Region specific anisotropy and rate dependence of Göttingen minipig brain tissue.

Traumatic brain injury is a major cause of morbidity in civilian as well as military populations. Computational simulations of injurious events are an important tool to understanding the biomechanics of brain injury and evaluating injury criteria and safety measures. However, these computational models are highly dependent on the material parameters used to represent the brain tissue.

Rate- and Region-Dependent Mechanical Properties of Göttingen Minipig Brain Tissue in Simple Shear and Unconfined Compression.

Traumatic brain injury (TBI), particularly from explosive blasts, is a major cause of casualties in modern military conflicts. Computational models are an important tool in understanding the underlying biomechanics of TBI but are highly dependent on the mechanical properties of soft tissue to produce accurate results. Reported material properties of brain tissue can vary by several orders of magnitude between studies, and no published set of material parameters exists for porcine brain tissue at strain rates relevant to blast.

A 3-D virtual human model for simulating heat and cold stress.

In this study, we extended our previously developed anatomically detailed three-dimensional (3-D) thermoregulatory virtual human model for predicting heat stress to allow for predictions of heat and cold stress in one unified model. Starting with the modified Pennes bioheat transfer equation to estimate the spatiotemporal temperature distribution within the body as the underlying modeling structure, we developed a new formulation to characterize the spatial variation of blood temperature between body elements and within the limbs. We also implemented the means to represent heat generated from shivering and skin blood flow that apply to air exposure and water immersion.

A Strain Rate-Dependent Constitutive Model for Göttingen Minipig Cerebral Arteries.

Computational simulations of traumatic brain injury (TBI) are commonly used to advance understanding of the injury-pathology relationship, tissue damage thresholds, and design of protective equipment such as helmets. Both human and animal TBI models have developed substantially over recent decades, partially due to the inclusion of more detailed brain geometry and representation of tissues like cerebral blood vessels. Explicit incorporation of vessels dramatically affects local strain and enables researchers to investigate TBI-induced damage to the vasculature.

A 3-D Finite-Element Minipig Model to Assess Brain Biomechanical Responses to Blast Exposure.

Despite years of research, it is still unknown whether the interaction of explosion-induced blast waves with the head causes injury to the human brain. One way to fill this gap is to use animal models to establish "scaling laws" that project observed brain injuries in animals to humans. This requires laboratory experiments and high-fidelity mathematical models of the animal head to establish correlates between experimentally observed blast-induced brain injuries and model-predicted biomechanical responses.

Cerebral Vasculature Influences Blast-Induced Biomechanical Responses of Human Brain Tissue.

Multiple finite-element (FE) models to predict the biomechanical responses in the human brain resulting from the interaction with blast waves have established the importance of including the brain-surface convolutions, the major cerebral veins, and using non-linear brain-tissue properties to improve model accuracy. We hypothesize that inclusion of a more detailed network of cerebral veins and arteries can further enhance the model-predicted biomechanical responses and help identify correlates of blast-induced brain injury. To more comprehensively capture the biomechanical responses of human brain tissues to blast-wave exposure, we coupled a three-dimensional (3-D) detailed-vasculature human-head FE model, previously validated for blunt impact, with a 3-D shock-tube FE model.

A 3-D virtual human thermoregulatory model to predict whole-body and organ-specific heat-stress responses.

Objective: This study aimed at assessing the risks associated with human exposure to heat-stress conditions by predicting organ- and tissue-level heat-stress responses under different exertional activities, environmental conditions, and clothing.

Methods: In this study, we developed an anatomically detailed three-dimensional thermoregulatory finite element model of a 50th percentile U.S.

Effects of body size and load carriage on lower-extremity biomechanical responses in healthy women.

Background: Musculoskeletal injuries, such as stress fractures, are the single most important medical impediment to military readiness in the U.S. Army.

Animal Orientation Affects Brain Biomechanical Responses to Blast-Wave Exposure.

In this study, we investigated how animal orientation within a shock tube influences the biomechanical responses of the brain and cerebral vasculature of a rat when exposed to a blast wave. Using three-dimensional finite element (FE) models, we computed the biomechanical responses when the rat was exposed to the same blast-wave overpressure (100 kPa) in a prone (P), vertical (V), or head-only (HO) orientation. We validated our model by comparing the model-predicted and the experimentally measured brain pressures at the lateral ventricle.

The importance of modeling the human cerebral vasculature in blunt trauma.

Background: Multiple studies describing human head finite element (FE) models have established the importance of including the major cerebral vasculature to improve the accuracy of the model predictions. However, a more detailed network of cerebral vasculature, including the major veins and arteries as well as their branch vessels, can further enhance the model-predicted biomechanical responses and help identify correlates to observed blunt-induced brain injury.

Methods: We used an anatomically accurate three-dimensional geometry of a 50th percentile U.

Does Blast Exposure to the Torso Cause a Blood Surge to the Brain?

The interaction of explosion-induced blast waves with the torso is suspected to contribute to brain injury. In this indirect mechanism, the wave-torso interaction is assumed to generate a blood surge, which ultimately reaches and damages the brain. However, this hypothesis has not been comprehensively and systematically investigated, and the potential role, if any, of the indirect mechanism in causing brain injury remains unclear.

