Fluidization of epithelial sheets by active cell rearrangements

TL;DR

This paper investigates how active cell rearrangements, specifically T1 neighbor exchanges, fluidize epithelial tissues, affecting their mechanical response and relaxation times, supported by theoretical models and simulations.

Contribution

It introduces a combined elastic and active fluid model to describe tissue fluidization driven by active cell rearrangements, validated by vertex model simulations.

Findings

Active noise controls tissue stress-relaxation time

Tissue behaves as a solid at short times and as an active fluid at long times

Cell rearrangements influence tissue shape under compression

Abstract

We theoretically explore fluidization of epithelial tissues by active T1 neighbor exchanges. We show that the geometry of cell-cell junctions encodes important information about the local features of the energy landscape, which we support by an elastic theory of T1 transformations. Using a 3D vertex model, we show that the degree of active noise driving forced cell rearrangements governs the stress-relaxation time-scale of the tissue. We study tissue response to in-plane shear at different time scales. At short time, the tissue behaves as a solid, whereas its long-time fluid behavior can be associated with an effective viscosity which scales with the rate of active T1 transformations. Furthermore, we develop a coarse-grained theory, where we treat the tissue as an active fluid and confirm the results of the vertex model. The impact of cell rearrangements on tissue shape is illustrated by studying axial compression of an epithelial tube.