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‣ Morphofunctional characterization of decellularized vena cava as tissue engineering scaffolds

Bertanha, Matheus; Moroz, Andrei; Jaldin, Rodrigo G.; Silva, Regina A. M.; Rinaldi, Jaqueline C.; Golim, Marjorie A.; Felisbino, Sergio L.; Domingues, Maria A. C.; Sobreira, Marcone L.; Reis, Patricia P.; Deffune, Elenice
Fonte: Elsevier B.V. Publicador: Elsevier B.V.
Tipo: Artigo de Revista Científica Formato: 103-111
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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); Processo FAPESP: 10/52549-8; Clinical experience for peripheral arterial disease treatment shows poor results when synthetic grafts are used to approach infrapopliteal arterial segments. However, tissue engineering may be an option to yield surrogate biocompatible neovessels. Thus, biological decellularized scaffolds could provide natural tissue architecture to use in tissue engineering, when the absence of ideal autologous veins reduces surgical options. The goal of this study was to evaluate different chemical induced decellularization protocols of the inferior vena cava of rabbits. They were decellularized with Triton X100 (TX100), sodium dodecyl sulfate (SDS) or sodium deoxycholate (DS). Afterwards, we assessed the remaining extracellular matrix (ECM) integrity, residual toxicity and the biomechanical resistance of the scaffolds. Our results showed that TX100 was not effective to remove the cells, while protocols using SDS 1% for 2 h and DS 2% for 1 h, efficiently removed the cells and were better characterized. These scaffolds preserved the original organization of ECM. In addition, the residual toxicity assessment did not reveal statistically significant changes while decellularized scaffolds retained the equivalent biomechanical properties when compared with the control. Our results concluded that protocols using SDS and DS were effective at obtaining decellularized scaffolds...

‣ Microfluidic biomechanical and electrical devices for rapid analysis of cells and organelles

Lu, Hang, 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 145 leaves; 11321288 bytes; 11321045 bytes; application/pdf; application/pdf
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This thesis focuses on micro devices aimed at rapid analysis of cells and subcellular organelles. These devices take advantage of microfabrication techniques to create environment suitable for biomechanical and biochemical stimulation of cells, to break cell membranes to extract the intracellular materials, and to separate or concentrate organelles and proteins of interest. These procedures greatly reduce the amounts of samples and reagents necessary and the process time required from their macro counterparts. Moreover, they demonstrate operational advantages, such as lower voltages, less heating, and no significant gas formation in electrolysis, over their macroscopic counterparts. First in line of the process stream are a series of microfluidic devices developed for the purpose of studying cell adhesion on biomaterials. Numerical models are developed to aid the quantitative analysis of fluid shear stresses on cells in these devices. The experimental results demonstrate that these devices are capable of capturing ligand-density-dependent, shear-dependent, and growth-factor-dependent adhesion behavior of cell cultures. Next, two electrical microfluidic devices are developed for the purpose of cell lysis and organelle separation. Both devices are fabricated using electroplating techniques to create three-dimensional electrodes...

‣ Inverse Monte Carlo simulation of biomolecular conformation and coarse-grained molecular modeling of chondroitin sulfate conformation, titration, and osmotic pressure

Bathe, Mark, 1975-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 170 p.; 6693490 bytes; 6714621 bytes; application/pdf; application/pdf
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The first part of this thesis is concerned with the solution structure determination problem. Whereas many biomacromolecules, such as proteins, can be adequately characterized by a single conformation in solution, numerous other important molecules (e.g., nucleic acids, carbohydrates, and polypeptides) exhibit conformational isomerism and disorder. For these molecules, the term "structure" does not correspond to a single conformation but rather to an ensemble of conformations. Given a molecular model and experimental data, the goal of the structure determination problem is to solve for an ensemble of conformations that is consistent with the data. Traditional computational procedures such as simulated annealing, however, are not guaranteed to generate a unique ensemble. The computed ensemble is often simply dependent on the user-specific protocol employed to generate it. As an alternative, a numerical method for determining the conformational structure of macromolecules is developed and applied to idealized biomacromolecules in solution. The procedure generates unique, maximum entropy conformational ensembles that reproduce thermodynamic properties of the macromolecule (mean energy and heat capacity) in addition to the target experimental data. As an evaluation of its utility in structure determination...

