Oscillating non-progressing flows induce directed cell motion

We present a deformation-dependent propulsion phenomenon for soft particles such as cells in microchannels. It is based on a broken time-reversal symmetry generated by a fast forward and a slow backward motion of a fluid which does not progress on average. In both sections, soft particles deform differently and thus progress relatively to the liquid. We demonstrate this by using Lattice-Boltzmann simulations of ubiquitous red blood cells in microchannels, as well as simulations for capsules and minimal-soft-tissue models in unbounded Poiseuille flows. The propulsion of the soft particles depends besides the oscil-lation asymmetry on their size, deformation type, and elasticity. This is also demonstrated by analytical calculations for a minimal model. Our findings may stimulate a rethinking of particle sorting methods. For example, healthy and malignant cells often differ in their elasticity. With the proposed method, several cell types with different deformabilities can be separated simultaneously without labeling or obstacles in a microfluidic device.

Automated summary

A deformation-dependent propulsion phenomenon for soft particles, such as cells, in microchannels is discovered. It is caused by a broken time-reversal symmetry generated by a fast forward and a slow backward motion of a fluid. The propulsion of soft particles is not only determined by their oscillation asymmetry but also depends on their size, deformation type, and elasticity. This finding has the potential to inspire the development of new particle sorting methods.