Analysis of velocity profiles of blood flow in microchannels using confocal micro-PIV and particle method

The combination of computational and experimental investigations provides an excellent approach to understand complex phenomena involved at a microscopic level. This paper emphasizes a new experimental technique capable to quantify the flow patterns inside microchannels with high spatial and temporal resolution. This technique, known as confocal micro-PIV, consists of a spinning disk confocal microscope, high speed camera and a diodepumped solid state (DPSS) laser. Velocity profiles of physiological fluids were measured within different microchannels. The measured results agree reasonably well with the predicted analytical values. This new PIV system is a very promising technique to confirm the validity of the data obtained by numerical simulations, such as the MPS particle method

Os métodos computacionais em hemodinâmica

Até à última década do século XX, a investigação realizada em hemodinâmica limitava-se, essencialmente, a estudos baseados em métodos experimentais e modelos matemáticos. No entanto, no final do século XX, os avanços tecnológicos na área da computação e o custo mais baixo de aquisição propiciaram uma nova forma de investigar os factores hemodinâmicos em termos fisiológicos e patológicos. Tal como tem acontecido em diversas áreas da ciência, os métodos computacionais constituem um complemento bastante promissor para investigar e analisar uma série de mecanismos fisiológicos e patológicos existentes nos vários órgãos do corpo humano. Este artigo trata, portanto, dos métodos computacionais em hemodinâmica e faz uma breve descrição do processo e da aplicação destes métodos no estudo do escoamento sanguíne

Velocity measurements of physiological flows in microchannels using a confocal micro-PIV system

The detail measurements of velocity profiles of in vitro blood flow in micorchannels are fundamental for a better understanding on the biomechanics of the microcirculation. Despite the high amount of research in microcirculation, there is not yet any detailed experimental information about flow velocity profiles, RBCs deformability and aggregation in microvessels (diameter in the order of 100μm or less). These lack of knowledge is mainly due to the absence of adequate techniques to measure and quantitatively evaluate fluid mechanical effects at a microscopic level [1, 2]. During the years the most research work in this area has focused in experimental studies using techniques such as laser Doppler anemometry (LDA) or conventional particle image velocimetry (PIV). However, due to limitations of those techniques to study effects at a micro-scale level, Meinhart and his colleagues [3] have proposed a measurement technique that combines the PIV system with an inverted epi-fluorescent microscope, which increases the resolution of the conventional PIV systems [3]. More recently, considerable progress in the development of confocal microscopy and consequent advantages of this microscope over the conventional microscopes [4, 5] have led to a new technique known as confocal micro-PIV. This technique combines the conventional PIV system with a spinning disk confocal microscope (SDCM). Due to its outstanding spatial filtering technique together with the multiple point light illumination system, this kind of microscope has the ability to obtain in-focus images with optical thickness less than 1 μm, task extremely difficult to be achieved by using a conventional microscope. As a result, by combining SDCM with the conventional PIV system it is possible to achieve a PIV system with not only extremely high spatial resolution but also with capability to generate 3D velocity profiles. The main purpose of the present study is to evaluate the performance of our confocal micro-PIV system in order to investigate its ability to study the behaviour of non-homogenous fluids such as physiological fluids

