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Bioengineering

2006;():1-6. doi:10.1115/IMECE2006-14207.

We report the development of completely releasable SU-8 based polymer microgripper and the manipulation of normal rat kidney (NRK) cells suspended in phosphate buffered saline (PBS) solution using a generic biological sample manipulator, which incorporates such a polymer microgripper as an end-effector. The electrically insulative polymer gripper consists of a thick (~50 μm), patterned high aspect ratio (~5:1) layer of SU-8 as the structural layer and a thin nickel layer as the electrothermal heating layer. The fabricated polymer gripper was completely released from the substrate and mounted onto a ceramic pad. The gripper was characterized in air and PBS, and the displacement at the tips was 12 μm for 0.5 V in air and for 2 V in PBS. The mounted gripper was assembled as end-effector onto a biological nano-manipulator (L200, Zyvex Corporation, Richardson, TX). Pick-and-place of a single cell from a cluster of suspended cells in aqueous medium has been demonstrated using this set-up.

Commentary by Dr. Valentin Fuster
2006;():7-16. doi:10.1115/IMECE2006-14401.

This paper presents the concept and simulation of a novel multiple electrospray emitters for electrospray ionization mass spectrometric (ESI-MS) applications. The proposed emitter is based on an array of carbon nanofibers (CNF) vertically grown around the orifice of a microscale thermoplastic capillary. The electrospray ionization process is simulated using a CFD code that utilizes Taylor-Melcher leaky-dielectric formulations for the electrohydrodynamics and volume-of-fluid (VOF) method for tracking the interface. The modeling results predict that under steady state conditions, individual cone-jets are established around each of the CNFs resulting in an array of electrosprays. Effects of several design and operational parameters on the electrospray performance are thoroughly investigated. The results of the present study will facilitate design, fabrication and experiments using the CNF emitter. Higher spray current and lower jet diameter indicate that the proposed emitter can perform equivalent to nanospray emitters exhibiting improved MS sensitivity while using a microscale orifice. Use of microscale orifice benefits in terms of higher sample throughput and eliminates potential clogging problem inherent in nanoscale capillaries. Overall, the proposed emitter is believed to be a suitable candidate for ESI-MS applications.

Topics: Modeling
Commentary by Dr. Valentin Fuster
2006;():17-18. doi:10.1115/IMECE2006-15408.

