No description available.

[pt] Nesta tese foi desenvolvida uma metodologia para caracterização tridimensional de espumas de poliuretano (PU) produzidas a partir de polióis de origem vegetal. Espumas obtidas a partir do caule e da folha da bananeira foram analisadas. Foi utilizada a microtomografia computarizada de raios x (μCT) associada a ensaios mecânicos in-situ e processamento e análise digital de imagens (PADI). Utilizou-se uma câmara de ensaios in-situ comercial e também foi desenvolvida uma câmara específica para esta tese. As imagens tridimensionais obtidas foram avaliadas por técnicas tradicionais de ADI e pela técnica de Correlação Volumétrica de Imagens (DVC). A sequência padrão envolveu a redução de ruídos e o método de watersheds para segmentar as células individuais que formam a estrutura das espumas. Assim, foi possível quantificar diferentes parâmetros de tamanho (volume, diâmetro médio) e forma (razão de aspectos, esfericidade) de cada célula em 3D e comparar estatisticamente as amostras. A técnica de DVC permitiu correlacionar sub volumes das espumas em diferentes estágios do processo de compressão, revelando alguns aspectos do mecanismo microscópico de concentração de tensões. Um ensaio de compressão tradicional permitiu escolher as duas amostras com maiores limites de resistência (CB8 e FB6). Estas amostras foram submetidas ao ensaio de compressão in-situ e analisadas para diferentes valores de deformação. A amostra FB6 apresentou cerca de 5 vezes mais células do que a amostra CB8, com diâmetro médio cerca de 2X menor. Considerando os primeiros estágios de deformação (0, 0,5 e 1 mm), que foram idênticos para as duas amostras, o número de células aumentou 5,9 porcento para CB8 e 1,7 porcento para FB6, enquanto o volume médio diminuiu 2,6 porcento e 1,9 porcento, respectivamente. As medidas de forma apontaram para células não equiaxiais (razão de aspectos e esfericidade próximos a 0,4), sem mudanças expressivas ao longo dos ensaios. / [en] In this thesis, a methodology was developed for the three-dimensional characterization of polyurethane (PU) foams produced from polyols of vegetable origin. Foams obtained from the banana stem and leaf were analyzed. X ray microtomography (μCT) associated with in-situ mechanical tests and digital image processing and analysis (PADI) was used. A commercial in situ test chamber was used and a specific chamber was also developed for this thesis. The three-dimensional images obtained were evaluated by traditional ADI techniques and by the Volumetric Image Correlation (CVD) technique. The standard sequence involved noise reduction and the watersheds method to segment the individual cells that make up the foam structure. Thus, it was possible to quantify different parameters of size (volume, average diameter) and shape (aspect ratio, sphericity) of each cell in 3D and to statistically compare the samples. The CVD technique made it possible to correlate subvolumes of the foams at different stages of the compression process, revealing some aspects of the microscopic stress concentration mechanism. A traditional compression test made it possible to choose the two samples with the highest strength limits (CB8 and FB6). These samples were submitted to the compression test in situ and analyzed for different strain values. The FB6 sample had about 5 times more cells than the CB8 sample, with an average diameter about 2X smaller. Considering the first deformation stages (0, 0,5 and 1 mm), which were identical for both samples, the number of cells increased 5,9 percent for CB8 and 1,7 percent for FB6, while the average volume decreased 2,6 percent and 1,9 percent, respectively. The shape measurements pointed to non-equiaxial cells (aspect ratio and sphericity close to 0,4), with no significant changes during the tests.

