Secondary flow enhancement in ultra-low aspect ratio microchannels with ordered Micro-obstacles for high-throughput cell focusing

The regulation of secondary flow through geometric confinement in low aspect ratio microchannels plays a crucial role in cell separation, blood plasma extraction, and single-cell analysis. However, a systematic investigation comparing the mechanisms of secondary flow acceleration encouraged by ordered micro-obstacles in two common channel configurations—straight and curved—has not been fully explored. In this study, we present an inertial microfluidic system to enable precise control of secondary flows within ultra-low aspect ratio (AR = 1: 9) microchannels. By introducing an identical number of micro-obstacles into both semicircular and straight microchannels, we observe distinct acceleration patterns of secondary flow at varying perfusion rates. Furthermore, each channel design demonstrates unique advantages in mixing efficiency across a broad range of flow capacities. Notably, high-throughput particle manipulation is achieved in both modified configurations, with effective targeting of cancer cells across a wide throughput spectrum (ranging from 2 × 10⁶ to 4 × 10⁶ cells/min). The approach employed to enhance secondary flow in this work provides valuable insights into the design of low aspect ratio microchannels, highlighting their ease of use, high throughput capabilities, and significant adaptability. This research paves the way for future explorations into innovative channel designs aimed at further improving the accuracy and efficiency of inertial microfluidics.