Shapes and dynamic regimes of a polar active fluid droplet under confinement

Abstract

Active droplets are artificial microswimmers built from a liquid dispersion by microfluidic tools and showing self-propelled motion. These systems hold particular interest for mimicking biological phenomena, such as some aspects of cell locomotion and collective behaviors of bacterial colonies, as well as for the design of droplet-based biologically inspired materials, such as engineered tissues. Growing evidence suggests that geometrical confinement crucially affects their morphology and motility, but the driving physical mechanisms are still poorly understood. Here we study the effect of activity on a droplet containing a contractile polar fluid confined within microfluidic channels of various sizes. We find a surprising wealth of shapes and dynamic regimes, whose mechanics is regulated by a subtle interplay between contractile stress, droplet elasticity and microchannel width. They range from worm-like and cell-like shaped droplets displaying an oscillating behavior within wider channels to bullet-shaped droplets exhibiting rectilinear motion in narrower slits. Our findings support the view that geometrical confinement can provide a viable strategy to control and predict the propulsion direction of active droplets. It would be of interest to look for analogues of these motility modes in biological cells or in synthetic active matter.

Accepted on Physics of Fluids

References in corpus (17)

• The hydrodynamics of swimming microorganisms
• Spontaneous motion in hierarchically assembled active matter
• Meso-scale turbulence in living fluids
• Diffusive transport without detailed balance in motile bacteria: Does microbiology need statistical physics?
• Turning bacteria suspensions into a "superfluid"
• Active Turbulence
• A minimal physical model captures the shapes of crawling cells
• Theory of defect-mediated morphogenesis
• Contractile and chiral activities co-determine the helicity of swimming droplet trajectories
• Phoretic and hydrodynamic interactions of weakly-confined autophoretic particles
• Flow of deformable droplets: discontinuous shear thinning and velocity oscillations
• Collective entrainment and confinement amplify transport by schooling micro-swimmers
• Tractionless Self-Propulsion of Active Drops
• Swimming droplet in 1D geometries, an active Bretherton problem
• How many ways a cell can move: the modes of self-propulsion of an active drop
• Lattice Boltzmann study of chemically-driven self-propelled droplets
• Anchoring-driven spontaneous rotations in active gel droplets