Synergistically enhancing inertial particle focusing using a curved microchannel with expansion-contraction arrays

Particle focusing, which organizes randomly dispersed particles into streamlines, is crucial for particle counting, enrichment, and detection. This process is widely applied in disease diagnosis, biochemical testing, and environmental monitoring. We designed a curved microchannel featuring integrated rectangular expansion-contraction arrays on its inner side. Our design diverges from conventional techniques by harnessing the synergistical effect of Dean flow induced by both structures based on the unique geometric configuration, resulting in a marked improvement in particle focusing efficiency. We validated the focusing performance of the combined microchannel and elucidated inertial focusing mechanisms by integrating experiments with simulations. At a Reynolds number of 83.33, a 4.34-cm-long microchannel can achieve the complete focusing of 10-μm particles, representing an advancement over current designs. Furthermore, our research uncovers a novel observation: the focusing width initially decreases with the expansion region's width and then increases, while the length of the expansion region leads to a gradual decrease in focusing width until it reaches a stable point. Through structural optimization, the dimensionless focusing width of 10-μm particles was reduced from 0.102 to 0.065 at a Reynolds number of 50, and particles of 5 and 15 μm can be completely focused, highlighting its adaptability and exceptional performance across a range of particle sizes. This study not only advances the un1derstanding of particle focusing dynamics but also paves the way for the development of more efficient and versatile microfluidic devices for a multitude of applications.