Fluorescent polystyrene particles are used as received from Bangs Labs, suspended in water at 1% solids. The particles are monodisperse and have a mean diameter, d p ≈ 4 µm. They are slightly negatively charged, with zeta potential, ζ = -8.2±0.9 mV (Anton Paar Litesizer 500). They are suspended in pure DI water, and do not aggregate over the duration of the flow test (see Fig. in SI). The density of the particles (ρ p ) is ∼1.06 g•cm -3 , which is approximately equal to the density of water, the suspend- ing fluid. Sedimentation is therefore negligible. We prepare dilute suspensions in DI water, at volume fractions (φ ) in the range [0.005, 0.25%]. We flow the dilute suspensions through the microfluidic device at constant driving pressures (∆P) in the range [200, 2000 mbar] using a a Fluigent LineUp Flow EZ TM device. The Flow EZ applies a constant pressure to a reservoir containing the suspension. The flowrate (Q) is measured with a flow meter (Fluigent FLOW UNIT TM ).