Polar Fluctuations Lead to Extensile Nematic Behavior in Confluent Tissues

TL;DR

This paper explains how confluent tissues composed of cells with contractile stresses can exhibit extensile nematic behavior at the tissue level due to polar fluctuations, combining analytical hydrodynamic theories and cell simulations.

Contribution

It demonstrates that microscopic contractile cells can collectively behave as extensile nematics through polar fluctuations, bridging cellular and tissue-level behaviors.

Findings

Microscopic contractile stresses lead to tissue-level extensile nematic behavior.

Polar fluctuations induce active extensile nematic states.

Analytical hydrodynamic models match cell simulation results.

Abstract

How can a collection of motile cells, each generating contractile nematic stresses in isolation, become an extensile nematic at the tissue-level? Understanding this seemingly contradictory experimental observation, which occurs irrespective of whether the tissue is in the liquid or solid states, is not only crucial to our understanding of diverse biological processes, but is also of fundamental interest to soft matter and many-body physics. Here, we resolve this cellular to tissue level disconnect in the small fluctuation regime by using analytical theories based on hydrodynamic descriptions of confluent tissues, in both liquid and solid states. Specifically, we show that a collection of microscopic constituents with no inherently nematic extensile forces can exhibit active extensile nematic behavior when subject to polar fluctuating forces. We further support our findings by performing cell level simulations of minimal models of confluent tissues.