Density-polarity coupling in confined active polar films: asters, spirals, and biphasic orientational phases

TL;DR

This study investigates how density variations influence flow and orientational patterns in confined active polar fluids, revealing a density-controlled transition from spirals to asters and the emergence of biphasic phases, with implications for biological systems.

Contribution

It demonstrates the coupling between density and polar order in active fluids, showing how density gradients can control flow patterns and orientational phases.

Findings

Density-controlled spiral-to-aster transition

Emergence of biphasic orientational phases

Density gradients influence flow and pattern formation

Abstract

Topological defects in active polar fluids can organise spontaneous flows and influence macroscopic density patterns. Both of them play, for example, an important role during animal development. Yet the influence of density on active flows is poorly understood. Motivated by experiments on cell monolayers confined to discs, we study the coupling between density and polar order for a compressible active polar fluid in presence of a +1 topological defect. As in the experiments, we find a density-controlled spiral-to-aster transition. In addition, biphasic orientational phases emerge as a generic outcome of such coupling. Our results highlight the importance of density gradients as a potential mechanism for controlling flow and orientational patterns in biological systems.