Revealing the role of material properties in impact-related injuries: Investigating the influence of brain and skull density variations on head injury severity.

Traumatic brain injuries (TBI) resulting from head impacts are a major public health concern, which prompted our research to investigate the complex relationship between the material properties of brain tissue and the severity of TBI. The goal of this research is to investigate how variations in brain and skull density influence the vulnerability of brain tissue to traumatic injury, thereby enhancing our understanding of injury mechanism. To achieve this goal, we employed a well-validated finite element head model (FEHM). The current investigation was divided into two phases: in the first one, three distinct brain viscoelastic materials that had been utilized in prior studies were analyzed. The review of the properties of these three materials has been meticulous, encompassing both the spectrum of mechanical properties and the behaviors that are relevant to the way in which brain tissue reacts to traumatic loading conditions. In the second phase, the material properties of both the brain and skull tissue, alongside the impact conditions, were held constant. After this step, the focus was directed towards the variation of density in the brain and skull, which was consistent with the results obtained from previous experimental investigations, in order to determine the precise impact of these variations in density. This approach allowed a more profound comprehension of the impacts that density had on the simulation results. In the first phase, Material No. 2 exhibited the highest maximum first principal strain value in the frontal region (εmax=15.41%), indicating lower stiffness to instantaneous deformation. This characteristic suggests that Material No. 2 may deform more extensively upon impact, potentially increasing the risk of injury due to its viscoelastic behavior. In contrast, Material No. 1, with a lower maximum first principal strain in the frontal region (εmax=7.87%), displayed greater stiffness to instantaneous deformation, potentially reducing the risk of brain injury upon head impact. The second phase provided quantitative findings revealing a proportional relationship between brain tissue density and the pressures experienced by the brain. A 2 % increase in brain tissue density corresponded to approximately a 1 % increase in pressure on the brain tissue. Similarly, changes in skull density exhibited a similar quantitative relationship, with a 6 % increase in skull density leading to a 2.5 % increase in brain pressure. This preliminary approximate ratio of 2 to 1 between brain and skull density variations provides an initial quantitative framework for assessing the impact of density changes on brain vulnerability. These findings have several implications for the development of protective measures and injury prevention strategies, particularly in contexts where head trauma is a major issue.

Quantifying the effect of cerebral atrophy on head injury risk in elderly individuals: Insights from computational biomechanics and experimental analysis of bridging veins.

The objective of this study was to quantitatively investigate the relationship between cerebral atrophy and the risk of injury in elderly individuals. To achieve this, a sophisticated computational biomechanics approach utilizing finite element analysis was employed to simulate the mechanical behavior of the brain and skull under various conditions. In addition, particular emphasis was placed on understanding the role of cerebral bridging veins (BVs) and their mechanical properties at different ages in the occurrence of head injuries. Head models representing healthy brains and five atrophy models were developed based on imaging data. After validation, the models underwent the identical impact loading conditions to enable the simulation of brain damage. The resulting outcomes of the models with brain atrophy were then compared to the results obtained from the healthy model, allowing for a comparative analysis. Simulations showed increased relative displacement with worsening brain atrophy, particularly in the frontal and occipital regions. Compared to the healthy brain model, relative displacement increased by 2.36 %-9.21 % in the atrophy models, indicating an elevated risk of injury. In severe brain atrophy (FEM 6), the strain reached 83.59 % in local model simulations, leading to damage and rupture of cerebral BVs in both young and elderly individuals. Mechanical tests on cerebral BVs demonstrated a negative correlation between age and ultimate force, stress, and strain, suggesting increased susceptibility to damage with age. An observed sharp decline of approximately 50 % in ultimate stress and 35 % in ultimate strain was noted as age increased. We implemented a 50 % reduction in the intensity of head impact forces; nevertheless, vascular damage continues to manifest in the elderly population. To establish a truly safe zone, it is imperative to further decrease the intensity of the impact. This investigation represents a significant step forward in our understanding of the complex interplay between cerebral atrophy, the mechanical properties of BVs at different age, and the risk of head injury in the elderly. Through continued research in this field, we can strive to improve the quality of care, enhance prevention strategies, and ultimately enhance the well-being and safety of the elderly population.

