Size-Dependent Inertial Focusing Position Shift and Particle Separations in Triangular Microchannels

Abstract

A recent study of inertial microfluidics within nonrectangular cross-section channels showed that the inertial focusing positions changes with cross-sectional shapes; therefore, the cross-sectional shape can be a useful control parameter for microfluidic particle manipulations. Here, we conducted detail investigation on unique focusing position shift phenomena, which occurs strongly in channels with the cross-sectional shape of the isosceles right triangle. The top focusing positions shift along the channel walls to the direction away from the apex with increasing Reynolds number and decreasing particle size. A larger particle with its center further away from the side walls experiences shear gradient lift toward the apex, which leads to an opposite result with changes of Reynolds and particle size. The focusing position shift and the subsequent stabilization of corner focusing lead to changes in the number of focusing positions, which enables a novel method for microparticle separations with high efficiency (>95%) and resolution (<2 μm). The separation method based on equilibrium focusing; therefore, the operation is simple and no complex separation optimization is needed. Moreover, the separation threshold can be easily modulated with flow rate adjustment. Rare cell separation from blood cell was successfully demonstrated with spiked MCF-7 cells in blood by achieving the yield of ∼95% and the throughput of ∼10 cells/min.

3D Printing of Inertial Microfluidic Devices

“…three separate points. This trend is similar to those reported in the literature 14,53,54 . The results for MDA-MB-231 cells at flow rate of 200 µl/min illustrate a single-line focusing position, and at flow rate of 500 µl/min depict three focusing positions.…”

“…However, due to the fabrication limitations, dependency of various cross-sections to channel geometries was not systematically investigated. Recently, triangular and semi-circular cross-sections were fabricated using Si anisotropic etching with potassium hydroxide 53 , a brass for mold fabrication 54 , FDM for creation of sacrificial mold 40 , or unconventional micromilling 14 . However, critical fabrication limitations do not allow for further investigation on the dependency of triangular angle or type (e.g., right-angled triangular) on focusing patterns of the particles.…”

“…The primary usage of MACS buffer is to prevent nonspecific adhesion of microbeads to the tubing of the microchannel. The distribution of particles is illustrated using standard deviation, minimum, or maximum light intensity plots, as reported previously 54 . Bonding quality test.…”

Numerical method for inertial migration of particles in 3D channels

“…Secondly, we study the dynamic of a ball due to inertial forces in a cylinder with a rectangular section. Finally, we consider the situation reported in [13] in the context of particle separation using inertial focusing. In what follows we compute the solution ( U 1 , U 3 ) of the linear system (26) for different geometric configurations.…”

“…These applications use an early observation of Segré and Silberberg that different sized particles have different equilibrium regions, or, with other words, different focusing positions. While for channels of circular sections the equilibrium regions are well understood, for channels of less symmetric sections the situation is far from being clear, different experimental or numerical studies giving different numbers of equilibrium points in cases as simple as a channel with rectangular section [3,2,4,12,13]. The mathematical models for the inertial migration of particles in fluid flows have mostly been studied for channels with circular section.…”