‣ The biomechanics of the knee following injury and reconstruction of the posterior cruciate ligament c Louis DeFrate.

DeFrate, Louis E., 1977-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 216 leaves; 9471560 bytes; 9485613 bytes; application/pdf; application/pdf
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Very little is known regarding the function of the posterior cruciate ligament in response to physiological loading conditions. A limited understanding of posterior cruciate ligament function might contribute to the poor clinical outcomes that are observed after reconstruction. Therefore, the objectives of this thesis were to quantify the biomechanical function of the posterior cruciate ligament both in-vitro and in-vivo and to investigate the effects of injury and reconstruction of the posterior cruciate ligament on knee joint biomechanics. First, muscle loading conditions were simulated in cadavers to measure the effects of posterior cruciate ligament injury and reconstruction on knee joint kinematics and contact pressures. Next, the structural properties of the grafts used in posterior cruciate ligament reconstructions were optimized using a theoretical model. In order to verify these results using an experimental model, an imaging system was developed to measure the strain distributions around the graft surface during tensile testing. Finally, the deformation of the posterior cruciate ligament was studied in living subjects using imaging and solid modeling techniques. Three-dimensional models of the knee joint, including the insertion sites of the posterior cruciate ligament were created from magnetic resonance images. The subjects then flexed their knees as they were imaged using fluoroscopy from two orthogonal directions. The models and orthogonal images were imported into a solid modeling software and used to reproduce the kinematics of the knee as a function of flexion. From these models...

‣ A multi finger electromagnetic actuator apparatus for biomechanical studies on the hand

Dobson, Kathleen L. (Kathleen Lynn), 1981-
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 86 leaves; 4419009 bytes; 4422593 bytes; application/pdf; application/pdf
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The focus of this thesis was on the design and construction of a multi-finger haptic device powered by electromechanical voice-coil actuators. Five actuators were designed and constructed and a position and force feedback control system was implemented for each. The maximum continuous force output for each actuator ranged from 12-16 N, which is about 15%-30% of the maximum force that can be exerted by an individual finger. The bandwidth of the controlled actuators ranged from 0.7 Hz to 1.7 Hz, the steady-state error was zero, and the overshoot ranged from 3.5% to 7.7%. Four actuators were constructed into an array, with finger contact points 23 mm apart. Additional structures, such as finger holders and a wrist rest, were developed to complete the human interface. With further modifications, the multi-finger apparatus can be used to conduct biomechanical and perceptual studies of the human hand.; by Kathleen L. Dobson; Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2005.; Includes bibliographical references (leaves 77-80).

‣ Skeletal muscle biomechanics drives intramuscular transport of locally delivered drugs

Wu, Peter I-Kung
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 97 leaves
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Introduction: Effective local drug delivery to contractile tissues such as skeletal muscle requires a thorough understanding of the impact of mechanical loads on intramuscular pharmacokinetics. Current preparations for studying skeletal muscle biomechanics typically use: mounting techniques that lead to mechanical disruption of the tissue, which can create drug transport artifacts. In order to accurately study mechanical influences on drug transport, experimental techniques and setups need to meet the particular design requirements of both biomechanical testing setups and local drug delivery preparations. Studies of intramuscular pharmacokinetics require anatomically physiologic and functionally viable conditions for accurate drug transport. In this study, we invent a method for the surgical isolation and mounting of whole skeletal muscles of small rodents that maintains the physiologic configuration of the tissue. We also invent a mounting assembly and dynamic loading system designed appropriately for in vitro drug transport studies. We present an effective protocol for tissue processing and visually quantifying intramuscular distribution of drug. With the primary objective of investigating muscle pharmacokinetics, we use these techniques in a study to elucidate the influence of mechanical loading on the intramuscular transport and distribution of locally delivered drug. Methods and Results: The dynamic loading system was characterized and used to investigate intramuscular transport of aqueous macromolecular drug. The loading system was designed to achieve a maximal force...

