UBB) loading conditions that are commonly seen in current military operations, and there are no data examining the influence of occupant posture on response. Additionally, no anthropomorphic test device (ATD) currently exists that can properly assess the response of humans to high-rate UBB loading. Therefore, the purpose of this research was to examine the response of post-mortem human surrogates (PMHS) in various seated postures to high-rate, vertical loading representative of those conditions seen in theater. In total, six PMHS tests were conducted using loading pulses applied directly to the pelvis and feet of the PMHS: three in an acute posture (foot, knee, and pelvis angles of 75°, 75°, and 36°, respectively), and three in an obtuse posture (15° reclined torso, and foot, knee, and pelvis angles of 105°, 105°, and 49.5°, respectively). Tests were conducted with a seat velocity pulse that peaked at ~4 m/s with a 30-40 ms time to peak velocity (TTP) and a floor velocity that peaked at 6.9-8.0 m/s (2-2.75 ms TTP). Posture condition had no influence on skeletal injuries sustained, but did result in altered leg kinematics, with leg entrapment under the seat occurring in the acute posture, and significant forward leg rotations occurring in the obtuse posture. These data will be used to validate a prototype ATD meant for use in high-rate UBB loading scenarios.

Biological tissue testing is inherently susceptible to the wide range of variability specimen to specimen. A primary resource for encapsulating this range of variability is the biofidelity response corridor or BRC. In the field of injury biomechanics, BRCs are often used for development and validation of both physical, such as anthropomorphic test devices, and computational models. For the purpose of generating corridors, post-mortem human surrogates were tested across a range of loading conditions relevant to under-body blast events. To sufficiently cover the wide range of input conditions, a relatively small number of tests were performed across a large spread of conditions. The high volume of required testing called for leveraging the capabilities of multiple impact test facilities, all with slight variations in test devices. A method for assessing similitude of responses between test devices was created as a metric for inclusion of a response in the resulting BRC. The goal of this method was to supply a statistically sound, objective method to assess the similitude of an individual response against a set of responses to ensure that the BRC created from the set was affected primarily by biological variability, not anomalies or differences stemming from test devices., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Three laboratory simulated sub-injurious under-body blast (UBB) test conditions were conducted with whole-body Post Mortem Human Surrogates (PMHS) and the Warrior Assessment Injury Manikin (WIAMan) Technology Demonstrator (TD) to establish and assess UBB biofidelity of the WIAMan TD. Test conditions included a rigid floor and rigid seat with independently varied pulses. On the floor, peak velocities of 4 m/s and 6 m/s were applied with a 5 ms time to peak (TTP). The seat peak velocity was 4 m/s with varied TTP of 5 and 10 ms. Tests were conducted with and without personal protective equipment (PPE). PMHS response data was compiled into preliminary biofidelity response corridors (BRCs), which served as evaluation metrics for the WIAMan TD. Each WIAMan TD response was evaluated against the PMHS preliminary BRC for the loading and unloading phase of the signal time history using Correlation Analysis (CORA) software to assign a numerical score between 0 and 1. A weighted average of all responses was calculated to determine body region and whole body biofidelity scores for each test condition. The WIAMan TD received UBB biofidelity scores of 0.62 in Condition A, 0.59 in Condition B, and 0.63 in Condition C, putting it in the fair category (0.44-0.65). Body region responses with scores below a rating of good (0.65-0.84) indicate potential focus areas for the next generation of the WIAMan design.

A new anthropomorphic test device (ATD) is being developed by the US Army to be responsive to vertical loading during a vehicle underbody blast event. To obtain design parameters for the new ATD, a series of non-injurious tests were conducted to derive biofidelity response corridors for the foot-ankle complex under vertical loading. Isolated post mortem human surrogate (PMHS) lower leg specimens were tested with and without military boot and in different initial foot-ankle positions. Instrumentation included a six-axis load cell at the proximal end, three-axis accelerometers at proximal and distal tibia, and calcaneus, and strain gages. Average proximal tibia axial forces for a neutral-positioned foot were about 2 kN for a 4 m/s test, 4 kN for 6 m/s test and 6 kN for an 8 m/s test. The force time-to-peak values were from 3 to 5 msec and calcaneus acceleration rise times were 2 to 8 msec. Compared to the neutral posture, the "off-axis" measures (e.g. shear and bending moment) were much greater in magnitude in plantar- or dorsi-flexed posture. The results as a function of velocity demonstrated uniform increases with increasing test velocities. The response corridors supplied from the present investigation will serve as initial design parameters for the ATD lower leg, and can also be used for validation for a human computational model.

