Parisa Saboori

Aerodynamic analysis of City-Climber robots

A multi-disciplinary robotics team at the City College of New York has developed a new generation wall-climbing robot named as City-Climber, which can operate on both smooth and rough surfaces and carry relatively large payload. This paper presents the adhesion mechanism and aerodynamic analysis of City-Climber robots using a computational fluid dynamics (CFD) simulation tool. The simulation results not only match the experimental test but also provide the directions to improve the adhesion mechanism design.

Histology and Morphology of the Brain Subarachnoid Trabeculae

The interface between the brain and the skull consists of three fibrous tissue layers, dura mater, arachnoid, and pia mater, known as the meninges, and strands of collagen tissues connecting the arachnoid to the pia mater, known as trabeculae. The space between the arachnoid and the pia mater is filled with cerebrospinal fluid which stabilizes the shape and position of the brain during head movements or impacts. The histology and architecture of the subarachnoid space trabeculae in the brain are not well established in the literature. The only recognized fact about the trabeculae is that they are made of collagen fibers surrounded by fibroblast cells and they have pillar- and veil-like structures. In this work the histology and the architecture of the brain trabeculae were studied, via a series of in vivo and in vitro experiments using cadaveric and animal tissue. In the cadaveric study fluorescence and bright field microscopy were employed while scanning and transmission electron microscopy were used for the animal studies. The results of this study reveal that the trabeculae are collagen based type I, and their architecture is in the form of tree-shaped rods, pillars, and plates and, in some regions, they have a complex network morphology.

Brain Subarachnoid Space Architecture: Histological Approach

Human brain is suspended in the skull through three fibrous tissue layers, dura mater, arachnoid and pia mater, known as the meninges layer. The space between the arachnoid and pia mater is known as subarachnoid space (SAS). SAS consists of arachnoid trabeculae and cerebrospinal fluid (CSF), which stabilizes the shape and the position of the brain during head movements. Through solid-fluid interaction, it has been shown that subarachnoid space (SAS) trabeculae plays an important role in damping and reducing the relative movement of the brain with respect to the skull, thereby reducing traumatic brain injuries (TBI), (Zoghi and Sadegh 2010). While the functionality of the SAS is understood, the architecture, the histology and biomechanics of this important region has not been fully investigated. In their modeling of the head, previous investigators have over simplified this important region. This is due to the trabeculae’s complex geometry, abundance of trabeculae and lack of the material properties. These simplifications could lead to inaccurate results of finite element head studies. Killer HE, et al, (2003) investigated the trabecular histology of optical nerves and Alcoldo, et al (1986) used Scanning Electron Microscopy (SEM) to study the arachnid mater of the SAS. The result of these studies reveal that the arachnoid is a thin vascular layer composed of fibroblast cells interspersed with bundles of collagen and the trabecula is also a collagen based structure. However, the brain SAS trabecular architecture and histology has not been fully investigated. The goal of this study is to investigate the mechanotransduction of the head impacts to the brain with the emphasis on the role of material modeling and architecture of the subarachnoid space as it relates to Traumatic Brain Injuries (TBI). This goal was accomplished through three aims including experimental studies, material modeling and a 3D finite element model. In this paper, to present a global view of this investigation, brief descriptions of each aim are presented. It was concluded that the trabeculae contain collagen Type I with tree-shaped architecture and the validated material properties of SAS is approximately E = 1000 Pa.© 2011 ASME

Mechanics of CSF Flow through Trabecular Architecture in the Brain

The importance of the subarachnoid space (SAS) and the meningeal region, which provides a restraining interface between the brain and the skull during a coup/ countercoup movement of the brain, has been addressed in the literature, [9,10,11]. During a contact or non-contact (angular acceleration) of the head, which is due to vehicular collisions, sporting injuries and falls, the brain moves relative to the skull thereby increasing the contact and shear stresses in the meningeal region leading to traumatic brain injuries (TBI). Previous studies have over simplified this region by modeling it as a soft solid, which could lead to unreliable results. The biomechanics of the SAS has not been addressed in the literature. In this paper the mechanotransduction of the cerebrospinal fluid (CSF) through the SAS has been investigated. This is accomplished through a proposed analytical model and finite element solution. The results indicate that Darcy’s permeability is an appropriate model for the SAS and the proposed analytical model can be used to further investigate the transduction of mechanical and hydrodynamic forces through the SAS.

Histology and Trabecular Architecture of the Brain for Modeling of Subarachnoid Space

Subarachnoid space (SAS) plays an important role in transferring and or damping the impact load or angular acceleration to the brain (Zoghi Sadegh 2009). Previous investigations have over simplified the complex architecture of the trabeculae of SAS and employed soft solid materials. The goal of this study is to investigate the histology, architecture and mechanotransduction of subarachnoid space and in particular the trabeculae. The results of this study facilitate future modeling of the brain and thereby better understanding of the TBI.Copyright

The Effect of SAS Materials and Modeling in Transferring Impact Loads to the Brain