Viscoelastic Characterization of a Thermoplastic Elastomer Processed through Material Extrusion.

Objective. We aim to characterize the viscoelastic behavior of Polyether-Block-Amide (PEBA 90A), provide reference values for the parameters of a constitutive model for the simulation of mechanical behaviors, and paying attention to the influence of the manufacturing conditions. Methods. Uniaxial relaxation tests of filaments of PEBA were used to determine the values of the parameters of a Prony series for a Quasi-Linear Visco-Elastic (QLVE) model. Additional, fast cyclic loading tests were used to corroborate the adequacy of the model under different test criteria in a second test situation. Results. The QLVE model predicts the results of the relaxation tests very accurately. In addition, the behavior inferred from this model fits very well with the measurements of fast cyclic loading tests. The viscoelastic behavior of PEBA under small strain polymer fits very well to a six-parameter QLVE model.

Injury Metrics for Assessing the Risk of Acute Subdural Hematoma in Traumatic Events.

Worldwide, the ocurrence of acute subdural hematomas (ASDHs) in road traffic crashes is a major public health problem. ASDHs are usually produced by loss of structural integrity of one of the cerebral bridging veins (CBVs) linking the parasagittal sinus to the brain. Therefore, to assess the risk of ASDH it is important to know the mechanical conditions to which the CBVs are subjected during a potentially traumatic event (such as a traffic accident or a fall from height). Recently, new studies on CBVs have been published allowing much more accurate prediction of the likelihood of mechanical failure of CBVs. These new data can be used to propose new damage metrics, which make more accurate predictions about the probability of occurrence of ASDH in road crashes. This would allow a better assessement of the effects of passive safety countermeasures and, consequently, to improve vehicle restraint systems. Currently, some widely used damage metrics are based on partially obsolete data and measurements of the mechanical behavior of CBVs that have not been confirmed by subsequent studies. This paper proposes a revision of some existing metrics and constructs a new metric based on more accurate recent data on the mechanical failure of human CBVs.

Viscoelastic Characterization of Parasagittal Bridging Veins and Implications for Traumatic Brain Injury: A Pilot Study.

Many previous studies on the mechanical properties of Parasagittal Bridging Veins (PSBVs) found that strain rate had a significant effect on some mechanical properties, but did not extensively study the viscoelastic effects, which are difficult to detect with uniaxial simple tensile tests. In this study, relaxation tests and tests under cyclic loading were performed, and it was found that PSBVs do indeed exhibit clear viscoelastic effects. In addition, a complete viscoelastic model for the PSBVs is proposed and data from relaxation, cyclic load and load-unload tests for triangular loads are used to find reference values that characterize the viscoelastic behavior of the PSBVs. Although such models have been proposed for other types of blood vessels, this is the first study that clearly demonstrates the existence of viscoelastic effects from an experimental point of view and also proposes a specific model to explain the data obtained. Finally, this study provides reference values for the usual viscoelastic properties, which would allow more accurate numerical simulation of PSBVs by means of computational models.

Mechanical Behavior of Blood Vessels: Elastic and Viscoelastic Contributions.

The mechanical properties of the cerebral bridging veins (CBVs) were studied using advanced microtensile equipment. Detailed high-quality curves were obtained at different strain rates, showing a clearly nonlinear stress-strain response. In addition, the tissue of the CBVs exhibits stress relaxation and a preconditioning effect under cyclic loading, unequivocal indications of viscoelastic behavior. Interestingly, most previous literature that conducts uniaxial tensile tests had not found significant viscoelastic effects in CBVs, but the use of more sensitive tests allowed to observe the viscoelastic effects. For that reason, a careful mathematical analysis is presented, clarifying why in uniaxial tests with moderate strain rates, it is difficult to observe any viscoelastic effect. The analysis provides a theoretical explanation as to why many recent studies that investigated mechanical properties did not find a significant viscoelastic effect, even though in other circumstances, the CBV tissue would clearly exhibit viscoelastic behavior. Finally, this study provides reference values for the usual mechanical properties, as well as calculations of constitutive parameters for nonlinear elastic and viscoelastic models that would allow more accurate numerical simulation of CBVs in Finite Element-based computational models in future works.