Traumatic brain injury (TBI) caused by explosive munitions, known as blast TBI, is the signature injury in recent military conflicts in Iraq and Afghanistan. Diagnostic evaluation of TBI, including blast TBI, is based on clinical history, symptoms, and neuropsychological testing, all of which can result in misdiagnosis or underdiagnosis of this condition, particularly in the case of TBI of mild-to-moderate severity. Prognosis is currently determined by TBI severity, recurrence, and type of pathology, and also may be influenced by promptness of clinical intervention when more effective treatments become available. An important task is prevention of repetitive TBI, particularly when the patient is still symptomatic. For these reasons, the establishment of quantitative biological markers can serve to improve diagnosis and preventative or therapeutic management. In this study, we used a shock-tube model of blast TBI to determine whether manganese-enhanced magnetic resonance imaging (MEMRI) can serve as a tool to accurately and quantitatively diagnose mild-to-moderate blast TBI. Mice were subjected to a 30 psig blast and administered a single dose of MnCl2 intraperitoneally. Longitudinal T1-magnetic resonance imaging (MRI) performed at 6, 24, 48, and 72 h and at 14 and 28 days revealed a marked signal enhancement in the brain of mice exposed to blast, compared with sham controls, at nearly all time-points. Interestingly, when mice were protected with a polycarbonate body shield during blast exposure, the marked increase in contrast was prevented. We conclude that manganese uptake can serve as a quantitative biomarker for TBI and that MEMRI is a minimally-invasive quantitative approach that can aid in the accurate diagnosis and management of blast TBI. In addition, the prevention of the increased uptake of manganese by body protection strongly suggests that the exposure of an individual to blast risk could benefit from the design of improved body armor.

The human skull is a multi-layered composite system critical in protecting the brain during head impact. Head impact studies investigating skull injury thresholds have suggested that the skull and scalp thickness affect the risk of fracture. Therefore, accurately determining the dimensions of skull-scalp constituents is a necessary step in attributing the contribution to response, failure mechanisms and in developing high fidelity human models. However, prior methods to collect these data include physical measurements of biopsies and manual segmentation in X-ray images. These methods are invasive and impractical for clinical applications, or insufficient to characterize the regional variance in the skull-scalp constituents for a full mechanical strength characterization. The newly developed methods in this study describe an automated, regional, and objective-based measurement technique to characterize the average thickness and variance in skull and scalp constituents using quantitative computed tomography (QCT). The developed approach was successfully employed on 7 specimens at 5 anatomically defined locations. Results report the thicknesses for each layer, with the layer of greatest variation being the trabecular bone (diploë) having a standard deviation of 35.6% of its mean thickness. These results will be used to define skull morphology for modeling relative impact injury risk that will be experimentally validated.

Underbody blast (UBB) events transmit high-rate vertical loads through the seated occupant’s lumbar spine and have a high probability of inducing severe injury. While previous studies have characterized the lumbar spine under quasi-static loading, additional work should focus on the complex kinetic and kinematic response under high loading rates. To discern the biomechanical influence of the lumbar spine’s anatomical structures during dynamic loading, the axial force, flexion-extension moments and range of motion for lumbar motion segments (n=18) were measured during different states of progressive dissection. Pre-compression was applied using a static mass while dynamic bending was applied using an offset drop mass. Dynamic loading resulted in peak axial loads of 4,224±133 N, while maximum peak extension and flexion moments were 19.6±12.5 and -44.8±8.6 Nm in the pre-dissected state, respectively. Upon dissection, transection of the interspinous ligament, ligamentum flavum and facet capsules resulted in significantly larger flexion angles, while the removal of the posterior elements increased the total peak angular displacement in extension from 3.3±1.5 to 5.0±1.7 degrees (p=0.002). This study provides insight on the contribution of individual anatomical components on overall lumbar response under high-rate loading, as well as validation data for numerical models.

Underbody blast (UBB) events impart vertical loads through a victim’s lumbar spine, resulting in fracture, paralysis, and disc rupture. Validated biofidelic lumbar models allow characterization of injury mechanisms and development of personal protective equipment. Previous studies have focused on lumbar mechanics under quasi-static loading. However, it is unclear how the role and response of individual spinal components of the lumbar spine change under dynamic loading. The present study leverages high-rate impacts of progressively dissected two-vertebra lumbar motion segments and Split-Hopkinson pressure bar tissue characterization to identify and validate material properties of a high-fidelity lumbar spine finite element model for UBB. The annulus fibrosus was modeled as a fiber-reinforced Mooney-Rivlin material, while ligaments were represented by nonlinear spring elements. Optimization and evaluation of material parameters was achieved by minimizing the root-mean-square (RMS) of compressive displacement and sagittal rotation for selected experimental conditions. Applying dynamic based material models and parameters resulted in a 0.42% difference between predicted and experiment axial compression during impact loading. This dynamically optimized lumbar model is suited for cross validation against whole-lumbar loading scenarios, and prediction of injury during UBB and other dynamic events.

