Browsing by Author "Cidre, Diana"
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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 do movimento preparatório de salto em alturaPublication . Fidalgo, Cátia; Cerqueira, Célio; Cidre, Diana; Barros, Diana; Silva, Hélder; Piloto, P.A.G.São apresentados resultados experimentais de medições efectuadas na análise do salto em altura com agachamento, na amostra de um conjunto de indivíduos do sexo masculino e feminino. Foram realizados cinco ensaios para três níveis de agachamento inicial, com monitorização de um acelerómetro colocado na zona pélvica e com um sistema de análise de movimento assistido por vídeo e computador. Os resultados permitiram efectuar a comparação, entre o conjunto de indivíduos, dos parâmetros cinemáticos mais importantes, tendo em consideração os dois métodos experimentais. O estudo da fase impulsiva permitiu concluir que a massa de cada indivíduo tem influência na taxa de variação da força propulsiva e pouca influência no tempo utilizado para preparação da descolagem.
- 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.
- Blood flow in microchannels manufactured by a low cost technique: xurographyPublication . Pinto, Elmano; Taboada, Bruna Rafaela Pereira; Faustino, Vera; Cidre, Diana; Rodrigues, Raquel Oliveira; Miranda, João Mário; Garcia, Valdemar; Dias, Ricardo P.; Lima, Rui A.The xurography is a technique that has been used to make molds to produce microchannels. In contrast to soft lithography [1, 2], xurography uses equipments and materials commonly used in the printing industry, such as cutting plotters, vinyl and other materials. The main advantage of this technique is to fabricate microchannels at a reduced cost [3, 4]. The Fahraeus-Lindqvist effect is a well know phenomenon that happens in microcirculation, where red blood cells (RBCs) have tendency to migrate toward the centre of the microtube resulting in a marginal cell-free layer (CFL) at regions adjacent to the wall [5]. Recently several studies showed strong evidence that the formation of the CFL is affected by the geometry of the microchannel [1, 6, 7] and the physiological conditions of the working fluid, such as the hematocrit (Hct) [2, 8]. The main objective of the present work is to fabricate polydimethysiloxane (PDMS) microchannels by using a soft xurography technique in order perform blood flow studies. Additionally, a high-speed video microscopy system is used to measure the CFL thickness in two different geometries, i. e., bifurcations and confluences.
- Flow of red blood cells in microchannel networks: in vitro studiesPublication . Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinto, Elmano; Pinho, Diana; Bento, David; Correia, Teresa Montenegro; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.Blood exhibits unique flow characteristics on micro-scale level, due to the complex biochemical structure of Red Blood Cells (RBCs) and their response to both shear and extensional flow, which influence the rheological properties and flow behavior of blood [1,2]. In the past years, several in vitro studies where made and have revealed some physiologically significant phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, that played a key role in recent developments of lab-onchip devices for blood sampling, analysis and cell culturing. However, the blood flow in microvascular networks phenomena it remains incompletely understood. Thus, it is important to investigate in detail the behavior of RBCs flow occurring at a microchannel network, such as with divergent and convergent bifurcations. Previews in vitro studies in microchannels with a simple divergent and convergent bifurcation, have shown a pronounced cell depleted zone immediately downstream of the apex of the convergent bifurcation. In the present work, by using a highspeed video microscopy system, we investigated the cell depleted zone in a microchannel network. The working fluid used in this study was dextran 40 (Dx40) containing about 10% of haematocrit level (10 Hct) of ovine red blood cells. The high-speed video microscopy system used in our experiments consists of an inverted microscope (IX71, Olympus, Japan) combined with a highspeed camera (i-SPEED LT, Olympus). A syringe pump Apparatus (PHD ULTRATM) with 1 ml syringe (Terumo) was used to push the working fluids through the microchannel network. Additionally, we investigated the effect of the flow rate on the formation of the cell free layer.
