The research presented in this study has been conducted in an effort to aid in the creation of a biomimetic shell that may be employed in full-scale field experiments to determine the efficacy of mitigation options to limit loggerhead mortality in boat strike incidents. The objectives of this research include the development of experimental testing procedures for the material characterization of the loggerhead carapace, and the design, fabrication, and evaluation of an artificial prototype carapace. A photographic database of wounded sea turtles in Georgia was evaluated in order to determine the primary sources of loggerhead collision injuries and the most common regions of the carapace damaged in boat strike incidents. Skeg impact was found to be the most common source of injury, with a frequency of 44%. In addition, 74% of the sea turtles reviewed sustained injuries to the center third of their carapace length, indicating this region as the most probable impact location. Material testing procedures were developed for evaluating the material properties of the loggerhead carapace. This was followed by the material testing of three loggerhead shells for the purpose of determining localized mechanical properties. Samples were harvested from the shells in a manner designed to identify potential variations in properties due the location and orientation of the coupons within the carapace. Each coupon was subjected to axial tension or three-point bending. Specialized tabs were designed for tension testing in order to accommodate the coupon's irregular geometry and minimize curvature-induced moments. The tensile test results indicated that the longitudinal and transverse properties of the loggerhead carapace were similar. The tensile strength, elongation at failure, and modulus of elasticity were determined to have percent variations of 12.2%, 10.7%, and 10.1% respectively. In contrast, the three-point bending test results indicated that the modulus of rupture and flexural modulus for the transverse samples were approximately four times greater than those of the longitudinal samples. This variation may be attributed to regions of weak tissue running transversely through the carapace. The results of the material testing were utilized in the design of two prototype composite shells. The prototypes were successful in simulating the strain at failure and force per unit width to within 10% of the loggerhead carapace. The resulting procedure may be used to create artificial shells suitable for prototype scale tests in natural environments. In addition, the material testing methods developed for this investigation may offer insight into procedures for evaluating alternate forms of rigid or curved biological specimens.

Recombinant synthesis of elastin-mimetic proteins has been employed for several decades, however, long-term biocompatibility and biostability of such proteins was not fully defined. We present virtually crosslinked elastin-mimetic proteins which exhibit exceptional biocompatibility and long-term biostability over a period of at least seven months. This report is the first evidence of a non-chemically or ionically crosslinked system that exhibits long-term in vivo stability. Although, physically crosslinked protein-based materials possess a number of advantages over their chemically crosslinked counterparts, physical crosslinks and the related domains so formed may be deformed or damaged at applied stresses lower than those required to disrupt covalent crosslinks. In this regard, we have synthesized a new class of recombinant elastin-mimetic triblock copolymer capable of both physical and chemical crosslinking. We have demonstrated that chemical crosslinking provides an independent mechanism for control of protein mechanical responses. Specifically, elastic modulus was enhanced and creep strain reduced through the addition of chemical crosslinking sites. A number of reports have described the design of synthetic genes, which encode elastin-like proteins for bacterial expression in Escherichia coli. Although advantages with this expression system exist, significant limitations including the lack of eukaryotic post-translational systems, the tendency to sequester mammalian proteins into inclusion bodies, difficult purification protocols, and endotoxin contamination have been noted. We demonstrate the expression of a recombinant elastin-mimetic protein from P. pastoris. A novel synthetic strategy, monomer library concatamerization, was utilized in designing non-repetitive elastin genes for highly repetitive protein sequences. It is likely that this strategy will be useful for creating large, repetitive genes for a variety of expression systems in order to more closely approach the genetic diversity inherent to native DNA sequences. All told, elastin-based protein polymers are a promising class of material characterized by high degree of biocompatibility, excellent biostability, and a tunable range of mechanical properties from plastic to elastic. A variety of options facilitate the processing of these biopolymers into chemically crosslinked or non-crosslinked gels, films, or nanofibers for any of a number of implant applications including structural components of artificial organs and engineered living tissues, carriers for controlled drug release, or biocompatible surface coatings.

