O presente estudo foi realizado para investigar a relação entre forças hemodinâmicas locais e remodelamento intimal e medial nos segmentos pré-estenose e pós-estenose da parede da aorta abdominal de ratos submetidos à estenose acentuada. Foram utilizados ratos Wistar machos divididos em dois grupos: sham-operado, grupo controle em que a aorta foi apenas manipulada, e grupo estenosado, animais submetidos à cirurgia de estenose da aorta abdominal. As aortas demonstraram duas respostas remodeladoras distintas e diferentes ao estímulo hemodinâmico induzido pela coarctação infra-diafragmática. A primeira é o remodelamento no segmento pré-estenótico hipertensivo com tensão circunferencial da parede aumentada associada com estresse tensional normal, fluxo laminar e tensão de cisalhamento normal. As células endoteliais eram heterogêneas, aumentadas em tamanho e alongadas em direção ao fluxo. Além disso, observou-se conspícuas placas neointimais difusamente distribuídas e espessamento medial. Nossos achados sugerem que a tensão circunferencial da parede aumentada devido a hipertensão tem papel fundamental no remodelamento desse segmento através de efeitos biomecânicos sobre o estresse oxidativo e expressão aumentada de TGF-?. A segunda é o remodelamento no segmento pós-estenótico normotenso com fluxo turbilhonar e baixa tensão de cisalhamento na parede associados a tensão circunferencial da parede e estresse tensional normais. As células endoteliais apresentavam-se semelhantes aos controles, exceto por alterações fenotípicas focais associadas à presença de conspícuas placas neointimais focalmente distribuídas, similares mas muito maiores que as encontradas no segmento pré-estenose. Mais estudos são necessários para se determinar como as forças mecânicas do fluxo turbilhonar e da baixa tensão de cisalhamento na parede são detectadas e traduzidas em sinais bioquímicos para as células e convertidas em alterações fenotípicas patofisiologicamente relevantes. / The present investigation was carried out to evaluate the relationship between local hemodynamic forces and intimal and medial remodeling in the proximal and distal segments of the arterial walls of rats in relation to severe stenosis of the aorta. Male Wistar young rats were divided randomly into: operated group, animals submitted to surgical abdominal aorta stenosis, and sham-operated group, a control group of animals submitted to sham operation to simulate abdominal aorta stenosis. Constricted aortas showed two distinct adaptive remodeling responses to hemodynamic stimuli induced by coarctation. The first is remodeling in the hypertensive prestenotic segment with increased circumferential wall tension associated with normal tensile stress, laminar flow/normal wall shear stress. The remodeling in this segment is characterized by enlarged heterogeneous endothelial cells, elongated in the direction of the blood flow, diffusely distributed neointimal plaques, appearing as discrete bulging toward the vascular lumen, and medial thickening. Our findings suggest that increased circumferential wall tension due to hypertension play a pivotal role in the remodeling of the prestenotic segment through biomechanical effects on oxidative stress and increased TGF-? expression. The second is remodeling in the normotensive poststenotic segment with turbulent flow/low wall shear stress and normal circumferential wall tension and tensile stress. The remodeling in this segment is characterized by groups of endothelial cells with phenotypic alterations and focally distributed neointimal plaques, similar but many of them larger than those found in the prestenotic segments. Further studies are needed to determine how the mechanical forces of turbulent flow/low shear stress are detected and transduced into biochemical signaling by the cells of the artery walls and then converted into pathophysiologic relevant phenotypic changes.

