Continuous sheath-free separation of particles by shape in viscoelastic fluids

Abstract

Shape is an important indicator of cell type, cycle, and state, etc., and can thus serve as a specific marker for label-free bioparticle separation. We demonstrate in this work a shape-based separation of equal-volumed spherical and peanut particles in viscoelastic fluids through straight rectangular microchannels. This continuous sheath-free separation arises from the shape-dependent equilibrium particle position(s) as a result of the flow-induced elasto-inertial lift and shear thinning effects. A continuous transition from single to dual and to triple equilibrium positions is observed for both types of particles with the increase in flow rate. However, the flow rate at which the transition takes place differs with the particle shape. This phenomenon occurs only in microchannels with a large aspect ratio (width/height) and has not been reported before. It is speculated to correlate with the dissimilar dependences of elastic and inertial lift forces on particle size and flow rate as well as the rotational effects of non-spherical particles.