Deformability-Based Electrokinetic Particle Separation

Abstract

Deformability is an effective property that can be used in the separation of colloidal particles and cells. In this study, a microfluidic device is proposed and tested numerically for the sorting of deformable particles of various degrees. The separation process is numerically investigated by a direct numerical simulation of the fluid⁻particle⁻electric field interactions with an arbitrary Lagrangian⁻Eulerian finite-element method. The separation performance is investigated with the shear modulus of particles, the strength of the applied electric field, and the design of the contracted microfluidic devices as the main parameters. The results show that the particles with different shear moduli take different shapes and trajectories when passing through a microchannel contraction, enabling the separation of particles based on their difference in deformability.

Keywords: arbitrary Lagrangian–Eulerian (ALE); dielectrophoresis; microfluidic; particle separation.

Figure 1

Electrokinetic motion of a deformable spherical particle of radius r_p in a microfluidic chip with a contraction throat. w: width of the main channel. Widths of the channels with outlet IH and FE are identical. r₁ and r₂ are the radii of the two quad-circles, respectively; d_p is the distance between the center of the spherical particle and the nearest channel wall.

Figure 2

Velocity of a rigid sphere translating along the axis of a cylindrical tube as a function of the ratio between the diameter d of the sphere and diameter a of the channel. The solid line and triangle symbols represent the analytical solution of Keh and Anderson [45] and the numerical results from the present model, respectively.

Figure 3

The spanwise component of dielectrophoretic (DEP) force along the channel for particles with two different shapes (identical volumes) with r₁ = 60 µm, r₂ = 120 µm. The radius of the circular particle is 5 µm, while the lengths of the major and minor axis of the ellipse are 6.25 and 4 µm, respectively.

Figure 4

Trajectories of particles with different shear moduli G with r₁ = 60 µm, r₂ = 120 µm, and the strength of the axial electric field in the channel E = 30 V/m. An enlarged view of the contraction region is on the right. GN: shear modulus of the particle of N Pa. (axis in μm).

Figure 5

Time trace of a deformable particle passing through the contraction with the shear modulus (a) G = 20 Pa and (b) G = 200 Pa while r₁ = 60 µm, r₂ = 120 µm, and E = 30 V/m. The positions from left to right represent time lapse of 0, 25, 40, 46, 51, 53.5, 55, 60, and 80 ms.

Figure 6

Velocity components of particles with different shear moduli in motion. (a) u, main flow direction; (b) v, orthogonal to main flow direction. Here r₁ = 60 µm, r₂ = 120 µm, and the electric field intensity in the channel is E = 30 V/m.

Figure 7

Trajectories of a particle for various combinations of the shear modulus G and strength of the axial electric field in the channel E_x with r₁ = 60 µm and r₂ = 120 µm. On the right is an enlargement of the contraction region. Ei_Gj stands for the electric field strength in the channel at i V/m and the shear modulus of the particle at j Pa. Axes are in μm.

Figure 8

Trajectories of particles with two different shear moduli G for various values of r₁ and r₂ when the axial electric field in the channel is E = 30 V/m. (a) r₁ = 90 µm and r₂ = 90 µm; (b) r₁ = 80 µm and r₂ = 100 µm; (c) r₁ = 40 µm and r₂ = 140 µm; (d) r₁ = 30 µm and r₂ = 150 µm. Axes are in μm.