‣ Movement Effects on the Flow Physics and Nutrient Delivery in Engineered Valvular Tissues

Salinas, Manuel
Fonte: FIU Digital Commons Publicador: FIU Digital Commons
Tipo: Artigo de Revista Científica Formato: application/pdf
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Mechanical conditioning has been shown to promote tissue formation in a wide variety of tissue engineering efforts. However the underlying mechanisms by which external mechanical stimuli regulate cells and tissues are not known. This is particularly relevant in the area of heart valve tissue engineering (HVTE) owing to the intense hemodynamic environments that surround native valves. Some studies suggest that oscillatory shear stress (OSS) caused by steady flow and scaffold flexure play a critical role in engineered tissue formation derived from bone marrow derived stem cells (BMSCs). In addition, scaffold flexure may enhance nutrient (e.g. oxygen, glucose) transport. In this study, we computationally quantified the i) magnitude of fluid-induced shear stresses; ii) the extent of temporal fluid oscillations in the flow field using the oscillatory shear index (OSI) parameter, and iii) glucose and oxygen mass transport profiles. Noting that sample cyclic flexure induces a high degree of oscillatory shear stress (OSS), we incorporated moving boundary computational fluid dynamic simulations of samples housed within a bioreactor to consider the effects of: 1) no flow, no flexure (control group), 2) steady flow-alone, 3) cyclic flexure-alone and 4) combined steady flow and cyclic flexure environments. We also coupled a diffusion and convention mass transport equation to the simulated system. We found that the coexistence of both OSS and appreciable shear stress magnitudes...

‣ A study of a Gough-Stewart platform-based manipulator for applications in biomechanical testing.

Ding, Boyin
Fonte: Universidade de Adelaide Publicador: Universidade de Adelaide
Tipo: Tese de Doutorado
Publicado em //2014 Português
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This thesis investigates the development and application of a robotic system for in-vitro biomechanical testing to study the mechanisms leading to human joint injury and degeneration in an ethical and safe manner. Six degree of freedom (6-DOF) robotic-based systems, in particular Gough-Stewart platform-based systems, have been increasingly used in applications of biomechanical testing where 6-DOF mobility, large load capacity, and high stiffness and positioning accuracy are required from the testing machine. This study proposes a novel Gough-Stewart platform-based manipulator with ultra-high stiffness and accuracy for use in biomechanical testing and investigates its mechanism and control. Not only restricted to biomechanical testing, the proposed manipulator concept can also be applied to other robotic-based applications, particularly those requiring ultra-high accuracy positioning under large external loads (e.g machining). Four main features of the proposed manipulator are individually studied in this thesis: namely, stiffness and control of a non-collocated actuator-sensor mechanism, active preload control using actuation redundancy for backlash elimination, adaptive velocity-based load control of human joints for unconstrained testing...

‣ A finite element approach towards biomechanical optimization of prophylactic vertebroplasty

