Universal motion of mirror-symmetric microparticles in confined Stokes flow

Particles of all shapes and sizes flowing through tight spaces are ever present in applications across length scales ranging from blood flow through tissue capillaries to industrial-scale processes. To date, separating these particles relies on methods employing external force fields. Currently underexplored, omnipresent fluid-structure interactions hold the key to shape-based separation independent of external intervention. By leveraging experiments, theory, and simulations, we show how the symmetry of a particle determines its overall trajectory: In particular, mirror-symmetric particles, both strongly and weakly confined, follow a universal path. We propose minimalistic scaling relations to describe how particle shape affects the parameterization of the universal path. These findings could be used to "program" particle trajectories in lab-on-a-chip devices and industrial separation processes.