A predictive model for fracture in human ribs based on in vitro acoustic emission data.

PURPOSE: The aim of this paper is to propose a fracture model for human ribs based on acoustic emission (AE) data. The accumulation of microcracking until a macroscopic crack is produced can be monitored by AE. The macrocrack propagation causes the loss of the structural integrity of the rib. METHODS: The AE technique was used in in vitro bending tests of human ribs. The AE data obtained were used to construct a quantitative model that allows an estimation of the failure stress from the signals detected. The model predicts the ultimate stress with an error of less than 3.5% (even at stresses 15% lower than failure stress), which makes it possible to safely anticipate the failure of the rib. RESULTS: The percolation theory was used to model crack propagation. Moreover, a quantitative probability-based model for the expected number of AE signals has been constructed, incorporating some ideas of percolation theory. The model predicts that AE signals associated with micro-failures should exhibit a vertical asymptote when stress increases. The occurrence of this vertical asymptote was attested in our experimental observations. The total number of microfailures detected prior to the failure is N ≈ 100 and the ultimate stress is σ ∞ = 197 ± 62 MPa. A significant correlation (p < 0.0001) between σ ∞ and the predicted value is found, using only the first N = 30 micro-failures (correlation improves for N higher). CONCLUSIONS: The measurements and the shape of the curves predicted by the model fit well. In addition, the model parameters seem to explain quantitatively and qualitatively the distribution of the AE signals as the material approaches the macroscopic fracture. Moreover, some of these parameters correlate with anthropometric variables, such as age or Body Mass Index. The proposed model could be used to predict the structural failure of ribs subjected to bending.

Influence of anthopometric variables on the mechanical properties of human rib cortical bone.

Objective. The mechanical properties of ribs from a large number ofpost-mortemhuman subjects (PMHS) were analyzed to search for variation according to age, sex or BMI in the sample. A large sample of specimens from different donors (N= 64) with a very wide range of ages and anthropometric characteristics was tested.Methods. Uniaxial tensile tests were used for a sample of coupons machined from cortical bone tissue in order to isolate the purely mechanical properties from the geometrically influenced properties of the rib. Each coupon is about 25 mm long and has a thickness of about 0.5 mm. The mechanical properties measured for each specimen/coupon include YM, yield stress, ultimate stress (maximum failure stress), ultimate strain, and resilience (energy to fracture of SED). The study provides new methodological improvements in DIC techniques.Results. This study is notable for using an atypically large sample of number of PMHS. The size of the sample allowed the authors to determine that age has a significant effect on failure stress (p< 0.0001), yield stress (p= 0.0047), ultimate strain (p< 0.0001) and resilience (p< 0.0001) [numbers in parentheses represent the correspondingp- values]. Finally, there is a combined effect, so that for a given age, an increase of BMI leads to a decrease of the maximum strain (i.e. cortical bone is less stiff when both age and BMI are higher).

Prediction of mechanical properties of human rib cortical bone using fractal dimension.

A large number of post mortem human subjects was used to investigate the relation between the micro-structure of rib cortical bone and the mechanical properties using Fractal Dimension. Uniaxial tensile tests were performed on coupons of rib cortical bone. Tensile strength, yield stress, Young's Modulus, maximum strain, and work to fracture were determined for each coupon. Fractal dimension was computed using CT images and Digital Image Correlation procedures. A highly significant effect of fractal dimension in the mechanical properties was found. In addition, the variation in mechanical properties was found to be adequately represented by Generalized Extreme Value type distributions.