Sun, Kay
Fonte: Universidade Rice Publicador: Universidade Rice
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Vertebroplasty has the potential to be a highly effective vertebral fracture prevention treatment, but the procedure must first be optimized for maximum benefit and minimal risk of safety to the patient. The procedure involves the percutaneous injection of a liquid bone cement into the vertebral body, which upon hardening provides instantaneous structural reinforcement. This research characterizes the effects of bone cement volume, material properties and distribution patterns on the global and internal vertebral biomechanics after prophylactic vertebroplasty in order to optimize these cement properties based on biomechanical efficacy and risk of complications which pose a threat to patient safety. In light of the many factors affecting the biomechanical outcome, a computational approach was employed since multiple analyses can be repeated on the same specimen. The accuracy of the models is assured by using realistic, image-based finite element models of human vertebral bodies that are specimen-specific, anatomically detailed and calibrated to experimental results. Prophylactic vertebroplasty was simulated on these models under various cement configurations and their biomechanical efficacies were evaluated based on the criteria for biomechanical success developed in this research---maximum mechanical reinforcement to reach low fracture risk levels with minimal amount of cement and maintenance of intravertebral mechanical compatibility to retain the normal dynamics of the weight-bearing spine. The biomechanically optimal bone cement is determined as one that results in a spatially dispersed distribution when injected into the vertebral body. The higher vertebral reinforcements achieved with a dispersed cement fill may lower the risk of complications due to cement leakages since smaller cement volume would be just as biomechanically effective. Furthermore...

‣ Optimizing a scaffoldless approach for cartilage tissue engineering

Elder, Benjamin Daniel
Fonte: Universidade Rice Publicador: Universidade Rice
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Articular cartilage has a poor intrinsic healing response, so tissue engineering provides a promising approach for cartilage regeneration. The major objective of this proposal was to enhance the self-assembling process, used in articular cartilage tissue engineering, by investigating the effects of construct confinement, hydrostatic pressure application, and growth factor addition. First, the effects of construct confinement in different directions and at different times were investigated. It was demonstrated that construct confinement resulted in enhanced biomechanical properties in the direction orthogonal to the confinement surface, either by enhancing collagen organization or by increasing collagen production. Next, the effects of hydrostatic pressure at different timepoints, magnitudes, and frequencies on the biomechanical and biochemical properties of self-assembled constructs were determined. It was demonstrated that the application of static hydrostatic pressure, at 10 MPa, for 1 h/day, from days 10-14 days led to significant increases in compressive and tensile properties, accompanied by significant increases in GAG and collagen content, respectively. To our knowledge, this was the first study to demonstrate increases in the biomechanical properties of tissue from pure HP application. Furthermore...

‣ Exogenous stimulation of meniscus cells for the purpose of tissue engineering the knee meniscus

Gunja, Najmuddin Juzer
Fonte: Universidade Rice Publicador: Universidade Rice
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Injuries to avascular regions of menisci do not heal and result in significant discomfort to patients. Current treatments, such as partial meniscectomy, alleviate the symptoms, but lead to premature osteoarthritis due to reduced stability and changes in knee biomechanics. An alternative treatment to overcome these problems involves functional tissue engineering. This thesis examined several exogenous factors to enhance the capability of meniscus cells (MCs) to synthesize relevant ECM markers and improve the functionality of constructs in vitro. First, the effect of passage on the phenotype of MCs in monolayer was investigated, and rapid changes were observed in collagen I, collagen II, and COMP expression. Collagen I and aggrecan protein coatings assisted in reversing expression levels of certain ECM markers; however, collagen II expression could not be reversed. Next, 3D tissue engineering studies were conducted using a cell-scaffold approach with MCs seeded on PLLA meshes. Anabolic stimuli that aided in meniscus regeneration included (1) hypoxia and bFGF, which resulted in synergistic increases in the total glycosaminoglycan content and compressive properties of constructs; (2) 10 MPa static hydrostatic pressure (HP), which resulted in increases in collagen content and the relaxation modulus of constructs; and (3) 10 MPa static HP and TGF-beta1...

