Rheology of soft and rigid micro particles in curved microfluidic channels

Abstract

We investigated the rheological behavior of micro particles in inertial flow in a curved microfluidic channel. Different from the typical microfluidic regime operating at low Reynolds number, inertial flow provides hydrodynamic manipulation, namely inertial focusing of particles at high flow speeds. Primary influences of inertial flow on particle motions are several: repulsive force from the wall due to a pressure buildup in the constriction between the wall and the particle, shear gradient lift force due to the parabolic flow profile at microscale, and secondary drag force in the crosssectional direction due to channel curvature. These forces result in particle moving across the streamlines to certain predictable equilibrium positions in the flow. With regard to soft particles, their flow behavior and equilibrium positions may deviate from the theoretical predictions based on rigid particles. This study provides a proof-of-concept of inertial focusing-based separation of particles with different deformability. We demonstrated its capability by separating yeast cells and polystyrene particles of similar sizes in a double spiral channel.