Biomecánica y mecanismo de producción del traumatismo cráneo-encefálico en el peatón atropellado. Evaluación de la normativa actual en la automoción / Pedestrian head injury biomechanics and damage mechanism. Pedestrian protection automotive regulation assessment

Introducción: Los atropellos son una de las principales causas de muerte entre los accidentes de tráfico. Recientemente, ha aumentado el estudio de los atropellos, principalmente debido a la aplicación de la normativa europea y japonesa en protección de peatones. Esta investigación presenta un análisis del traumatismo cráneo-encefálico del peatón atropellado, asociándolo con la estructura del vehículo responsable de la lesión, su mecanismo de daño y comparando el resultado con la normativa existente. Métodos: La metodología empleada ha consistido en un estudio epidemiológico descriptivo y transversal, mediante el estudio de datos de peatones atropellados recogidos en la base de datos americana (PCDS) que analiza a un total de 552 peatones atropellados y un total de 4.500 lesiones documentadas. Resultados: De acuerdo con este estudio, el capó es el causante del 15,1% de las lesiones de la cabeza del peatón, mientras que el parabrisas es responsable de 41,8% de todas las lesiones. En el caso de los vehículos tipo utilitario la ubicación del impacto de la cabeza se produce por encima de lo que se espera en la regulación actual y, por lo tanto, no se aplican las contramedidas necesarias. De todas las lesiones en la cabeza sufridas por los peatones solo el 20% tiene la aceleración lineal como mecanismo de lesión, el 40% de las lesiones se deben a la aceleración rotacional. Conclusiones: En esta investigación se pone de manifiesto la importancia de la aceleración rotacional como mecanismo de daño en la cabeza del peatón atropellado. En la normativa actual solo la aceleración lineal está contemplada en la formulación del principal criterio biomecánico utilizado para predecir el traumatismo cráneo-encefálico

Introduction: Pedestrian-vehicle collisions are a leading cause of death among motor vehicle accidents. Recently, pedestrian injury research has been increased, mostly due to the implementation of European and Japanese regulations. This research presents an analysis of the main head injury vehicle sources and injury mechanisms observed in the field, posteriorly the data are compared with the current pedestrian regulations. Methods: The analysis has been performed through an epidemiologic transversal and descriptive study, using the Pedestrian Crash Data Study (PCDS) involving 552 pedestrians, sustaining a total of 4.500 documented injuries. Results: According to this research, the hood surface is responsible for only 15,1% of all the head injuries. On the other hand, the windshield glazing is responsible for 41,8%. In case of sedan vehicles the head impact location exceeds what is expected in the current regulation, and therefore no countermeasures are applied. From all the head injuries sustained by the pedestrians just 20% have the linear acceleration as isolated injury mechanism, 40% of the injuries are due to rotational acceleration. Conclusions: In this research, the importance of the rotational acceleration as injury mechanism, in case of pedestrian-vehicle collision is highlighted. In the current pedestrian regulation just the linear acceleration is addressed in the main injury criteria used for head injury prediction

[Pedestrian head injury biomechanics and damage mechanism. Pedestrian protection automotive regulation assessment]. / Biomecánica y mecanismo de producción del traumatismo cráneo-encefálico en el peatón atropellado. Evaluación de la normativa actual en la automoción.

INTRODUCTION: Pedestrian-vehicle collisions are a leading cause of death among motor vehicle accidents. Recently, pedestrian injury research has been increased, mostly due to the implementation of European and Japanese regulations. This research presents an analysis of the main head injury vehicle sources and injury mechanisms observed in the field, posteriorly the data are compared with the current pedestrian regulations. METHODS: The analysis has been performed through an epidemiologic transversal and descriptive study, using the Pedestrian Crash Data Study (PCDS) involving 552 pedestrians, sustaining a total of 4.500 documented injuries. RESULTS: According to this research, the hood surface is responsible for only 15,1% of all the head injuries. On the other hand, the windshield glazing is responsible for 41,8%. In case of sedan vehicles the head impact location exceeds what is expected in the current regulation, and therefore no countermeasures are applied. From all the head injuries sustained by the pedestrians just 20% have the linear acceleration as isolated injury mechanism, 40% of the injuries are due to rotational acceleration. CONCLUSIONS: In this research, the importance of the rotational acceleration as injury mechanism, in case of pedestrian-vehicle collision is highlighted. In the current pedestrian regulation just the linear acceleration is addressed in the main injury criteria used for head injury prediction.

New insights in the analysis of blunt force trauma in human bones. Preliminary results.

