Force localization in contracting cell layers

TL;DR

This paper demonstrates analytically that force localization at the edges of contracting cell layers on elastic substrates can occur naturally from elastic mechanics, without requiring increased local cell activity, and explores effects of contractility and anisotropic stiffness.

Contribution

It provides an analytical framework explaining force localization in cell layers, linking it to elastic properties and contractility patterns, challenging previous assumptions about cell activity.

Findings

Force localization arises from elastic mechanics, not increased cell activity.

A dimensionless parameter interpolates force profiles between soft and stiff substrates.

Anisotropic stiffness causes force localization in the stiffer direction.

Abstract

Epithelial cell layers on soft elastic substrates or pillar arrays are commonly used as model systems for investigating the role of force in tissue growth, maintenance and repair. Here we show analytically that the experimentally observed localization of traction forces to the periphery of the cell layers does not necessarily imply increased local cell activity, but follows naturally from the elastic problem of a finite-sized contractile layer coupled to an elastic foundation. For homogeneous contractility, the force localization is determined by one dimensionless parameter interpolating between linear and exponential force profiles for the extreme cases of very soft and very stiff substrates, respectively. If contractility is sufficiently increased at the periphery, outward directed displacements can occur at intermediate positions, although the edge itself still retracts. We also show that anisotropic extracellular stiffness leads to force localization in the stiffer direction, as observed experimentally.