‣ Novel Exogenous Agents for Improving Articular Cartilage Tissue Engineering

Responte, Donald Joseph
Fonte: Universidade Rice Publicador: Universidade Rice
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This thesis demonstrated the effects of exogenous stimuli on engineered articular cartilage constructs and elucidated mechanisms underlying the responses to these agents. In particular, a series of studies detailed the effects of chondroitinase-ABC (C-ABC), hyaluronic acid (HA), and TGF-β1 on the biochemical and biomechanical properties of self-assembled articular cartilage. Work with C-ABC showed that this catabolic agent can be employed to improve the tensile properties of constructs. When constructs were cultured for 6 weeks, treating with C-ABC at 2 weeks enhanced the tensile stiffness. Furthermore, treating at 2 and 4 weeks synergistically increased tensile properties and allowed compressive stiffness to recover to control levels. Another study showed that combining C-ABC and TGF-β1 synergistically enhanced the biochemical and biomechanical properties of neotissue. Microarray analysis demonstrated that TGF-β1 increased MAPK signaling in self-assembled neocartilage whereas C-ABC had minimal effects on gene expression. SEM analysis showed that C-ABC increased collagen fibril diameter and fibril density, indicating that C-ABC potentially acts via a biophysical mechanism. Constructs treated with C-ABC and TGF-β1 also showed stability and maturation in vivo ...

‣ Characterization of the Temporomandibular Joint Disc and Fibrocartilage Engineering using Human Embryonic Stem Cells

Willard, Vincent P.
Fonte: Universidade Rice Publicador: Universidade Rice
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Fibrocartilages in the body, including the temporomandibular joint (TMJ) disc and knee meniscus, lack intrinsic healing capacity following trauma or disease. Current treatments only address the symptoms of fibrocartilage damage and do nothing to prevent further degradation of the joint. A tissue engineered replacement, with biochemical and biomechanical properties approaching those of native tissue, could provide a solution. This thesis investigates two components critical to the generation of a tissue engineered TMJ disc: 1) characterization of the native disc to identify a suitable animal model and create design parameters, and 2) development of approaches to use human embryonic stem cells (hESCs) in fibrocartilage tissue engineering. The first step to achieving this goal was to identify an animal model for the human TMJ disc based on quantitative biochemical and biomechanical properties. To this end, rabbit, goat, pig, cow, and human discs were analyzed, and the pig disc was shown to possess properties most similar to the human. The next step was to further characterize the pig TMJ, as many aspects of the joint were still poorly understood. Though the TMJ disc is anchored to the surrounding bony tissue on all sides by discal attachments...

‣ Virtual Dinosaurs - Developing Computer Aided Design and Computer Aided Engineering Modeling Methods for Vertebrate Paleontology; Virtuelle Dinosaurier - Entwicklung von Modellierungsmethoden für Computer Aided Design und Computer Aided Engineering für die Wirbeltierpaläontologie

Mallison, Heinrich
Fonte: Universität Tübingen Publicador: Universität Tübingen
Tipo: Dissertation; info:eu-repo/semantics/doctoralThesis
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The use of personal computers offers many benefits to researchers compared to conventional methods, not the least of them the easy visualization of three-dimensional (3D) structures. With rapidly increasing computing power, the last few decades have seen the rise of a large number of new applications for many purposes, some of which have been successfully employed for vertebrate paleontology. Here, a description is given on how to use several commercially available computer aided design (CAD) and kinetic/dynamic Computer Aided Engineering (CAE) modeling software programs as tools for paleontological research. The focus rests on the creation and use of 'virtual' bones, for biomechanical analyses and use in reconstruction of entire skeletons, the use of these 'virtual' skeletons as tools for the creation of 3D 'flesh' models, which are helpful in mass estimates, and finally on multi-body kinetic/dynamic modeling, using these 'flesh' models to analyze posture and gait of extinct dinosaurs. Specifically, the following techniques are described, most of which have been newly developed or significantly improved: - Mechanical digitizing of fossil bones using Rhinoceros 3.0® and NURBS curves - Mechanical digitizing of fossil bones using Rhinoceros 3.0® and point clouds - Mounting 'virtual' skeletons from either mechanically digitized bones or CT-based data - Creating 3D 'flesh' models from 'virtual' skeletons - Creating 3D 'flesh' models from laser scan point cloud data of mounted skeletons - Creating 3D 'flesh' models from silhouette drawings of skeletons - Evaluating the accuracy of 2D and 3D reconstructions using 'virtual' skeletons - Modeling posture...