One of the obstacles of culturing functioning vital tissues in vitro is to obtain a substantial biomass at a physiological cell density (>108 cells/cm3 ). At this high density, the diffusion length of metabolites is limited to ~100um. As a matter of fact, in real tissue, almost all the cells are located within 100um distance from the capillaries [1]. Studies [2, 3] also confirmed that the cells in the artificial tissue cannot be properly cultured when they are further than 400um from the external nutrient source. Therefore, to culture three dimensional artificial tissue with substantial biomass, vascularization is necessary to enhance the metabolites transport. The short diffusion length of the metabolites requires high capillary density (>100/mm2 ) in vascularization. To meet this need, we have developed a novel high resolution and high speed 3D microfabrication technique, the projection microstereolithography[4] to explore microcirculatory networks with high density (>150/mm2 ). Using this technology we designed and fabricated the microreactors as shown in Figure 1. In our samples, 800um PEG microcapillaries with 20um inner radius and 40um outer radius with pitch of 96um are fabricated. Two rings as inlet and outlet are connected to external supply of culture medium. We designed the parameters of the vascularized microbioreactor based on the simulations of oxygen and carbon dioxide transport and metabolism in hepatocytes. As shown in Figure 2, the capillaries are arranged in a hexagonal way. According to the geometric symmetry, the final simulation domain is divided into 2 regions, the polymer capillary wall and the tissue. We assumed that a culture media with dissolved oxygen is pumped through the capillaries at 1.5mm/s rate and diffuses through the capillary wall, into the hepatocytes. The consumption of oxygen follows Michaelis-Menten kinetics [5, 6] and the metabolic rate of carbon dioxide is assumed to be proportional to that of oxygen by a fixed quotient (-0.81) which is addressed and studied by other groups [7]. The carbon dioxide diffuses into the capillaries and can be carried away through the flow of the culture medium. Our simulation indicates that the bottleneck of effective oxygen transport is the permeability of the polymer materials. The oxygen concentration drops off about 90% after diffusing through the capillary wall. It is predicted that the diffusion length at the inlet is 74um and 48um at the outlet; the rapid drop of carbon dioxide concentration also happens across the capillary wall. The predicted carbon dioxide concentration in the tissue is ~80nmol/cm3 ; this value is much smaller than the toxic value (100mmHg or 3umol/cm3 ) reported by David Gray and coworkers [8]. In Figure 2, we present the effect of the permeability of the capillary polymer materials on the diffusion length of oxygen and the concentration of carbon dioxide in the tissue. Our study indicates the existence of an optimal permeability for the capillary network, at which the overall diffusion length of oxygen is maximized. Interestingly, we also found a maximum concentration of carbon dioxide in the cultured tissue as the permeability of the polymer material changes. We attribute it to the competition between the tissue thickness and the permeability. Higher permeability increases the cultured tissue thickness, and also increases the ability of capillary to empty carbon dioxide. Not only is this model applicable for oxygen and carbon dioxide, but also for the transport of other metabolites. As an ongoing experimental effort, our fluorescent microscopy measurement validated the diffusion transport of fluorescent species from the capillary (Figure 3). Experiments are also in progress on the oxygen diffusion from the capillaries will cell cultures of high density on the PEG scaffold by introducing proper indicators. In summary, we have established a method to design and manufacture vascularized microcirculatory network to enhance the mass transport during the tissue culture. To ensure the effective nutrient delivery and wastes removal, our numerical simulation also confirms that it is essential to embed high density microcapillaries with optimal permeability.

Topics: Polymers , Networks
Commentary by Dr. Valentin Fuster
2006;():19-25. doi:10.1115/IMECE2006-16045.

Magnetic fluid deformable mirrors (MFDMs) present a simple alternative to the expensive and delicate wavefront correctors currently in use in adaptive optics (AO) systems. Such mirrors are particularly suitable for retinal imaging AO systems. The practical implementation of a retinal imaging AO system incorporating a MFDM requires an effective control system to control the shape of the mirror surface. The real-time control of the mirror surface requires a model of the mirror that can be used to determine the dynamic response of the mirror to a magnetic field applied as the control input. This paper presents such a model that not only determines the dynamic response of the MFDM but also takes into account the unique requirements of the retinal imaging application of the mirrors. The mirror is modeled as a horizontal layer of a magnetic fluid. The dynamic response of the mirror to the applied magnetic field is represented by the deflection of the free surface of the layer. The surface deflection is determined by the modal analysis of the coupled fluid-magnetic system. Considering the requirements of the retinal imaging application, the effects of surface tension and depth of the fluid layer are duly represented in the model. The mirror model is described in a state-space form and can be readily used in the design of a controller to regulate the mirror surface shape.

Commentary by Dr. Valentin Fuster
2006;():27-33. doi:10.1115/IMECE2006-16086.

Accurate interpretation of functional brain images requires knowledge of the relationship between neurons and their supporting cells and vasculature. Our understanding of this complex and dynamic system would improve if we measure multiple aspects of brain function simultaneously. We have developed a semi-transparent electrode array which allows for concurrent multi-site electrophysiological recording and high-resolution optical imaging of intrinsic signals. The 8-channel electrode array is fabricated on a transparent glass substrate with platinum recording surfaces. We map stimulus-induced field potentials (evoked potentials) and changes in cerebral blood volume in rat somatosensory cortex. We also examine the evolution of these responses during the neuro-pathological state of cortical spreading depression. We have developed a planar multi-electrode array that is fully compatible with Optical imaging of Intrinsic Signals. It provides a sensitive and reliable tool to use in the study of neurovascular coupling in brain activation.