New 3D multi-scale modeling approaches for the structural analysis of native and prosthetic Aortic Valves (AV) are investigated. Three different nonlinear hyperelastic constitutive material models for the mechanical behavior of the AV tissue are introduced. The first is the well-known Holzapfel hyperelastic, anisotropic and homogeneous model. The second model, termed the Collagen Fiber Network (CFN), is a heterogeneous model that recognizes the hyperelastic collagen and elastin layers using different layered finite elements. The third hyperelastic model is implemented using a new nonlinear micromechanical formulation of the High Fidelity Generalized Method of Cells (HFGMC) originally proposed by Aboudi. The latter two material models are heterogeneous and explicitly recognize the in-situ tissue constituents. Initially, a full scale 3D structural model of a polymeric-based prosthetic AV model is studied. This model is verified using deformation metrics obtained from images taken with high speed cameras during in-vitro experiments. The predictions from the proposed polymeric AV model are in good agreement with the test data. Next, the three tissue material models are examined in their ability to predict the anisotropic material behavior of porcine AV leaflet tissue. The Holzapfel model is calibrated from the overall anisotropic uni- and biaxial stress-strain data while the in-situ elastin and collagen constituents in the CFN and HFGMC models are calibrated to match the overall effective responses. Dynamic structural analysis is performed for the porcine AV with applied transvalvular pressure measured from repeated in-vitro tests conducted in this study. Principal stretches are computed from the experimental measurements and compared with the AV material-structural predictions. The proposed multi-scale modeling approach for the native AV is capable of predicting the structural behavior during the entire cardiac cycle without suffering from numerical convergence problems. Finally, new nonlinear micromechanical formulations based on the HFGMC method are developed and applied for various types of tissue materials including the human arterial wall layers and porcine AV leaflets. The proposed hyperelastic HFGMC model is compared to the CFN model and the Holzapfel models. It is shown that the HFGMC is an effective modeling approach for the arteries especially when the collagen fiber network has a periodic microstructure.

The electrical stimulation of appropriate components of the human visual system can result in the perception of blobs of light (or phosphenes) in totally blind patients. By stimulating an array of closely aligned electrodes it is possible for a patient to perceive very low-resolution images from spatially aligned phosphenes. Using this approach, a number of international research groups are working toward developing multiple electrode systems (called Artificial Human Vision (AHV) systems or visual prostheses) to provide a phosphene-based substitute for normal human vision. Despite the great promise, there are currently a number of constraints with current AHV systems. These include limitations in the number of electrodes which can be implanted and the perceived spatial layout and display frequency of phosphenes. Therefore the development of computer vision techniques that can maximise the visualisation value of the limited number of phosphenes would be useful in compensating for these constraints. The lack of an objective method for comparing different AHV system displays, in addition to comparing AHV systems and other blind mobility aids (such as the long cane), has been a significant problem for AHV researchers. Finally, AHV research in Australia and many other countries relies strongly on theoretical models and animal experimentation due to the difficult of prototype human trials. Because of this constraint the experiments conducted in this thesis were limited to simulated AHV devices with normally sighted research participants and the true impact on blind people can only be regarded as approximated. In light of these constraints, this thesis has two general aims. The first aim is to investigate, evaluate and develop effective techniques for mobility assessment which will allow the objective comparison of different AHV system phosphene presentation methods. The second aim is to develop a useful display framework to guide the development of AHV information presentation, and use this framework to guide the development of an AHV simulation device. The first research contribution resulting from this work is a conceptual framework based on literature reviews of blind and low vision mobility, AHV technology, and computer vision. This framework incorporates a comprehensive number of factors which affect the effectiveness of information presentation in an AHV system. Experiments reported in this thesis have investigated a number of these factors using simulated AHV with human participants. It has been found that higher spatial resolution is associated with accurate walking (reduced veering), whereas higher display rate is associated with faster walking speeds. In this way it has been demonstrated that the conceptual framework supports and guides the development of an adaptive AHV system, with the dynamic adjustment of display properties in real-time. The second research contribution addresses mobility assessment which has been identified as an important issue in the AHV literature. This thesis presents the adaptation of a mobility assessment method from the blind and low vision literature to measure simulated AHV mobility performance using real-time computer based analysis. This method of mobility assessment (based on parameters for walking speed, obstacle contacts and veering) is demonstrated experimentally in two different indoor mobility courses. These experiments involved sixty-five participants wearing a head-mounted simulation device. The final research contribution in this thesis is the development and evaluation of an original real-time looming obstacle detector, based on coarse optical flow, and implemented on a Windows PocketPC based Personal Digital Assistant (PDA) using a CF card camera. PDA based processors are a preferred main processing platform for AHV systems due to their small size, light weight and ease of software development. However, PDA devices are currently constrained by restricted random access memory, lack of a floating point unit and slow internal bus speeds. Therefore any real-time software needs to maximise the use of integer calculations and minimise memory usage. This contribution was significant as the resulting device provided a selection of experimental results and subjective opinions.

