Self-organization and cyclic positioning of active condensates

Abstract

Cohesive active assemblies are often regulated by spatially heterogeneous nonequilibrium driving, such as gradients in motility, biochemical turnover, or mechanical activity. Such heterogeneous driving can influence where condensates or cell collectives accumulate, how stable they are, and how they exchange material with their surroundings. However, the minimal physical mechanisms by which activity gradients control the positioning and turnover of cohesive active matter remain unclear. Here, we address this question using a model of attractive active Brownian particles (ABPs) in a spatially varying activity field. Using Brownian dynamics simulations, we show that these particles undergo liquid-gas phase separation, and spatially varying activity fields induce striking emergent dynamics. Attractive active droplets migrate up activity gradients, and at sufficiently high activity, they can fragment or evaporate into a dilute phase. For finite clusters, evaporated ABPs can redistribute through the simulation box, reassemble into new clusters in lower-activity regions, and migrate again toward higher activity, giving rise to cyclic positioning through repeated nucleation, migration, evaporation, and reassembly.