Cervical spinal injuries are a significant concern in all trauma injuries. Recent military conflicts have demonstrated the substantial risk of spinal injury for the modern warfighter. Finite element models used to investigate injury mechanisms often fail to examine the effects of variation in geometry or material properties on mechanical behavior. The goals of this study were to model geometric variation for a set of cervical spines, to extend this model to a parametric finite element model, and, as a first step, to validate the parametric model against experimental data for low-loading conditions. Individual finite element models were created using cervical spine (C3-T1) computed tomography data for five male cadavers. Statistical shape modeling (SSM) was used to generate a parametric finite element model incorporating variability of spine geometry, and soft-tissue material property variation was also included. The probabilistic loading response of the parametric model was determined under flexion-extension, axial rotation, and lateral bending and validated by comparison to experimental data. Based on qualitative and quantitative comparison of the experimental loading response and model simulations, we suggest that the model performs adequately under relatively low-level loading conditions in multiple loading directions. In conclusion, SSM methods coupled with finite element analyses within a probabilistic framework, along with the ability to statistically validate the overall model performance, provide innovative and important steps toward describing the differences in vertebral morphology, spinal curvature, and variation in material properties. We suggest that these methods, with additional investigation and validation under injurious loading conditions, will lead to understanding and mitigating the risks of injury in the spine and other musculoskeletal structures.

In order to replicate the fracture behavior of the intact human skull under impact it becomes necessary to develop a material having the mechanical properties of cranial bone. The most important properties to replicate in a surrogate human skull were found to be the fracture toughness and tensile strength of the cranial tables as well as the bending strength of the three-layer (inner table-diplöe-outer table) architecture of the human skull. The materials selected to represent the surrogate cranial tables consisted of two different epoxy resins systems with random milled glass fiber to enhance the strength and stiffness and the materials to represent the surrogate diplöe consisted of three low density foams. Forty-one three-point bending fracture toughness tests were performed on nine material combinations. The materials that best represented the fracture toughness of cranial tables were then selected and formed into tensile samples and tested. These materials were then used with the two surrogate diplöe foam materials to create the three-layer surrogate cranial bone samples for three-point bending tests. Drop tower tests were performed on flat samples created from these materials and the fracture patterns were very similar to the linear fractures in pendulum impacts of intact human skulls, previously reported in the literature. The surrogate cranial tables had the quasi-static fracture toughness and tensile strength of 2.5 MPa√ m and 53 ± 4.9 MPa, respectively, while the same properties of human compact bone were 3.1 ± 1.8 MPa√ m and 68 ± 18 MPa, respectively. The cranial surrogate had a quasi-static bending strength of 68 ± 5.7 MPa, while that of cranial bone was 82 ± 26 MPa. This material/design is currently being used to construct spherical shell samples for drop tower and ballistic tests.

Underbody blast (UBB) events created by improvised explosive devices are threats to warfighter survivability. High intensity blast waves emitted from these devices transfer large forces through vehicle structures to occupants, often resulting in injuries including debilitating spinal fractures. The vertical loading vector through the spine generates significant compressive forces at high strain rates. To better understand injury mechanisms and ultimately better protect vehicle occupants against UBB attacks, high-fidelity computational models are being developed to predict the human response to dynamic loading characteristic of these events. This effort details the results from a series of 23 high-rate compression tests on vertebral body specimen. A high-rate servo-hydraulic test system applied a range of compressive loading rates (.01 mm/s to 1238 mm/s) to vertebral bodies in the thoracolumbar region (T7-L5). The force-deflection curves generated indicate rate dependent sensitivity of vertebral stiffness, ultimate load and ultimate deflection. Specimen subjected to high-rate dynamic loading to failure experienced critical structural damage at 5.5% ± 2.1% deflection. Compared to quasi-static loading, vertebral bodies had greater stiffness, greater force to failure, and lower ultimate failure deflection at high rates. Post-failure, an average loss in height of 15% was observed, along with a mean reduction in strength of 48%. The resulting data from these tests will allow for enhanced biofidelity of computational models by characterizing the vertebral stiffness response and ultimate deflection at rates representative of UBB events.