Confocal micro-PIV measurements of blood flow in microchannels

The detail measurements of velocity profiles of blood flow in microchannels are fundamental for a better understanding on the biomechanics of the microcirculation. It is therefore very important to obtain measurements with high accuracy and spatial resolution of the influence of the blood cells on the plasma flow behaviour. This paper presents and compares measurements of in vitro blood with different hematocrits within a square microchannel obtained by a confocal particle image velocimetry (PIV) system. This emerging technology by combining the conventional PIV system with a spinning confocal microscope has the ability to obtain not only high spatial resolution images but also three-dimensional (3D) optical sectioning velocity measurements. Velocity measurements of plasma seeded with 1 ~tm diameter fluorescent particles were performed at different locations along the depth of 100 ~tm square microchannel at a constant flow rate (0.15~tl/min) and Reynolds number (Re) of 0.025. By using our confocal micro-PIV system, it was possible to obtain time-series of instantaneous velocity profiles with high spatial resolution of 28.24 18.83 ~tm at time intervals of 5 ms between two images. The ensemble-averaged velocity results of blood flow with different hematocrits (up to 25%) have shown velocity profiles very close to a parabolic shape. However, by analysing the temporal variance of the instantaneous velocity profiles of different hematocrits, we have observed a substantial increase of the instantaneous velocity fluctuations by increasing the hematocrit within the plasma flow. Besides, some possible effects from the measurements accuracy and flow rate instabilities from the syringe pump, this observation also suggests that there is a direct correlation between the level of hematocrit and the temporal instantaneous velocity fluctuations

Confocal micro-PIV measurements of three-dimensional profiles of cell suspension flow in a square microchannel

A detailed measurement of the blood flow velocity profile in microchannels in vitro is fundamental to better understand the biomechanics of microcirculation. Therefore it is very important to determine the influence of suspended blood cells on the flow behaviour with high accuracy and spatial resolution. We measured the flow of blood cells suspended in a physiological fluid within a square microchannel using a confocal particle image velocimetry (PIV) system and compared it to pure water. This emerging technology combines a conventional PIV system with a spinning confocal microscope and has the ability to obtain high-resolution images and three-dimensional (3D) optical section velocity measurements. The good agreement obtained between the measured and estimated results suggests that macroscale flow theory can be used to predict the flow behaviour of a homogeneous fluid within a 100 μm square microchannel. Our results also demonstrated the potential of the confocal system for generating 3D profiles and consequently obtaining detailed information on microscale effects in microchannels using both homogeneous and non-homogeneous fluids, such as a suspension of blood cells. Furthermore, the results obtained from our confocal micro-PIV system show the ability of this system to measure velocities up to 0.52 mm s−1 in a blood cell suspension fluid

In vitro confocal micro-PIV measurements of blood flow in a square microchannel: the effect of the haematocrit on instantaneous velocity profiles

A confocal microparticle image velocimetry (micro-PIV) system was used to obtain detailed information on the velocity profiles for the flow of pure water (PW) and in vitro blood (haematocrit up to 17%) in a 100-μm-square microchannel. All the measurements were made in the middle plane of the microchannel at a constant flow rate and low Reynolds number (Re=0.025). The averaged ensemble velocity profiles were found to be markedly parabolic for all the working fluids studied. When comparing the instantaneous velocity profiles of the three fluids, our results indicated that the profile shape depended on the haematocrit. Our confocal micro-PIV measurements demonstrate that the root mean square (RMS) values increase with the haematocrit implying that it is important to consider the information provided by the instantaneous velocity fields, even at low Re. The present study also examines the potential effect of the RBCs on the accuracy of the instantaneous velocity measurements

A particle method computer simulation: applications to the study of blood flow

The need to analyse the microscopic mechanical behaviour of blood flow was one of the main reasons to develop a new computer simulation using a particle method. This new mesh free method is based on a moving-particle semi-implicit (MPS) method, which has been developed to simulate incompressible fluids based on the Navier-Stokes equations. The simulation region was discretized by particles that moves in Lagrangian coordinates, where the plasma and platelets were modelled as fluid particles, red blood cells (RBC) as elastic particles and vessel wall as rigid particles. In this paper, some applications of the MPS method to study the blood flow are briefly analysed, such as the motion and deformation of red blood cells (RBC) in plasma flow and the platelet aggregation process in blood flow. Some preliminary studies suggest that there is evidence that the proposed method enables the analysis of the RBC motion and deformation in the plasma flow and also the initial thrombogenesis, growth and destruction of thrombus

