Browsing by Author "Fernandes, Carla S."
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- Análise do escoamento sanguíneo em microcanais com bifurcaçõesPublication . Cidre, Diana; Oliveira, Brigitte; Lagoela, Marco; Fernandes, Carla S.; Lima, Rui A.; Dias, Ricardo P.; Balsa, Carlos; Ishikawa, Takuji; Yamaguchi, TakamiVários estudos revelaram que a informação obtida sobre as propriedades reológicas do sangue em capilares de vidro difere da situação in vivo (Pries et al. 1994). As principais causas potenciais para estas discrepâncias podem ser devidas à camada superficial formada por células endoteliais e às redes microvasculares compostas por segmentos de vasos irregulares e curtos que estão ligados por numerosas bifurcações e convergências (Maeda 1996).O principal objectivo deste trabalho é analisar as propriedades não-Newtonianas do sangue durante o escoamento em modelos microvasculares. Neste estudo foi utilizado o método de litografia suave para fabricar microcanais bifurcados com secção rectangular em polidimetisiloxano (PDMS). Usando um sistema “confocal micro-PTV” (Lima et al. 2008), mediu-se o efeito da bifurcação no escoamento de partículas fluorescentes diluídas em água pura e em suspensões concentradas de eritrócitos. Os resultados experimentais obtidos pelo sistema “confocal micro-PTV” foram complementados por modelos hemodinâmicos computacionais. Após a execução de várias simulações com o software comercial de elementos finitos POLYFLOW®, compararam-se alguns resultados experimentais com resultados numéricos. Os resultados preliminares sugerem que as trajectórias dos eritrócitos podem sofrer alterações na direcção transversal ao escoamento devido à colisão com os eritrócitos que se encontram na vizinhança do ponto de divergência da bifurcação (Brigitte et al. 2009).
- Análise do escoamento sanguíneo em microcanais com bifurcaçõesPublication . Cidre, Diana; Lagoela, Marco; Oliveira, Brigitte; Fernandes, Carla S.; Balsa, Carlos; Lima, Rui A.; Dias, Ricardo P.; Ishikawa, Takuji; Yamaguchi, TakamiA dinâmica do escoamento sanguíneo na microcirculação depende fortemente das redes microvasculares compostas por segmentos de vasos curtos irregulares que estão ligados por inúmeras bifurcações. Este trabalho apresenta a aplicação de um sistema micro-PTV confocal para medir o comportamento dos eritrócitos durante o escoamento em um microcanal polidimetisiloxano (PDMS) rectangular com uma bifurcação. O efeito da bifurcação no escoamento de partículas fluorescentes diluídas em água pura e em suspensões concentradas com eritrócitos foi medido através de um sistema micro-PTV confocal. Numericamente, estudou-se o escoamento do sangue recorrendo ao software comercial de elementos finitos POLYFLOW® utilizando diferentes modelos reológicos. Os resultados preliminares sugerem que as trajectórias dos eritrócitos podem sofrer alterações na direcção transversal devido à acumulação de eritrócitos na vizinhança do ponto de divergência da bifurcação.
- Análise experimental e numérica de quedas de pressão em canais estenosadosPublication . Lopes, Sara Helena Carvalho; Fernandes, Carla S.; Pereira, Ana I.; Pinho, DianaOs estudos relacionados com o escoamento de fluidos em microcanais têm sido alvo de várias investigações, tendo permitido prever que o escoamento sanguíneo é influenciado por várias patologias, como por exemplo, a aterosclerose. A aterosclerose consiste num estreitamento das artérias, devido a aglomerados de gordura que se acumulam no seu interior e que pode diminuir o abastecimento de sangue aos tecidos do organismo, nomeadamente órgãos vitais. Neste trabalho foi realizado uma análise experimental e numérica de quedas de pressão em canais estenosados. Os resultados experimentais e numéricos foram ainda otimizados recorrendo ao método dos mínimos quadrados por forma a encontrar uma expressão que traduza o problema em estudo. Por fim, com o presente trabalho pretende-se dar algum contributo na área do diagnóstico.