Since 2000, the Department of Defense has documented more than 253,000 cases of Traumatic Brain Injury (TBI). A significant portion of these injuries were attributed to explosive events, yet ninety-eight percent were non-penetrating. Understanding the response of the brain to blast events is critical, yet the mechanisms of brain injury from explosive trauma are poorly understood. This knowledge gap has led to an increased research focus on devices capable of investigating human brain response to non-penetrating, blast-induced loading. Furthermore, traumatic brain injury is a major issue for the civilian population as well with over 1.7 million cases of TBI per year in the US, primarily from falls and motor vehicle accidents. Current head surrogates and instrumentation are incapable of directly measuring critical parameters associated with TBI, such as brain motion, during dynamic loading. To this end, a novel sensor system for measuring brain motion inside of a human head surrogate was conceptualized and developed. The positioning system is comprised of a set of three fixed “generator” coils and a plurality of mobile, miniaturized “receiver” coil triads. Each generator coil transmits a sinusoidal electromagnetic signal at a unique frequency, and groups of three orthogonally arranged “receiver” coils detect these signals. Because of the oscillatory nature of these signals, the magnetic flux through the coil is always changing, allowing the application of Faraday’s Law of Induction and the point dipole model of an electric field to model the strength and direction of the field vector at any given point. Thus, the strength of the signal measured by a particular receiver coil depends on its position and orientation relative to the fixed position of the generators. These predictable changes are used to determine the six degrees of freedom (6-DOF) motion of the receiver. To calibrate and validate the system, a receiver coil was moved about in a controlled manner, and its actual position recorded by optical methods. Comparing the known position to the computed position at each time instance, a set of calibration constants were developed for each receiver triad. These constants were then utilized to convert receiver signal data into actual receiver position and orientation. Comparing this test case and several others like it, mean error was determined to be almost always less than 1.0 mm, and less than 0.5 mm >85% of the time. Additionally, high rate validation was conducted to confirm operation of the system in the impact domain. A coil was accelerated to approximately 15 m/sec along a fixed axis by ballistic impact and tracked by high speed video. The computed position was within 1 mm of the actual position 93% of the time and within 0.5 mm 83% of the time. The successful development and calibration of this sensing system now enables the direct measurements of brain displacement due to mechanical insults applied to a human head surrogate.

The skull-brain complex is typically modeled as an integrated structure, similar to a fluid-filled shell. Under dynamic loads, the interaction of the skull and the underlying brain, cerebrospinal fluid, and other tissue produces the pressure and strain histories that are the basis for many theories meant to describe the genesis of traumatic brain injury. In addition, local bone strains are of interest for predicting skull fracture in blunt trauma. However, the role of skull flexure in the intracranial pressure response to blunt trauma is complex. Since the relative time scales for pressure and flexural wave transmission across the skull are not easily separated, it is difficult to separate out the relative roles of the mechanical components in this system. This study uses a finite element model of the head, which is validated for pressure transmission to the brain, to assess the influence of skull table flexural stiffness on pressure in the brain and on strain within the skull. In a Human Head Finite Element Model, the skull component was modified by attaching shell elements to the inner and outer surfaces of the existing solid elements that modeled the skull. The shell elements were given the properties of bone, and the existing solid elements were decreased so that the overall stiffness along the surface of the skull was unchanged, but the skull table bending stiffness increased by a factor of 2.4. Blunt impact loads were applied to the frontal bone centrally, using LS-Dyna. The intracranial pressure predictions and the strain predictions in the skull were compared for models with and without surface shell elements, showing that the pressures in the mid-anterior and mid-posterior of the brain were very similar, but the strains in the skull under the loads and adjacent to the loads were decreased 15% with stiffer flexural properties. Pressure equilibration to nearly hydrostatic distributions occurred, indicating that the important frequency components for typical impact loading are lower than frequencies based on pressure wave propagation across the skull. This indicates that skull flexure has a local effect on intracranial pressures but that the integrated effect of a dome-like structure under load is a significant part of load transfer in the skull in blunt trauma.

A human head finite element model (HHFEM) was developed to study the effects of a blast to the head. To study both the kinetic and kinematic effects of a blast wave, the HHFEM was attached to a finite element model of a Hybrid III ATD neck. A physical human head surrogate model (HSHM) was developed from solid model files of the HHFEM, which was then attached to a physical Hybrid III ATD neck and exposed to shock tube overpressures. This allowed direct comparison between the HSHM and HHFEM. To develop the temporal and spatial pressures on the HHFEM that would simulate loading to the HSHM, a computational fluid dynamics (CFD) model of the HHFEM in front of a shock tube was generated. CFD simulations were made using loads equivalent to those seen in experimental studies of the HSHM for shock tube driver pressures of 517, 690 and 862 kPa. Using the selected brain material properties, the peak intracranial pressures, temporal and spatial histories of relative brain-skull displacements and the peak relative brain-skull displacements in the brain of the HHFEM compared favorably with results from the HSHM. The HSHM sensors measured the rotations of local areas of the brain as well as displacements, and the rotations of the sensors in the sagittal plane of the HSHM were, in general, correctly predicted from the HHFEM. Peak intracranial pressures were between 70 and 120 kPa, while the peak relative brain-skull displacements were between 0.5 and 3.0mm., (Copyright © 2012 Elsevier Ltd. All rights reserved.)