Velocity fields of blood flow in microchannels using a confocal micro-PIV system

The in vitro experimental investigations provide an excellent approach to understand complex blood flow phenomena involved at a microscopic level. This paper emphasizes an emerging experimental technique capable to quantify the flow patterns inside microchannels with high spatial and temporal resolution. This technique, known as confocal micro-PIV, consists of a spinning disk confocal microscope, high speed camera and a diode-pumped solid state (DPSS) laser. Velocity profiles of pure water (PW), physiological saline (PS) and in vitro blood were measured in a 100mm glass square and rectangular polydimethysiloxane (PDMS) microchannel. The good agreement obtained between measured and estimated results suggests that this system is a very promising technique to obtain detail information about micro-scale effects in microchannels by using both homogeneous and non-homogeneous fluids such as blood flow.This study was supported in part by the following grants: 21st Century COE Program for Future Medical Engineering based on Bio-nanotechnology, International Doctoral Program in Engineering from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), “Revolutionary Simulation Software (RSS21)” next-generation IT program of MEXT; Grants-in-Aid for Scientific Research from MEXT and JSPS Scientific Research in Priority Areas (768) “Biomechanics at Micro- and Nanoscale Levels,” Scientific Research (A) No.16200031 “Mechanism of the formation, destruction, and movement of thrombi responsible for ischemia of vital organs.” The authors also thank all members of Esashi, Ono and Tanaka Lab. for their assistance in fabricating the PDMS microchannel

Velocity measurements of blood flow in a rectangular PDMS microchannel assessed by confocal micro-PIV system

This paper examines the ability to measure the velocity of both physiological saline (PS) and in vitro blood in a rectangular polydimethysiloxane (PDMS) microchannel by means of the confocal micro-PIV system. The PDMS microchannel, was fabricated by conventional soft lithography, had a microchannel near to a perfect rectangular shape (300μm wide, 45μm deep) and was optically transparent, which is suitable to measure both PS and in vitro blood using the confocal system. By using this latter combination, the measurements of trace particles seeded in the flow were performed for both fluids at a constant flow rate (Re=0.021). Generally, all the velocity profiles were found to be markedly blunt in the central region mainly due to the low aspect ratio (h/w=0.15) of the rectangular microchannel. Predictions by a theoretical model for the rectangular microchannel have showed fairly good correspondence with the experimental micro-PIV results for the PS fluid. Conversely, for the in vitro blood with 20% haematocrit, small fluctuations were found on velocity profiles.This study was supported in part by the following grants: International Doctoral Program in Engineering from the Ministry of Education, Culture, Sports, Science and Technology of Japan (MEXT), “Revolutionary Simulation Software (RSS21)” next-generation IT program of MEXT; Grants-in-Aid for Scientific Research from MEXT and JSPS Scientific Research in Priority Areas (768) “Biomechanics at Micro- and Nanoscale Levels,” Scientific Research (A) No.16200031 “Mechanism of the formation, destruction, and movement of thrombi responsible for ischemia of vital organs.” The authors also thank all members of Esashi, Ono and Tanaka Lab. for their assistance in fabricating the PDMS microchannel

Measurement of erythrocyte motions in microchannels by using a confocal micro-PTV system

Detailed knowledge on the motion of individual red blood cells (RBCs) flowing in microchannels is essential to provide a better understanding on the blood rheological properties and disorders in microvessels. 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. Recently, considerable progress in the development of confocal microscopy and consequent advantages of this microscope over the conventional microscopes have led to a new technique known as confocal micro-PIV. This technique combines the conventional PIV system with a spinning disk confocal microscope (SDCM). Due to its outstanding spatial filtering technique together with the multiple point light illumination system, this kind of microscope has the ability to obtain in-focus images with optical thickness less than 1 μm, a task extremely difficult to be achieved by using a conventional microscope. The main purpose of this paper is to investigate the ability of our confocal micro-PTV system to measure the motion of individual RBCs at different haematocrit (Hct) through microchannels