Diss. (sammanfattning) Stockholm : Karolinska institutet, 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Umeå : Univ., 2005. / Härtill 4 uppsatser.

Diss. (sammanfattning) Linköping : Linköpings universitet, 2006. / Härtill 6 uppsatser.

Thesis (M.S.)--Mississippi State University. Department of Agricultural and Biological Engineering. / Title from title screen. Includes bibliographical references.

O pericárdio bovino é um tecido biológico utilizado na fabricação de vários produtos para a saúde e também em válvulas cardíacas desde o início da década de setenta, porém, ainda requer estudos mais aprofundados no que diz respeito às mudanças que os tratamentos químicos utilizados para confecção das válvulas ocasionam. Atualmente a engenharia de tecidos estuda a descelularização do pericárdio bovino como um processo para retirar os componentes celulares, mantendo intacta a matriz extracelular (MEC), preservando a integridade do colágeno e também pode atuar como anticalcificante. Porém, é necessário saber qual o impacto que o tratamento químico trará nas propriedades mecânicas do tecido, como tensão máxima, deformação específica e alongamento. Nos trabalhos observados, os testes mecânicos realizados nos pericárdios bovinos descelularizados foram feitos no tecido sem serem submetidos a uma pré-tensão, a qual é necessária na maioria das vezes, para formação das cúspides durante a confecção das válvulas cardíacas ou outro dispositivo médico. Por essa razão, foi realizado um estudo do efeito na propriedade mecânica que uma determinada pressão exerce sobre o pericárdio bovino, que passou pelo processo de descelularização. Em paralelo também foi feito uma avaliação histológica do tecido para verificar a ausência de células e a preservação das fibras de colágeno no tecido descelularizado. Foram preparados quatro grupos diferentes para a realização dos testes. O grupo I chamado de grupo controle. O grupo II, onde os pericárdios foram descelularizados com o método PUC I. O grupo III foi tratado como o grupo I, porém sob pressão de 240 mmHg. Já o grupo IV, os pericárdios foram descelularizados e em seguida submetidos à mesma pressão utilizando solução de glutaraldeído 0,2% e 0,5%. Após os tratamentos dos grupos, todas as amostras foram tingidas em solução de azul de metileno 0,03% para melhor visualização das fibras do tecido. Em seguida os tecidos foram cortados a laser para obtenção dos corpos de prova e submetidos ao ensaio de tração. Obteve-se a partir do ensaio, a tensão máxima das amostras, a deformação específica e o alongamento na ruptura. Foi observado que nos grupos onde foram submetidos à pressão tiveram uma tensão máxima menor do que os grupos sem pressão e um maior alongamento. Verificou-se que o efeito da pressão diminuiu a espessura dos tecidos. O processo de descelularização se mostrou eficaz uma vez que foi demonstrada a ausência de células e a preservação das fibras de colágeno após técnica utilizada. / The pericardium is a biological tissue used in the manufacture of various products for medical advices and manufacture of heart valves since the early seventies, however, it still requires further study with regard to the changes that the chemical treatments used to manufacture the valves cause. Several studies show that the tissue often undergoes a process of calcification generated by mechanical stress of opening and closing of the leaflets, damaging the hydrodynamics making valvular replacement necessary. Currently tissue engineering study decellularization process of the bovine pericardium to remove cellular components while preserving the extracellular the matrix (ECM), preserving the integrity of collagen it and can also act as anti-calcification. However, one must know the impact that chemical treatment will bring on the mechanical properties of the tissue, such as tensile strength, strain and elongation percentage. In examined studies, the mechanical tests performed on bovine pericardium decellularized tissue was made without being subjected to a pre-tension which is necessary in most cases for formation of the leaflets during the manufacturing of heart valves. For this reason, a study of the effect on mechanical property that a certain pressure exerts on the pericardium, which passed the decellularization process was made. In parallel it was also made a histological evaluation of the tissue to verify the absence of cells and preservation of collagen fibers in decellularized tissue. Four different groups were prepared for test. The group I was called a control group. In group II, the pericardia were decellularized with the PUC method I. Group III was treated as group I, but under pressure of 240 mmHg. The group IV, the pericardia were decellularized and then subjected to pressure using glutaraldehyde 0.2% and 0.5%. After treatment of the groups, all samples were stained in a solution of blue methylene 0.03% for better visualization of the fibers of the tissue. Then the tissues were cut by laser to obtain the specimens and subjected to tensile test. It was obtained from the test, the tensile strength of the samples, the strain and elongation percentage at break. It is observed that the groups which underwent pressure had a lower tensile strength than those without pressure and on the other hand showed a greater elongation percentage. Thus, it can be verified that the effect of the pressure decreased the thickness of the tissues. The decellularization process has show efficient since it has demonstrated the absence of cells and preservation of collagen fibers after technique.

