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Many microscale systems must perform tasks in the presence of noisy environments. Here, authors present exact optimal protocols for non-equilibrium systems that use time-dependent forces as a resource for minimizing or extracting work, revealing general energetic bounds.

Confinement is encountered in systems varying from simple liquids to biological cells. Williams et al. introduce an adaptive confinement with an elastic wall composed of colloidal particles, whereby the osmotic pressure of the confined system can be directly obtained from the displacement of the wall.

Cooling in natural systems typically requires external contact with a cold reservoir, with the final temperature determined by the environment, as dictated by thermodynamics. The authors demonstrate a spontaneous, selfsustained frictional cooling effect driven by the interplay of activity, dry friction, and crowding.

Entanglement of polymers underlies a variety of phenomena across multiple scales that are driven by different active processes. Here, the authors study the viscoelastic properties of highly entangled, flexible, self-propelled polymers using Brownian dynamics simulations and show that the active motion of the polymers increase the elasticity of the solution by orders of magnitude due to the emergence of grip forces at entanglement points and increases with polymer length and activity.

Active matter systems, such as zebrafish groups, demonstrate similar collective dynamics to assemblies of particles, or interacting agents. The authors show that majority of dynamics patterns seen in large zebrafish groups are exhibited by a minimal group of three fish.

Colloidal rod-like mesogens make the study of liquid crystal structures available to simple optical microscopy. Wittmann et al. study topological defects in smectic phases under annular confinement and reveal a remarkable, quantitative agreement with a theoretic density functional description.

Ultrafast spectroscopy enables characterization and control of non-equilibrium states. Here the authors introduce a stochastic thermodynamics approach to calculate entropy production in a material under ultrafast excitation, using ionic displacement data from time-resolved X-ray scattering experiments.

Gravitaxis describes the ability of microorganisms to adjust their swimming motion on the gravitational field, yet its mechanism remains unclear. Here, the authors show that an asymmetric shape of colloidal particles is alone sufficient to induce gravitactic motion in the absence of density inhomogeneity.

The collective motion of microswimmers is determined by not only their direct interaction, but also the hydrodynamics forces mediated by the surrounding flow field. Here, the authors detail in simulation the spontaneous assembly and disassembly of magnetic microswimmers into various structures.

The capability to move towards or away from light sources, namely phototaxis, is an essential feature of many microorganisms like bacteria or motile cells. Lozano et al. show an artificial phototaxis system that enables autonomous navigation of colloidal Janus spheres in a laser-generated light landscape.

Active matter can spontaneously form complex patterns and assemblies via a one-way energy flow from the environment into the system. Here, the authors demonstrate that a two-way coupling, where active particles act back on the environment can give rise to novel superstructures, named as active droploids.

Fick’s laws describe the essential physics of diffusion, but it is challenging to extend them to systems out of equilibrium. The authors derive the diffusivity of particles near active carpets - a surface covered with hydrodynamic actuators, which provides a framework for transport in living matter.

Navigation through porous environments poses a major challenge for swimming microorganisms and future microrobots. This study predicts that their spreading becomes optimal when their run length is comparable to the longest available pore length.

Stimuli-responsive emulsions are useful for long-term storage combined with controlled release, but the fundamental mechanism behind this release is not established. Here, the authors report a study into the effect of individual microgel morphology on the destabilisation of responsive emulsions.

A study of a composite soft-matter nanomechanical system consisting of a rotating ring of optically trapped colloidal particles confining a set of untrapped colloids demonstrates the possibility of gearwheel-like torque transmission on the nanoscale.

Casimir forces are normally attractive and cause stiction, that is, static friction preventing surfaces in contact from starting to move. Now, a system exhibiting tunable repulsive critical Casimir forces, relevant for the development of micro- and nanodevices, is demonstrated.

Active matter describes a group of interacting units showing collective motions by constantly consuming energy from the environment, but inertia has largely been overlooked in this context. Scholz et al. show how important it can be by characterizing the dynamics of self-propelled particles in a model system.

The Y-junction is an essential element in synthetic and biological microfluidic networks. This study investigates how the flow behavior of colloidal particles through a microfluidic Y-junction can be controlled by tuning the interparticle interactions and the nature of confinement.

It is intriguing but challenging to control the complex dynamics of topological defects that emerge in nonequilibrium spatiotemporal systems. Through an effective modelling this work explores a viable way to controllably vary the properties of persistent defect dynamics in self-propelled active smectics via the competition of activity and boundary confinements with different topology and geometry.

Active matter systems composed of self-propelled agents exhibit dynamical clustering. In this work, the authors demonstrate that inertia induces a solid-liquid transition within the cluster structure and suppresses wetting phenomena at the container boundary.

Living in groups is a key survival strategy for biological systems, yet its dependency on environmental characteristics is not fully understood. Exploiting active colloids in controlled optical landscapes as a model system, the authors demonstrated that the spatial complexity of the environment determines both the size and stability of these groups.

Einstein relations in non-equilibrium active matter systems break upon increase of fluctuations and changes in the system’s dissipative properties. By observing the tapping collisions of a tracer in a bath of vibrationally excited active granular particles, the authors propose a generalized active Einstein relation accounting for memory effects.

Environmental factors such as mechanical stresses govern the cellular behavior and physiology, but the role of selfinduced biomechanical stresses in growing bacterial colonies is still unclear. The authors reveal how the response to collective mechanical forces acting on the individual cells regulates the size of growing bacteria.

Anisotropic environments affect the motion of many living organisms but studying these systems in a controlled environment can be challenging. We employ experiments using active granular particles on a striated substrate and use the theory of active Brownian motion to replicate and describe such anisotropic motility.

While control theory for optimal navigation is relevant across scales, from aeronautics to targeted drug delivery, the role of thermal fluctuations and hydrodynamic interactions with interfaces, walls and obstacles at the microscale remains an open question. Here, the authors explore optimal microswimming in the presence of walls or obstacles, and study how hydrodynamic microswimmer-wall interactions impact on optimal microswimming strategies.

An outstanding challenge in active matter physics is to control the motion of active particles. Here, the authors present a motility trap that can be applied to any self-propulsion scheme, and combine experiments, theory, and simulations to demonstrate robust spatio-temporal control of active particles.