Modified Mouse Model of Repetitive Mild Traumatic Brain Injury Incorporating Thinned-Skull Window and Fluid Percussion.

Mild traumatic brain injury is a clinically highly heterogeneous neurological disorder. Highly reproducible traumatic brain injury (TBI) animal models with well-defined pathologies are urgently needed for studying the mechanisms of neuropathology after mild TBI and testing therapeutics. Replicating the entire sequelae of TBI in animal models has proven to be a challenge. Therefore, the availability of multiple animal models of TBI is necessary to account for the diverse aspects and severities seen in TBI patients. CHI is one of the most common methods for fabricating rodent models of rmTBI. However, this method is susceptible to many factors, including the impact method used, the thickness and shape of the skull bone, animal apnea, and the type of head support and immobilization utilized. The aim of this protocol is to demonstrate a combination of the thinned-skull window and fluid percussion injury (FPI) methods to produce a precise mouse model of CHI-associated rmTBI. The primary objective of this protocol is to minimize factors that could impact the accuracy and consistency of CHI and FPI modeling, including skull bone thickness, shape, and head support. By utilizing a thinned-skull window method, potential inflammation due to craniotomy and FPI is minimized, resulting in an improved mouse model that replicates the clinical features observed in patients with mild TBI. Results from behavior and histological analysis using hematoxylin and eosin (HE) staining suggest that rmTBI can lead to a cumulative injury that produces changes in both behavior and gross morphology of the brain. Overall, the modified CHI-associated rmTBI presents a useful tool for researchers to explore the underlying mechanisms that contribute to focal and diffuse pathophysiological changes in rmTBI.

Comprehensively characterizing heterogeneous and transversely isotropic properties of femur cortical bones.

Comprehensive characterization of the transversely isotropic mechanical properties of long bones along both the longitudinal and circumferential gradients is crucial for developing accurate mathematical models and studying bone biomechanics. In addition, mechanical testing to derive elastic, plastic, and failure properties of bones is essential for modeling plastic deformation and failure of bones. To achieve these, we machined a total of 336 cortical specimens, including 168 transverse and 168 longitudinal specimens, from four different quadrants of seven different sections of 3 bovine femurs. We conducted three-point bending tests of these specimens at a loading rate of 0.02 mm/s. Young's modulus, yield stress, tangential modulus, and effective plastic strain for each specimen were derived from correction equations based on classical beam theory. Our statistical analysis reveals that the longitudinal gradient has a significant effect on the Young's modulus, yield stress, and tangential modulus of both longitudinal and transverse specimens, whereas the circumferential gradient significantly influences the Young's modulus, yield stress, and tangential modulus of transverse specimens only. The differences in Young's modulus and yield stress between longitudinal specimens from different sections are greater than 40%, whereas those between transverse specimens are approximately 30%. The Young's modulus and yield stress of transverse specimens in the anterior quadrant were 18.81%/15.46% and 18.34%/14.88% higher than those in the posterior and lateral quadrants, respectively. There is no significant interaction between the longitudinal gradient and the circumferential gradient. Considering the transverse isotropy, it is crucial to consider loading direction when investigating the impact of circumferential gradients in the anterior, lateral, medial, and posterior directions. Our findings indicate that the conventional assumption of homogeneity in simulating the cortical bone of long bones may have limitations, and researchers should consider the anatomical position and loading direction of femur specimens for precise prediction of mechanical responses.

Advancing Commotio cordis Safety Standards Using the Total Human Models for Safety (THUMS).