In this paper, the synthesis, structural and spectroscopic characterization of a series of new Ru(III)-nitrosyls of {RuNO}(6) type with the coligand TPA (tris(2-pyridylmethyl)amine) are presented. The complex [Ru(TPA)Cl(2)(NO)]ClO(4) (2) was prepared from the Ru(III) precursor [Ru(TPA)Cl(2)]ClO(4) (1) by simple reaction with NO gas. This led to the surprising displacement of one of the pyridine (py) arms of TPA by NO (instead of the substitution of a chloride anion by NO), as confirmed by X-ray crystallography. NO complexes where TPA serves as a tetradentate ligand were obtained by reacting the new Ru(II) precursor [Ru(TPA)(NO(2))(2)] (3) with a strong acid. This leads to the dehydration of nitrite to NO(+), and the formation of the {RuNO}(6) complex [Ru(TPA)(ONO)(NO)](PF(6))(2) (4), which was also structurally characterized. Derivatives of 4 where nitrite is replaced by urea (5) or water (6) were also obtained. The nitrosyl complexes obtained this way were then further investigated using IR and FT-Raman spectroscopy. Complex 2 with the two anionic chloride coligands shows the lowest N-O and highest Ru-NO stretching frequencies of 1903 and 619 cm(-1) of all the complexes investigated here. Complexes 5 and 6 where TPA serves as a tetradentate ligand show ν(N-O) at higher energy, 1930 and 1917 cm(-1), respectively, and ν(Ru-NO) at lower energy, 577 and 579 cm(-1), respectively, compared to 2. These vibrational energies, as well as the inverse correlation of ν(N-O) and ν(Ru-NO) observed along this series of complexes, again support the Ru(II)-NO(+) type electronic structure previously proposed for {RuNO}(6) complexes. Finally, we investigated the photolability of the Ru-NO bond upon irradiation with UV light to determine the quantum yields (φ) for NO photorelease in complexes 2, 4, 5, and additional water-soluble complexes [Ru(H(2)edta)(Cl)(NO)] (7) and [Ru(Hedta)(NO)] (8). Although {RuNO}(6) complexes are frequently proposed as NO delivery agents in vivo, studies that investigate how φ is affected by the solvent water are lacking. Our results indicate that neutral water is not a solvent that promotes the photodissociation of NO, which would present a major obstacle to the goal of designing {RuNO}(6) complexes as photolabile NO delivery agents in vivo.

Hydrotris(triazolyl)borate (Ttz) ligands form CuNO(x) (x = 2, 3) complexes for structural and functional models of copper nitrite reductase. These complexes have distinct properties relative to complexes of hydrotris(pyrazolyl)borate (Tp) and neutral tridentate N-donor ligands. The electron paramagnetic resonance spectra of five-coordinate copper complexes show rare nitrogen superhyperfine couplings with the Ttz ligand, indicating strong σ donation. The copper(I) nitrite complex [PPN](+)[(Ttz(tBu,Me))Cu(I)NO(2)](-) has been synthesized and characterized and allows for the stoichiometric reduction of NO(2)(-) to NO with H(+) addition. Anionic Cu(I) nitrite complexes are unusual and are stabilized here for the first time because Ttz is a good π acceptor.

The reduction of nitrite to nitric oxide in dissimilatory denitrification is carried out by copper nitrite reductases (CuNIRs) via a type 2 copper site. Extended studies on CuNIRs in combination with model complexes have allowed for the establishment of two potential mechanisms for this transformation. Recent experimental and computational results have revealed further details of this process. In addition, the interaction of NO with copper sites has recently gained much attention. This review discusses recent results in the context of the known coordination chemistry of CuNIRs.

Predicting spinal injury under high rates of vertical loading is of interest, but the success of computational models in modeling this type of loading scenario is highly dependent on the material models employed. Understanding the response of these biological materials at high strain rates is critical to accurately model mechanical response of tissue and predict injury. While data exists at lower strain rates, there is a lack of the high strain rate material data that are needed to develop constitutive models. The Split Hopkinson Pressure Bar (SHPB) has been used for many years to obtain properties of various materials at high strain rates. However, this apparatus has mainly been used for characterizing metals and ceramics and is difficult to apply to softer materials such as biological tissue. Recently, studies have shown that modifications to the traditional SHPB setup allow for the successful characterization of mechanical properties of biological materials at strain rates and peak strain values that exceed alternate soft tissue testing techniques. In this paper, the previously-reported modified SHPB technique is applied to characterize human intervertebral disc material under simple shear. The strain rates achieved range from 5 to 250 strain s-1. The results demonstrate the sensitivity to the disc composition and structure, with the nucleus pulposus and annulus fibrosus exhibiting different behavior under shear loading. Shear tangent moduli are approximated at varying strain levels from 5 to 20% strain. This data and technique facilitates determination of mechanical properties of intervertebral disc materials under shear loading, for eventual use in constitutive models.