Determining the time of injury is an important but still a challenging task in forensic anthropology. In literature, many descriptions can be found to make a distinction between perimortem and postmortem fractures. Characteristics that are more related to fractures in fresh conditions, however, are not extensively investigated. This study compared 28 perimortem fractures from autopsies and 21 both fresh and dry experimentally reproduced human bone fractures. Preliminary results showed the following five distinct traits that might be related to perimortem conditions: layered breakage, bone scales, crushed margins, wave lines and flakes with matching flake defect. These distinct traits might not only be good estimators of perimortem trauma but also may be an indicator of trauma in intra vitam conditions, especially related with muscular reaction to injury. Furthermore, layered breakage seems to be a good trait to infer the biomechanics of trauma.

Injury pattern in lethal motorbikes-pedestrian collisions, in the area of Barcelona, Spain.

INTRODUCTION: There are several studies about M1 type vehicle-pedestrian collision injury pattern, and based on them, there has been several changes in automobiles for pedestrian protection. However, the lack of sufficient studies about injury pattern in motorbikes-pedestrian collisions leads to a lack of optimization design of these vehicles. The objective of this research is to study the injury pattern of pedestrians involved in collisions with motorized two-wheeled vehicles. METHODS: A retrospective descriptive study of pedestrian's deaths after collisions with motorcycles in an urban area, like Barcelona was performed. The cases were collected from the Forensic Pathology Service database of the Institute of Legal Medicine of Catalonia. The selected cases were categorized as pedestrian-motorcycle collision, between January 1st, 2005 and December 31st, 2014. Data were collected from the autopsy, medical, and police report. The collected information was then analyzed using Microsoft Excel statistical functions. RESULTS: Traumatic Brain Injury is the main cause of death in pedestrian hit by motorized two-wheeled vehicles (62.85%). The most frequent injury was the subarachnoid hemorrhage, in 71.4% of cases, followed by cerebral contusions and skull base fractures (65.7%). By contrast, pelvic fractures and tibia fractures only appeared in 28.6%. CONCLUSIONS: The study characterizes the injury pattern of pedestrians involved in a collision with motorized two-wheeled vehicles in an urban area, like Barcelona, which has been found to be different from other vehicle-pedestrian collisions, with a higher incidence of brain injuries and minor frequency of lower extremities fractures in pelvis, tibia and fibula.

A review of pelvic fractures in adult pedestrians: experimental studies involving PMHS used to determine injury criteria for pedestrian dummies and component test procedures.

OBJECTIVES: Perform a systematic review for the most relevant pelvic injury research involving PMHS. The review begins with an explanation of the pelvic anatomy and a general description of pelvic fracture patterns followed by the particular case of pelvic fractures sustained in pedestrian-vehicle collisions. Field data documenting the vehicle, crash, and human risk factors for pedestrian pelvic injuries are assessed. METHOD: A summary of full-scale PMHS tests and subsystem lateral pelvic tests is provided with an interpretation of the most significant findings for the most relevant studies. CONCLUSIONS: Based on the mechanisms of pedestrian pelvic injury, force, acceleration, and velocity and compression have been assessed as predictive variables by researchers although no consensus criterion exists.

Indentation response of human patella with elastic modulus correlation to localized fractal dimension and bone mineral density.

The goal of this study was to determine material properties for the anterior cortex and subcortical regions of human patellae and relate those properties to mineral density and fractal dimension of the bone. Ten human patellae were obtained from eight fresh frozen human cadavers and subjected to anteriorly-directed spherical indentation-relaxation experiments using two different sized indenters to two different indentation depths. Response data were fit to a three-mode viscoelastic model obtained through elastic-viscoelastic correspondence of the Hertzian contact relation for spherical indentation. A location-specific effective bone density measurement that more heavily weighted bone material close to the indentation site (by von Mises stress distribution) was determined from micro-computed tomography (38µm resolution) data captured for each specimen. The same imagery data were used to compute location specific fractal dimension estimates for each indentation site. Individual and averaged patella material models verified the hypothesis that when the larger indenter and greater indentation depth is used to engage the surface and deeper (trabecular) bone, the bone exhibits a more compliant response than when only the surface (cortical) bone was engaged (instantaneous elastic modulus was 325MPa vs. 207MPa, p<0.05). Effective bone mineral density was shown to be a significant predictor of the elastic modulus for both small and large indentation types (p<0.05) despite relatively low correlations. Exponential regressions of fractal dimension on elastic modulus showed significant relationships with high correlation for both the small (R(2)=0.93) and large (R(2)=0.97) indentations.

