# Active wetting of epithelial tissues

## TL;DR

This study demonstrates that tissue wetting transitions in epithelial tissues are governed by active cellular forces, revealing a new physical framework that explains morphological changes during development and disease.

## Contribution

It introduces an active wetting model for epithelial tissues, highlighting the role of active forces and a critical size in tissue morphology transitions.

## Key findings

- Wetting transition depends on traction and contractile stresses.
- Identifies a critical tissue size for wetting behavior.
- Active shape fluctuations are amplified during dewetting.

## Abstract

Development, regeneration and cancer involve drastic transitions in tissue morphology. In analogy with the behavior of inert fluids, some of these transitions have been interpreted as wetting transitions. The validity and scope of this analogy are unclear, however, because the active cellular forces that drive tissue wetting have been neither measured nor theoretically accounted for. Here we show that the transition between 2D epithelial monolayers and 3D spheroidal aggregates can be understood as an active wetting transition whose physics differs fundamentally from that of passive wetting phenomena. By combining an active polar fluid model with measurements of physical forces as a function of tissue size, contractility, cell-cell and cell-substrate adhesion, and substrate stiffness, we show that the wetting transition results from the competition between traction forces and contractile intercellular stresses. This competition defines a new intrinsic lengthscale that gives rise to a critical size for the wetting transition in tissues, a striking feature that has no counterpart in classical wetting. Finally, we show that active shape fluctuations are dynamically amplified during tissue dewetting. Overall, we conclude that tissue spreading constitutes a prominent example of active wetting --- a novel physical scenario that may explain morphological transitions during tissue morphogenesis and tumor progression.