NUMERICAL MODEL FOR MICROPARTICLE AND LYMPHOCYTE
MOTIONS IN DIELECTROPHORETIC MANIPULATION DEVICE
K. Tatsumi1*, K. Imajou, H. Shintani, Y. Katsumoto2 and K. Nakabe1
1

Department of Mechanical Engineering and Science, Kyoto University, JAPAN and
2
Sony Corporation, JAPANABSTRACTThis paper describes the development of numerical model and scheme that can accurately solve the particle/cell motion
dynamics in microchannels considering the physics of the AC electric field, dielectrophoresis (DEP) force, electrothermalflow, and hydrodynamic forces in three-dimensional form. This numerical model can be used to aid the designing of the microchip particularly intended for cell manipulation and separation. To demonstrate the performance of the model, a particle/cell manipulation device using semicircle electrode and microchannel flows was designed and evaluated experimentally.
KEYWORDS: Numerical simulation, Cell manipulation, Dielectrophoresis, Microparticle, Lymphocyte
INTRODUCTION
Cell manipulation and separation technology using DEP force and microchannels has been keenly investigated in the past
decade providing various types of electrodes and channels [1,2]. However, the manipulation performance has not sufficiently
reached the level for practical use in terms of manipulation speed and accuracy. One of the practical issues in developing thedevices is the absence of a simulation model that can predict the cell motion and phenomena accurately. The numericalmodel originally coded in this study considers not only the AC electric field, shell model of the cell and DEP force applied tothe cell or particle, but also the flow/particle conjugate problem including the three-dimensional interaction between the solid
particle and flow. Further, the influence of the electrothermal flow appearing in the microchannel attributed to the Joule heating is considered in the simulation. Based on the authors’ knowledge, such a detail and accurate scheme has not been provided yet, and it will largely contribute to the fields of micro fluidic devices, electrochemistry and medicine. In this study, thenumerical scheme was used to design a manipulation device shown in Fig. 1 (a), paying attention particularly on the patternof the electric fields that can provide stable and effective particle motion. In the manipulation area, comb shape electrodes
attached to the channel bottom wall and aligned in the streamwise direction were basically considered to generate a negative
DEP force on the particles and move them apart from the straight comb electrodes.
NUMERICALThe numerical model mainly consists of two parts: the electric field and DEP force for the particle or lymphocyte, andfluids and particle motions. The electric field was calculated using a commercially available software COMSOL multiphysics.
The DEP force Fdep was then evaluated from the electric field considering the Clausius-Mossotti function of a spherical particle. In this case, the lymphocyte was modeled as a sphere with uniform electric properties which were calculated on the basis of a multi shell model described in reference [3]. Once the Fdep was obtained, the equation of fluid and particle motions
were calculated. A particle with finite diameter was considered in this study, where the interaction between the particle andfluid was solved using the Immersed Boundary method [4]. Namely, the force applied to the particle surface by the flow
shear stress and pressure was considered in the equation of motion, while the particle momentum is then transferred and applied to the surrounding fluids. The flow field was calculated solving the mass and momentum conservation equations using(a) particle/cell manipulation device(b) numerical model
Figure 1: Schematic diagram of (a) the electrodes and microchannel in the particle/cell manipulation device (the dimensions are in μm) (b) three-dimensional numerical model applied to solve lymphocyte motion in the device.
978-0-9798064-4-5/µTAS 2011/$20©11CBMS-0001

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15th International Conference on
Miniaturized Systems for Chemistry and Life SciencesOctober 2-6, 2011, Seattle, Washington, USAFigure 2: Trajectory of the micro polystyrene particles manipulated by the DEP force.
finite volume method and SIMPLE algorism. Further, the energy conservation equation in the channel was solved considering the Joule
heating of the electric field in order to calculate the temperature field.
The resulting electrothermal flow was then simulated by applied an external force based on the temperature distribution to the momentum
equation of the flow field [5]. These computations were carried out in acomputational domain presenting a single periodic unit of the manipulation (electrode) area.

Figure 3: Probability density function at theinlet and outlet positions.
|Erms| [kV/m]

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Figure 4: (a) Electric field intensity |Erms| and(b) spanwise dielectrophoresis force FDEP,y distributions on x-y plane at z=7.5μm.

