# Crawling in a fluid

## TL;DR

This paper develops a coupled actin-myosin and fluid flow model to understand how mammalian cells initiate motility in fluids, revealing bifurcations and spontaneous oscillations in cell movement.

## Contribution

It introduces a novel analytical model linking actin-myosin kinetics with fluid dynamics to explain cell motility onset in suspension.

## Key findings

- Identification of super- and subcritical bifurcations leading to motility.
- Discovery of spontaneous polarity oscillations via Hopf bifurcation.
- Predicted cell shape trends beyond spherical assumptions.

## Abstract

There is increasing evidence that mammalian cells not only crawl on substrates but can also swim in fluids. To elucidate the mechanisms of the onset of motility of cells in suspension, a model which couples actin and myosin kinetics to fluid flow is proposed and solved for a spherical shape. The swimming speed is extracted in terms of key parameters. We analytically find super- and subcritical bifurcations from a non-motile to a motile state and also spontaneous polarity oscillations that arise from a Hopf bifurcation. Relaxing the spherical assumption, the obtained shapes show appealing trends.