Made available in DSpace on 2014-06-11T19:28:55Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-03-22Bitstream added on 2014-06-13T19:16:51Z : No. of bitstreams: 1 haneda_ig_me_arafo.pdf: 7045744 bytes, checksum: ddacde6ea8ff0160e149c1f3eaf1e2ce (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / O reparo de restaurações metalocerâmicas fraturadas pode ser considerado um desafio, principalmente quando grande quantidade de metal é exposta. O estabelecimento de uma união forte e durável entre material reparador e substrato da restauração fraturada é essencial para o sucesso do reparo. Este estudo avaliou a resistência ao cisalhamento entre diferentes sistemas de reparo e liga de NiCr e a durabilidade desta união após armazenamento em água por um longo período. Foram confeccionados 100 discos (9 OE 3 mm) em liga de NiCr. Esses foram incluídos em anel de PVC com resina acrílica e tiveram suas superfícies regularizadas com lixas (120, 220 e 320) em politriz. Cada espécime recebeu um dos seguintes tratamentos: 1) Clearfil SE Bond, 2)Bistite II DC, 3)Cojet, 4) Scotchbond Multi Uso Plus (Grupo controle), e 5) uma variação do Grupo controle, na qual foram empregadas partículas de sílica do sistema Cojet Sand em substituição às de óxido de alumínio. Os espécimes foram armazenados água destilada a 37ºC por 24 horas, termociclados (1.000 ciclos - 5º e 55ºC) e, então, armazenados nas mesmas condições descritas anteriormente, por um período adicional de 24 horas ou 6 meses. O ensaio de cisalhamento foi realizado em máquina de ensaios Material Test System 810 com velocidade de 0,5 mm/minuto. Para cada período de armazenamento, os resultados foram analisados por meio de análise de variância (ANOVA) e teste de Tukey. Para cada sistema, os valores obtidos às 24 horas foram comparados aos encontrados após 6 meses empregando-se teste t de Student não pareado. / When clinical fractures of metal-ceramic prostheses occur, exposing the metal substructure, repair may be considered a challenge. The clinical success of repair depends on establishing a strong and long-term durable bond between the repair material and the metal surface of the failed restoration. This study evaluated shear bond strength of different repair systems to NiCr alloy and bond durability after long-term water storage. One hundred cylindrical specimens (9 OE 3 mm) were fabricated in a nickel-chromium alloy. The NiCr cylinders were embedded in a PVC ring and all specimen bonding surfaces were smoothed with silicon carbide papers (120, 220, and 320 grit) using a polisher. Specimens were divided into 5 groups of 20, which received one of the following bonding and resin composite repair systems (n=10): 1) Clearfil SE Bond/Clearfil AP-X, 2) Bistite II DC/Palfique, 3) Cojet /Z100, 4) Scotchbond Multipurpose Plus /Z100 (control group), and 5) Cojet Sand plus Scotchbond Multipurpose Plus /Z100. The specimens were stored in distilled water for 24 hours at 37ºC, thermal cycled (1,000 cycles - 5º to 55ºC) and stored in distilled water at 37ºC for either 24 hours or 6 months. Shear bond tests were performed in a mechanical testing machine with a crosshead speed of 0.5 mm/minute. Data (MPa) were analyzed using 1-way ANOVA and Tukey HSD test (a=.05) for each storage time. The results obtained at 24 hours for each repair system were compared with those found at 6 months using Student's t-test. Each specimen was examined under a stereoscopic lens with OE30 magnification, and mode of failure was classified as adhesive, cohesive or combination. (Complete abstract, click electronic access below)