Spatiotemporal organization in an active viscoelastic suspension: a dissipative particle dynamics study

Abstract

Microorganisms such as bacteria and spermatozoa often inhabit confined viscoelastic environments. These organisms exhibit self-organization/collective dynamics in such complex surroundings. Here, we report a simulation study of active particle suspensions in viscoelastic fluids under confinement—representing an experimental scenario where motile organisms suspended in aqueous viscoelastic fluid are surrounded by an oil medium. We employed dissipative particle dynamics, a particle-based mesoscopic approach, to model the system with minimalistic ingredients and qualitatively reproduced some of the experimental observations by Liu et al. Nature, 2021, 590 (7844), 80–84. The collective dynamics within the suspended drop, mediated by the viscoelastic nature of the medium, manifest into two steady state configurations, namely a unidirectional vortex or an oscillatory vortex. We present a phase diagram for the drop's steady state configuration as a function of system parameters, such as strength and packing fraction of active agents, polymer concentration etc.