(a) Schematic diagram of the particle focusing principle in a straight microchannel with a symmetrical CEA structure. Reproduced with permission from Cha et al., Rheol. Acta 53, 127 (2014). Copyright 2014 Springer Publishing. (b) Schematic diagram of a two-stage viscoelastic microfluidic device for particle elasto-inertial focusing and viscoelastic separation. Reproduced with permission from Yuan et al., RSC Adv. 7, 6 (2017). Copyright 2017 Royal Society of Chemistry. (c) Schematic diagram of the unilateral CEA microchannel using viscoelastic fluid sheath flow and the principle of size-based particle separation. Reproduced with permission from Shi et al., Analyst 144, 20 (2019). Copyright 2019 Royal Society of Chemistry. (d) Schematic diagram of a sandwich structure microfluidic device with three inlets for label-free and size-based sorting of tumor cells. Reproduced with permission from Shi et al., Anal. Bioanal. Chem. 412, 5513 (2020). Copyright 2020 Springer Publishing. (e) Schematic diagram of the microchannel for elasto-inertial fluid mixing, and the images of Newtonian fluids and viscoelastic fluids after mixing. Reproduced with permission from Hong et al., Appl. Phys. Lett. 108, 1 (2016). Copyright 2016 AIP Publishing LLC. (f) Schematic diagram of a micromixer combining a serpentine channel and a tooth-shaped contraction–expansion structure. Reproduced with permission from Julius et al., Biochip J. 10, 1 (2016). Copyright 2016 Springer Publishing.