- Flow of red blood cells in microchannel networks: in vitro studiesPublication . Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinto, Elmano; Pinho, Diana; Bento, David; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.Human blood is a multiphase biofluid primarily composed by the deformable red blood cells (RBCs) suspended in plasma. Because the complex structure of RBCs, blood exhibits unique flow characteristics on micro-scale level, due to their complex biochemical mechanisms and their response to both shear and extensional flow, which influence the rheological properties and flow behaviour of blood [1,2]. In the past years in vitro blood studies have been extensively performed and some important physiological phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, were revealed [1,3]. This pioneer studies performed by Fahraeus and Fahraeus-Lindqvist in straight glass microchannels [4] revealed that for narrow tubes (diameter<300 μm), the apparent viscosity of blood declines with decreasing diameter. More recently, due to the developments in microscopy, computers and image analysis techniques, several researchers have used new measuring methods to obtain deeper quantitative understanding of the blood flow dynamics, in vitro [5-8] and in vivo experiments [9-10]. The increasing interest by the microfluidic and biomedical communities has also played a key role in several recent developments of lab-on-chip devices for blood sampling, analysis and cell culturing, aimed in a near future, the development of blood diagnostic devices, as an alternative tool to the traditional diagnostic strategies. However, the blood flow in microvascular networks phenomena remains incompletely understood. Thus, it is important to investigate in detail the behaviour of RBCs flow occurring in a microchannel network, such as, with divergent and convergent bifurcations, which mimics the irregular vessel segments linked by numerous diverging and converging bifurcations. Previously, we made in vitro studies in microchannels with a simple divergent and convergent bifurcation, that showed a pronounced cell-free layer (CFL) immediately downstream of the apex of the convergent bifurcation [1,4]. This interesting result led us to the present work, where the CFL in a microchannel network is investigated by using a high-speed video microscopy system in order to further understand the blood flow behaviour in microvessels networks.
- Flow of red blood cells in microchannel networks: in vitro studiesPublication . Cidre, Diana; Rodrigues, Raquel Oliveira; Faustino, Vera; Pinto, Elmano; Pinho, Diana; Bento, David; Fernandes, Carla S.; Dias, Ricardo P.; Lima, Rui A.Blood exhibits unique flow characteristics on micro-scale level, due to the complex biochemical structure of Red Blood Cells (RBCs) and their response to both shear and extensional flow, which influence the rheological properties and flow behavior of blood [1,2]. In the past years, several in vitro studies where made and have revealed some physiologically significant phenomena, such as Fahraeus and Fahraeus-Lindqvist effect, that played a key role in recent developments of lab-onchip devices for blood sampling, analysis and cell culturing. However, the blood flow in microvascular networks phenomena it remains incompletely understood. Thus, it is important to investigate in detail the behavior of RBCs flow occurring at a microchannel network, such as with divergent and convergent bifurcations. Previews in vitro studies in microchannels with a simple divergent and convergent bifurcation, have shown a pronounced cell depleted zone immediately downstream of the apex of the convergent bifurcation. In the present work, by using a highspeed video microscopy system, we investigated the cell depleted zone in a microchannel network. The working fluid used in this study was dextran 40 (Dx40) containing about 10% of haematocrit level (10 Hct) of ovine red blood cells. The high-speed video microscopy system used in our experiments consists of an inverted microscope (IX71, Olympus, Japan) combined with a highspeed camera (i-SPEED LT, Olympus). A syringe pump Apparatus (PHD ULTRATM) with 1 ml syringe (Terumo) was used to push the working fluids through the microchannel network. Additionally, we investigated the effect of the flow rate on the formation of the cell free layer.
- Método automático para a medição da espessura camada de plasma em microcanais com bifurcaçõesPublication . Bento, David; Cidre, Diana; Lima, José; Dias, Ricardo P.; Lima, Rui A.Ao longo dos anos, a espessura da camada de plasma tem sido determinada com o auxílio de métodos manuais. Apesar destes métodos serem bastante fiáveis, estes são morosos e podem introduzir erros do utilizador nos dados. No presente trabalho, foi desenvolvido um método automático de processamento de imagem para a determinação da espessura camada de plasma de uma forma automática.
- Micro-flow visualization of in vitro blood through a microchannel with a bifurcation and confluencePublication . Cidre, Diana; Lima, Rui A.; Fernandes, Carla S.; Dias, Ricardo P.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiMicro-visualization techniques have been used to investigate the in vitro blood flow through straight glass capillaries. Although the glass microchannels present certain similarities to in vivo microcirculation, it is also clear that these kind of in vitro experiments differ from microvessels in several respects, such as: elasticity of microvessels, effect of the endothelial surface layer and microvascular networks composed with short irregular vessel segments which are linked by numerous bifurcations and convergences. Thus it was not surprising that several studies on blood flow in glass microtubes and in microvessels have yielded conflicting results with respect to blood viscosity and flow resistance. The main purpose of this work is to improve our understanding about the effect of a bifurcation and convergence on the rheological properties of in vitro blood. The microchannel containing a bifurcation and confluence will be fabricated in PDMS by using a soft lithography technique. The flow behaviour of both pure water (PW) and dextran 40 (Dx40) containing about 14% (14Hct) of human red blood cells (RBCs) will be investigated by means of a confocal micro-PTV system. Additionally, the experimental measurements obtained with PW will be also compared numerically by using the commercial finite element software package POLYFLOW®.