(323d) Numerical Model for Streaming Dielectrophoresis

Numerical Model for
Streaming Dielectrophoresis

Rucha
Natu, Monsur Islam and
Rodrigo Martinez-Duarte

Department of
Mechanical Engineering, Clemson University, Clemson, SC, USA

Here we present initial results
for developing a simulation based model for particle separation using streaming
dielectrophoresis (DEP). The technique of DEP induces
particle movement in the presence of non-uniform electric field, towards or
away from the field. This technique has been widely used for selective manipulation
and trapping of wide variety of particles and cells. Combination of DEP with a
flow field is an important technique for rapid separation. Streaming DEP works
with an interaction of DEP and Drag force to form concentrated streams of
selected particles. In the DEP Drag force field, the dominance of DEP force
gives rise to trapping of particles, whereas dominance of Drag force gives rise
to flow of particles. The effective manipulation of these two forces can create
concentrated streams of the particles. The variation of particle streams as an
effect of these forces is studied here by implementing COMSOL simulations. The
stream widths are computed for different flow rates, frequencies, and voltages
in a microfluidic chip. Simulations are also carried out for different shapes
of electrodes to study the streaming zones for each case. Simulation considers
1um latex particles suspended in water as media. Simulations were
experimentally using a 3D carbon electrode set up.

Simulation model considers a 3D carbon
electrode set up, as fabricated by use of SU-8 photolithography. [1] The
electrode domain consists of an array of 80 rows with 5 electrodes in each row,
with alternate polarization. Streams are analyzed for circular, diamond and
triangular shaped electrodes. The flow rate is varied from 10 to 1000ul/min and
the frequencies used are 10-1000 kHz. The conductivity for the media is varied
from 0.0005-0.5 S/m. The analysis of streams  to compute the width of concentrated
streams is completed using Matlab 2014, as detailed
in our previous work. [2] By varying each parameter, the average magnitude of
DEP and Drag force in the domain were calculated.

The stream width was obtained for
different ratios of average Drag and DEP forces. It was observed that, for
every shape of electrode, the device showed streaming only is a certain range
of force ratio. In the regions with ratio being higher than this range, no
streams were seen, whereas for the domain with force ratio lower than the
range, all particles were trapped. For a particular electrode geometry, this
range remained unchanged irrespective of the voltage, flow rate and the
frequency used in the simulation. The plot for force ratio and the change in
stream width for triangles, circles and diamonds is shown in the Figure 1a.
Figure 1b shows the comparison for streams obtained in simulation compared to
experiments. This comparison is at the flow rate of 100ul/min, with voltage 14V
and frequency of 50 kHz. In case of the simulation, the streams are seen to
leave the electrodes at the lateral sides, whereas in the case of experiment,
streams focus at the center of the electrode. This difference in behavior is
due to the nature of boundary layer mesh used in the simulations and the fact
that the electrodes have a larger active surface area due to surface roughness
than simulated. Irrespective of these differences, the nature of the streams in
both cases is very similar.

The ongoing work is develop a
technique to predict the streaming behavior in the dielectrophoretic
chip based on applied parameters, i.e. voltage, frequency, flow rate, media
conductivity and electrode geometry. The objective of this tool is to vary the
parameters to cater the trapping or streaming behavior of cells in a dielectrophoretic chip as desired.

Figure 1: a) The figure shows the
width of stream obtained at different simulated voltages, frequencies, flow rates and media conductivities with respect to
corresponding force ratio for different shapes of electrodes. B) Validation of
simulation using experiment at the flow rate of 100 ul/min
and the frequency of 50kHz.

References:

1. Martinez-Duarte
R., Renaud P., and Madou M., 2011, “A novel approach to dielectrophoresis using
carbon electrodes,” Electrophoresis, 32(17), pp. 2385–92.

2.  Natu R., and Martinez-Duarte R., 2016,
“Numerical Model of Streaming DEP for Stem Cell Sorting,” Micromachines,
7(12), p. 217.