Controlling topological defects and contractile flow in confined nematic cell population

TL;DR

This paper demonstrates how geometric confinement can control topological defect positioning and induce contractile flow in nematic cell populations, revealing insights into the interplay between geometry, topology, and collective cell dynamics.

Contribution

It introduces a geometry-based method to manipulate defect pairing and flow in active nematic cell systems, advancing control over collective behaviors.

Findings

Stable pairing of topological defects under geometric constraints

Induction of robust contractile flow with negative divergence

Mechanical stimulation evidenced by nuclear stretching

Abstract

Topological defects in nematically aligned cell populations play a critical role in modulating collective motion, from microbial colonies to epithelial tissues. Despite the potential of manipulating such topological defects to control diverse self-organized structures and collective dynamics, defect manipulation in active matter remains an challenging area of research. In this study, we investigated the geometric control of defect positioning and alignment in a nematic cell population by imposing spatial constraints consisting of two or three overlapping circular boundaries. The confined cell population exhibited an ordered pairing of half-integer topological defects that remained stable even when the size of the spatial constraint was altered using geometric parameters. These defects also elicited robust contractile flow that induced a negative divergence in the velocity field of collective motion. Such net contractile flow can contribute to mechanical stimulation on confined cells, as evidenced by the stretched cell nucleus. Our geometry-based approach paves the way for controlling defect pairing, providing a deeper understanding of the interplay among geometry, topology, and collective dynamics.