Integer topological defects of cell monolayers -- mechanics and flows

TL;DR

This study links the mechanics of cell monolayers to topological defects by applying liquid crystal physics and hydrodynamics, revealing how defects can characterize active biological tissues.

Contribution

It introduces a hydrodynamical model incorporating multiple activity sources to analyze topological defects in cell monolayers, providing a new method to determine their mechanical parameters.

Findings

Mechanical parameters of cell monolayers were quantitatively determined.

Topological defects reveal key insights into tissue mechanics.

The approach applies to C2C12 cell monolayers in confined geometries.

Abstract

Monolayers of anisotropic cells exhibit long-ranged orientational order and topological defects. During the development of organisms, orientational order often influences morphogenetic events. However, the linkage between the mechanics of cell monolayers and topological defects remains largely unexplored. This holds specifically at the time scales relevant for tissue morphogenesis. Here, we build on the physics of liquid crystals to determine material parameters of cell monolayers. In particular, we use a hydrodynamical description of an active polar fluid to study the steady-state mechanical patterns at integer topological defects. Our description includes three distinct sources of activity: traction forces accounting for cell-substrate interactions as well as anisotropic and isotropic active nematic stresses accounting for cell-cell interactions. We apply our approach to C2C12 cell monolayers in small circular confinements, which form isolated aster or spiral topological defects. By analyzing the velocity and orientational order fields in spirals as well as the forces and cell number density fields in asters, we determine mechanical parameters of C2C12 cell monolayers. Our work shows how topological defects can be used to fully characterize the mechanical properties of biological active matter.