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

TLDR

The study presents the principle and design of a contraction–expansion array microchannel that achieves complete three‑dimensional hydrodynamic sheathing of sample fluids, including water and human red blood cells. The device uses centrifugal forces in contraction and expansion regions to generate counter‑rotating vortices that envelop the sample flow, and its focusing performance depends on the number of rectangular structures, flow rate, and sample‑to‑sheath flow ratio. The contraction–expansion array microchannel enables three‑dimensional hydrodynamic focusing with a single sheath flow in a single‑layer device, is easy to fabricate, and operates simply while successfully sheathing water and human red blood cells.

Abstract

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.