Viscoelastic microfluidics: progress and challenges

Abstract

The manipulation of cells and particles suspended in viscoelastic fluids in microchannels has drawn increasing attention, in part due to the ability for single-stream three-dimensional focusing in simple channel geometries. Improvement in the understanding of non-Newtonian effects on particle dynamics has led to expanding exploration of focusing and sorting particles and cells using viscoelastic microfluidics. Multiple factors, such as the driving forces arising from fluid elasticity and inertia, the effect of fluid rheology, the physical properties of particles and cells, and channel geometry, actively interact and compete together to govern the intricate migration behavior of particles and cells in microchannels. Here, we review the viscoelastic fluid physics and the hydrodynamic forces in such flows and identify three pairs of competing forces/effects that collectively govern viscoelastic migration. We discuss migration dynamics, focusing positions, numerical simulations, and recent progress in viscoelastic microfluidic applications as well as the remaining challenges. Finally, we hope that an improved understanding of viscoelastic flows in microfluidics can lead to increased sophistication of microfluidic platforms in clinical diagnostics and biomedical research.

Tunable Viscoelastic Properties of Sodium Polyacrylate Solution via CO2-Responsive Switchable Water

“…Figure S2 shows the viscosity-shear rate curves of the samples containing 0.65 wt% and 1.30 wt% NaPAA in the absence and presence of CO 2 . It can be found that the fluids showed Newtonian behavior with high, near-constant viscosities at low shear rates, then exhibited shear thinning properties in which the viscosities sharply decreased with the increment in shear rate, which was consistent with typical rheological properties of viscoelastic fluids [3,9]. After bubbling CO 2 for 10 min until the conductivity of the solutions stabilized, the viscosity of each fluid underwent an apparent decrease over the entire range of tested shear rates, and the lower the shear rate, the larger the decrement in viscosity.…”

“…As a non-Newtonian fluid, a viscoelastic solution usually exhibits unique rheological properties (i.e., both liquid-like fluidity under some circumstances and solid-like elasticity under others) [1][2][3][4], which endow it with many distinct behaviors, such as the Weissenberg effect [2,5], extrudate swell [3], and fading memory [6]. Those characteristics allow for great potential applications in fields like food science [4], damping [7], tissue engineering [8], and oil development [9,10].…”

Flow of Non-Newtonian Fluids in a Single-Cavity Microchannel

“…where is the fluid density (assumed to be the density of the solven dilute solutions), is the average fluid speed in the main channel, We did not consider the thixotropy [78] of the prepared non-Newtonian fluids as these polymer solutions have been commonly treated as shear thinning and viscoelastic fluids in the literature [11][12][13][16][17][18]70]. However, the occurrence of low-inertia instabilities in the flow of thixotropic fluids [79] may be an interesting direction for future work.…”

“…The applications pertain to the areas of point-of-care technologies, chemical synthesis, microfluidic rheometry, etc. [ 14 , 15 , 16 , 17 , 18 ].…”

“…The goal is to obtain a unified understanding of the effects of fluid inertia, shear thinning, and elasticity, as well as confinement. It is important to note that our tested fluids have been commonly used in microfluidic applications [ 13 , 16 , 17 , 18 , 70 ], rendering them useful to be studied directly. These fluids possess different elastic and shear thinning properties, though their infinite-shear-rate viscosity values are comparable.…”