Oscillatory rheotaxis of active droplets in microchannels

Abstract

Biological microswimmers are known to navigate upstream of an external flow (positive rheotaxis) in trajectories ranging from linear, spiral to oscillatory. Such rheotaxis stems from the interplay between the motion and complex shapes of the microswimmers, e.g. the chirality of the rotating flagella, the shear flow characteristics, and the hydrodynamic interaction with a confining surface. Here, we show that an isotropic, active droplet microswimmer exhibits a unique oscillatory rheotaxis in a microchannel despite its simple spherical geometry. The swimming velocity, orientation, and the chemical wake of the active droplet undergo periodic variations between the confining walls during the oscillatory navigation. Using a hydrodynamic model and concepts of dynamical systems, we demonstrate that the oscillatory rheotaxis of the active droplet emerges primarily from the interplay between the hydrodynamic interaction of the finite-sized microswimmer with all the microchannel walls, and the shear flow characteristics. Such oscillatory rheotactic behavior is different from the directed motion near a planar wall observed previously for artificial microswimmers in shear flows. Our results provide a realistic understanding of the behaviour of active particles in confined microflows, as will be encountered in majority of the applications like targeted drug delivery.

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Cited by in corpus (14)

• Self-propulsion of chemically-active droplets
• We the Droplets: A Constitutional Approach to Active and Self-Propelled Emulsions
• Microbes in porous environments: From active interactions to emergent feedback
• Jeffery's orbits and microswimmers in flows: A theoretical review
• Deforming Active Droplets in Viscoelastic Media
• Confinement induced three-dimensional trajectories of microswimmers in rectangular channels
• Kinetic temperature and pressure of an active Tonks gas
• Steady state propulsion of isotropic active colloids along a wall
• Activity-induced asymmetric dispersion in confined channels with constriction
• Arrested on heating: controlling the motility of active droplets by temperature
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• Trapping microswimmers in acoustic streaming flow
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• Effect of the background flow on the motility induced phase separation