Microparticle separation based on size, density and shape in a sharp-corner MOFF channel using hydrodynamic effects

High-purity fractionation of microparticles of different particle features is of great importance, especially in clinical diagnosis, recycling applications, and the food industry. We show that high-purity particle separation driven purely by hydrodynamic effects in a microchannel can be realized, achieving not only size, but also density and shape fractionation. For this, a microchannel with periodic contraction-expansion sections is used. A key feature of the method is that the Reynolds number at which a transition between particle equilibrium focusing regimes occurs decreases with increasing particle size, density, or aspect ratio. The evolution of inertial lift forces and centrifugal forces acting on individual particles is studied based on experimentally-determined, local features of the flow field, to gain a deeper insight into the particle migration dynamics. For this purpose, the General Defocusing Particle Tracking method is employed to reconstruct the three-dimensional positions of ellipsoidal and spherical particles. By enabling efficient, purely hydrodynamic separation of microparticles based on size, density, and shape, this approach opens new possibilities for passive separation in microfluidic applications.