ehind Armor Blunt Trauma (BABT) is a persistent concern for both the military and civil law enforcement. Although personal protective equipment (PPE), including soft and hard body armor, mitigates penetrating injuries from ballistic threats, the impact generates a backface deformation which creates a high-rate blunt impact to the body and potential internal injury (i.e., BABT). A critical need exists to understand the mechanics of the human response and subsequently evaluate the efficacy of current and proposed PPE in mitigating BABT injury risk. Current human surrogate test platforms lack anatomical fidelity or instrumentation for capturing the dynamic transfer of energy during the event. Therefore, we have developed and tested a Human Surrogate Torso Model (HSTM) composed of biosimulants representing soft tissues and skeleton of the human torso. A matrix of pressure transducers were embedded in the soft tissue and a custom displacement sensor was mounted to the skeletal structure to measure sternum displacement. A series of non-penetrating, high energy ballistic tests were performed with the HSTM. Results indicate that both sternum displacement and internal localized pressure are sensitive to impact energy and location. These data provide a spatial and temporal comparison to the current standard (static clay measurements) and a method for evaluating the applicability of thoracic injury metrics, including the Viscous Criterion, for BABT. The HSTM provides an advanced, biomechanically relevant test platform for determining the thoracic response to dynamic loading events due to non-penetrating ballistic impacts.

Under-Body Blast (UBB) has emerged as the predominant threat to ground vehicles and Warfighter survivability. The force transference from the vehicle structure to the human body has resulted in serious injuries, with the thoracolumbar spine frequently damaged. Computational models of the human body are being generated to model human response and develop injury mitigation strategies. To effectively model the spine mechanics, the thoracolumbar ligaments, which serve varying roles in contributing to spine stability, must be characterized at relevant strains and strain rates. Adaptation of cervical spine testing methods has allowed for testing of isolated spinal ligaments including the Anterior Longitudinal Ligament (ALL), Posterior Longitudinal Ligament (PLL), and Ligamentum Flavum (LF). A high-rate servo-hydraulic test machine was used to execute a tensile test protocol for 24 complexes with loading rates ranging from 240 - 2800 mm/s and displacements of 25%, 50%, 75%, 100%, and 300% of the measured ligament length. Non-contact strain field measurements were recorded to produce a three dimensional strain field of the ligament surface. In order to provide the ligament data in a form which can be incorporated in the human computational models, analytical methods for modeling the ligament response are being investigated. Ultimately, this model will be optimized to be utilized in computational models of the lumbar spine.

The Mn-nitrosyl complexes [Mn(PaPy(3))(NO)](ClO(4)) (1; PaPy(3)(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-pyridine-2-carboxamide) and [Mn(PaPy(2)Q)(NO)](ClO(4)) (2, PaPy(2)Q(-) = N,N-bis(2-pyridylmethyl)amine-N-ethyl-2-quinoline-2-carboxamide) show a remarkable photolability of the NO ligand upon irradiation of the complexes with UV-vis-NIR light [Eroy-Reveles, A. A.; Leung, Y.; Beavers, C. M.; Olmstead, M. M.; Mascharak, P. K. J. Am. Chem. Soc. 2008, 130, 4447]. Here we report detailed spectroscopic and theoretical studies on complexes 1 and 2 that provide key insight into the mechanism of NO photolabilization in these compounds. IR- and FT-Raman spectroscopy show N-O and Mn-NO stretching frequencies in the 1720-1750 and 630-650 cm(-1) range, respectively, for these Mn-nitrosyls. The latter value for ν(Mn-NO) is one of the highest transition-metal-NO stretching frequencies reported to this date, indicating that the Mn-NO bond is very strong in these complexes. The electronic structure of 1 and 2 is best described as Mn(I)-NO(+), where the Mn(I) center is in the diamagnetic low-spin state and the NO(+) ligand forms two very strong π backbonds with the d(xz) and d(yz) orbitals of the metal. This explains the very strong Mn-NO bonds observed in these complexes, which even supersede the strengths of the Fe- and Ru-NO bonds in analogous (isoelectronic) Fe/Ru(II)-NO(+) complexes. Using time-dependent density functional theory (TD-DFT) calculations, we were able to assign the electronic spectra of 1 and 2, and to gain key insight into the mechanism of NO photorelease in these complexes. Upon irradiation in the UV region, NO is released because of the direct excitation of d(π)_π* → π*_d(π) charge transfer (CT) states (direct mechanism), which is similar to analogous NO adducts of Ru(III) and Fe(III) complexes. These are transitions from the Mn-NO bonding (d(π)_π*) into the Mn-NO antibonding (π*_d(π)) orbitals within the Mn-NO π backbond. Since these transitions lead to the population of Mn-NO antibonding orbitals, they promote the photorelease of NO. In the case of 1 and 2, further transitions with distinct d(π)_π* → π*_d(π) CT character are observed in the 450-500 nm spectral range, again promoting photorelease of NO. This is confirmed by resonance Raman spectroscopy, showing strong resonance enhancement of the Mn-NO stretch at 450-500 nm excitation. The extraordinary photolability of the Mn-nitrosyls upon irradiation in the vis-NIR region is due to the presence of low-lying d(xy) → π*_d(π) singlet and triplet excited states. These have zero oscillator strengths, but can be populated by initial excitation into d(xy) → L(Py/Q_π*) CT transitions between Mn and the coligand, followed by interconversion into the d(xy) → π*_d(π) singlet excited states. These show strong spin-orbit coupling with the analogous d(xy) → π*_d(π) triplet excited states, which promotes intersystem crossing. TD-DFT shows that the d(xy) → π*_d(π) triplet excited states are indeed found at very low energy. These states are strongly Mn-NO antibonding in nature, and hence, promote dissociation of the NO ligand (indirect mechanism). The Mn-nitrosyls therefore show the long sought-after potential for easy tunability of the NO photorelease properties by simple changes in the coligand.

