Particle recirculating orbits within microvortices using microfluidics

Abstract Particle/cell separation from a mixture using a hydrodynamic vortex has been attracting much interest for the isolation of circulating tumor cells in basic biological studies and clinical applications. However, some issues regarding the particle recirculating orbits within the vortex in microcavities remain unclear. In this work, using micro-particle image velocimetry and a high-speed microscopy system, we quantitatively investigate the effects of inlet Reynolds numbers ( Re ) on the microcavity flow characteristics and particle recirculating behavior. The results show that due to the evolution of microcavity flow patterns ( Re = 15–313), the particle orbit topology expands gradually, developing from a single small orbit ( Re = 39–79) to a single semicircular orbit (98–117), then to alternating double orbits ( Re = 136–215), and at last to a single large orbit ( Re = 254–352). The alternating double orbits are observed for the first time. The particle orbit periods and topologies (lengths and area) have also been characterized. Moreover, the variations of the recirculating particle velocity are also quantitatively measured. The results deepen the fundamental understanding of particle recirculating behavior and could provide useful guidance for vortex-based microfluidics.