Topics: Electrodes , Signals , Imaging
Commentary by Dr. Valentin Fuster
2006;():35-36. doi:10.1115/IMECE2006-15696.

In paper, we report our recent results of using the air force ultrasound transducer to study the resonance of rubber tubes. Experiments were carried out on a rubber latex tube. Seven resonant frequencies were measured between 50 Hz and 200 Hz. Theoretical calculation of the resonant frequency on the tube was done with the wave propagation approach. The relative differences of the seven resonant frequencies between the experiment and the theory are less than 6 %. This research shows that the air force ultrasound transducer can be used for tube resonance measurement.

Commentary by Dr. Valentin Fuster
2006;():37-39. doi:10.1115/IMECE2006-15795.

The static and dynamic stiffnesses of contracted trachea smooth muscles are determined before, during and after length oscillations in isometric contraction. An appropriate Neural Network model is developed to normalize the data. The results indicate that the dynamic stiffness has the tendency of decreasing as the frequency and/or amplitude of external excitation increases. However, the static stiffness decreases with an increase in the frequency and amplitude of excitation until it reaches a critical value of frequency where no variation in stiffness is observed. It is postulated that the tissue elasticity and inertia are the main contributors to the dynamic stiffness while the myosin-actin cross bridge cycling is the main contributor to the static stiffness.

Commentary by Dr. Valentin Fuster
2006;():41-45. doi:10.1115/IMECE2006-16010.

MRI guided focused ultrasound (FUS) has been shown to create thermal lesions where tissue stiffness changes significantly. To assess the correlation between tissue stiffness change and tissue ablation, a pilot animal based study was conducted to treat LNCaP tumors in vivo and Hep3B tumors immediately post mortem. MR elastography was used to analyze tissue stiffness before and after ablation. Treated tissue was excised immediately after each experiment and processed by routine histological analysis. Four prostate cancer tumors and four liver cancer tumors showed, on average, a threefold increase in stiffness due to FUS thermal treatment. Histology showed complete (100%) coagulation necrosis in these cases. These data suggest that MRE may be an effective means to assess tissue ablation.

Commentary by Dr. Valentin Fuster
2006;():47-54. doi:10.1115/IMECE2006-16241.

The use of respiratory support devices using pressure oscillations has been shown to improve alveolar recruitment in animals and provide clinical benefits over traditional ventilators to infants with respiratory distress syndrome (RDS). The interactions and mechanisms of human lungs with such "bubble oscillation" (BO) devices is unknown. A simple mathematical model of the respiratory system and a BO type device is developed to explore the use of a new assessment parameter to study the effect of the pressure oscillations on lung performance. A mean square spectral density (MSSD) approach is employed in an attempt to observe the contribution of each pressure oscillation frequency on the work rate of unhealthy lungs. Further improvements to the respiratory system model are suggested for more detailed studies into human lung interactions with BO type devices.

Commentary by Dr. Valentin Fuster
2006;():55-64. doi:10.1115/IMECE2006-16297.

An acoustic boundary element (BE) model for porous compliant material like the lung parenchyma is developed and validated theoretically and experimentally. This BE model is coupled with a source localization algorithm to predict the position of an acoustic source within a lung phantom. The BE model is also coupled with a finite element (FE) model to simulate the surrounding shell-like chest wall. Experimental studies validate the BE-based source localization algorithm and show that the same algorithm fails if the BE simulation is replaced with a free field assumption that neglects reflections and standing wave patterns created within the finite-size lung phantom. This research is relevant to the development of advanced auscultatory techniques for lung, vascular and cardiac sounds within the torso that utilize multiple noninvasive sensors to create acoustic images of the sound generation and transmission to identify certain pathologies.

Topics: Acoustics , Sound , Lung
Commentary by Dr. Valentin Fuster
2006;():65-71. doi:10.1115/IMECE2006-16385.