Modeling human body response to dynamic loading events and developing biofidelic human surrogate systems require accurate material properties over a range of loading rates for various human organ tissues. This work describes a technique for measuring the shear properties of soft biomaterials at high rates of strain (100-1000 s(-1)) using a modified split Hopkinson pressure bar (SHPB). Establishing a uniform state of stress in the sample is a fundamental requirement for this type of high-rate testing. Input pulse shaping was utilized to tailor and control the ramping of the incident loading pulse such that a uniform stress state could be maintained within the specimen from the start of the test. Direct experimental verification of the stress uniformity in the sample was obtained via comparison of the force measured by piezoelectric quartz force gages on both the input and the output sides of the shear specimen. The technique was demonstrated for shear loading of silicone gel biosimulant materials and porcine brain tissue. Finite element simulations were utilized to further investigate the effect of pulse shaping on the loading rate and rise time. Simulations also provided a means for visualization of the degree of shear stress and strain uniformity in the specimen during an experiment. The presented technique can be applied to verify stress uniformity and ensure high quality data when measuring the dynamic shear modulus of soft biological simulants and tissue., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Current experimental models of blast injuries used to study blast-induced neurotrauma (BINT) vary widely, which makes the comparison of the experimental results extremely challenging. Most of the blast injury models replicate the ideal Friedländer type of blast wave, without the capability to generate blast signatures with multiple shock fronts and refraction waves as seen in real-life conditions; this significantly reduces their clinical and military relevance. Here, we describe the pathophysiological consequences of graded blast injuries and BINT generated by a newly developed, highly controlled, and reproducible model using a modular, multi-chamber shock tube capable of tailoring pressure wave signatures and reproducing complex shock wave signatures seen in theater. While functional deficits due to blast exposure represent the principal health problem for today's warfighters, the majority of available blast models induces tissue destruction rather than mimic functional deficits. Thus, the main goal of our model is to reliably reproduce long-term neurological impairments caused by blast. Physiological parameters, functional (motor, cognitive, and behavioral) outcomes, and underlying molecular mechanisms involved in inflammation measured in the brain over the 30 day post-blast period showed this model is capable of reproducing major neurological changes of clinical BINT., (Copyright © 2010 Elsevier Inc. All rights reserved.)

Density functional theory calculations were used to investigate the binding mode of copper(I) nitrosyl (Cu(I)-NO) in copper nitrite reductase (CuNIR). The end-on Cu(I)-NO geometry (2) was found to be the global energy minimum, while the side-on binding mode (1) corresponds to a local minimum. Isoleucine-257 severely interacts sterically with the Cu(I)-NO unit when bound end-on but not in the side-on case. In addition, the side-on geometry is also stabilized by a hydrogen bond between aspartic acid-98 and NO, estimated to be approximately 3 kcal/mol. The steric constraint of the CuNIR active site is mainly responsible for the observed side-on coordination of NO in the CuNIR crystal structure. We speculate that a small conformational change of the active site that slightly changes the position of isoleucine-257 would allow NO to bind end-on. This explains the observed end-on binding of NO to copper(I) when CuNIR is in solution.

