Equilibrium transport velocity of deformable cells and rigid sheres in micro-channels under laminar flow conditions

Inertial migration of particles to a characteristic lateral equilibrium position in laminar micro-flows has been investigated under various aspects during the last decades. The majority of the studies deal with the equilibrium position of rigid particles and viscous droplets. Here, we compare the equilibrium velocity of viscoelastic cells and rigid polystyrene spheres in flow by applying the method of spatially modulated emission. The technique allows the precise determination of the equilibrium velocity of an object in flow, which has been found to depend on object characteristics like size in earlier studies. Here, we first show that the deformable cells move at higher equilibrium velocity than rigid polystyrene particles, thus revealing that a particle's equilibrium velocity is related to its deformability-in addition to size. In a second set of experiments, we treat cells with the cytostatic agent colchicine, which results in a systematic decrease of the equilibrium velocity that is attributed to cell stiffening. This study thus provides evidence that the parameter cell deformability can be extracted from the equilibrium velocity based on spatially modulated emission, which opens up an alternative way for high-throughput cell-deformability characterization.