“From the Edge to the Center”: Viscoelastic Migration of Particles and Cells in a Strongly Shear-Thinning Liquid Flowing in a Microchannel

Abstract

Controlling the fate of particles and cells in microfluidic devices is critical in many biomedical applications, such as particle and cell alignment and separation. Recently, viscoelastic polymer solutions have been successfully used to promote transversal migration of particles and cells toward fixed positions in straight microchannels. When inertia is negligible, numerical simulations have shown that strongly shear-thinning polymer solutions (fluids with a shear viscosity that decreases with increasing flow rates) promote transversal migration of particles and cells toward the corners or toward the centerline in a straight microchannel with a square cross section, as a function of particle size, cell deformability, and channel height. However, no experimental evidence of such shifting in the positions for particles or cells suspended in strongly shear-thinning liquids has been presented so far. In this work, we demonstrate that particle positions over the channel cross section can be shifted "from the edge to the center" in a strongly shear-thinning liquid. We investigate the viscoelasticity-induced migration of both rigid particles and living cells (Jurkat cells and NIH 3T3 fibroblasts) in an aqueous 0.8 wt % hyaluronic acid solution. The combined effect of fluid elasticity, shear-thinning, geometric confinement, and cell deformability on the distribution of the particle/cell positions over the channel cross section is presented and discussed. In the same shear-thinning liquid, separation of 10 and 20 μm particles is also achieved in a straight microchannel with an abrupt expansion. Our results envisage further applications in viscoelasticity-based microfluidics, such as deformability-based cell separation and viscoelastic spacing of particles/cells.

Fluid Viscoelasticity Drives Self-Assembly of Particle Trains in a Straight Microfluidic Channel

“…A constant spacing between particles is also beneficial for the real-time analysis of flowing cells since it reduces computational costs associated with data analysis [18]. Shear-thinning fluids display an almost flat velocity profile near the channel centerline at De > 1, thus flowing cells would potentially be undeformed (or only slightly deformed), which is optimal for manipulation of delicate cells [32]. Furthermore, as compared to inertial microfluidics, the relatively low flow rates needed to achieve ordering are more compatible with downstream droplet generation systems.…”

“…It should also be emphasised that shear-thinning liquids have always been considered as detrimental for particle alignment, since particles tend to migrate towards the channel walls [30,31]. Only very recently, Del Giudice et al [32] showed that moving particles can be aligned on the centreline of a straight squareshaped microchannel, even in a shear-thinning liquid, by increasing the ratio of the particle size to the channel height. Therefore, further investigation on viscoelastic particle ordering seems at order.…”

Focusing and splitting streams of soft particles in microflows via viscosity gradients

“…Ref. [21]). Since in such non-Newtonian liquids shear thinning, leading to a non-constant viscosity, comes often simultaneously into play with a fluid elasticity, the specific contribution of a non-constant viscosity to particle CSM is not clear.…”

Manipulation of micro‐ and nanoparticles in viscoelastic fluid flows within microfluid systems

“…Particle focusing methods have been further characterized in detail in other studies. Particle motion was, in particular, investigated via shear‐thinning VEF flows where the lateral migration of particles was characterized accordingly (Del Giudice, D'Avino, Greco, Netti, & Maffettone, ; Del Giudice, Sathish, D'Avino, & Shen, ; Li, McKinley, & Ardekani, ; Lim, Nam, & Shin, ; Villone, D'Avino, Hulsen, Greco, & Maffettone, ). Individual and combined effects of fluid inertia, elasticity, and shear thinning on particle focusing were studied by Li and Xuan ().…”