Oscillatory, non-progressing flows induce directed cell motion

TL;DR

This paper demonstrates that oscillatory, non-progressing flows can induce directed motion in soft particles like cells due to deformation asymmetries, enabling label-free cell sorting based on deformability.

Contribution

It introduces a novel propulsion mechanism for soft particles in oscillatory flows, combining simulations and analytical models to show how deformation asymmetry leads to directed motion.

Findings

Soft particles move directionally in oscillatory flows due to deformation differences.

Particle size, deformation, and elasticity influence propulsion.

Potential for label-free cell sorting based on deformability.

Abstract

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 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 oscillation 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 deformability can be separated simultaneously without labeling or obstacles in a microfluidic device.