‣ The impact of topical prostaglandin analogs on the biomechanical properties of the cornea in patients with open angle glaucoma

Meda, Roman
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Thèse ou Mémoire numérique / Electronic Thesis or Dissertation
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Justification: Le glaucome entraîne une perte progressive de la vision causée par la détérioration du nerf optique. Le glaucome est répandu dans le monde et cause la cécité dans environ sept millions de personnes. Le glaucome touche plus de 400 000 Canadiens et sa prévalence augmente avec le vieillissement de la population.1,2 Il s'agit d'une maladie chronique surnoise dont les symptômes se manifestent uniquement lors des stades avancés et qui peuvent mener à la cécité. Présentement, le seul moyen possible d’arrêter la progression du glaucome au stade initial est de diminuer la pression intra-oculaire (PIO). Les analogues de prostaglandines (APG) topiques sont fréquemment utilisées comme traitement de première ligne. Cependant, la recherche démontre que cette classe de médicaments peut changer certaines propriétés de la cornée, et possiblement influencer la mesure de la PIO.3 Objectif: À déterminer si l'utilisation d'APG affecte les propriétés biomécaniques de la cornée. La conclusion sera basée sur l'analyse intégrée des résultats obtenus de l'analyseur Reichert oculaire Réponse (ORA), la tonométrie par applanation de Goldmann (TAG) et la pachymétrie ultrasonographique. Le deuxième objectif potentiel de cette étude est de déterminer la corrélation...

‣ Silk-Fibroin/Methacrylated Gellan Gum Hydrogel as an novel scaffold for application in meniscus cell-based tissue engineering

Pereira, H.; Correia, Joana Silva; Yan, Leping; Caridade, S. G.; Frias, A. M.; Oliveira, A. L.; Mano, J. F.; Oliveira, Joaquim M.; Mendes, João Espregueira; Reis, R. L.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em /10/2013 Português
Relevância na Pesquisa
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Introduction: Knee meniscus injury is highly prevalent and there is a demand for new cost-effective treatment solutions. Tissue engineering (TE) and regenerative medicine strategies using acellular scaffolds are being used in clinical application for total or partial meniscus replacement [1]. Although this strategy has been considered as a safe and promising approach, progressive volume reduction of the implant and early failure have been described. Advances in the field of meniscus TE are required and greatly depend on increased knowledge of meniscus biology, improvement of biomaterials and cell-based therapies [2]. Advanced scaffolds for meniscus TE should possess adequate mechanics, biodegradability and biocompatibility, and also be able to mimic and preserve the asymmetric vascular network of this complex tissue, i.e. enable controlling the segmental vascularization during the regeneration process. Silk fibroin scaffolds derived from Bombyx mori cocoon have been recognized as a versatile biomaterial for application in meniscus TE [3]. The purpose of this study is to: 1) contribute to the knowledge of meniscus aiming future clinical applications (namely, the aspects dealing with the characterization of cellular phenotypes and density...

‣ Robust execution of bipedal walking tasks from biomechanical principles

Hofmann, Andreas G. (Andreas Gunther)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 406 p.
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Effective use of robots in unstructured environments requires that they have sufficient autonomy and agility to execute task-level commands successfully. A challenging example of such a robot is a bipedal walking machine. Such a robot should be able to walk to a particular location within a particular time, while observing foot placement constraints, and avoiding a fall, if this is physically possible. Although stable walking machines have been built, the problem of task-level control, where the tasks have stringent state-space and temporal requirements, and where significant disturbances may occur, has not been studied extensively. This thesis addresses this problem through three objectives. The first is to devise a plan specification where task requirements are expressed in a qualitative form that provides for execution flexibility. The second is to develop a task-level executive that accepts such a plan, and outputs a sequence of control actions that result in successful plan execution. The third is to provide this executive with disturbance handling ability. Development of such an executive is challenging because the biped is highly nonlinear and has limited actuation due to its limited base of support. We address these challenges with three key innovations.; (cont.) To address the nonlinearity...

