Light-dependent switching between two flagellar beating states selects versatile phototaxis strategies in microswimmers.

Microorganisms have evolved sophisticated sensor-actuator circuits to perform taxis in response to various environmental stimuli. How any given circuit can select between different taxis responses in noisy vs. saturated stimuli conditions is unclear.

Reinforcement learning of biomimetic navigation: a model problem for sperm chemotaxis.

Motile biological cells can respond to local environmental cues and exhibit various navigation strategies to search for specific targets. These navigation strategies usually involve tuning of key biophysical parameters of the cells, such that the cells can modulate their trajectories to move in response to the detected signals. Here we introduce a reinforcement learning approach to modulate key biophysical parameters and realize navigation strategies reminiscent to those developed by biological cells.

Reconfigurability-Encoded Hierarchical Rectifiers for Versatile 3D Liquid Manipulation.

Manipulating small-volume liquids is crucial in natural processes and industrial applications. However, most liquid manipulation technologies involve complex energy inputs or non-adjustable wetting gradient surfaces. Here, a simple and adjustable 3D liquid manipulation paradigm is reported to control liquid behaviors by coupling liquid-air-solid interfacial energy with programmable magnetic fields.

Propulsion of a three-sphere microrobot in a porous medium.

Microorganisms and synthetic microswimmers often encounter complex environments consisting of networks of obstacles embedded into viscous fluids. Such settings include biological media, such as mucus with filamentous networks, as well as environmental scenarios, including wet soil and aquifers. A fundamental question in studying their locomotion is how the impermeability of these porous media impacts their propulsion performance compared with the case of that in a purely viscous fluid.

Learning to cooperate for low-Reynolds-number swimming: a model problem for gait coordination.

Biological microswimmers can coordinate their motions to exploit their fluid environment-and each other-to achieve global advantages in their locomotory performance. These cooperative locomotion require delicate adjustments of both individual swimming gaits and spatial arrangements of the swimmers. Here we probe the emergence of such cooperative behaviors among artificial microswimmers endowed with artificial intelligence.

Activity-induced instability of phonons in 1D microfluidic crystals.

One-dimensional crystals of passively-driven particles in microfluidic channels exhibit collective vibrational modes reminiscent of acoustic 'phonons'. These phonons are induced by the long-range hydrodynamic interactions among the particles and are neutrally stable at the linear level. Here, we analyze the effect of particle activity - self-propulsion - on the emergence and stability of these phonons.

Density Shock Waves in Confined Microswimmers.

Motile and driven particles confined in microfluidic channels exhibit interesting emergent behavior, from propagating density bands to density shock waves. A deeper understanding of the physical mechanisms responsible for these emergent structures is relevant to a number of physical and biomedical applications. Here, we study the formation of density shock waves in the context of an idealized model of microswimmers confined in a narrow channel and subject to a uniform external flow.

Circularly confined microswimmers exhibit multiple global patterns.

Geometric confinement plays an important role in the dynamics of natural and synthetic microswimmers from bacterial cells to self-propelled particles in high-throughput microfluidic devices. However, little is known about the effects of geometric confinement on the emergent global patterns in such self-propelled systems. Recent experiments on bacterial cells report that, depending on the cell concentration, cells either spontaneously organize into vortical motion in thin cylindrical and spherical droplets or aggregate at the inner boundary of the droplets.

Flagella-induced transitions in the collective behavior of confined microswimmers.

Bacteria are usually studied in free-swimming planktonic state or in sessile biofilm state. However, little is known about intermediate states where variability in the environmental conditions and/or energy supply to the flagellar propulsive system alter flagellar activity. In this Rapid Communication, we propose an idealized physical model to investigate the effects of flagellar activity on the hydrodynamic interactions among a population of microswimmers.