O aprimoramento dos meios para obtenção do bioetanol a partir de diferentes tipos de biomassa traz novos problemas e desafios para a engenharia. O Brasil, devido a fatores climáticos e uma produção de etanol a partir da cana de açúcar já estabilizada, possui uma posição mundial vantajosa na produção sucroalcooleira. Otimizar os meios já existentes e os em desenvolvimento pode não somente aumentar a eficiência da produção, como também reduzir os impactos ambientais causados pelo modelo de produção atualmente utilizado. O processo de fermentação é utilizado tanto na produção de etanol de primeira como de segunda geração, portanto melhorias no desempenho dos fermentadores contribui de maneira significante para o melhor aproveitamento da matéria prima. Diversas tentativas de melhorias são apresentadas na literatura, principalmente por meio do estudo de parâmetros do escoamento que podem influenciar o processo fermentativo, como tensão de cisalhamento, perfis de velocidade e tempo de residência, assim como a influência da geometria do fermentador sobre esses parâmetros. Em alguns estudos, algoritmos de otimização são utilizados para determinar os melhores coeficientes das reações químicas, mas não há estudos, até o momento, que proporcionem otimização simultânea dos parâmetros da geometria e do escoamento em um fermentador contínuo, presentes em cerca de 30% das usinas brasileiras. O objetivo deste trabalho é obter os parâmetros geométricos ideais para um fermentador contínuo, de forma a minimizar a tensão de cisalhamento a variância da distribuição de tempos de residência (DTR) no fermentador. O Ansys CFX® foi utilizado como ferramenta na simulação computacional do escoamento. As geometrias dos fermentadores ideais para cada um dessas análises, obtidas utilizando Algoritmos Genéticos e otimização univariada, respectivamente, foram propostas neste estudo. / The enhancement of bioethanol production means from different types of biomass presents significant problems and engineering challenges. Due to climate and a well-established sugar-cane ethanol production, Brazil is in a privileged position in the global ethanol production scenario. Providing effective means to optimize existing production methods can both improve the efficiency and reduce the environmental impact of the currently used production model. Improvements on this process can have a significant effect in several stages of production, once the production process is used both for first and second-generation ethanol. Several attempts to improve the ethanol production process are presented in the literature. Most studies have investigated how to improve parameters such as shear stress, velocity profiles and residence time, and of the influence of the bioreactor geometry on the parameters. The use of genetic algorithms has been reported in some cases, but there have not been reports on studies combining the optimization of flow parameters and algorithms to choose ideal geometric parameters for continuous fermenters, used in 30% of Brazilian industries in the field. The main aim of this study is to obtain ideal geometric parameters for a continuous fermenter, in order to maximize or minimize flow parameters that can influence on the fermenting process. The aim of this study is obtain the ideal geometry parameters for a continuous fermenter, minimizing two of flow parameters which can influence the fermentation process, namely the shear stress and the variance of residence time distribution (RTD). The flow parameters was obtained by computational fluid dynamics. The ideal fermenter geometries was obtained by two different optimization methods: the genetic algorithms and univariate optimization. The ideal geometries was proposed in this study.

The pathophysiology of atherosclerotic cardiovascular disease (CVD) is highlighted by vascular dysfunction and low-grade vascular inflammation. Furthermore, the site-specific distribution of atherosclerosis throughout the arterial vasculature is primarily determined by local hemodynamic force. Therefore, this dissertation outlines three experiments designed to investigate the role of acute mental and physical (i.e., aerobic exercise), and vascular wall shear stress (SS) on the inflammatory aspects of atherosclerosis. Chapter 2 examines the effect of acute laboratory-induced mental stress on intracellular pro-inflammatory signaling pathways in peripheral blood mononuclear cells. Chapter 3 investigates the impact of acute laboratory-induced mental stress and maximal aerobic exercise on the concentration of soluble VCAM-1 (sVCAM-1) and CX3CL1/fractalkine (sCX3CL1) in human serum. Lastly, Chapter 4 examines the role of short- (30 min) and long-term (24 hr) low-to-negative oscillating SS (LOSS) and high laminar SS (HLSS) on the expression and secretion (i.e., cleavage) of cell-membrane VCAM-1 and CX3CL1 by human umbilical vein endothelial cell cultures in vitro. Together, these experiments provide evidence that acute psychological stress, maximal aerobic exercise, and HLSS influence vascular inflammation and adhesive properties of the vessel wall. More specifically, the results from Chapter 2 provide evidence that acute mental stress promotes the immune-cell mediated synthesis of pro-inflammatory cytokines in circulation. In addition, Chapter 3 and Chapter 4 demonstrate that the elevations in blood flow and hemodynamic force associated with maximal aerobic exercise, and unidirectional high SS may have the capacity to alter the expression of endothelial-bound cellular adhesion molecules, in part by eliciting their release from the vessel wall.