Commotio cordis is one of the leading causes of sudden cardiac death in youth baseball. Currently, there are chest protector regulations regarding the prevention of Commotio cordis in baseball and lacrosse; however, they are not fully optimized. For the advancement of Commotio cordis safety, it is vital to include various age groups and a variety of impact angles in the testing process. This study employed finite element models and simulated Commotio cordis-inducing baseball collisions for different velocities, impact angles, and age groups. Commotio cordis risk response was characterized in terms of left ventricular strain and pressure, chest band and rib deformation, and force from impact. Normalized rib and chest band deformation when correlated with left ventricular strain resulted in R2 = 0.72, and R2 = 0.76, while left ventricular pressure resulted in R2 = 0.77, R2 = 0.68 across all velocities and impact angles in the child models. By contrast, the resultant reaction force risk metric as used by the National Operating Committee on Standards for Athletic Equipment (NOCSAE) demonstrated a correlation of R2 = 0.20 in the child models to ventricular strain, while illustrating a correlation to pressure of R2 = 0.74. When exploring future revisions to Commotio cordis safety requirements, the inclusion of deformation-related risk metrics at the level of the left ventricle should be considered.

Mechanical properties of young mice tibia in four circumferential quadrants under nanoindentation.

Characterizing the mechanical properties of different anatomical quadrants of bones has been conducted in the literature to help understand the correlations among bone morphometric, densitometric, and material properties. However, although there are data to compare four quadrants of the long bones of the adult, there is very limited research on the young adult especially young female. Hence, nine tibia mid-shaft specimens were harvested from nine 8-week-old C57BL/6J female mice, which roughly correspond to the age range of juvenile to young adult, with one left tibia being harvested from one animal. A total of 144 indentation tests were performed with four indentations per quadrant and each of nine tibia specimens being divided into four quadrants. The Oliver and Pharr methods were used to calculate the indentation modulus and hardness. One-way ANOVA and the Kruskal-Wallis nonparametric test were used to study the influence of different anatomical quadrants on the indentation modulus and hardness. The results showed that the indentation modulus of the 8-week-old mouse tibia shaft was 18.94 ± 0.91 GPa, and the hardness was 0.51 ± 0.02 GPa. The influence of circumferential anatomical quadrants on the tibial shaft indentation modulus (p = 0.398) and hardness (p = 0.895) was not statistically significant. These methods and results could potentially help study treatments for young female long bones by comprehensively understanding the effect of treatments on four quadrants, considering collagen fiber, the degree of mineralization, and the changes of collagen cross-linking through high-resolution nanoindentation.

Use of Brain Biomechanical Models for Monitoring Impact Exposure in Contact Sports.

Head acceleration measurement sensors are now widely deployed in the field to monitor head kinematic exposure in contact sports. The wealth of impact kinematics data provides valuable, yet challenging, opportunities to study the biomechanical basis of mild traumatic brain injury (mTBI) and subconcussive kinematic exposure. Head impact kinematics are translated into brain mechanical responses through physics-based computational simulations using validated brain models to study the mechanisms of injury. First, this article reviews representative legacy and contemporary brain biomechanical models primarily used for blunt impact simulation. Then, it summarizes perspectives regarding the development and validation of these models, and discusses how simulation results can be interpreted to facilitate injury risk assessment and head acceleration exposure monitoring in the context of contact sports. Recommendations and consensus statements are presented on the use of validated brain models in conjunction with kinematic sensor data to understand the biomechanics of mTBI and subconcussion. Mainly, there is general consensus that validated brain models have strong potential to improve injury prediction and interpretation of subconcussive kinematic exposure over global head kinematics alone. Nevertheless, a major roadblock to this capability is the lack of sufficient data encompassing different sports, sex, age and other factors. The authors recommend further integration of sensor data and simulations with modern data science techniques to generate large datasets of exposures and predicted brain responses along with associated clinical findings. These efforts are anticipated to help better understand the biomechanical basis of mTBI and improve the effectiveness in monitoring kinematic exposure in contact sports for risk and injury mitigation purposes.

A Neuropathological Study of Diffuse Vascular Injury in Fatal Motor Vehicle Collisions.