Ultrasound vibro-acoustography is a novel medical imaging modality that combines the high resolution of high-frequency ultrasound with the speckle-free images obtained using low-frequency methods. This imaging modality relies on the non-linear interaction of two high frequency beams at slightly different frequencies. We describe the physics of ultrasound vibro-acoustography and outline a strategy for its modeling, simulation, and optimal design.

Commentary by Dr. Valentin Fuster

Biomedical and Safety Systems

2006;():75-80. doi:10.1115/IMECE2006-13081.

This paper presents a method to determine the contact force and pressure on the surface of viscoelastic objects grasped by an endoscopic grasper, used in Minimally Invasive Surgery (MIS). Normally, an endoscopic grasper is corrugated (teeth-like) in order to grasp slippery tissues. It is highly important to avoid damage to the tissues during grasping and manipulation in endoscopic surgery. Therefore, it is essential to determine the exact contact force on the surface of the tissue. To this end, initially a comprehensive closed form analysis of grasping contact force and pressure on elastic and particularly viscoelastic materials which have similar behavior as that of biological tissues is studied. The behavior of a rigid grasper with wedge-like teeth, when pressed into a delayed elasticity material is being examined. Initially, a single wedge penetrating into a solid is studied and then is extended to the grasper. The elastic wedge indentation is the basis of this study and the effects of time are included in the equations by considering the corresponding integral operator from viscoelastic stress-stain relations. Under the action of a constant normal load, the penetration of the indenter and the contact area will change. In this research, the variation of the contact area with time and the grasping contact force is studied. The results of this study which provides a closed form expression for grasping contact force and contact area are compared with those from elastic analysis.

Commentary by Dr. Valentin Fuster
2006;():81-87. doi:10.1115/IMECE2006-13116.

A Soloflex machine was analyzed mathematically. Dimensions of the components of the machine were measured, and calculations were made to determine a resistance curve. The machine consists of a mainframe bent into an L-shape, having a vertical post height of 6 ft. A loading post with 27 drilled holes is attached along the back of the vertical post. The loading piece receives a bench pin and the barbell arm pin. To perform an exercise, the barbell arm is attached with the barbell arm pin to the loading piece. Weight straps of equal rating are placed on both sides of the load and barbell arm pins. Pushing upward on the barbell arm will stretch the weight straps which provides resistance to the motion of the barbell arm. The weight straps behave like springs. The straps were stretched with a Tinius-Olsen machine to determine the force vs deflection behavior for a standard set of weight straps, including one pair each of 2.5 lb, 5 lb, 10 lb, 25 lb, 50 lb and 100 lb weight straps. The objective of this study was to make measurements of force versus deflection for each matched pair of weight straps, and then to calculate the force required at the barbell arm to perform an exercise for a particular "weight." Although several different exercises can be performed, the focus here is on a simple bench press, for which the resistance curve was determined.

Commentary by Dr. Valentin Fuster
2006;():89-94. doi:10.1115/IMECE2006-13982.

The research results presented here are part of a more extensive effort regarding sustained bioconvection in porous media. Bioconvection is the phenomenon of gravity driven fluid motion due to buoyancy forces resulting from density differences between the fluid and motile micro-organisms suspended in the fluid. While the field of bio-convection in pure fluids emerged substantially over the past decade the corresponding effects of bio-convection in porous media received much less attention, despite the fact that micro-organisms grow naturally in porous environments; soil, food and human tissues serve as basic examples. The research focuses in two major new directions. The first deals with the theoretical and experimental investigation of bio-convection in porous media. The second major new direction is linked to the sustainability of the bio-convection motion. The existing work on bio-convection in both pure fluids and porous media exclude micro-organism growth during the bio-convection because the time scales concerned were very short. However, when the question of the sustainability of this convection over long times arises, microorganism growth has to be accounted for. If sustained bio-convection in porous media is possible it opens the avenue to investigate its impact on microbial proliferation in soil, food and human tissue, an important avenue for application of the theoretical results. Then, if bio-convection enhances microbial proliferation it may be undesirable in some cases, e.g. in food, or it might be desirable if specific micro-organisms that can be used for contaminated soil remediation will be "helped" by the bio-convection process to access contaminated regions in the soil. The theoretical and experimental results presented in this paper reflect the process of monotonic growth of motile microorganisms (e.g. the PAOI strain of Pseudomonas Aeruginosa) to be included in the bioconvection process. A new proposed model is shown to be the appropriate one to better reflect both conceptually as well as practically the microbial growth process.

