Continuous and straightforward sorting of particles in microcavities with side outlets using inertial microfluidics

Inertial microfluidic technology has emerged as a highly promising approach for the separation of particles/cells, characterized by high throughput and label-free features. This study presents a novel inertial microfluidic chip design that enables the continuous separation of target particles at low Reynolds numbers (Re ≤ 36). To enhance its sorting performance, the influences of Reynolds numbers (Re = 3.7–60), particle sizes (d = 10 and 20 μm), and outlet flow rates on the particle separation efficiency and purity are further examined, and a phase diagram of the optimal working conditions is obtained. The evolution of the flow field structure within the microfluidic chip is comprehensively analyzed, which can be divided into three distinct regions, namely, the main flow, sheath flow, and vortex. The mechanism of particle migration behavior across curved streamlines is further explored. This device can achieve a maximum separation efficiency of 94% for target large particles (d = 20 μm), with a fivefold increase in the enrichment concentration, a 31.3-fold increase in purity, and a removal efficiency of small particles reaching 97.1%. The results demonstrate that this device can facilitate the continuous and direct separation of target larger particles based on their size, presenting numerous advantages, such as a short microchannel length, low Reynolds number, minimal cell damage, and ease of operation. Hence, this method represents an easy-to-use and straightforward approach for microfluidic sorting techniques and is anticipated to have practical application in the sorting of rare circulating tumor cells from complex cell solutions.