In Canada, 42 929 people were involved in fatal motor vehicle collisions (MVCs) between 1999 and 2018. Traumatic brain injuries (TBIs), including diffuse vascular injury (DVI), were the most frequent cause of death. The neuroanatomical injury pattern and severity of DVI in relation to data on MVC dynamics and other MVC factors were the focus of the current study. Five cases of fatal MVCs investigated by Western University's Motor Vehicle Safety (MOVES) Research Team with the neuropathological diagnosis of DVI were reviewed. DVI was seen in single and multiple vehicle collisions, with/without rollover and with/without partial occupant ejection. DVI occurred regardless of seatbelt use and airbag deployment and in vehicles equipped with/without antilock brakes. All DVI cases sustained head impacts and had focal TBIs, including basal skull fractures and subarachnoid hemorrhages. DVI was seen in MVCs that ranged in severity based on the change in velocity (delta-V) during the crash (minimum 31 km/hour) and occupant compartment intrusion (minimum 25 cm). In all cases, DVI in frontal white matter, corpus callosum and pontine tegmentum were common. In cases with more extensive DVI, pronounced vehicle rotation occurred before the final impact. Extensive DVI was seen in drivers who experienced sudden acceleration during vehicle rotation and deceleration.

The Effect of Three-Dimensional Whole, Major, and Small Vasculature on Mouse Brain Strain Under Both Diffuse and Focal Brain Injury Loading.

Blood vessels are much stiffer than brain parenchyma and their effects in finite element (FE) brain models need to be investigated. Despite the publication of some comprehensive three-dimensional (3D) brain vasculature models, no mechanical model exists for the mouse brain vasculature. Moreover, how the vasculature affects the mechanical behavior of brain tissue remains controversial. Therefore, we developed FE mouse brain models with detailed 3D vasculature to investigate the effect of the vasculature on brain strains under both diffuse (closed-head impact) and focal injury (controlled cortical impact (CCI)) loading, two commonly laboratory models of traumatic brain injury. The effect of the vasculature was examined by comparing maximum principal strain in mouse brain FE models with and without the vasculature. On average, modeling comprehensive vasculature under diffuse injury loading reduced average brain strain predictions by 32% with nonlinear elastic properties. Nearly three-fourths of the 32% strain reduction was attributable to the effects of the major branches of the vasculature. Meanwhile, during focal open-skull CCI injury loading, the contribution of the vasculature was limited, producing a less than 5% reduction in all cases. Overall, the vasculature, especially the major branches, increased the load-bearing capacity of the brain FE model and thus reduced brain strain predictions.

Developing commotio cordis injury metrics for baseball safety: unravelling the connection between chest force and rib deformation to left ventricle strain and pressure.

Commotio cordis is a sudden death mechanism that occurs when the heart is impacted during the repolarization phase of the cardiac cycle. This study aimed to investigate commotio cordis injury metrics by correlating chest force and rib deformation to left ventricle strain and pressure. We simulated 128 chest impacts using a simulation matrix which included two initial velocities, 16 impact locations spread across the transverse and sagittal plane, and four baseball stiffness levels. Results showed that an initial velocity of 17.88 m/s and an impact location over the left ventricle was the most damaging setting across all possible settings, causing the most considerable left ventricle strain and pressure increases. The impact force metric did not correlate with left ventricle strain and pressure, while rib deformations located over the left ventricle were strongly correlated to left ventricle strain and pressure. These results lead us to the recommendation of exploring new injury metrics such as the rib deformations we have highlighted for future commotio cordis safety regulations.

Identifying Vulnerable Impact Locations to Reduce the Occurrence of Deadly Commotio Cordis Events in Children's Baseball: A Computational Approach.

