Order, intermittency and pressure fluctuations in a system of proliferating rods

TL;DR

This study uses simulations to explore how proliferating rods in confined environments exhibit collective nematic order, pressure fluctuations, and intermittency, revealing complex behaviors influenced by aspect ratio and friction.

Contribution

It introduces a detailed simulation analysis of proliferating rods, highlighting the effects of aspect ratio and friction on nematic order and pressure fluctuations in confined systems.

Findings

Rods with aspect ratio >3.0 achieve near-perfect nematic order at low friction.

Intermittent fluctuations in nematic order follow power-law distributions.

Pressure fluctuations are abrupt, heterogeneous, and follow inverse power-law distributions.

Abstract

Non-motile elongated bacteria confined in two-dimensional open micro-channels can exhibit collective motion and form dense monolayers with nematic order if the cells proliferate, i.e., grow and divide. Using soft molecular dynamics simulations of a system of rods interacting through short range mechanical forces, we study the effects of the cell growth rate, the cell aspect ratio and of the sliding friction on nematic ordering and on pressure fluctuations in confined environments. Our results indicate that rods with aspect ratio >3.0 reach quasi-perfect nematic states at low sliding friction. At higher frictions, the global nematic order parameter shows intermittent fluctuations due to sudden losses of order and the time intervals between these bursts are power-law distributed. The pressure transverse to the channel axis can vary abruptly in time and shows hysteresis due to lateral crowding effects. The longitudinal pressure field is on average correlated to nematic order, but it is locally very heterogeneous and its distribution follows an inverse power-law, in sharp contrast with non-active granular systems. We discuss some implications of these findings for tissue growth.