‣ Investigating the role of calcium in the biomechanical response of neutrophils to mechanical deformation experienced in the pulmonary capillaries

Hsu, Jeffrey J
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 122 p.
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Neutrophils in the pulmonary microcirculation are subjected to mechanical deformation while traveling through capillaries of sizes much smaller than the mean neutrophil diameter. This deformation has been shown to result in significant reductions in both the shear storage and shear loss moduli of the cell, with subsequent recovery towards their initial values. Also, deformation above a threshold stimulus results in neutrophil activation, evidenced by pseudopod projection from the cell. These two events are thought to occur via independent pathways, yet little is known about the mechanosensing signaling involved. Other work has demonstrated that physiological deformation of neutrophils induces a marked increase in the levels of cytosolic calcium, suggesting that this occurrence may trigger the biomechanical response observed in the cell. The aim of this thesis was to elucidate the role of calcium in the neutrophil response to the mechanical deformation experienced during transit through the pulmonary capillaries.; (cont.) Chelating intracellular calcium in neutrophils resulted in (i) decreased deformability of the cells into a microchannel, (ii) attenuation of the drop in shear storage modulus (G') observed in untreated cells upon deformation...

‣ Biomechanical properties of engineered collagen scaffolds

Bonebreak, Christina M. (Christina Michelle)
Fonte: Massachusetts Institute of Technology Publicador: Massachusetts Institute of Technology
Tipo: Tese de Doutorado Formato: 35 leaves; 2188306 bytes; 2187505 bytes; application/pdf; application/pdf
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An experiment was performed to determine the effect of crosslinking on the stiffness of collagen scaffolds. Engineered non-crosslinked and dehydrothermally crosslinked chondroitin-6-sulfate collagen scaffolds were hydrated and loaded in tension, and their mechanical properties were compared. It was found that non-crosslinked scaffolds experience an average increase in weight after hydration of 10,353%, compared to 7,265% for crosslinked scaffolds. Hyperelastic material parameters were determined by the Arruda-Boyce eight-chain model, which was fit to the experimental data. This model predicted an average number of rigid links per collagen fiber of 1.3 and 1.21 for crosslinked and non-crosslinked scaffolds, respectively. Additionally, the collagen fiber densities were found to be 2.92 x 1017 for crosslinked networks and 1.68 x 1017 for non-crosslinked networks. These results can be applied to the changes that take place in the cervix at the onset of delivery. It is hypothesized that the crosslinking between collagen fibers in the cervix breaks down during preparation for delivery, allowing more fluid to enter the extracellular matrix and weaken the tissue. By performing tension tests on cervix tissue in vivo, one can produce a theoretical fit to predict relevant collagen network parameters...

‣ RESULTS OF A STUDY WITH THE GOAL TO OPTIMISE HARNESSES BY MEANS OF UP-TO-DATE BIOMECHANICAL ENGINEERING

Thomas, Bertels
Fonte: Myoelectric Symposium Publicador: Myoelectric Symposium
Tipo: Artigo de Revista Científica Formato: 280336 bytes; application/pdf
Publicado em //2002 Português
Relevância na Pesquisa
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Body harnesses control body-powered and hybrid prostheses of the upper extremities. They transfer muscular forces from the amputee through motion of the shoulder girdle or stump directly to the artificial limb. The development of body harnesses requires not only to look at technical possibilities, but even more important, to take the biomechanical abilities of the patient into consideration. Different tests were performed to identify typical motion patterns of the patients and to measure the forces produced thereby. Founded on the results of this biomechanical study and the comparison between different harnesses, a new above elbow body harness has been developed. It was ergonomically optimised to provide a more efficient force transmission. Modern materials and easily replaceable axillar pads complete the advantages and support today’s hygienic aspects. There are new accessories available allowing easy and fast adaptation of the harness to patient and prostheses without any need for sewing.