Confocal micro-PIV/PTV measurements of the blood flow in micro-channels

The 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

Confocal micro-flow visualization of blood cells

Progress 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.This study was supported in part by the following grants: Grant-in-Aid for Science and Technology (PTDC/SAU-BEB/108728/2008 and PTDC/SAU-BEB/105650/2008) from the Science and Technology Foundation (FCT) and COMPETE, Portugal and Grant-in- Aid for Scientific Research (S) from the Japan Society for the Promotion of Science (JSPS; No.19100008). We also acknowledge the support from the 2007 Global COE Program “Global Nano-Biomedical Engineering Education and Research Network”

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

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

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