Failure criteria play a vital role in the numerical analysis of reinforced concrete structures. The current failure criteria can be classified into two types, namely the empirical and theoretical failure criteria. Empirical failure criteria normally lack reasonable theoretical backgrounds, while theoretical ones either involve too many parameters or ignore the effects of intermediate principal stress on the concrete strength. Based on the octahedral shear stress model and the concrete tensile strength under the state of triaxial and uniaxial stress, a new failure criterion, that is, the simplified unified strength theory (UST), is developed by simplifiing the five-parameter UST for the analysis of reinforced concrete structures. According to the simplified UST failure criterion, the concrete strength is influenced by the maximum and intermediate principal shear stresses together with the corresponding normal stresses. Moreover, the effect of hydrostatic pressure on the concrete strength is also taken into account. The failure criterion involves three concrete strengths, namely the uniaxial tensile and compressive strengths and the equal biaxial compressive strength. In the numerical analysis, a degenerated shell element with the layered approach is adopted for the simulation of concrete structures. In the layered approach, concrete is divided into several layers over the thickness of the elements and reinforcing steel is smeared into the corresponding number of layers of equivalent thickness. In each concrete layer, three-dimensional stresses are calculated at the integration points. For the material modelling, concrete is treated as isotropic material until cracking occurs. Cracked concrete is treated as an orthotropic material incorporating tension stiffening and the reduction of cracked shear stiffness. Meanwhile, the smeared craclc model is employed. The bending reinforcements and the stirrups are simulated using a trilinear material model. To verify the correctness of the simplified UST failure criterion, comparisons are made with concrete triaxial empirical results as well as with the Kupfer and the Ottosen failure criteria. Finally, the proposed failure criterion is used for the flexural analysis of simply supported reinforced concrete beams. Also conducted are the punching shear analyses of single- and multi-column-slab connections and of half-scale flat plate models. In view of its accuracy and capabilities, the simplified UST failure criterion may be used to analyse beam- and slab-type reinforced concrete structures.

<p>By applying a segmentation procedure to two different sets of computed tomography scans, two geometrical models of the abdominal aorta, containing one inlet and two outlets have been constructed. One of these depicts a healthy blood vessel while the other displays one afflicted with a Abdominal Aortic Aneurysm. </p><p>After inputting these geometries into the computational dynamics software FLUENT, six simulations of laminar, stationary flow of a fluid that was assumed to be Newtonian were performed. The mass flow rate across the model outlet boundaries was varied for the different simulations to produce a basis for a parameter analysis study. </p><p>The segmentation data was also used as input data to a surface description procedure which produced not only the surface itself, but also the first and second directional derivatives in every one of its defining spatial data points. These sets of derivatives were followingly applied in an additional procedure that calculated values of Gaussian curvature. </p><p>A parameter variance analysis was carried out to evaluate the performance of the surface generation procedure. An array of resultant surfaces and surface directional derivatives were obtained. Values of Gaussian curvature were calculated in the defining spatial data points of a few selected surfaces. </p><p>The curvature values of a selected data set were visualized through a contour plot as well as through a surface map. Comparisons between the curvature surface map and one wall shear stress surface map were made.</p>

Aortic valve (AV) disease is a major cause of cardiovascular-linked deaths globally. In addition, AV disease is a strong risk factor for additional cardiovascular events; however, the mechanism by which it initiates and progresses is not well-understood. We hypothesize that low and oscillatory flow is present on the fibrosa side of the AV and stimulates ECs to differentially regulate microRNA (miRNA) and mRNAs and influence AV disease progression. This hypothesis was tested employing both in vitro and in vivo approaches, high throughput microarray and pathway analyses, as well as a variety of functional assays. First, we isolated and characterized side-dependent, human aortic valvular endothelial cells (HAVECs). We found that HAVECs express both endothelial cell markers (VE-Cadherin, vWF, and PECAM) as well as smooth muscle cell markers (SMA and basic calponin). Using microarray analysis on sheared, side-specific HAVECs, we identified side- and shear-induced changes in miRNA and mRNA expression profiles. More specifically, we identified over 1000 shear-responsive mRNAs which showed robust validation (93% of those tested). We then used Ingenuity Pathway Analysis to identify key miRNAs, including those with many relationships to other genes (for example, thrombospondin and I&B) and those that are members of over-represented pathways and processes (for example, sulfur metabolism). Furthermore, we validated five shear-sensitive miRNAs: miR-139-3p, miR-148a, miR-187, miR-192, and miR-486-5p and one side-dependent miRNA, miR-370. To prioritize these miRNAs, we performed in silico analysis to group these key miRNAs by cellular functions related to AV disease (including tissue remodeling, inflammation, and calcification). Next, to compare our in vitro HAVEC results in vivo, we developed a method to isolate endothelial-enriched, side-dependent total RNA and identify and validate side-dependent (fibrosa vs. ventricularis) miRNAs in porcine aortic valvular endothelium. From this analysis, we discovered and validated eight side-dependent miRNAs in porcine endothelial-enriched AV RNA, including one miRNA previously identified in vitro, miR-486-5p. Lastly, we determined the relationship between important miRNAs (specifically miR-187 and miR-486-5p) and AV disease by modulating levels of miRNAs and performing functional assays. Preliminary studies overexpressing miR-187 in HAVECs have shown a reduction in inflammatory state through monocyte adhesion (p<0.05). Further, miR-486-5p overexpression reveals an increase in migration (p<0.05) and a trend for a decrease in early apoptosis, linking miR-486-5p to tissue remodeling in the AV. Better understanding of AV biology and disease in terms of gene-regulation under different hemodynamic conditions will facilitate the design of a tissue-engineered valve and provide alternative treatment options.

