Prediction and control of geometry-induced nematic order in growing multicellular systems

TL;DR

This paper presents a simple analytical framework that predicts nematic orientation patterns in growing multicellular systems based on domain geometry, simplifying previous complex models and enabling design of specific patterns.

Contribution

The authors introduce a unified, analytical approach to predict and control nematic order in growing cell systems, extending beyond active nematic theories.

Findings

Analytical prediction matches experimental and numerical patterns

Geometry can be used to systematically tune nematic order and defects

Framework extends to quantify alignment strength and cross-geometry prediction

Abstract

In densely-packed two-dimensional systems of growing cells, such as rod-shaped bacteria, a number of experimental and numerical studies report distinct patterns of nematic orientational order in the presence of confinement. So far, these effects have been explained using variations of growing active nematic continuum theories, which incorporate feedback between growth-induced active stresses, the resulting material flow and nematic orientation, and were adapted to the specific geometry under investigation. Here, we first show that a direct, analytical prediction of orientation patterns based on a simple isotropic-growth assumption and the shear rate tensor of the expansion flow already covers previously observed cases. We use this method to tune orientation patterns and net topological defect charge in a systematic way using domain geometry, confirmed by agent-based simulations. We then show how this framework can be extended to quantitatively capture alignment strength, and explore its potential for cross-prediction across different geometries. Our simplified and unifying theoretical framework highlights the role of domain geometry in shaping nematic order of growing systems, and thereby provides a way to forward-engineer desired orientation patterns.