Browsing by Author "Ishikawa, Takuji"
Now showing 1 - 10 of 43
Results Per Page
Sort Options
- 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.
- 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.
- 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.
- Axisymmetric PDMS (polydimethysiloxane) microchannels for in vitro haemodynamic studiesPublication . Lima, Rui A.; Oliveira, Mónica S.N.; Ishikawa, Takuji; Kaji, Hirokazu; Tanaka, Shuji; Nishizawa, Matsuhiko; Yamaguchi, TakamiThe current microdevices used for biomedical research are often manufactured using microelectromechanical systems (MEMS) technology. Although it is possible to fabricate precise and reproducible rectangular microchannels using soft lithography techniques, this kind of geometry may not reflect the actual physiology of the microcirculation. Here, we present a simple method to fabricate circular PDMS microchannels aiming to mimic in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal uPIV/PTV. By using a confocal uPTV system individual red blood cells (RBCs) were successfully tracked trough a 75 um circular PDMS microchannel. The results show that RBC lateral dispersion increases with the volume fraction of RBCs in the solution, i.e. with the hematocrit.
- Blood cell motions and interactions in microchannelsPublication . Lima, Rui A.; Ishikawa, Takuji; Fujiwara, Hiroki; Takeda, Motohiro; Imai, Yohsuke; Tsubota, Ken-ichi; Wada, Shigeo; Yamaguchi, TakamiDetailed knowledge on the motions and interactions of individual blood cells flowing in microchannels is essential to provide a better understanding on the blood rheological properties and disorders in microvessels. This paper presents the ability of a confocal micro-PTV system to track red blood cells (RBCs) through a 100 μm circular glass microchannel. The technique consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser combined with a single particle tracking (SPT) software (MtrackJ). Detailed measurements on the motions of RBCs were measured at different haematocrits (Hct). Our results show clearly that this technique can provide detailed information about microscale disturbance effects caused by the blood cells.
- Blood flow behavior in microchannels: past, current and future trendsPublication . Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiOver the years, various experimental methods have been applied in an effort to understand the blood flow behavior in microcirculation. Most of our current knowledge in microcirculation is based on macroscopic flow phenomena such as Fahraeus effect and Fahraeus-Linqvist effect. The development of optical experimental techniques has contributed to obtain possible explanations on the way the blood flows through microvessels. Although the past results have been encouraging, detailed studies on blood flow behavior at a microscopic level have been limited by several factors such as poor spatial resolution, difficulty to obtain accurate measurements at such small scales, optical errors arisen from walls of the microvessels, high concentration of blood cells, and difficulty in visualization of results due to insufficient computing power and absence of reliable image analysis techniques. However, in recent years, due to advances in computers, optics, and digital image processing techniques, it has become possible to combine a conventional particle image velocimetry (PIV) system with an inverted microscope and consequently improve both spatial and temporal resolution. The present review outlines the most relevant studies on the flow properties of blood at a microscale level by using past video-based methods and current micro-PIV and confocal micro-PIV techniques. Additionally the most recent computational fluid dynamics studies on microscale hemodynamics are also reviewed.
- Blood flow in microchannel with stenosis measured by a confocal micro PTV systemPublication . Fujiwara, Hiroki; Ishikawa, Takuji; Lima, Rui A.; Imai, Yohsuke; Matsuki, Noriaki; Kaji, Hirokazu; Mori, Daisuke; Nishizawa, Matsuhiko; Yamaguchi, TakamiBlood in microcircualtion is not a homogenous fluid but the suspension of Red Blood Cells(RBC). So individual RBCs behavior is essential to get good comprehension about the blood flow in microcirculation. In this study we observe the RBCs behavior through the stenosis by using confocal-micro- PTV system. And we can observe the difference of the cell free layer thickness according to Hct.
- Blood-on-chips: flow through complex geometriesPublication . Lima, Rui A.; Oliveira, Mónica; Ishikawa, Takuji; Matsuki, Noriaki; Imai, Yohsuke; Yamaguchi, TakamiBlood is a complex body fluid, composed of cells and plasma, which holds a massive amount of information about several physiological and pathologic events happening throughout the body. Hence, blood sampling and analysis are used extensively in traditional clinical laboratories for the diagnosis of several diseases. Since the inception of microfluidics, there has been a growing interest, by both microfluidic and biomedical communities, to develop blood-on-chip devices as an alternative tool for the diagnosis of major diseases, such as cancer and cardiovascular diseases. Therefore, it is essential to understand the blood flow behaviour involved in this kind of microfluidic channels in order to design reliable blood-on-a-chip devices able to efficiently treat and diagnose a variety of diseases. The present experimental study shows the effect of micro-scale contractions and expansions, such as those found in an artificial stenosis, on the blood flow and cell behaviour. The micro-channels were fabricated in PDMS using softlithography and the experiments were carried out by using dextran 40 containing different fractions of human erythrocytes. The in vitro blood flow was measured by means of a high-speed video microscopy system composed with an inverted microscope, a high-speed camera and a thermo plate to control the surrounding temperature.
- Confocal micro-flow visualization of blood cellsPublication . Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiProgress in the development of confocal microscopy and the advantages of this technique over conventional microscopy have led to a new technique known as confocal micro-PTV. This technique combines a manual tracking method with a spinning disk confocal microscope. By combining its spatial filtering technique with a multipoint illumination system, this technique has the ability to obtain in-focus images with optical thickness less than 5 mm. The present study shows the ability of our confocal micro-PTV system to obtain detailed qualitative and quantitative information on the blood flow behavior in both glass capillaries and polydimethylsiloxane(PDMS) microchannels. By labeling the blood cells with a lipophilic carbocyanime derivative it was possible to measure both translational and rotational motion occurring during flow. Our results demonstrate the ability of our confocal micro-PTV system to obtain both translational and rotational motion of individual RBCs flowing in concentrated suspensions. Owing to its optical sectioning ability and consequent improvement of the image contrast and definition, the proposed confocal system can provide additional detailed description on the blood cells motion not obtainable by other conventional methods.