Topics: Microorganisms
Commentary by Dr. Valentin Fuster
2006;():95-98. doi:10.1115/IMECE2006-13984.

Accounting for metabolic mass transfer and abiotic resource dynamics is not common in modeling microbial population growth. In this paper it is demonstrated that the latter is an essential feature that needs to be considered if reliable results are sought. The results of a model that takes the metabolic mass transfer and abiotic resource dynamics into account are shown to capture a variety of features that appear in experiments such as a Lag phase, a Logarithmic Inflection Point, growth followed by decline and oscillations. The results have a wide variety of implications and applications, from food microbiology and wine fermentation, up to human cell growth, where the latter includes tumor growth.

Commentary by Dr. Valentin Fuster
2006;():99-107. doi:10.1115/IMECE2006-14900.

In the current paper we introduce the localized meshless method to resolve the two-dimensional blood flow in the vicinity of a peripheral bypass graft end-to-side distal anastomosis. The goal is to incorporate this new numerical technique in extracting the values of the fluid mechanics wall parameters, such as the wall shear stress and the wall shear stress gradients, which are suggested as contributory factors to the growth of post-operative intimal hyperplasia at the anastomosis. The localized meshless method depends on the Hardy Multiquadrics radial basis function to locally expand the flow variables over a set of nodes distributed in the computational domain. An explicit scheme is adapted for the meshless formulation of the laminar incompressible Navier Stokes equations. Our special interest in the localized meshless method arises from its automated point distribution feature that significantly facilitates the pre-processing of the solution. The blood flow is simulated in three different anastomosis model geometries; the conventional or direct model, the Miller Cuff model, and the Taylor Patch model. The results of the current localized meshless numerical method show a great agreement with the results provided by a well-established finite volume method commercial software.

Commentary by Dr. Valentin Fuster
2006;():109-115. doi:10.1115/IMECE2006-15596.

Crash analysis and head injury biomechanics are very important fields in biomedical research due to the devastating consequences of traumatic brain injuries (TBI). Complex geometry and constitutive models of multiple materials can be combined with the loading conditions in finite element head model to study the dynamic behavior of brain and the TBI. In such a modeling, the proper regional material properties of brain tissues are important. Brain tissues material properties have not been finally determined by experiments, and large variations in the test data still exist and the data is very much situation-dependent. Therefore, parametric analysis should be performed to study the relationship between the material properties and the brain response. The main purpose of presenting this paper is to identify the influence of material constitutive properties on brain impact response, to search for an improved material model and to arrive at a better correlation between the finite element model and the cadaver tests data. In this paper a 3-D nonlinear finite element method will be used to study the dynamic response of the human head under dynamic loading. The finite element formulation includes detailed model of the skull, brain, cerebral-spinal fluid (CSF), dura mater, pia mater, falx and tentorium membranes. The brain is modeled as linear viscoelastic material, whereas linear elastic material behavior is assumed for all the other tissue components. The proper contact and compatibility conditions between different components have been implemented in the modeling procedure. The results for the direct frontal impacts will be shown for three groups of material parameters. The parametrical analysis of tissue material models allows to examines the accuracy of three different set of material parameters for brain in a comparison with the prediction of the head dynamic response of Nahum's human cadaver direct impact experiment. Three sets of suggested material parameters are examined. It is concluded that although all three groups of material models will follow the dynamic behavior of the head and brain behavior, but the parametric data considered in this paper have a closer resemblance to the experimental behavior.