Biomecánica del latigazo cervical: conceptos cinemáticos y dinámicos / Whiplash biomechanics: kinematics and dynamics

Los impactos posteriores a baja velocidad son el accidente de tráfico más frecuente y uno de los principales campos de investigación por parte de la comunidad científica. La lesión sufrida en el cuello por el ocupante se conoce como síndrome de latigazo cervical. La dificultad de encontrar una lesión claramente objetivable, que explique y justifique la sintomatología de los pacientes, lleva con frecuencia a litigar y conlleva costes sociales muy elevados. Las indemnizaciones asociadas en Europa han sido estimadas entre 5-10.000 millones de euros cada año, siendo este número incrementado anualmente. El objetivo de este artículo es explicar de forma clara a la vez que rigurosa el mecanismo cinemático que sufre el cuello durante un impacto posterior a baja velocidad. Se expondrá el principal criterio biomecánico aceptado por la comunidad científica y utilizada por la industria automovilística. Finalmente, se abordará un repaso a los diferentes aspectos que pueden modificar sustancialmente la naturaleza de la colisión(AU)

Rear-impact collisions at low speed are the most frequent type of accident among all motor vehicle crashes. These collisions are also the subject of substantial investigation in the scientific literature neck injuries associated with them are commonly known as whiplash. The difficulty to identify an injury of this kind with an objective basis leads to litigation and high social costs. Costs in Europe have been estimated at between 5-10 billion euros each year, and this number increases annually. The aim of this paper is to establish clearly and rigorously the kinematic mechanism that the neck undergoes during a low-speed rear impact. The main criteria for injury accepted by the scientific community and used in the automotive industry will be analyzed. Finally, an analysis of the different aspects that could modify the nature of the collision will be conducted(AU)

Increased risk of driver fatality due to unrestrained rear-seat passengers in severe frontal crashes.

While belt usage among rear-seat passengers is disproportionately lower than their front-seat counterpart, this may have serious consequences in the event of a crash not only for the unbelted rear-seat passenger but also for the front-seat passengers as well. To quantify that effect, the objective of the study is to evaluate the increased likelihood of driver fatality in the presence of unrestrained rear-seat passengers in a severe frontal collision. U.S.-based census data from 2001 to 2009 fatal motor vehicle crashes was used to enroll frontal crashes which involved 1998 or later year vehicle models with belted drivers and at least one adult passenger in the rear left seat behind the driver. Results using multivariate logistic regression analysis indicated that the odds of a belt restrained driver sustaining a fatal injury was 137% (95% CI=95%, 189%) higher when the passenger behind the driver was unbelted in comparison to a belted case while the effects of driver age, sex, speed limit, vehicle body type, airbag deployment and driver ejection were controlled in the model. The likelihood of driver fatality due to an unrestrained rear left passenger increased further (119-197%) in the presence of additional unrestrained rear seat passengers in the rear middle or right seats. The results from the study highlight the fact that future advances to front row passive safety systems (e.g. multi-stage airbag deployment) must be adapted to take into account the effect of unrestrained rear-seat passengers.

Fractal dimension and mechanical properties of human cortical bone.

Fractal dimension (FD) can be used to characterize microstructure of porous media, particularly bone tissue. The porous microstructure of cortical bone is observable in micro-CT (µCT) images. Estimations of fractal dimensions of µCT images of coupons of human cortical bone are obtained. The same samples were tested on a tensile test machine and Young's modulus (YM) and Failure stress were obtained. When both types of measures were compared, a clear correlation was found (R=-81%, P<0.01). Young's modulus of each sample and the FD of its µCT images are correlated. From the assumption that cortical bone is approximately a fractal set, a non-linear constitutive relation involving FD is obtained for YM. Experimental results show good agreement with this constitutive relation. Additional parameters in the non-linear relation between YM and FD have been estimated from experimental results and related to physical parameters.