Carbon fabric-reinforced polymer (CFRP) composites are widely used in aerospace, automotive and construction structures thanks to their high specific strength and stiffness. They can also be used in various products in sports industry. Such products can be exposed to different in-service conditions such as large bending deformations caused by quasi-static and dynamic loading. Composite materials subjected to such bending loads can demonstrate various damage modes - matrix cracking, delamination and, ultimately, fabric fracture. Damage evolution in composites affects both their in-service properties and performance that can deteriorate with time. Such damage modes need adequate means of analysis and investigation, the major approaches being experimental characterisation and numerical simulations. This work deals with a deformation behaviour and damage in carbon fabric-reinforced polymer (CFRP) laminates caused by quasi-static and dynamic bending. Experimental tests are carried out first to characterise the behaviour of a CFRP material under tension, in-plane shear and large-deflection bending in quasi-static conditions. The dynamic behaviour of these materials under large-deflection bending is characterised by Izod-type impact tests employing a pendulum-type impactor. A series of impact tests is performed on the material at various impact energy levels up to its fracture, to obtain a transient response of the woven CFRP laminate. Microstructural examination of damage is carried out by optical microscopy and X-ray micro computed tomography (Micro-CT). The damage analysis revealed that through thickness matrix cracking, inter-ply delaminations, intra-ply delamination such as tow debonding, and fabric fracture was the prominent damage modes. These mechanical tests and microstructural studies are accompanied by advanced numerical models developed in a commercial code Abaqus. Among those models are (i) 2D FE models to simulate experimentally observed inter-ply delamination, intra-ply fabric fracture and their subsequent interaction under quasi-static bending conditions and (ii) 3D FE models based on multi-body dynamics used to analyse interacting damage mechanisms in CFRP under large-deflection dynamic bending conditions. In these models, multiple layers of bilinear cohesive-zone elements are placed at the damage locations identified in the Micro CT study. Initiation and progression of inter-laminar delamination and intra-laminar ply fracture are studied by employing cohesive elements. Stress-based criteria are used for damage initiation while fracture-mechanics techniques are employed to capture its progression in composite laminates. The developed numerical models are capable to simulate the studied damage mechanisms as well as their subsequent interaction observed in the tests and microstructural damage analysis. In this study, a novel damage modelling technique based on the cohesive-zone method is proposed for analysis of interaction of various damage modes, which is more efficient than the continuum damage mechanics approach for coupling between failure modes. It was observed that the damage formation in the specimens was from the front to the back at the impact location in the large-deflection impact tests, unlike the back-to-front one in drop-weight tests. The obtained results of simulations showed a good agreement with experimental data, thus demonstrating that the proposed methodology can be used for simulations of discrete damage mechanisms and their interaction during the ultimate fracture of composites in bending. The main outcome of this thesis is a comprehensive experimental and numerical analysis of the deformation and fracture behaviours of CFRP composites under large-deflection bending caused by quasi-static and dynamic loadings. Recommendations on further research developments are also suggested.

Die Struktur des Knochenmaterials wird während des gesamten Lebens durch dynamische Prozessen verändert. Diese sind der Umbauprozess, bei dem existierendes Material entfernt und durch neues, vorerst weiches ersetzt wird. In dieses weiche Material wird im sog. Mineralisierungsprozess Mineral eingelagert und somit die Steifigkeit erhöht. Diese zwei Prozesse führen zu einem heterogenen Knochenmaterial. Das komplexe Zusammenspiel kann durch Knochenkrankheiten beeinflusst werden und zu einem mechanischen Versagen des Materials führen. Wie viel Einfluss dabei allein dem Umbauprozess und dem Mineralisierungsprozess zuzuschreiben sind, konnte bislang nicht geklärt werden. An diese Fragestellungen wird in der vorliegenden Dissertation mit physikalischen und numerischen Methoden herangegangen. Das heterogene Material ist das Ergebnis des Mineralisierungs- und Umbauprozesses und wird abkürzend BMDD (für bone mineralization density distribution) genannt, die für alle gesunden Menschen gleich ist und bei Knochenkrankheiten davon abweicht. Mittels Modellierung wird eine Störung in der Mineralisierung simuliert, die zu Verschiebungen in der BMDD führt. Diese Verschiebungen können verglichen werden mit einem veränderten Umbauprozess. Der unterschiedliche Einfluss der beiden Prozesse liegt im zeitlichen Verlauf. Die Mineralisierungskinetik im Knochen konnte durch die neuartige Auswertung von 3D in vivo micro-CT-Bildern von Mäusen erstmals quantifiziert werden. Die Auswertung bestätigte, die schnellere Mineralisierung im neugeformten und die langsamere in bereits vorhandenem Knochen. Wie der Umbauprozess im kompakten Knochen gesteuert sein kann, wurde mittels Anordnungsmechanismen der Osteone beschrieben. Für einen solchen Knochenbaustein war es verboten innerhalb einer definierten Zone eines anderen Bausteins gebildet zu werden. Diese Zone ließ sich am besten durch einen normalverteilten Radius, mit einer dazugehörigen Variabilität beschreiben. / The structure of the bone material is continuously changed during the life by dynamic processes. These are the remodeling process during which the existing material is replaced by new, initially soft material. In this soft material mineral is incorporated during the so called mineralization process, thus increasing the stiffness. These two processes lead to a heterogeneous bone material. Their interplay can be perturbed by bone diseases, which can lead to material failure. It remains unclear to which degree each of these two processes contributes during diseases. Yet, while the remodeling process is known to be mechanically controlled, it is unclear how mechanical stimuli affect the mineralization process. The heterogeneous mineral distribution in trabecular bone is the result of the complex interplay between the mineralization and the remodeling process and is called bone mineralization density distribution (BMDD). The BMDD is similar for all healthy adult humans. A deviation from this healthy distribution is indicative of bone diseases. With a mathematical model the influence of changed mineralization kinetics on the BMDD is investigated and compared to a remodeling change. The different influences lie in the time development. With a novel 3D analysis of in vivo micro-CT of the vertebra in a mouse tail the mineralization kinetics could be quantified for the first time. It could be e.g. shown that the bone is demineralized before it is completely resorbed. An algorithm was developed to understand how the remodeling process can be regulated. The arrangement of the building blocks could be described when such a block could only be placed within a defined zone of another building block. This zone could be best quantified when its radius was normally distributed with a corresponding standard deviation.

