Enhanced particle focusing and sorting by multiple sheath stream in contraction-expansion microchannel

Microfluidic devices have great potential in cell analysis, and cell focusing/sorting is one of the basic manipulation processes required for cell analysis. This paper proposes a microchannel with a contraction-expansion structure to improve the focusing and sorting performances of particles, integrating multiple sheath fluid inputs from a single inlet. To prove its applicability, the influences of the main structural parameters on the performance were studied using a fluid-particle interaction model. The focusing and sorting performances improved by 31.9% and 55.2%, respectively, when the sheath streams increased from one to two due to the strengthening Dean vortex. Optimization of each parameter significantly improved the performance, and the improvement exceeded 40%. The forces on the particles in this contraction-expansion microchannel with multiple sheath liquid flows were analyzed. A fitting correlation between the particle diameter and the minimum channel length required to achieve complete focusing was obtained, and the formula's accuracy was verified. This result is expected to be significant for selecting and optimizing contraction-expansion-type microchannels with sheath flows.