EXPERIMENTAL
As shown in Fig. 1(a), the device has three flow inlets by which asheath flow is generated and the spanwise position of the particle entering the electrode area is controlled precisely. In the downstream regionof the manipulation area, the channel is bifurcated where the particles
are normally guided to one side while the specific particles are selectedto flow to the other side by activating the dielectrophoretic force. Platinum electrodes were sputtered and patterned on the glass plate onto
which the PDMS channel was attached. The motion of the particles
was measured using a microscope and high-speed digital video camera,
and the particle/cell positions and velocities were measured from therecorded images. Experiment was carried out for polystyrene microparticles (Thermofisher scientific; 4212A) and lymphocyte (ATCC; CRL2570) suspended in PBS solution using the micro manipulation devise
shown in Fig. 1 (a). AC voltage of 19Vp-p and 10MHz was applied tothe electrodes. The total flow rate in the main channel was 1.2μL/min.
RESULTS and DISCUSSION
Several types of comb shape electrodes were investigated in advance of the experiment employing the present numerical scheme.
Among these, the semicircle type electrode shown in Fig. 1 showed agood performance in the meanings of providing large and stable DEP
force on the particles for manipulation. The experimental results areshown here to demonstrate the performances. Figure 2 shows the photographs of the polystyrene particle passing the manipulation area. The
probability density function (PDF) distributions measured at the inlet
and outlet are shown in Fig. 3. As shown in Fig. 2, the particle is effectively driven in the spanwise direction due to the DEP force. The PDF
distributions show that the particles led to the electrode tip at the inletof the manipulation area by the sheath flow are manipulated and separated to the opposite side at the outlet successfully and accurately.
Figure 4 shows the numerical results of the electric field |Erms | distributions, and the spanwise component of the DEP force that works on
the particle, FDEP, y. Since the semicircle shape electrode encircles theother straight electrode, |Erms | gradually deceases toward the semicircle
electrode side. As a result, FDEP, y shows a positive value in the overall
area located between the electrodes. This leads to a stable cell manipulation that was not obtained in other electrode shapes additionallytested in the simulation and experiment.
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x [μm](b) lymphocytes(b) lymphocytes
Figure 5: Trajectories of the polystyrene Figure 6: Instantaneous streamwise and spanwise velocity distributions ofparticle and lymphocytes.
polystyrene particles and lymphocytes.
Figure 5 shows the experimental and numerical results of the trajectories projected on the x−y plane in the cases of theparticle and lymphocyte motions. Figure 6 shows the streamwise and spanwise velocities, up and vp, of both cases. To demonstrate the accuracy of the present scheme, the numerical results applying the model that assumes the particle as a masspoint and neglecting the influence of the particle on the flow are also depicted in the figure.
Focusing on the pattern of the trajectories and the velocity distributions, the particle moves in the spanwise direction in astaircase pattern with a large displacement observed in the area close to the electrode tip. This agrees well with the feature ofthe FDEP, y distribution shown in Fig. 4 (b). Comparing the numerical and experimental results, the calculation using the masspoint model over-predicts the velocity and the spanwise position of the particle. This is mainly attributed to the lack of consideration on the particle-fluid interaction that markedly influence the flow field and resulting particle behavior. Therefore, inthe case of the calculation employing the present numerical scheme, an excellent agreement is achieved for the trajectories
and velocities in both cases of polystyrene particle and lymphocyte. The calculation predicts the motions even at the positions of the electrode tip showing that the influence of the 3D distribution of the FDEP, y field and the resulting behavior of theparticle and cells observed in a 3D form can be simulated accurately.
CONCLUSION
A numerical scheme that considers the electric field, DEP force, flow field, fluid-particle interaction, and the electrothermal flow was developed in this study in order to accurately predict the particle and lymphocyte motions in the manipulation
device using the DEP force. On the basis of the numerical results, a semicircle shape electrode was designed and was evaluated experimentally showing a high and stable performance. Furthermore, an excellent correspondence between the numerical and experimental results was obtained showing the validity of the numerical scheme.
ACKNOWLEDGEMENTS
This work is supported by Japan Agency of Science and Technology (Development of Systems and Technology for Advanced Measurement and Analysis).
REFERENCES[1] M. P. Hughes, "Strategies for Dielectrophoretic Separation in Laboratory-on-a-chip Systems," Electrophoresis, 23, 2569-2582, (2002).
[2] P. R. C. Gascoyne and J. Vykoukal, "Particle Separation by Dielectrophoretic," Electrophoresis, 23, 1973-1983, (2002).
[3] K. Asami, Y. Takahashi and S. Takashima, “Dielectric Properties of Mouse Lymphocytes and Erythrocytes”, Biochimica et Biophysica
Acta - Molecular Cell Research, 1010, 49-55, (1989).
[4] R. Mittal and G. Iaccarino, "Immersed Boundary Methods”, Ann. Rev. Fluid Mech, 37, 231-261, (2005).
[5] R. Ramos, H. Morgan, N. G. Green and A. Castellanos, "AC Electrokinetics: a review of forces in Microelectrode Structures”, J. Physics D, 31, 2338-2353, (1998).

CONTACT*K. Tatsumi, tel: +81-75-7535224; tatsumi@me.kyoto-u.ac.jp1366