Multi-population dissolution in confined active fluids.

Area of Science:

• Physics
• Biophysics
• Fluid Dynamics

Background:

• Autonomous out-of-equilibrium agents (e.g., cells, bacteria) are common in nature and engineering.
• These agents convert chemical energy into mechanical stress, driving activity and large-scale dynamics in their environment.
• Systems often involve multiple populations, such as different species or phenotypes, leading to complex interactions.

Purpose of the Study:

• To present a novel computational method for modeling multi-population active fluids under confinement.
• To investigate the spatiotemporal dynamics of confined bacterial suspensions and swarms.
• To elucidate the role of hydrodynamic effects in collective phenomena like active dissolution.

Main Methods:

• A continuum multi-scale mean-field approach representing each population by its first three orientational moments.
• Coupling the evolution of each population with the suspending fluid dynamics.
• Utilizing a parallel adaptive level-set-based solver for efficient computation and geometric flexibility.

Main Results:

• The method successfully models spatiotemporal dynamics in confined multi-population active fluids.
• Simulations reproduce emergent collective patterns observed in bacterial suspensions.
• Key features of active dissolution in two-population active-passive swarms were captured, highlighting the dominance of hydrodynamic effects.

Conclusions:

• The developed method provides a powerful tool for studying complex active matter systems.
• Hydrodynamic interactions play a dominant role in the dissolution dynamics of multi-population active swarms.
• This work lays the groundwork for systematic characterization of collective phenomena in diverse natural and synthetic systems.