Geometric Confinement Reveals Scale-Free Velocity Correlations in Epithelial Cell Monolayer

TL;DR

This study reveals that epithelial cell monolayers exhibit scale-free velocity correlations and critical-like behavior influenced by substrate properties and boundary conditions, providing insights into tissue dynamics.

Contribution

It demonstrates that epithelial monolayers display scale-free velocity correlations and long-range stress propagation, influenced by substrate and boundary conditions, revealing critical-like tissue behavior.

Findings

Velocity correlations follow a power law, indicating scale-free behavior.

Substrate stiffness and boundary conditions affect flow organization.

Correlation length and velocity patterns evolve during tissue maturation.

Abstract

Collective cell flows are a hallmark of tissue dynamics in development, wound healing, and various diseases. Here, we perform experiments on epithelial MDCK cell monolayers, over tens of hours without jamming, on millimeter-scale micropatterned substrates with or without free front (a strip or a closed racetrack). During maturation in time, domains and long-range correlations of the velocity field appear. Enstrophy increases (along with kinetic energy) during 5 hours, then passes through a maximum and decreases. Spatial velocity correlations are scale-free, following a power law, which challenges the notion of a single intrinsic correlation length. It suggests that the monolayer behaves as a critical-like system where information is transmitted across its entire size, a feature consistent with models of active solids capable of long-range stress propagation. The spatial correlation exponent significantly evolves with time, probably reflecting the monolayer maturation. The size, shape, topology and rigidity of patterned substrate influence the organization of flows and mechanical fields. Spontaneous collective motions are stronger on soft than on hard substrate. The presence of a free front accumulates vimentin on a much larger length scale than a fixed boundary ($65\pm 4$~$\mu$m vs $3.2 \pm 0.7$~$\mu$m), possibly revealing an underlying polarizing cue on the cell velocity field.