Os testes utilizados rotineiramente na avaliação de danos mecânicos, danos causados por insetos e danos por deterioração de tecidos em sementes de soja e de milho são destrutivos, impossibilitando a associação dos resultados obtidos com os testes fisiológicos (germinação e vigor). Dessa forma, a avaliação da qualidade de sementes por meio de análise de imagens tem despertado interesse da pesquisa, devido ao fato de serem técnicas rápidas e não destrutivas, permitindo tal associação. Dentre as técnicas de análise de imagens existentes, as técnicas de microtomografia computadorizada de raios X (micro-TC) e imagem por ressonância magnética (IRM) tem se mostrado promissoras na pesquisa com sementes, por gerarem imagens tridimensionais, que permitem verificar, com precisão, a localização dos danos internos nas sementes. Assim, o objetivo deste trabalho foi utilizar as técnicas de micro-TC e IRM para avaliar danos internos em sementes de milho e de soja, verificar suas relações com a germinação e compará-las a técnica de raios X, que vem sendo utilizada na pesquisa com sementes. Para tanto foram selecionadas previamente, 32 sementes de soja e 30 sementes de milho, que foram submetidas aos testes de raios X, micro-TC e IRM, para obtenção das imagens e, posteriormente, ao teste de germinação, para associar os resultados obtidos com o desempenho das sementes. Pode-se concluir para as sementes de soja que as três técnicas se mostraram eficientes na detecção de danos nas sementes. Por outro lado, para as sementes de milho, pode-se haver necessidade de utilização das técnicas de micro-TC e IRM para avaliar, com maior precisão, a morfologia interna das sementes. / The current tests used in the evaluation of mechanical, insect, and tissue damage in soybean and corn seeds are destructive, making it impossible to associate those with the results obtained with physiological tests (germination and vigor).Therefore, evaluation of the seed quality by imaging analysis techniques aroused interest in seed research for being fast and non-destructive techniques, allowing association with physiological tests. X-ray computerized microtomography (micro-CT) and magnetic resonance imaging (MRI) seem promising techniques due to the fact they generate three-dimensional imagens allowing more accurately evaluation of the seed\'s internal morphology. The objective of this study was to use the micro-CT and MRI techniques to evaluate internal morphology of soybean and corn seeds, correlate their relationship with the physiological test (germination test) and to compare them with the X-ray technique, which has been used in seed research. For that 32 soybena seeds and 30 corn seeds were selected. Seeds were tested with X-ray, micro-CT, MRI, to obtain the images. Then germination test was conducted to associate the results obtained with the performance of the seeds. Overall, the three techniques were efficient in detecting damage in soybean seeds. On the other hand for corn, it may be necessary to use the micro-CT and MRI techniques to evaluate more accurately the internal morphology of the seeds.