By applying a segmentation procedure to two different sets of computed tomography scans, two geometrical models of the abdominal aorta, containing one inlet and two outlets have been constructed. One of these depicts a healthy blood vessel while the other displays one afflicted with a Abdominal Aortic Aneurysm. After inputting these geometries into the computational dynamics software FLUENT, six simulations of laminar, stationary flow of a fluid that was assumed to be Newtonian were performed. The mass flow rate across the model outlet boundaries was varied for the different simulations to produce a basis for a parameter analysis study. The segmentation data was also used as input data to a surface description procedure which produced not only the surface itself, but also the first and second directional derivatives in every one of its defining spatial data points. These sets of derivatives were followingly applied in an additional procedure that calculated values of Gaussian curvature. A parameter variance analysis was carried out to evaluate the performance of the surface generation procedure. An array of resultant surfaces and surface directional derivatives were obtained. Values of Gaussian curvature were calculated in the defining spatial data points of a few selected surfaces. The curvature values of a selected data set were visualized through a contour plot as well as through a surface map. Comparisons between the curvature surface map and one wall shear stress surface map were made.

The genetic disorder sickle cell anemia causes hemolytic anemia and sickle pain crisis, episodes of microvascular occlusion resulting in painful ischemic tissue damage. Pain crisis is thought to occur when sickle erythrocytes adhere in the post-capillary venule, partially occluding the vessel. The resulting slowed blood flow causes more extensive cell adherence and entrapment of rigid, deoxygenated erythrocytes until the vessel is entirely occluded. It was hypothesized that the inflammatory mediators histamine and tumor necrosis factor-, factors known to cause endothelial expression of adhesive ligands, might significantly increase sickle erythrocyte adhesion, and thus be capable of initiating sickle pain crisis. It was also hypothesized that the perfusion shear stress environment of the endothelium, known to be oscillatory and reduced in sickle cell patients, was a significant mediating factor of sickle cell adhesion. An in-vitro flow chamber using cultured endothelial cells and erythrocytes from blood samples of sickle cell anemic patients was used to quantify sickle erythrocyte adherence to stimulated and unstimulated endothelial cells under shear stresses from 1.0 to 0.1 dyne/cm2. Results showed that both endothelial stimulation and reduction of the perfusion shear stress increased sickle erythrocyte adherence. In combination, the use of inflammatory stimulation with reduced shear stress resulted in further increased adhesion, but only when above the range of 0.1 V 0.2 or 0.4 dyne/cm2, depending on the inflammatory mediator. Adhesion below this level of shear is not significantly increased by endothelial stimulation. The mechanism by which histamine mediates adhesion was investigated, and found to involve the endothelial H2 and H4 receptors and expression of the P-selectin ligand. These data suggest that irregular flow, typical of sickle microvasculature, may act in conjunction with the pro-inflammatory state of sickle vasculature and the histaminergic nature of some pain treatments to initiate or propagate sickle vaso-occlusion. Findings concerning histamine, tumor necrosis factor-alpha, and shear stress effects on adherence are discussed in relation to their possible applicability to patient health, future studies are outlined to confirm the relation of in vitro data to in vivo patient condition, and proposals are made for applying these methodologies to other potential mediators of sickle erythrocyte adhesion.