- Análise experimental e numérica de quedas de pressão em canais estenosadosPublication . Lopes, Sara Helena Carvalho; Fernandes, Carla S.; Pereira, Ana I.; Pinho, DianaO interesse nos estudos relacionados com o escoamento de fluidos em microcanais tem assumido um lugar de destaque na área de biomédica, uma vez que que estes estudos permitem analisar escoamentos sanguíneos evitando questões de ética que se colocam quando se trabalha fisicamente com o sangue. Numa primeira fase deste trabalho foram fabricados modelos anatómicos tridimensionais, mais concretamente canais circulares, um sem patologia e dois com ateromas de alturas diferentes, onde foram efetuadas medições de quedas de pressão. Com os resultados obtidos foi possível concluir que a presença de ateromas influencia o escoamento sanguíneo, verificando-se que as quedas de pressão aumentam com o aumento do grau da estenose. Numa segunda fase os escoamentos estudados experimentalmente foram alvo de um estudo numérico com o objetivo de comparar os resultados da simulação com os obtidos experimentalmente. As simulações numéricas foram efetuadas recorrendo a um software comercial que implementa o método dos volumes finitos e os resultados obtidos revelaram-se concordantes com os obtidos experimentalmente, o que permitiu concluir que a dinâmica de fluidos computacional é de facto uma boa estratégia a ser utilizada. Na fase final do trabalho, procedeu-se à identificação da melhor modelação matemática para caracterizar a diferença de valores obtidos nos estudos experimental e numérico. Após diversas estratégias conclui-se que a diferença de valores pode ser caracterizada por uma função polinomial.
- Analysis of the blood flow in a microchannel with a bifurcationPublication . Oliveira, Brigitte; Lagoela, Marco; Cidre, Diana; Fernandes, Carla S.; Lima, Rui A.; Dias, Ricardo P.; Balsa, Carlos; Ishikawa, Takuji; Yamaguchi, TakamiIn vitro experiments allow precise measurement and control over relevant physiological variables. Thus, in the present study we have used a lithography technique to fabricate a rectangular PDMS microchannel with a bifurcation. By using a confocal micro-PTV system, we have measured the effect of bifurcation on the flow behaviour of both fluorescent particles diluted in pure water and red blood cells (RBCs) in concentrated suspensions. After performing simulations with the commercial finite element software package POLYFLOW®, some experimental results were compared with the numerical results. Our preliminary results suggest that the RBC paths may suffer fluctuations on the transversal direction caused by RBCs obstruction around the neighbourhood of the diverging point of the bifurcation.
- Assessment of the deformability and velocity of healthy and artificially impaired red blood cells in narrow polydimethylsiloxane (PDMS) microchannelsPublication . Vilas Boas, Liliana; Faustino, Vera; Lima, Rui A.; Miranda, João; Minas, Graça; Fernandes, Carla S.; Catarino, SusanaMalaria is one of the leading causes of death in underdeveloped regions. Thus, the development of rapid, efficient, and competitive diagnostic techniques is essential. This work reports a study of the deformability and velocity assessment of healthy and artificially impaired red blood cells (RBCs), with the purpose of potentially mimicking malaria effects, in narrow polydimethylsiloxane microchannels. To obtain impaired RBCs, their properties were modified by adding, to the RBCs, different concentrations of glucose, glutaraldehyde, or diamide, in order to increase the cells' rigidity. The effects of the RBCs' artificial stiffening were evaluated by combining image analysis techniques with microchannels with a contraction width of 8 µm, making it possible to measure the cells' deformability and velocity of both healthy and modified RBCs. The results showed that healthy RBCs naturally deform when they cross the contractions and rapidly recover their original shape. In contrast, for the modified samples with high concentration of chemicals, the same did not occur. Additionally, for all the tested modification methods, the results have shown a decrease in the RBCs' deformability and velocity as the cells' rigidity increases, when compared to the behavior of healthy RBCs samples. These results show the ability of the image analysis tools combined with microchannel contractions to obtain crucial information on the pathological blood phenomena in microcirculation. Particularly, it was possible to measure the deformability of the RBCs and their velocity, resulting in a velocity/deformability relation in the microchannel. This correlation shows great potential to relate the RBCs' behavior with the various stages of malaria, helping to establish the development of new diagnostic systems towards point-of-care devices.