Commotio cordis is the second leading cause of sudden cardiac death in young athletes. Currently available chest protectors on the market are ineffective in preventing cases of commotio cordis in young athletes who play baseball. This study focused on using contour maps to identify specific baseball impact locations to the chest that may result in instances of commotio cordis to children during baseball games. By identifying these vulnerable locations, we may design and develop chest protectors that can provide maximum protection to prevent commotio cordis in young athletes. Simulation cases were run using the validated CHARM-10 chest model, a detailed finite element model representing an average 10-year-old child's chest. A baseball model was developed in company with the chest model, and then used to impact the chest at different locations. A 7 × 8 impact location matrix was designed with 56 unique baseball impact simulations. Left ventricle strain and pressure, reaction force between the baseball and chest, and rib deformations were analyzed. Left ventricle strain was highest from baseball impacts directly over the left ventricle (0.34) as well as impacts slightly lateral and superior to the cardiac silhouette (0.34). Left ventricle pressure was highest with impacts directly over the left ventricle (82.94 kPa). We have identified the most dangerous impact locations resulting in high left ventricle strain and pressure. This novel study provided evidence of where to emphasize protective materials for establishing effective chest protectors that will minimize instances of commotio cordis in young athletes.

Understanding Head Injury Risks During Car-to-Pedestrian Collisions Using Realistic Vehicle and Detailed Human Body Models.

Traumatic brain injury (TBI) is the leading cause of death and long-term disability in road traffic accidents (RTAs). Researchers have examined the effect of vehicle front shape and pedestrian body size on the risk of pedestrian head injury. On the other hand, the relationship between vehicle front shape parameters and pedestrian TBI risks involving a diverse population with varying body sizes has yet to be investigated. Thus, the purpose of this study was to comprehensively study the effect of vehicle front shape parameters and various pedestrian bodies ranging from 95th percentile male (AM95) to 6 years old (YO) child on the dynamic response of the head and the risk of TBIs during primary (vehicle) impact. At three different collision speeds (30, 40, and 50 km/h), a total of 36 car-to-pedestrian collisions (CPCs) were reconstructed using three different vehicle types (Subcompact passenger sedan, mid-sedan, and sports utility vehicle (SUV)) and four distinct THUMS pedestrian finite element (FE) models (AM50, AM95, AF05, and 6YO). We assessed skull stress and brain strains besides head linear and rotational kinematics. Our findings indicate that vehicle shape parameters especially bonnet leading edge height (BLEH), when being divided by the height of the Center of Gravity of the human body, correlated positively to head kinematics. The data from this study using realistic vehicle structures and detailed human body models showed that smaller BLEH/CG ratios reduced head injury criteria (HIC) and brain injury criteria (BrIC) values for the car center to mid-stance walking pedestrian impacts but with low-to-moderate R squared values between 0.2 to 0.5. Smaller BLEH/CG reduced head lateral bending velocities with R squared values of 0.57 to 0.63 for all impact velocities, and reduced HIC with R squared value of 0.62 for 50 km/h cases. In the future, simulations with realistic car structures and detailed human body models will be further used to simulate impacts at different locations and with various body shapes/postures.

Purposeful Heading Performed by Female Youth Soccer Players Leads to Strain Development in Deep Brain Structures.

Head impacts in soccer have been associated with both short- and long-term neurological consequences. Youth players' brains are especially vulnerable given that their brains are still developing, and females are at an increased risk of traumatic brain injury (TBI) compared to males. Approximately 90% of head impacts in soccer occur from purposeful heading. Accordingly, this study assessed the relationship between kinematic variables and brain strain during purposeful headers in female youth soccer players. A convenience sample of 36 youth female soccer players (13.4 [0.9] years of age) from three elite youth soccer teams wore wireless sensors to quantify head impact magnitudes during games. Purposeful heading events were categorized by game scenario (e.g., throw-in, goal kick) for 60 regular season games (20 games per team). A total of 434 purposeful headers were identified. Finite element model simulations were performed to calculate average peak maximum principal strain (APMPS) in the corpus callosum, thalamus, and brainstem on a subset of 110 representative head impacts. Rotational velocity was strongly associated with APMPS in these three regions of the brain (r = 0.83-0.87). Linear acceleration was weakly associated with APMPS (r = 0.13-0.31). Game scenario did not predict APMPS during soccer games (p > 0.05). Results demonstrated considerable APMPS in the corpus callosum (mean = 0.102) and thalamus (mean = 0.083). In addition, the results support the notion that rotational velocity is a better predictor of brain strain than linear acceleration and may be a potential indicator of changes to the brain.