Background: Although soft armor vests serve to prevent penetrating wounds and dissipate impact energy, the potential of nonpenetrating injury to the thorax, termed behind armor blunt trauma, does exist. Currently, the ballistic resistance of personal body armor is determined by impacting a soft armor vest over a clay backing and measuring the resulting clay deformation as specified in National Institute of Justice (NIJ) Standard-0101.04. This research effort evaluated the efficacy of a physical Human Surrogate Torso Model (HSTM) as a device for determining thoracic response when exposed to impact conditions specified in the NIJ Standard., Methods: The HSTM was subjected to a series of ballistic impacts over the sternum and stomach. The pressure waves propagating through the torso were measured with sensors installed in the organs. A previously developed Human Torso Finite Element Model (HTFEM) was used to analyze the amount of tissue displacement during impact and compared with the amount of clay deformation predicted by a validated finite element model. All experiments and simulations were conducted at NIJ Standard test conditions., Results: When normalized by the response at the lowest threat level (Level I), the clay deformations for the higher levels are relatively constant and range from 2.3 to 2.7 times that of the base threat level. However, the pressures in the HSTM increase with each test level and range from three to seven times greater than Level I depending on the organ., Conclusions: The results demonstrate the abilities of the HSTM to discriminate between threat levels, impact conditions, and impact locations. The HTFEM and HSTM are capable of realizing pressure and displacement differences because of the level of protection, surrounding tissue, and proximity to the impact point. The results of this research provide insight into the transfer of energy and pressure wave propagation during ballistic impacts using a physical surrogate and computational model of the human torso.

Background: To assess the possibility of injury as a result of behind armor blunt trauma (BABT), a study was undertaken to determine the conditions necessary to produce the 44-mm clay deformation as set forth in the National Institute of Justice (NIJ) Standard 0101.04. These energy levels were then applied to a three-dimensional Human Torso Finite Element Model (HTFEM) with soft armor vest. An examination will be made of tissue stresses to determine the effects of the increased kinetic energy levels on the probability of injury., Methods: A clay finite element model (CFEM) was created with a material model that required nonlinear properties for clay. To determine these properties empirically, the results from the CFEM were matched with experimental drop tests. A soft armor vest was modeled over the clay to create a vest over clay block finite element model (VCFEM) and empirical methods were again used to obtain material properties for the vest from experimental ballistic testing. Once the properties for the vest and clay had been obtained, the kinetic energy required to produce a 44-mm deformation in the VCFEM was determined through ballistic testing. The resulting kinetic energy was then used in the HTFEM to evaluate the probability of BABT., Results: The VCFEM, with determined clay and vest material properties, was exercised with the equivalent of a 9-mm (8-gm) projectile at various impact velocities. The 44-mm clay deformation was produced with a velocity of 785 m/s. This impact condition (9-mm projectile at 785 m/s) was used in ballistic exercises of the HTFEM, which was modeled with high-strain rate human tissue properties for the organs. The impact zones were over the sternum anterior to T6 and over the liver. The principal stresses in both soft and hard tissue at both locations exceeded the tissue tensile strength., Conclusions: This study indicates that although NIJ standard 0101.04 may be a good guide to soft armor failure, it may not be as good a guide in BABT, especially at large projectile kinetic energies. Further studies, both numerical and experimental, are needed to assist in predicting injury using the NIJ standard.

The dynamic response of soft human tissues in hydrostatic compression and simple shear is studied using the Kolsky bar technique. We have made modifications to the technique that allow loading of a soft tissue specimen in hydrostatic compression or simple shear. The dynamic response of human tissues (from stomach, heart, liver, and lung of cadavers) is obtained, and analyzed to provide measures of dynamic bulk modulus and shear response for each tissue type. The dynamic bulk response of these tissues is easily described by a linear fit for the bulk modulus in this pressure range, whereas the dynamic shearing response of these tissues is strongly non-linear, showing a near exponential growth of the shear stress.

Both computational finite element and experimental models of the human torso have been developed for ballistic impact testing. The human torso finite element model (HTFEM), including the thoracic skeletal structure and organs, was created in the finite element code LS-DYNA. The skeletal structure was assumed to be linear-elastic while all internal organs were modeled as viscoelastic. A physical human surrogate torso model (HSTM) was developed using biosimulant materials and the same anthropometry as the HTFEM. The HSTM response to impact was recorded with piezoresistive pressure sensors molded into the heart, liver and stomach and an accelerometer attached to the sternum. For experimentation, the HSTM was outfitted with National Institute of Justice (NIJ) Level I, IIa, II and IIIa soft armor vests. Twenty-six ballistic tests targeting the HSTM heart and liver were conducted with 22 caliber ammunition at a velocity of 329 m/s and 9 mm ammunition at velocities of 332, 358 and 430 m/s. The HSTM pressure response repeatability was found to vary by less than 10% for similar impact conditions. A comparison of the HSTM and HTFEM response showed similar pressure profiles and less than 35% peak pressure difference for organs near the ballistic impact point. Furthermore, the peak sternum accelerations of the HSTM and HTFEM varied by less than 10% for impacts over the sternum. These models provide comparative tools for determining the thoracic response to ballistic impact and could be used to evaluate soft body armor design and efficacy, determine thoracic injury mechanisms and assist with injury prevention.