Myung Gwon Lee

Label-free cancer cell separation from human whole blood using inertial microfluidics at low shear stress.

We report a contraction-expansion array (CEA) microchannel device that performs label-free high-throughput separation of cancer cells from whole blood at low Reynolds number (Re). The CEA microfluidic device utilizes hydrodynamic field effect for cancer cell separation, two kinds of inertial effects: (1) inertial lift force and (2) Dean flow, which results in label-free size-based separation with high throughput. To avoid cell damages potentially caused by high shear stress in conventional inertial separation techniques, the CEA microfluidic device isolates the cells with low operational Re, maintaining high-throughput separation, using nondiluted whole blood samples (hematocrit ~45%). We characterized inertial particle migration and investigated the migration of blood cells and various cancer cells (MCF-7, SK-BR-3, and HCC70) in the CEA microchannel. The separation of cancer cells from whole blood was demonstrated with a cancer cell recovery rate of 99.1%, a blood cell rejection ratio of 88.9%, and a throughput of 1.1 × 10(8) cells/min. In addition, the blood cell rejection ratio was further improved to 97.3% by a two-step filtration process with two devices connected in series.

Three-dimensional hydrodynamic focusing with a single sheath flow in a single-layer microfluidic device

We report a contraction-expansion array (CEA) microchannel that allows three-dimensional hydrodynamic focusing with a single sheath flow in a single-layer device. The CEA microchannel exploits centrifugal forces acting on fluids travelling along the contraction and expansion regions of the microchannel. Around an entrance of the contraction region, the centrifugal forces induce a secondary flow field where two counter-rotating vortices enable to envelop a sample flow with a sheath flow in three dimensions. We herein describe an underlying principle and a design of the CEA microchannel and demonstrate complete sheathing of a sample fluid (water and human red blood cells) in three dimensions. The focusing characteristics of the CEA microchannel are investigated in terms of the number of the rectangular structures, flow rate, and flow ratio between sample and sheath flows. This microfluidic channel for three-dimensional hydrodynamic focusing is easy to fabricate in a single-layer fabrication process and simple to operate with a single sheath flow.

Inertial separation in a contraction-expansion array microchannel.

We report a contraction-expansion array (CEA) microchannel that allows inertial size separation by a force balance between inertial lift and Dean drag forces in fluid regimes in which inertial fluid effects become significant. An abrupt change of the cross-sectional area of the channel curves fluid streams and produces a similar effect compared to Dean flows in a curved microchannel of constant cross-section, thereby inducing Dean drag forces acting on particles. In addition, the particles are influenced by inertial lift forces throughout the contraction regions. These two forces act in opposite directions each other throughout the CEA microchannel, and their force balancing determines whether the particles cross the channel, following Dean flows. Here we describe the physics and design of the CEA microfluidic device, and demonstrate complete separation of microparticles (polystyrene beads of 4 and 10 μm in diameter) and efficient exchange of the carrier medium while retaining 10 μm beads.

Inertial blood plasma separation in a contraction–expansion array microchannel

Continuous inertial blood plasma separation is demonstrated in a contraction–expansion array microchannel with a low aspect ratio (AR). The separation cutoff value of the particle size can be controlled by modulation of the force balance between inertial lift and Dean drag forces. The modulation is achieved by changing the channel AR at contraction region, which causes the change in magnitudes of the inertial lift forces on the particles. The presented blood plasma separator provides a level of yield and throughput of 62.2% and 1.2 ml/h(∼1.0×108 cells/min), respectively.

Rapid laminating mixer using a contraction-expansion array microchannel

Three-dimensional lamination mixing is demonstrated in a simple and easily fabricated contraction-expansion array microchannel. The abrupt change of the cross-sectional area of the channel curves fluid streams and accelerates the flow velocity especially at the entrance of the contraction region. Centrifugal effects at that region result in Dean vortices that continuously split and redirect fluid streams, thereby enabling appreciable mixing. The presented mixer provides a level of 90% mixing in the relatively large range of Reynolds number from 4.3 to 28.6 by employing the channel with 30 contraction-expansion units.

Microfluidic parallel circuit for measurement of hydraulic resistance

We present a microfluidic parallel circuit that directly compares the test channel of an unknown hydraulic resistance with the reference channel with a known resistance, thereby measuring the unknown resistance without any measurement setup, such as standard pressure gauges. Many of microfluidic applications require the precise transport of fluid along a channel network with complex patterns. Therefore, it is important to accurately characterize and measure the hydraulic resistance of each channel segment, and determines whether the device principle works well. However, there is no fluidic device that includes features, such as the ability to diagnose microfluidic problems by measuring the hydraulic resistance of a microfluidic component in microscales. To address the above need, we demonstrate a simple strategy to measure an unknown hydraulic resistance, by characterizing the hydraulic resistance of microchannels with different widths and defining an equivalent linear channel of a microchannel with repeated patterns of a sudden contraction and expansion.

Inertia-activated cell sorting of immune-specifically labeled cells in a microfluidic device

This paper demonstrates an inertia-activated cell sorting method to separate cells based on their surface protein expression by using inertial microfluidics. Target cells are immune-specifically reacted with antibody-coated microbeads and then separated from nontarget cells. As a proof of concept, separation of MCF-7 breast cancer cells from U937 lymphoma cells was achieved with 97.6% target cell recovery rate, 95% nontarget cell rejection ratio, 73.8% purity, and an enrichment ratio of 93 at a total flow rate of 8.75 mL h−1 without using any external forces.

High-throughput nanoscale lipid vesicle synthesis in a semicircular contraction-expansion array microchannel

Towards potential applications in the field of nanomedicine, a new high-throughput synthesis method of lipid vesicles with tunable size as well as enhanced monodispersity is demonstrated using a semicircular contraction-expansion array (CEA) microchannel. Lipid vesicles are generated in the CEA microchannel by injecting lipids in isopropyl alcohol as a sample flow and phosphate buffered saline as a buffer flow, leading to spontaneous formation of lipid vesicles. In the CEA microchannel, Dean vortices cause three-dimensional (3D) lamination by continuously splitting and redirecting fluid streams, resulting in enhancement of fluid mixing. When considered only 3D laminating effect, it showed the best mixing efficiency in the range of flow rates of 12–15 mL/h. However, shear force effect also gives a strong influence on the formation of lipid vesicles, leading to the smallest size and uniform size distribution of lipid vesicles at a total flow rate of 18 mL/h. Consequently, from the interplay between high shear stress and 3D laminating effect, the lipid vesicles were generated with monodispersity and high throughput. The formation of lipid vesicles can be controlled with a total flow rate and a flow rate ratio between the sample and buffer fluids. The throughput of the lipid generation in the CEA microchannel was 10 times higher than previous works. In addition, the generated lipid vesicle populations were confirmed using a cryogenic transmission electron microscopy (cryo-TEM) technique.