Modeling small remotely piloted aircraft system to head impact for investigating craniocerebral response.

Understanding small remotely piloted aircraft system (sRPAS) to human head impacts is needed to better protect human head during sRPAS ground collision accidents. Recent literature reported cadaveric data on sRPAS to human head impacts, which provided a unique opportunity for developing validated computational models. However, there lacks an understanding of skull stress and brain strain during these impacts. Meanwhile, how slight changes in sRPAS impact setting could affect human head responses remains unknown. Hence, a representative quadcopter style sRPAS finite element (FE) model was developed and applied to a human body model to simulate a total of 45 impacts. Among these 45 simulations, 17 were defined according to cadaveric setting for model validation and the others were conducted to understand the sensitivity of impact angle, impact location, and impacted sRPAS components. Results demonstrated that FE-model-predicted head linear acceleration and rotational velocity agreed with cadaveric data with average predicted linear acceleration 4.5% lower than experimental measurement and average predicted of rotational velocity 2% lower than experimental data. Among validated simulations, high skull stresses and moderate level of brain strains were observed. Also, sensitivity study demonstrated significant effect of impact angle and impact location with 3° variation inducing 30% changes in linear acceleration and 29% changes in rotational velocity. Arm-first impact was found to generate more than two times higher skull stresses and brain strains compared to regular body-shell-first impact.

Head Kinematics and Injury Metrics for Laboratory Hockey-Relevant Head Impact Experiments.

Investigating head responses during hockey-related blunt impacts and hence understanding how to mitigate brain injury risk from such impacts still needs more exploration. This study used the recently developed hockey helmet testing methodology, known as the Hockey Summation of Tests for the Analysis of Risk (Hockey STAR), to collect 672 laboratory helmeted impacts. Brain strains were then calculated from the according 672 simulations using the detailed Global Human Body Models Consortium (GHBMC) finite element head model. Experimentally measured head kinematics and brain strains were used to calculate head/brain injury metrics including peak linear acceleration, peak rotational acceleration, peak rotational velocity, Gadd Severity Index (GSI), Head Injury Criteria (HIC15), Generalized Acceleration Model for Brain Injury Threshold (GAMBIT), Brain Injury Criteria (BrIC), Universal Brain Injury Criterion (UBrIC), Diffuse Axonal Multi-Axis General Equation (DAMAGE), average maximum principal strain (MPS) and cumulative strain damage measure (CSDM). Correlation analysis of kinematics-based and strain-based metrics highlighted the importance of rotational velocity. Injury metrics that use rotational velocity correlated highly to average MPS and CSDM with UBrIC yielding the strongest correlation. In summary, a comprehensive analysis for kinematics-based and strain-based injury metrics was conducted through a hybrid experimental (672 impacts) and computational (672 simulations) approach. The results can provide references for adopting brain injury metrics when using the Hockey STAR approach and guide ice hockey helmet designs that help reduce brain injury risks.

Brain microvascular damage linked to a moderate level of strain induced by controlled cortical impact.

