3,435 research outputs found
Axisymmetric polydimethysiloxane microchannels for in vitro hemodynamic studies
The 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 polydimethysiloxane (PDMS) microchannels aiming to mimic an in vivo microvascular environment and suitable for state-of-the-art microscale flow visualization techniques, such as confocal µPIV/PTV. By using a confocal µPTV system individual red blood cells (RBCs) were successfully tracked trough a 75 µm 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
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
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
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
Açaí e o ensino de química: uma atividade de extensão no interior do Amazonas
O objetivo deste trabalho foi apresentar o açaí Amazônico como tema de aplicação do ensino de Química. A atividade de extensão foi realizada para discentes do Instituto Federal do Amazonas, na cidade Coari, com três turmas do 2º ano do Ensino Médio. A metodologia consistiu na recepção, palestra, atividade experimental e duas atividades lúdicas. A atividade apresentou resultados positivos, com uma boa aceitação dos discentes participantes e dos acadêmicos da extensão, ampliando o aprendizado sobre o ensino de Química e ressignificando os conhecimentos sobre esta fruta tão consumida na região. O projeto contribuiu com a divulgação do conhecimento científico e demonstrou o papel social e tecnológico que os conteúdos de Química apresentam, contribuindo para a aproximação e troca de conhecimentos e experiências entre a comunidade e o meio universitári
Automatic tracking of labeled red blood cells in microchannels
The current study proposes an automatic method for the segmentation and tracking of red blood cells
flowing through a 100- m glass capillary. The original images were obtained by means of a confocal system
and then processed in MATLAB using the Image Processing Toolbox. The measurements obtained with the
proposed automatic method were compared with the results determined by a manual tracking method. The
comparison was performed by using both linear regressions and Bland–Altman analysis. The results have
shown a good agreement between the two methods. Therefore, the proposed automatic method is a powerful
way to provide rapid and accurate measurements for in vitro blood experiments in microchannels.The authors acknowledge the financial support provided by: Student Mobility Placements with the program Lifelong Learning(Erasmus Program), PTDC/SAUBEB/108728/2008, PTDC/SAU-BEB/105650/2008, PTDC/EMEMFE/099109/2008 and PTDC/SAU-ENB/116929/2010 from the FCT (Science and Technology Foundation) and COMPETE, Portugal
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