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

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.