Changes in Volumetric Bone Mineral Density Over 12 Months After a Tibial Bone Stress Injury Diagnosis: Implications for Return to Sports and Military Duty.

Background: Bone stress injuries (BSIs) occur in up to 20% of runners and military personnel. Typically, after a period of unloading and gradual return to weightbearing activities, athletes return to unrestricted sports participation or military duty approximately 4 to 14 weeks after a BSI diagnosis, depending on the injury location and severity. However, the time course of the recovery of the bone's mechanical competence is not well-characterized, and reinjury rates are high.

Injury Length and Arteriole Constriction Shape Clot Growth and Blood-Flow Acceleration in a Mouse Model of Thrombosis.

Objective: Quantitative relationships between the extent of injury and thrombus formation in vivo are not well understood. Moreover, it has not been investigated how increased injury severity translates to blood-flow modulation. Here, we investigated interconnections between injury length, clot growth, and blood flow in a mouse model of laser-induced thrombosis.

Effects of load carriage on biomechanical variables associated with tibial stress fractures in running.

Background: Military personnel are required to run while carrying heavy body-borne loads, which is suggested to increase their risk of tibial stress fracture. Research has retrospectively identified biomechanical variables associated with a history of tibial stress fracture in runners, however, the effect that load carriage has on these variables remains unknown.

Research Question: What are the effects of load carriage on running biomechanical variables associated with a history of tibial stress fracture?

Methods: Twenty-one women ran at 3.

Skeletal loading score is associated with bone microarchitecture in young adults.

Unlabelled: Physical activity that involves high strain magnitudes and high rates of loading is reported to be most effective in eliciting an osteogenic bone response. Whether a history of participation in osteogenic activities during youth, as well as current participation in osteogenic activities, contributes to young adult bone microarchitecture and strength is unknown.

Purpose: We determined the association between a new skeletal loading (SkL) score reflecting physical activity from age 11 to adulthood, the bone specific physical activity questionnaire (BPAQ) and bone microarchitecture in young Black and White men and women.

Individual Differences in Women During Walking Affect Tibial Response to Load Carriage: The Importance of Individualized Musculoskeletal Finite-Element Models.

Subject-specific features can contribute to the susceptibility of an individual to stress fracture. Here, we incorporated tibial morphology and material properties into a standard musculoskeletal finite-element (M/FE) model and investigated how load carriage influences joint kinetics and tibial mechanics in women. We obtained the morphology and material properties of the tibia from computed tomography images for women of three distinctly different heights, 1.

A 3-D Rat Brain Model for Blast-Wave Exposure: Effects of Brain Vasculature and Material Properties.

Exposure to blast waves is suspected to cause primary traumatic brain injury. However, existing finite-element (FE) models of the rat head lack the necessary fidelity to characterize the biomechanical responses in the brain due to blast exposure. They neglect to represent the cerebral vasculature, which increases brain stiffness, and lack the appropriate brain material properties characteristic of high strain rates observed in blast exposures.

Regional Changes in Density and Microarchitecture in the Ultradistal Tibia of Female Recruits After U.S. Army Basic Combat Training.

Musculoskeletal injuries, such as stress fracture, are responsible for over 10-million lost-duty days among U.S. Army Soldiers.

Regional variation of bone density, microarchitectural parameters, and elastic moduli in the ultradistal tibia of young black and white men and women.

Whole-bone analyses can obscure regional heterogeneities in bone characteristics. Quantifying these heterogeneities might improve our understanding of the etiology of injuries, such as lower-extremity stress fractures. Here, we performed regional analyses of high-resolution peripheral quantitative computed tomography images of the ultradistal tibia in young, healthy subjects (age range, 18 to 30 years).

Changes in tibial bone microarchitecture in female recruits in response to 8 weeks of U.S. Army Basic Combat Training.

Background: U.S. Army Basic Combat Training (BCT) is a physically-demanding program at the start of military service.

Material Properties of Rat Middle Cerebral Arteries at High Strain Rates.

Traumatic brain injury (TBI), resulting from either impact- or nonimpact blast-related mechanisms, is a devastating cause of death and disability. The cerebral blood vessels, which provide critical support for brain tissue in both health and disease, are commonly injured in TBI. However, little is known about how vessels respond to traumatic loading, particularly at rates relevant to blast.

An analytical poroelastic model for ultrasound elastography imaging of tumors.

The mechanical behavior of biological tissues has been studied using a number of mechanical models. Due to the relatively high fluid content and mobility, many biological tissues have been modeled as poroelastic materials. Diseases such as cancers are known to alter the poroelastic response of a tissue.

Differences in Trabecular Microarchitecture and Simplified Boundary Conditions Limit the Accuracy of Quantitative Computed Tomography-Based Finite Element Models of Vertebral Failure.

Vertebral fractures are common in the elderly, but efforts to reduce their incidence have been hampered by incomplete understanding of the failure processes that are involved. This study's goal was to elucidate failure processes in the lumbar vertebra and to assess the accuracy of quantitative computed tomography (QCT)-based finite element (FE) simulations of these processes. Following QCT scanning, spine segments (n = 27) consisting of L1 with adjacent intervertebral disks and neighboring endplates of T12 and L2 were compressed axially in a stepwise manner.