Atherosclerosis is a major contributor to cardiovascular disease and accounts for an estimated one third of deaths overall. In order to address the hemodynamic components of disease pathogenesis, researchers have focused on mechanotransduction of flow-dependent shear stress in the vascular endothelium as a source of novel pathological mechanisms. Understanding how unidirectional, laminar blood flow protects vessels from atherogenesis, while disturbed, oscillatory blood flow promotes it, stands to provide enormous insight into disease pathogenesis and may provide powerful, specific new therapies for cardiovascular disease intervention. The overall objective of this dissertation was to determine which microRNAs (miRNAs) and mRNAs are regulated by different flow conditions in vascular endothelial cells in vitro and in mouse carotid artery endothelium in vivo, and to identify which miRNAs mediate flow-dependent vascular inflammation. The overall hypothesis of this project was that oscillatory shear (OS) and laminar shear (LS) stress differentially alter the expression of mechanosensitive miRNAs each capable of regulating complex networks of gene expression, which in turn leads to inflammation in endothelial cells. This hypothesis was tested using both in vitro and in vivo approaches, high throughput microarray analyses, and functional validation of specific targets by PCR. The findings from the partial carotid ligation model show that acute exposure to disturbed flow results in accelerated endothelial dysfunction and atherosclerosis in vivo. High-throughput microarrays reveal distinct expression profiles of both miRNAs and mRNAs in mouse endothelium exposed to disturbed flow suggesting the regulatory mechanisms by which miRNAs regulate mRNAs resulting in EC inflammation, the earliest stage of atherosclerosis. This in vivo study provides new insight into the mechanisms of flow induced atherosclerosis. In particular, the upregulation of miR-663 due to OS in HUVEC causes monocyte adhesion, but not endothelial apoptosis, in an ICAM-1 dependent manner. miR-663 regulates a group of genes including transcriptional factors and inflammatory genes which may also mediate OS-induced EC inflammation. Collectively, revealing the profiles of miRNAs and mRNAs regulated by hemodynamic flow provides a better understanding in vascular diseases and provide potential target for developing effective preventative therapeutic approaches in cardiovascular diseases.

Neovascularization, or the formation of blood vessels, is important in both normal physiological processes as well as pathophysiological processes. The main players in neovascularization, endothelial cells (EC), are highly influenced by hemodynamic shear stress and this may play an important role in neovascularization. Two typical types of shear stress found in the vascular system are a unidirectional laminar shear stress (LS) found in straight regions and a disturbed, oscillatory shear stress (OS) found at branches or curves. At the cellular level, LS is thought to promote EC quiescence whereas OS is thought to promote EC dysfunction. Oscillatory sheared EC are pro-proliferative, pro-migratory, and secrete growth factors, all functions important in neovascularization. There are several diseases that involve both disturbed shear stress and neovascularization, such as atherosclerosis, aortic valve disease, and occlusive vascular disease. In these pathophysiological scenarios fluid shear stress may provide a driving force for neovascularization. Therefore, we hypothesized that oscillatory shear stress promotes greater neovascularization compared to unidirectional laminar shear stress through the secretion of angiogenic factors, which play a physiological role in neovascularization in vivo. To test this hypothesis, we first performed tubule formation and migration assays, two important functions in neovessel formation. We found that OS promotes greater tubule formation and migration of EC as compared to LS and this was mediated through secreted factors. Using gene and protein array analysis, we identified Angiopoietin-2 (Ang2) as being upregulated by OS compared to LS in EC. We found that inhibiting Ang2 blocked OS-mediated tubule formation and migration and that LS-inhibited tubule formation could be rescued by addition of Ang2. In addition, Ang2 was found to be upregulated at sites of disturbed flow in vivo, implicating a physiological role for Ang2. To further investigate the physiological role of Ang2 in neovascularization, we examined the effects of inhibiting Ang2 in a mouse model of hindlimb ischemia, which involves both disturbed flow and neovascularization. We found that Ang2 was upregulated in the ischemic adductor muscle suggesting that it plays a role in recovery during hindlimb ischemia. In addition, we found that inhibiting Ang2 decreased blood flow recovery. Ang2 inhibition resulted in decreased smooth muscle cell coverage of vessels as well as decreased macrophage infiltration. These findings suggest that Ang2 promotes blood flow recovery through the recruitment of smooth muscle cells and formation of collaterals, as well as the recruitment of macrophages that secrete important growth factors and help degrade the extracellular matrix in order for neovascularization to occur. In conclusion, this work illustrates the shear stress regulation of neovessel formation through the expression of Ang2, and the role of Ang2 in neovascularization in vivo. By understanding how angiogenic factors are regulated and what role they play in vivo, we can better understand human disease and develop important therapeutic targets.