Cerebral blood vessels play an important role in brain metabolic activity in general and following traumatic brain injury (TBI) in particular. However, the extent to which TBI alters microvessel structure is not well understood. Specifically, how intracranial mechanical responses produced during impacts relate to vascular damage needs to be better studied. Therefore, the objective of this study was to investigate the biomechanical mechanisms and thresholds of brain microvascular injury. Detailed microvascular damage of mouse brain was quantified using Arterial Spin Labeling (ASL) magnetic resonance imaging (MRI) and ex vivo Serial Two-Photon Tomography (STPT) in seven mice that had undergone controlled cortical impact. Mechanical strains were investigated through finite element (FE) modeling of the mouse brain. We then compared the post-injury vessel density map with FE-predicted strain and found a moderate correlation between the vessel length density and the predicted peak maximum principal strains (MPS) (R2 = 0.52). High MPS was observed at the impact regions with low vessel length density, supporting the mechanism of strain-triggered microvascular damage. Using logistic regression, the MPS corresponding to a 50% probability of injury was found to be 0.17. Given the literature reporting MPS of over 0.2 in the human brain for mild TBI/concussion cases, it is highly recommended to consider microvascular damage when investigating mild TBI/concussion in the future.

Repetitive mild traumatic brain injury in mice triggers a slowly developing cascade of long-term and persistent behavioral deficits and pathological changes.

We have previously reported long-term changes in the brains of non-concussed varsity rugby players using magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI) and functional magnetic imaging (fMRI). Others have reported cognitive deficits in contact sport athletes that have not met the diagnostic criteria for concussion. These results suggest that repetitive mild traumatic brain injuries (rmTBIs) that are not severe enough to meet the diagnostic threshold for concussion, produce long-term consequences. We sought to characterize the neuroimaging, cognitive, pathological and metabolomic changes in a mouse model of rmTBI. Using a closed-skull model of mTBI that when scaled to human leads to rotational and linear accelerations far below what has been reported for sports concussion athletes, we found that 5 daily mTBIs triggered two temporally distinct types of pathological changes. First, during the first days and weeks after injury, the rmTBI produced diffuse axonal injury, a transient inflammatory response and changes in diffusion tensor imaging (DTI) that resolved with time. Second, the rmTBI led to pathological changes that were evident months after the injury including: changes in magnetic resonance spectroscopy (MRS), altered levels of synaptic proteins, behavioural deficits in attention and spatial memory, accumulations of pathologically phosphorylated tau, altered blood metabolomic profiles and white matter ultrastructural abnormalities. These results indicate that exceedingly mild rmTBI, in mice, triggers processes with pathological consequences observable months after the initial injury.

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. For all three orientations, the maximum difference between the predicted and measured pressures was 11%. Animal orientation markedly influenced the predicted peak pressure at the anterior position along the midsagittal plane of the brain (P = 187 kPa; V = 119 kPa; and HO = 142 kPa). However, the relative differences in the predicted peak pressure between the orientations decreased at the medial (21%) and posterior (7%) positions. In contrast to the pressure, the peak strain in the prone orientation relative to the other orientations at the anterior, medial, and posterior positions was 40-88% lower. Similarly, at these positions, the cerebral vasculature strain in the prone orientation was lower than the strain in the other orientations. These results show that animal orientation in a shock tube influences the biomechanical responses of the brain and the cerebral vasculature of the rat, strongly suggesting that a direct comparison of changes in brain tissue observed from animals exposed at different orientations can lead to incorrect conclusions.

Is the 0.2%-Strain-Offset Approach Appropriate for Calculating the Yield Stress of Cortical Bone?

The 0.2% strain offset approach is mostly used to calculate the yield stress and serves as an efficient method for cross-lab comparisons of measured material properties. However, it is difficult to accurately determine the yield of the bone. Especially when computational models require accurate material parameters, clarification of the yield point is needed. We tested 24 cortical specimens harvested from six bovine femora in three-point bending mode, and 11 bovine femoral cortical specimens in the tensile mode. The Young's modulus and yield stress for each specimen derived from the specimen-specific finite element (FE) optimization method was regarded as the most ideal constitutive parameter. Then, the strain offset optimization method was used to find the strain offset closest to the ideal yield stress for the 24 specimens. The results showed that the 0 strain offsets underestimated (- 25%) the yield stress in bending and tensile tests, while the 0.2% strain offsets overestimated the yield stress (+ 65%) in three-point bending tests. Instead, the yield stress determined by 0.007 and 0.05% strain offset for bending and tensile loading respectively, can effectively characterize the biomechanical responses of the bone, thereby helping to build an accurate FE model.