A new model of a critically-sized segmental femoral bone defect in rats was developed to enable in vivo imaging and facilitate post-mortem mechanical testing of samples. The critically-sized nature of the model was assessed and confirmed. The efficacy of sustained co-delivery of osteogenic (BMP-2 and TGF- Ò3) and angiogenic (VEGF) growth factors in promoting functional bone repair was assessed. Effects of scaffold modification in terms of geometry and composition were evaluated. The results indicated that co-delivery of BMP-2 and TGF- Ò3 resulted in a dose-dependent improvement in functional bone repair. Modification of the polylactide scaffold to include an absorbable ceramic component and a cored out geometry enhanced rate of union. Addition of VEGF to the scaffold treatment did not significantly impact revascularization of the defect site or functional repair of the bone defect. These data demonstrate that the complex environment of an acute bone defect requires different treatment strategies than simple ectopic models would suggest. A positive predictive correlation between bone repair parameters measured in vivo and mechanical functionality was established. The novel defect model demonstrated robustness and reproducibility. Implications for further research are discussed.

Das Ziel der hier durchgeführten Studie war es, die Möglichkeiten der zerstörungsfreien Untersuchungsmethode, 3-D-Röntgenmikrotomographie, bei der Bewertung von Wurzelkanalfüllungen anhand der modifizierten lateralen Kondensation, der lateralen Kondensation und bei Thermafil zu untersuchen. Es sollte gezeigt werden, dass die einzelnen Bestandteile der Wurzelkanalfüllung zu differenzieren und im Anschluss auch zu quantifizieren sind. Die ersten 21 mit dieser zerstörungsfreien Methode untersuchten Proben wurden im Anschluss nochmals mit einer klassischen Untersuchungsmethode, der Lichtmikroskopie, beurteilt. Die hier erzielten Ergebnisse wurden bei einem Methodenvergleich mit den Ergebnissen der 3-D-Röntgenmikrotomographie verglichen und auf eine mögliche Korrelation überprüft. Ziel war es zu überprüfen, ob verschiedene Methoden zur Qualitätsprüfung von Wurzelkanalfüllungen als gleichwertig angenommen werden können. Im Rahmen dieser Untersuchung wurde eine neue modifizierte laterale Kondensation eingeführt, die hinsichtlich ihrer Qualität anhand der bereits genannten Parameter mit zwei bereits eingeführten Wurzelkanalfüllmethoden verglichen werden sollte. Die 3-D-Röntgenmikrotomographie ermöglichte eine selektive Darstellung der einzelnen Komponenten in 400 bis 750 Ebenen, welche ebenfalls quantifizierbar waren. Es wurden Füllgrade zwischen 71 % und 92 % erzielt. Das Thermafil-System schien den auf lateraler Kondensation basierenden Systemen bezüglich der bestimmten Volumen vereinzelt signifikant überlegen. Bei der lichtmikroskopischen Auswertung ergaben sich diesbezüglich ähnliche Ergebnisse. Die Farbstoffpenetrationstiefen zeigten weder tendenzielle noch signifikante Unterschiede zwischen den einzelnen Fülltechniken. Beim Vergleich der Methoden zur Bewertung der Obturation bezüglich der erhobenen Volumen konnte keine Korrelation nachgewiesen werden. Auch beim Vergleich der Farbstoffpenetrationstiefen und der bestimmten Volumen bei der 3-D-Röntgenmikrotomographie konnten keine Korrelationen ermittelt werden. Unter Berücksichtigung der Grenzen dieser Untersuchung lässt sich festhalten, dass die Methode der 3-D-Röntgenmikrotomographie zur Bewertung und zum Vergleich von Wurzelkanalfüllungen geeignet ist. Die Ergebnisse korrelieren jedoch nicht mit denen der Lichtmikroskopie.

No description available.