While subarachnoid space (SAS) trabeculae play an important role in damping and reducing the relative movement of the brain with respect to the skull, thereby reducing traumatic brain injuries, their mechanical properties and modeling are not well established in the literature. A few studies, e.g., Zhang et al. (2002) and Xin Jin et al. (2008) have reported a wide range the elastic modulus of the trabeculae up to three orders of magnitudes. The histology of the trabeculae reveals a collagen based structure. Thus, a few investigators have estimated the mechanical properties of trabeculae based on collagen’s properties. The objective of this study is to determine the stress/strain changes in the brain as a function of the mechanical properties and modeling methodology of the trabeculae, when the loading and the boundary conditions of the model are kept the same. This study was performed through several modeling steps. A wide range of the mechanical properties of the trabeculae was employed and the transductions of blunt impact loads from the skull to the brain were determined. The mechanical properties of the SAS trabeculae were determined based on the validation of the models with experimental results of Sabet et al. (2009). The result indicated that when we use softer material properties for the trabeculae the meningeal layers absorb and damp the impact load. It is also concluded that the material properties of the trabeculae can be simulated by only tension element since the trabeculae buckles with minimal compressive load. Finally, an optimum material property of SAS was proposed.Copyright

Accelerations and Jerks Associated With Shaken Baby Syndrome

Shaken Baby Syndrome is a collection of injuries that have been associated with the violent shaking of an infant or small child. These injuries can then lead to serious brain damage or even death. It is therefore important to identify the exact mechanism that leads from the shaking to the observed injuries, but little experimental work has been done in this area.The first part of this study was designed to identify if a correlation exists between the physical characteristics of a person shaking a crash test dummy (CRABI) and the resulting accelerations and jerks associated with the motion of the dummy’s head. This was done by placing a three axis accelerometer in the head and two in the body (one in the chest and one in the groin) of a median twelve month old male dummy to determine the acceleration of the head and body. In particular, the relative angular acceleration and jerk of the head relative to the body was determined, since it was felt to be a better predictor of brain damage than would be the absolute linear acceleration of the head.Similar work has been done in the past; however that study only considered the absolute acceleration of the head, and in only one direction. Since the present study allows the attitude of the head to be determined, a true relative angular acceleration of the head relative to the body was found. Consequently, it was found that no strong correlation existed between the absolute linear acceleration and any body characteristic, however a correlation (R2) of 0.6 was found to exist between the body weight of the shaker and the maximum angular jerk of the dummy’s head relative to its body, as compared to only a correlation of 0.5 when the shaker’s body weight was compared to the absolute linear acceleration of the head.A two dimensional dynamic simulation was also developed that modelled the behavior of a child crash test dummy. The model included the legs, torso, and head of the dummy, and the elastic behavior of the neck. The model was created to allow the associated accelerations and jerks to be determined for inputs of various magnitude and temporal profiles. The model was then validated by comparing the simulation results to the test results obtained from the experimental study described above.Copyright

On the Trabecular Morphologies and Load Transfer to the Brain

The human brain trabeculae contain strands of collagen tissues connecting the arachnoid to the pia mater. In this paper the mechanotransductions of the external loads to the head passing through different trabecular architectures of the subarachnoid space were investigated. This has been accomplished by creating several local 2-D models consist of skull, dura mater, arachnoid, trabecular architecture and the brain. Different orientations of several architectures of the trabeculae were also analyzed. All models were subjected to the same loading and constraints. The strains in the brain for each model of the architecture and morphology were determined and compared to other corresponding models. It is concluded that the strain in the brain is less where the tree-shape trabeculae are upright, where the branches are attached to the arachnoid mater and the stems are attached to the pia mater. In addition, in the case of other morphologies the strain in the brain is less when the ratio of the trabecular area to the CSF space is less.Copyright

Evaluation of Head Injury Criteria Under Different Impact Loading

The Head Injury Criterion (HIC) has been employed as a measure of traumatic brain injury arising from an impact involving linear acceleration. Some investigators have been reported the shortcomings of the HIC regarding the angular accelerations, head mass and the precise threshold of injury level [1, 2]. In this study the effect of acceleration curves, as a frontal impact, and the HIC values on the strain in the brain was critically analyzed. Specifically in this paper, the strains in the brain for three sets of acceleration pulses, where the peak of the curve takes place early or later (advanced or delayed) during the pulse time, were investigated. The results of this study indicate that for two different acceleration pulses, with the same peak value, duration and the same HIC values the strains in the brain are different. Therefore there is a need for further research leading to better criteria or modification of the HIC as it relates to the Traumatic Brain Injury (TBI).Copyright

The Effect of the Sulcus Morphology on the Transduction of Impacts to the Brain

The human head, being a vulnerable body region, is most frequently involved in traumatic brain injuries (TBI) and life threatening injuries. Accurate modeling of the variability of the brain morphology is a fundamental problem in investigating TBI. Improved computational/mathematical structural models of the brain are needed to help investigators to have a better understanding of the phenomena of different traumatic brain injuries such as concussion. The human brain is the most complex region of the body. There is a very thin membrane known as a pia mater that covers all the surface of the brain. The pia mater follows all the fissure of the brain and covers all the surface of the sulci and gyri. Sulcus is referred to any furrow in the brain. Statistically there are about 72 main sulci in the human brain. Previous FE studies of TBI have ignored sulcus morphology in their modeling and thus, their results could be unreliable.In this paper, the effect of the brain sulcus structure on mechanotransduction of impacts to the brain has been investigated. This was accomplished by using series of parametric studies and comparing the results with the model without sulci. The results of this study reveal that the brain’s strain is reduced in the present of sulcus and gyrus structures. We have hypothesized that the presence of sulcus increases the surface area of the brain thereby decreases the normal and shear strain in the brain. That is, the presence of sulcus and gyrus reduce the transduction of the external load and impacts to the white and gray matters of the brain and thereby reduces the risk of TBI. Ignoring sulci in any FE modeling and analysis of the brain may lead to unreliable results.Copyright