Mechanisms and variances of rotation-induced brain injury: a parametric investigation between head kinematics and brain strain.

There lacks a comprehensive understanding of the correlation between head kinematics and brain strain especially deep-brain strain, partially resulting the deficiency of understanding brain injury mechanisms and the difficulty of choosing appropriate brain injury metrics. Hence, we simulated 76 impacts that were focused on concussion-relevant rotational kinematics and evaluated cumulative strain damage measure (CSDM) and average strain that could represent brain strain distribution. For the whole brain, axial rotation induced the highest CSDM, while lateral bending produced the lowest CSDM. However, for the deep-brain components, lateral bending produced the highest CSDM to the corpus callosum and thalamus. We further confirmed that brain strain was mainly produced by rotational kinematics, for which the effect of rotational deceleration could not be ignored with the deceleration influencing CSDM20 up to 27%. Our data supported that peak rotational velocity correlated to brain strain with an average R2 of 0.77 across various impact directions and different shapes of loading curves. The correlation between peak rotational velocity and brain strain reached to an average R2 of 0.99 for each specific impact direction. Our results supported using direction-specific peak rotation velocity for predicting strain-related brain injury. Additionally, we highlighted the importance of investigating whole-brain and deep-brain strain, as well as considering rotational deceleration.

Porcine growth plate experimental study and estimation of human pediatric growth plate properties.

Growth plate (GP) is a type of tissue widely found in child's immature skeleton. It may have significant influence on the overall injury pattern since it has distinguishing mechanical properties compared to the surrounding bony tissue. For more accurate material modeling and advanced pediatric human body modeling, it is imperative to investigate the material property of GPs in different loading conditions. In this study, a series of tensile and shearing experiments on porcine bone-GP-bone units were carried out. Total 113 specimens of bone-GP-bone unit from the femoral head, distal femur, and proximal tibia of four 20-weeks-old piglets were tested, under different strain rates (average 0.0053 to 1.907 s-1 for tensile tests, and 0.0085 to 3.037 s-1 for shearing tests). Randomized block ANOVA was conducted to determine the effects of anatomic region and strain rate on the material properties of GPs. It was found that, strain rate is a significant factor for modulus and ultimate stress for both tensile and shearing tests; the ultimate strains are not sensitive to the input factors in both tensile and shearing tests; the GPs at knee region could be grouped due to similar properties, but statistically different from the femoral head GP. Additionally, the tensile test data from the experimental study were comparing to the limited data obtained from tests on human subjects reported in the literature. An optimal conversion factor was derived to correlate the material properties of 20-week-old piglet GPs and 10 YO child GPs. As a result, the estimated material properties of 10 YO child GPs from different regions in different loading conditions became available given the conversion law stays legitimate. These estimated material properties for 10 YO child GPs were reported in the form of tensile and shearing stress-strain curves and could be subsequently utilized for human GP tissue material modeling and child injury mechanism studies.

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. To address these limitations, we developed a high-fidelity three-dimensional FE model of a rat head. We explicitly represented the rat's cerebral vasculature and used high-strain-rate material properties of the rat brain. For a range of blast overpressures (100 to 230 kPa) the brain-pressure predictions matched experimental results and largely overlapped with and tracked the incident pressure-time profile. Incorporating the vasculature decreased the average peak strain in the cerebrum, cerebellum, and brainstem by 17, 33, and 18%, respectively. When compared with our model based on rat-brain properties, the use of human-brain properties in the FE model led to a three-fold reduction in the strain predictions. For simulations of blast exposure in rats, our findings suggest that representing cerebral vasculature and species-specific brain properties has a considerable influence in the resulting brain strain but not the pressure predictions.