# Correlating Cell Shape and Cellular Stress in Motile Confluent Tissues

## TL;DR

This study links cell shape, traction forces, and stress in motile tissues using a model that reveals how mechanical interactions influence tissue rheology and transitions between fluid-like and solid-like states.

## Contribution

We developed a generalized inference method connecting traction forces to cellular stresses and characterized tissue rheology and phase transitions in motile confluent tissues.

## Key findings

- Traction-based stresses match those from cell shapes.
- Identified a motility-induced swim stress affecting tissue contractility.
- Discovered divergence of effective viscosity at the liquid-solid transition.

## Abstract

Collective cell migration is a highly regulated process involved in wound healing, cancer metastasis and morphogenesis. Mechanical interactions among cells provide an important regulatory mechanism to coordinate such collective motion. Using a Self-Propelled Voronoi (SPV) model that links cell mechanics to cell shape and cell motility, we formulate a generalized mechanical inference method to obtain the spatio-temporal distribution of cellular stresses from measured traction forces in motile tissues and show that such traction-based stresses match those calculated from instantaneous cell shapes. We additionally use stress information to characterize the rheological properties of the tissue. We identify a motility-induced swim stress that adds to the interaction stress to determine the global contractility or extensibility of epithelia. We further show that the temporal correlation of the interaction shear stress determines an effective viscosity of the tissue that diverges at the liquid-solid transition, suggesting the possibility of extracting rheological information directly from traction data.