Topics: Brain
Commentary by Dr. Valentin Fuster
2006;():117-124. doi:10.1115/IMECE2006-15794.

Window-type high-pressure optical cells (HPOC) such as the one designed by Paladini and Weber [Rev. Sci. Instrum. 52, (1981) p. 419] have provided biophysicists a powerful tool to understand the structure-function relationships of biological molecules. However, the conventional HPOC is only good for single solution testing and does not allow for quick mixing and stirring of additional components while the sample is under pressure. To mix two solutions under pressure, Zhou et al [Rev. Sci. Instrum. 69, (1998) p. 3958] developed a laser activated dual chamber HPOC. However, the expensive laser device and its unavailability in most laboratories make the application difficult. In a later study, Zhou et al. [Rev. Sci. Instrum. 71, (2000) p. 4249] introduced shape memory alloy (SMA) as an actuator to unplug a urethane stopper with a biasing spring for agitation. The drawback is that the biasing spring blocks the observing light beam and creates unwanted reflections. This research is to construct an actuator with concentric SMA spring and compressive biasing spring: an SMA helical tensile spring to pull out the stopper to let two solutions mix; and a helical compressive spring to bias and to agitate solutions, and to leave the lower half cuvette clear for optical observation. Due to the limited space in the cuvette, the alignment of two springs is critical for both motion and heat response to activate each spring separately. This paper discusses the design of SMA actuator, SMA spring testing and mixing testing by the SMA spring actuator. Since SMA (nickel-titanium) spring is not solderable and crimping method is limited due to the space, a conductive adhesive is used not only to fix the alignment between springs and cap, but also to conduct electric current. Spring force testing was done by INSTRON. Mixing testing used flourescein intensity change to trace the mixing process. The bio-compatibility of the nickel-titanium SMA with proteins and phospholipids has also been tested.

Commentary by Dr. Valentin Fuster
2006;():125-131. doi:10.1115/IMECE2006-15963.

Basel cell carcinoma (BCC) is the most common human skin malignancy. Its incidence has increased significantly in Australia, Europe and North America over the past decade. A number of modalities are currently used for treatment of BCC, including cryosurgery which offers a potential for high cure rate, low cost, minimal bleeding and good cosmetic effect. However, cryosurgery is not used frequently for BCC because no current method exists to design adequate treatment parameters. We present a numerical analysis on the thermal history of the target tissue during cryosurgery of a nodular BCC using liquid nitrogen (LN2 ) spray. The model uses Pennes equation to describe the heat transfer within the target tissue. A convective thermal boundary is used to describe the heat interaction between the tissue and LN2 , and the apparent heat capacity method is applied to address the tissue phase change process. A parametric study is conducted on the convective heat transfer coefficient (hs : 104 ~106 W/m2 ·K), cooling site area (rs /R0 : 0.5~1.0) and spray time (t: 0~30 sec.), with the objective to understand the thermal history during tissue freezing, including lethal temperature (-50 °C) and cooling rate (CR). Results demonstrate that propagation of the lethal isotherm is sensitive to the convective heat transfer coefficient, hs , with a range of 104 ~5×104 W/m2 ·K. Increasing the cooling site area can significantly enhance cooling efficiency, producing dramatic increase in the amount of tissue encompassed by the lethal isotherm. The cooling rate (CR) shows a highly dynamic distribution during the cooling process: the highest CR drops quickly from 140 °C/sec. (t=0.5 sec.) to 20 °C/sec. (t=5 sec.). The highest CR is initially located close to the cooling site but moves toward the inside of the tissue as treatment proceeds. The model presented herein provides a simulation tool for treatment planning of cryosurgery using LN2 spray, in which the protocol parameters, e.g. cooling site area and spray time, can be determined for an optimal outcome. The quantitative predictions on the propagation of lethal isotherm and the distribution of CR should help to optimize cryosurgery efficacy.

Commentary by Dr. Valentin Fuster
2006;():133-137. doi:10.1115/IMECE2006-16057.

