Viscous Fingering-like Instability of Cell Fragments

TL;DR

This paper identifies a new flow instability in cytoskeletal cell fragments resembling viscous fingering, driven by actin polymerization and substrate friction, with implications for cell motility.

Contribution

It introduces a novel instability mechanism in cell fragments that parallels viscous fingering, independent of myosin interaction strength, and driven solely by actin polymerization energy.

Findings

Instability occurs at high substrate friction levels.

The instability mimics viscous fingering in Hele-Shaw flows.

It is driven by actin polymerization energy, not myosin interaction.

Abstract

We present a novel flow instability that can arise in thin films of cytoskeletal fluids if the friction with the substrate on which the film lies is sufficiently strong. We consider a two dimensional, membrane-bound fragment containing actin filaments that is perturbed from its initially circular state, where actin polymerizes at the edge and flows radially inward while depolymerizing in the fragment. Performing a linear stability analysis of the initial state due to perturbations of the fragment boundary, we find, in the limit of very large friction, that the perturbed actin velocity and pressure fields obey the very same laws governing the viscous fingering instability of an interface between immiscible fluids in a Hele-Shaw cell. A feature of this instability that is remarkable in the context of cell motility, is that its existence is independent of the strength of the interaction between cytoskeletal filaments and myosin motors, and moreover that it is completely driven by the free energy of actin polymerization at the fragment edge.