Depuis une dizaine d’années, l’essor des minivis d’ancrage orthodontique a été grandissant jusqu’à devenir, aujourd’hui, un outil incontournable dans l’arsenal thérapeutique de l’orthodontiste. Très peu d’études ont été publiées quant à la nature de la réponse tissulaire face à l’insertion et la mise en charge de ces minivis. De plus, une partie des patients concernés par l’orthodontie étant des adolescents, il serait intéressant de savoir si le tissu osseux en croissance est propice à l’utilisation de ces dispositifs. L’influence de la nature du matériau sur cette réaction tissulaire reste également à définir. L’objectif de cette étude a été d’évaluer la biointégration de deux systèmes de minivis orthodontiques présents sur le marché, l’un en acier chirurgical et l’autre en titane-aluminium-vanadium, en conduisant une analyse clinique, histomorphométrique et microtomographique chez le porc en croissance. Les résultats ont montré que la réponse osseuse se caractérise, dans un os en croissance peu compact, par un épaississement des travées osseuses au contact des dispositifs, probablement pour résister à la contrainte locale. Le tissu osseux en croissance permet la biointégration des minivis d’ancrage orthodontique, mais le taux de succès relativement faible observé implique l’adaptation des protocoles cliniques par une analyse préalable du ratio os trabéculaire/os cortical, une augmentation du délai avant mise en charge, et l’application de forces légères. La réponse tissulaire est similaire, quel que soit le système étudié. L’acier chirurgical, grandement utilisé en orthopédie, présente donc un intérêt en orthopédie dento-faciale, dans une indication temporaire / The miniscrew implants are increasingly used over the last decade in orthodontics and gradually replacing the use of extraoral forces because of their greater efficiency and because their effectiveness is not subject to patient compliance. Few studies seeking to understand the response to orthodontic anchorage devices at bone-tissue interface have been published over the last ten years. Despite the large use of miniscrews in teenagers, very few have included young subjects in their protocol. Furthermore, despite the use of stainless steel miniscrew implants, no studies have investigated biointegration of such devices. The aim of the present study was to evaluate tissue response to immediately loaded miniscrew implants (of Ti6Al4V and of stainless steel) in growing pigs in order to answer to the following questions: Is it possible to implant and load miniscrew implants in a growing bone? Does stainless steel devices present the same biointegration than titanium devices? A clinical evaluation, and histomorphometrical and micro-CT analyses were performed. Results showed that the growing bone seems compatible with the orthodontic anchorage. In the growing pig with low bone density areas, the trabecular thickness increase appears as the bone response to withstand the local strains induced by loaded orthodontic miniscrews. Stainless steel devices presented similar behavior to the Ti6Al4V devices in pigs. This study showed the possibility to place stainless steel miniscrew implants for orthodontic anchorage in growing models

In human pregnancy, the feto-placental vessels are crucial for efficient materno-fetal transfer; hence they play a pivotal role in the pathogenesis of fetal growth restriction (FGR). We, as well as other research groups, have observed abnormalities in the FGR feto-placental vasculature, which, though inconclusive, were suggestive of a state of panhypovascularity. The goal of the work presented in this thesis was to investigate this. We hypothesised that the placenta may be panhypovascular in FGR due to failed angiogenesis; and enhancing angiogenesis in the placenta may improve fetal growth. Custom-designed techniques including advanced imaging, computer-aided analyses and tube-forming experiments were employed to compare feto-placental vessels and endothelial cells in placentas from normal and FGR-complicated pregnancies while aiming to answer two main research questions: (i) is the FGR placenta panhypovascular? (ii) can angiogenesis be induced or enhanced to improve placental vascularity?Findings include: (i) shorter arterial [p = 0.03 and 0.009 when data adjusted for placental surface area (PA) and weight (PW) respectively] and longer venous path [p = 0.05 and 0.03, adjusted for PA and PW respectively] in FGR placentas though no difference in the total number of arterial or venous branches, diameter, and tortuosity of the vessels compared to normal; (ii) altered angiogenic behaviour/response of FGR placental endothelial cells following in vitro pharmacological manipulation of WNT signalling; (iii) human placental endothelial cells are capable of regaining their angiogenic potential following withdrawal of WNT inhibition. These findings discount the hypothesis of panhypovascularity in FGR placentas, but identify additional, previously unreported, feto-placental vascular abnormalities associated with FGR. Also, the findings provide evidence that impairment of WNT signalling may play a role in defective angiogenesis and consequent dysvascularity in the FGR placenta. The evidence suggests the WNT pathway should be explored as a potential new target for therapeutic interventions to correct placental dysvascularity in FGR.