- Asymmetry of red blood cell motions in a microchannel with a diverging and converging bifurcationPublication . Leble, Vladimir; Lima, Rui A.; Dias, Ricardo P.; Fernandes, Carla S.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiIn microcirculation, red blood cells (RBCs) flowing through bifurcations may deform considerably due to combination of different phenomena that happen at the micro-scale level, such as: attraction effect, high shear and extensional stress, all of which may influence the rheological properties and flow behavior of blood. Thus, it is important to investigate in detail the behavior of blood flow occurring at both bifurcations and confluences. In the present paper, by using a micro-PTV system, we investigated the variations of velocity profiles of two working fluids flowing through diverging and converging bifurcations - human red blood cells suspended in dextran 40 with about 14% of haematocrit level (14Hct) and pure water seeded with fluorescent trace particles. All the measurements were performed in the center plane of rectangular microchannels using a constant flow rate of about 3.0×10-12 m3/s. Moreover, the experimental data was compared with numerical results obtained for Newtonian incompressible fluid. The behavior of RBCs was asymmetric at the divergent and convergent side of the geometry, whereas the velocities of tracer particles suspended in pure water were symmetric and well described by numerical simulation. The formation of a red cell-depleted zone immediately downstream of the apex of the converging bifurcation was observed and its effect on velocity profiles of RBCs flow has been investigated. Conversely, a cell-depleted region was not formed around the apex of the diverging bifurcation and as a result the adhesion of RBCs to the wall surface was enhanced in this region.
- Biomechanical analysis of PDMS channels using different hyperelastic constitutive modelsPublication . Cardoso, Cátia; Fernandes, Carla S.; Ribeiro, J.E.; Lima, Rui A.Brain aneurysms are pathological dilatations of cerebral arteries and are known as one of the most common and serious cerebrovascular events. Most cerebral aneurysms do not cause symptoms until they become large, beginning to break up. This study's main objective is the numerical characterization of biomechanical behavior of aneurysms, taking into ac-count different geometric and physiological parameters, in order to analyze the blood vessel wall behavior during the formation of an aneurysm in order to understand what leads to its formation and where are most conducive to its rupture zones. Simulation of the Newtonian fluid flow (glycerin, with well-known properties and sufficient viscosity to measure the pressure drops) was performed using the commercial finite method package Ansys® - Fluent, and pressure along the channel was determined. These pressures were imported into the channel, in the Ansys®- Static Structural, in order to be able to evaluate and analyse the deformations and stresses in the channel wall, caused by internal pressure induced by the fluid flow. To do this, the most known hyper-elastic constitutive models were used. and it was concluded that any constitutive model can be applied to this kind of studies, allowing to visualize where pressure achieve maximums and consequently, the most favorable areas to the rupture.
- Biomechanical analysis of PDMS channels using different hyperelastic numerical constitutive modelsPublication . Cardoso, Cátia; Fernandes, Carla S.; Lima, Rui A.; Ribeiro, J.E.Brain aneurysms are pathological dilatations of cerebral arteries and are known as one of the most com- mon and serious cerebrovascular events. However, patients with cerebral aneurysms do not exhibit ev- ident symptoms until they rupture. The main objective of the present study is to perform numerical characterizations of the biomechanical behavior of aneurysms in order to analyze the blood vessel wall behavior during the formation of an aneurysm. By taking into account different geometric and physi- ological parameters, flow simulations of a well-known Newtonian fluid (glycerin) was performed using the commercial finite volume method package Ansys®-Fluent, and pressure along the channel was de- termined. These pressures were imported into the channel, in the Ansys®- Static Structural, in order to evaluate and analyze the displacement and strain fields in the channel wall, caused by the internal pressure induced by the fluid flow. All calculations were performed by using the most widely accepted hyperelastic constitutive models and it was found that any constitutive model can be applied to this kind of studies, allowing to visualize where pressure achieves its maximum value and consequently, the most favorable region where the rupture is more likely to occur.
- Blood flow in a bifurcation and confluence microchannel: effect of the cell-free layer in velocity profilesPublication . Pinho, Diana; Bento, David; Rodrigues, Raquel Oliveira; Fernandes, Carla S.; Garcia, Valdemar; Lima, Rui A.A few detailed studies have been performed in complex in vitro microvascular networks composed by bifurcations and confluences. The main purpose of the present work is to numerically simulate the flow of two distinct fluids through bifurcation and confluence geometries, i. e red blood cells (RBCs)suspended in Dextran40 with about 14% of heamatocrit and pure water. The simulations of pure water and RBCs flows were performed resorting to the commercial finite volume software package FLUENT. A well known hemodynamic phenomenon, known as Fahraeus-Lindqvist effect, observed in both in vivo and in vitro studies, results in the formation of a marginal cell-free layer (CFL) at regions adjacent to the wall. Recently, studies have shown that the formation of the CFL is affected by the geometry of the microchannel and for the case of the confluences a CFL tend to appear in the middle of the microchannel after the apex of the confluence. By using the CFL experimental data, the main objective of this work is to implement a CFL in the numerical simulations in order to obtain a better understanding of the effect of this layer on the velocity profiles.