Mechanical characterization of disordered and anisotropic cellular monolayers

TL;DR

This paper models the mechanical behavior of disordered, anisotropic cellular monolayers using a vertex-based approach, revealing how tissue stress and strain relate and how stretching induces cellular alignment and ordering.

Contribution

It introduces a vertex model that links cellular configurations to tissue-level mechanical properties, including stress-strain relations and anisotropic responses.

Findings

Uniaxial stretching induces cellular alignment with the stretch direction.

The model derives tissue stress-strain relations accounting for anisotropy.

Tissue properties can be tuned to exhibit high shear resistance or low area change resistance.

Abstract

We consider a cellular monolayer, described using a vertex-based model, for which cells form a spatially disordered array of convex polygons that tile the plane. Equilibrium cell configurations are assumed to minimize a global energy defined in terms of cell areas and perimeters; energy is dissipated via dynamic area and length changes, as well as cell neighbour exchanges. The model captures our observations of an epithelium from a Xenopus embryo showing that uniaxial stretching induces spatial ordering, with cells under net tension (compression) tending to align with (against) the direction of stretch, but with the stress remaining heterogeneous at the single-cell level. We use the vertex model to derive the linearized relation between tissue-level stress, strain and strain-rate about a deformed base state, which can be used to characterize the tissue's anisotropic mechanical properties; expressions for viscoelastic tissue moduli are given as direct sums over cells. When the base state is isotropic, the model predicts that tissue properties can be tuned to a regime with high elastic shear resistance but low resistance to area changes, or vice versa.