Controllable trajectory of inertial focusing in microfluidics

Inertial focusing in microfluidics has been widely utilized to sort cells based on cell specific properties for clinical assay, the detection of environmental pathogenic microorganisms and cell biology research. Especially, cell inertial focusing in microchannels, containing slant groove structures, has been utilized for cell separation, enrichment and sample preparation. However, cell inertial focusing in slant-groove-structure-based microchannels, including slant-groove-structure (SGS), asymmetric-herringbone-structure (AHS) and integrated-asymmetric-herringbone-structure (IAHS) microchannels, has not been systematically explored. In this report, three types of microfluidic channels, including SGS, AHS and IAHS microchannels, were fabricated to study cell movement and cell inertial focusing. One single trajectory and two trajectories of inertial focusing were observed in SGS and AHS microchannels, respectively. The trajectories of inertial focusing were interpreted by the combination of lift force and Dean force, according to the results from fluid filed simulation and experiments. On the basis of the theoretical analysis, it was found that the number of inertial focusing trajectories was controllable through the design of slant-groove-structure-based microchannels. Furthermore, IAHS microchannels were fabricated and multiple trajectories of inertial focusing were obtained. These results demonstrate the controllability of inertial focusing trajectories in microfluidics. This work contributes to the control of the number of inertial focusing trajectories, provides an opportunity to increase the throughput of cell sorting due to the augment of cell inertial focusing trajectories and make microfluidics more applicable to the research of cell biology, disease diagnosis and clinical testing.