(a) Schematic diagram of a three-stage straight microchannel with different structures for particle single-stream focusing. Reproduced with permission from Chung et al., Lab Chip 13, 15 (2013). Copyright 2013 Royal Society of Chemistry. (b) Schematic diagram of several different geometric shape combinations of curved channels and contraction–expansion channels. Reproduced with permission from Shamloo et al., Aiche J. 65, 11 (2019). Copyright 2019 John Wiley and Sons. (c) Schematic diagram of a spiral microchannel with obstacles. Reproduced with permission from Shen et al., Lab Chip 17, 21 (2017). Copyright 2017 Royal Society of Chemistry. (d) Schematic diagram of a spiral contraction–expansion microchannel for efficient and stable particle separation. Reproduced with permission from Gou et al., Anal. Chem. 92, 2 (2020). Copyright 2020 American Chemical Society. (e) Schematic diagram of a centrifugal microfluidic platform with a unilateral contraction–expansion channel and a serpentine channel with obstacles for cell sorting and lysis. Reproduced with permission from Nasiri et al., Micromachines 11, 7 (2020). Copyright 2020 Molecular Diversity Preservation International.