Continuous positive airway pressure (CPAP) therapy is considered the most effective treatment for patients with Obstructive Sleep Apnea (OSA) symptom. A CPAP mask is the interface between the patient and the CPAP humidifier, which contains a series of orifice to circulate the air and ensure that the expired carbon dioxide from the patient's breathing is not rebreathed. The flow through those orifices is called bias flow. For the existing CPAP mask, this bias flow rate increases as the CPAP pressure increases. This raised bias flow rate usually causes a bigger pressure swing inside the mask when the patient is breathing, which is unfavorable for OSA therapy due to the much bigger breathing load required. However, a minimum bias flow rate needs to be maintained inside the mask in order to keep carbon dioxide concentration low. Therefore, this paper introduces a novel mask that can produce a relatively constant bias flow rate (CBFR) over a CPAP range of 0-20cm H2 O. Dynamic response tests have proved that this CBFR mask can constrict the mask pressure swing by an order of two so as to offer better comfort for OSA patients.

Commentary by Dr. Valentin Fuster
2006;():139-148. doi:10.1115/IMECE2006-16068.

It has long been recognized within the automotive safety community and by numerous biomechanical research studies that providing effective occupant protection in automotive rollover crashes requires effective occupant restraint. Effective occupant restraint includes, at the most basic level, preventing occupant ejection and providing sufficient control of occupant kinematics through the rollover event to prevent potentially injurious contacts with interior vehicle components. This paper examines both laboratory and real-world accident analysis of restraint performance in rollover-type environments. This includes studies involving static and dynamic testing with human surrogates and anthropometric test devices (ATDs). Additionally, the effects of rollover roof deformation on the restraint systems ability to control or affect occupant kinematics, when those restraint systems are anchored to the dynamically deforming structural components of the vehicle, are examined. Finally, various production and alternative restraint system designs are considered and discussed relative to their ability to control occupant kinematics and their influence on belted occupants' injury potential in the rollover crash mode. This paper will focus on the effect of seat belt looseness, or slack, and its relationship to occupant excursion during a rollover. Literature is referenced establishing that increased occupant excursion produces increased injury potential in rollovers, both by increasing the likelihood of injurious contacts with interior vehicle components as well as an increased risk of full and partial ejection. Four complete vehicle inversion studies (spit tests) are conducted with live surrogate occupants in production vehicle restraint systems. These studies document occupant excursions under a 1G inverted environment with various amounts of seat belt slack in production restraint systems as well as comparison tests using various alternative restraint configurations. Additionally three complete vehicle inverted drop tests are conducted in which the vehicles' roof structures and the upper torso belt anchors (D-ring) are instrumented to document their displacement while producing typical real-world type roof structure damage. The effect of this restraint anchor deformation is then examined relative to the occupant excursions evaluated in the spit tests. Lastly, a complete dolly rollover test conducted on a contemporary production mini van with production restrained anthropometric test devices (ATDs) is examined with a focus on the restraint system's geometry alterations and effectiveness through the multiple roll/roof contact events.

Commentary by Dr. Valentin Fuster
2006;():149-154. doi:10.1115/IMECE2006-16076.

Occupant kinematics during rollover or inverted impacts has been the subject of significant research. Controlled experiments have utilized complete vehicles, partial vehicles and seat/restraints systems attached to various platforms. Previous experiments, which included the element of a deforming roof, have required the destruction of a complete vehicle. The Deformable Occupant Compartment Impact Tester (DOCIT) was developed to incorporate functions similar to previously research devices, but has a roof capable of deforming under impact, which can be reset without the destruction of a vehicle. The DOCIT is designed to simulate an occupant compartment including a roof, seat, restraint system in which an Anthropometric Test Device (ATD) is placed and subjected to a repeatable inverted impact environment. Two test series are reviewed, in which baseline tests that based upon real-world rollover accidents are compared with alternate design systems under the same impact environments.

Commentary by Dr. Valentin Fuster

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