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Bioengineering

Micro-particle Image Velocimetry for Velocity Profile Measurements of Micro Blood Flows

Published: April 25th, 2013

DOI:

10.3791/50314

1Department of Chemical and Biological Engineering, University of Ottawa , 2Department of Mechanical Engineering, University of Ottawa

Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows which are cross-correlated to give an accurate velocity profile. Shear rate, maximum velocity, velocity profile shape, and flow rate, each of which has clinical applications, can be derived from these measurements.

Micro-particle image velocimetry (μPIV) is used to visualize paired images of micro particles seeded in blood flows. The images are cross-correlated to give an accurate velocity profile. A protocol is presented for μPIV measurements of blood flows in microchannels. At the scale of the microcirculation, blood cannot be considered a homogeneous fluid, as it is a suspension of flexible particles suspended in plasma, a Newtonian fluid. Shear rate, maximum velocity, velocity profile shape, and flow rate can be derived from these measurements. Several key parameters such as focal depth, particle concentration, and system compliance, are presented in order to ensure accurate, useful data along with examples and representative results for various hematocrits and flow conditions.

The human body contains numerous vessels with diameters less than 50 μm, which are the main exchange site between blood and tissues. The study of blood flow in these vessels represents a considerable challenge due to both the scale of the measurements and the fluid properties of blood. These measurements, including the pressure gradient, the shear at the wall, and velocity profiles in arterioles and venules, are key factors linked with physiological responses. There are now unprecedented opportunities to resolve these measurement challenges, thanks to new experimental techniques at the micro scale to study the microcirculation and solve this multiscale problem.

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1. Microchip Fabrication

The first step is to create or purchase your microchannel. There are many options for microchip material.

One of the most common materials chosen is poly(dimethylsiloxane) (PDMS). There are many publications on directions for PDMS fabrication through soft lithography 16,17,18.

Once the PDMS channel is fabricated, there are several surface treatments available to reverse its natural hydrophobicity. Oxygena.......

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In all figures, flow is left to right in raw images, and upwards in calculated velocity profiles. An example of the raw data obtained with blood at hematocrit H=10 flowing at 10 μl/hr is shown in Figure 2. Raw data may be cross-correlated without any data processing to achieve velocity profiles. The impact of pre-processing and data processing methods is discussed by Pitts, et al., (2012b). An example of a resultant velocity profiles from data similar to Figure 2 at hematorcr.......

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Using μPIV for blood flow measurements at the scale of the microcirculation can give insight into a great number of relevant biomedical, mechanical and chemical engineering processes. Some of the key factors to account for are the density of the RBC themselves, the aggregation and deformability of the RBC, aggregation or movement of the fluorescing micro particles, and the settling of the RBC in the channels. All of these can be accounted for if the general guidelines laid out above are followed. There is a basic chec.......

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The authors would like to thank NSERC (Natural Sciences and Engineering Council of Canada) for funding, Catherine Pagiatikis for her help in initial runs, Sura Abu-Mallouh and Frederick Fahim for testing the protocol, Richard Prevost of LaVision, Inc for technical support, and Guy Cloutier of the University of Montréal for the loan of the Dalsa high-speed camera.

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Name Company Catalog Number Comments
Name of Reagent/Material Company Catalog Number Comments
poly(dimethylsiloxane) (PDMS), i.e. Sylgard-184 Dow-Corning 3097358-1004  
ethylenediaminetetraacetic acid (EDTA) Sigma Aldrich E9884-100G  
poshpate buffered saline (PBS) Sigma Aldrich P5368-10PAK  
fluorescing micro particles Microgenics/FisherSci R900  
glycerol (OPTIONAL) Sigma Aldrich G6279-500 ml  
microcentrifuge, i.e. CritSpin FisherSci 22-269-291  
syringe, i.e. 50 μl Gastight Hamilton 80965  
camera, i.e. Imager Intense, high speed LaVision, Dalsa Imager Intense  
microscope, i.e. MITAS LaVision MITAS  
Nd:YAG laser New Wave Research Solo-II  
syringe pump, i.e. Nexus3000 Chemyx, Inc. Nexus-3000  
flexible tubing, i.e. Tygon FisherSci 14-169-1A  
data processing software, i.e. DaVis LaVision DaVis  
centrifuge, i.e. Thermo Scientific CL2 Thermo Scientific 004260F  

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