Research Papers

Investigation of Hydrodynamic Focusing in a Microfluidic Coulter Counter Device

[+] Author and Article Information
Muheng Zhang, Ellen Brehob

Mechanical Engineering Department,  University of Louisville, Louisville, KY 40292

Yongsheng Lian

Mechanical Engineering Department,  University of Louisville, Louisville, KY 40292y0lian05@louisville.edu

Cindy Harnett

Electrical and Computer Engineering Department,  University of Louisville, Louisville, KY 40292

J Biomech Eng 134(8), 081001 (Aug 06, 2012) (9 pages) doi:10.1115/1.4007091 History: Received October 04, 2011; Revised May 09, 2012; Posted July 06, 2012; Published August 06, 2012; Online August 06, 2012

The Coulter technique enables rapid analysis of particles or cells suspended in a fluid stream. In this technique, the cells are suspended in an electrically conductive solution, which is hydrodynamically focused by nonconducting sheath flows. The cells produce a characteristic voltage signal when they interrupt an electrical path. The population and size of the cells can be obtained through analyzing the voltage signal. In a microfluidic Coulter counter device, the hydrodynamic focusing technique is used to position the conducting sample stream and the cells and also to separate close cells to generate distinct signals for each cell and avoid signal jam. The performance of hydrodynamic focusing depends on the relative flow ratio between the sample stream and sheath stream. We use a numerical approach to study the hydrodynamic focusing in a microfluidic Coulter counter device. In this approach, the flow field is described by solving the incompressible Navier-Stokes equations. The sample stream concentration is modeled by an advection-diffusion equation. The motion of the cells is governed by the Newton-Euler equations of motion. Particle motion through the flow field is handled using an overlapping grid technique. A numerical model for studying a microfluidic Coulter counter has been validated. Using the model, the impact of relative flow rate on the performance of hydrodynamic focusing was studied. Our numerical results show that the position of the sample stream can be controlled by adjusting the relative flow rate. Our simulations also show that particles can be focused into the stream and initially close particles can be separated by the hydrodynamic focusing. From our study, we conclude that hydrodynamic focusing provides an effective way to control the position of the sample stream and cells and it also can be used to separate cells to avoid signal jam.

Copyright © 2012 by American Society of Mechanical Engineers
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Figure 1

Schematic of a multiple-inlets Coulter counter microfluidic device

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Figure 2

Multiple-inlets configurations (the color variation means the concentration variation). (a) Single outlet design; (b) multiple-outlet design.

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Figure 3

Overlapping grids

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Figure 4

Schematic of the channel and its dimensions

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Figure 5

Comparison of downstream velocity distribution at the fully developed region with the analytical solution

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Figure 6

Concentration for a sample stream injected into a single channel

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Figure 7

Concentration profiles at distances x = 1, x = 2, and x = 3 from the inlet for a single channel

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Figure 8

Concentration contours show the sample flow concentration due to hydrodynamic focusing

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Figure 9

The concentration profiles at different locations

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Figure 10

Comparison of concentration profile at different diffusivities. (a) Distribution along the center line. (b) Distribution at cross section x = 4.5.

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Figure 11

Concentration along the center line for varied relative flow rates

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Figure 12

Concentration profiles for varied relative flow rate at x = 4.5

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Figure 15

Snapshots of the cell position at different time instants (the circle represents the cell)

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Figure 16

Computational setup for the simulation of multiple cells in a micro-channel

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Figure 17

Snapshots of the cell motion in a micro-channel

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Figure 18

Distance between the two cells as a function of time

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Figure 19

Motion of multiple cells under hydrodynamic focusing (multiple cells)

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Figure 20

Streamlines in a three-inlet/three-outlet micro-channel device

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Figure 21

Concentration contours in the micro-channel with different relative flow rates

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Figure 13

Micro-channel with the mark of p and q

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Figure 14

Distribution of concentration with unequal sheath flow rates



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