Browsing by Author "Imai, Yohsuke"
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- 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.
- 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.
- Confocal micro-PIV/PTV measurements of the blood flow in micro-channelsPublication . Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiThe development of optical experimental techniques has contributed to obtain explanations on the blood flow behaviour through micro-channels. Although the past results have been valuable, detailed studies on the flow properties of in vitro blood in micro-channels have been limited by several technical factors such as poor spatial resolution and difficulty to obtain quantitative detailed meas-urements at such small scales. In recent years, due to advances in computers, op-tics, and digital image processing techniques, it became possible to combine both particle image velocimetry (PIV) and particle tracking velocimetry (PTV) methods with confocal microscopes. As a result, this combination has greatly increased the resolution of the conventional micro-PIV/PTV systems and consequently pro-vided additional detailed description on the blood cells motion not obtainable by traditional methods. In this chapter the most relevant theoretical and technical is-sues related to both conventional and confocal micro-PIV/PTV methods are dis-cussed. In addition, a comparison between them is presented. Furthermore, the most relevant results of in vitro blood flowing in both glass and polydime-thylsiloxane (PDMS) micro-channels are shown.
- Determination of blood cells motions and interactions by a confocal micro-PIV systemPublication . Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Takeda, Motohiro; Wada, Shigeo; Yamaguchi, TakamiThe development of optical experimental techniques has contributed to obtain explanations on the way the blood flows through microvessels. Although the past results have been encouraging, detailed studies on the flow properties of blood in the microcirculation has been limited by several technical factors such as poor spatial resolution and difficulty to obtain quantitative detailed measurements at such small scales. In recent years, due to advances in computers, confocal microscopy, and digital image processing techniques, it has become possible to combine a micro-particle tracking velocimetry (PTV) system with a confocal microscope. The present study shows for the first time confocal micro-PTV measurements of the dynamic flow behaviour of red blood cells (RBCs) in concentrated suspensions. The measurements were performed at several depths of a 100 um glass capillaries
- Determination of the cell-free layer in circular PDMS microchannelsPublication . Cerdeira, Tânia Filipa Alves; Lima, Rui A.; Oliveira, Mónica; Monteiro, Fernando C.; Ishikawa, Takuji; Imai, Yohsuke; Yamaguchi, TakamiIn microcirculation the cell-free layer is believed to reduce the friction between red blood cells (RBCs) and endothelial cells and consequently reduce blood flow resistance. However, the complex formation of the cell-free layer has not yet been convincingly described mainly due to multi-physical and hemorheological factors that affect this phenomenon. In this experimental work, we study the effect of hematocrit (Hct) on the thickness of the cell-free layer in straight circular polydimethylsiloxane (PDMS) microchannels. The channels studied are 73 ± 2 mm in diameter, flexible and circular to mimic blood vessels. The images are captured using confocal microscopy and are post-processed using Image J and MATLAB. The formation of a cell-free layer is clearly visible in the images captured and by using a combination of image analysis techniques we are able to detect an increase in the cell-free layer thickness as Hct decreases.
- Dispersion of red blood cells in microchannels : a confocal micro-PTV assessmentPublication . Lima, Rui A.; Ishikawa, Takuji; Imai, Yohsuke; Fujiwara, Hiroki; Takeda, Motohiro; Matsuki, Noriaki; Wada, Shigeo; Yamaguchi, TakamiBlood in large arteries may be treated as a homogenous fluid from a macroscopic prospective. However, in reality blood is a suspension of deformable cells in viscous fluid plasma. In microcirculation, which comprises the smallest arteries and veins, the flow behavior of individual blood cells and their interactions provide the microrheological basis of flow properties of blood at a macroscopic level. Hence, in microcirculation it is fundamental to study the flow behavior of blood at cellular level. Several studies on both individual and concentrated RBCs have already been performed in the past. However, all studies used conventional microscopes and also ghost cells to obtain visible trace RBCs through the microchannel. The present study is concerned in providing further insights into the microscale blood flow behavior through microchannels by applying an emerging optical technique known as confocal micro-PIV/PTV. 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) and the correspondent radial dispersion coefficient was determined.