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Scientists have created soft microrobots whose body shapes can be controlled by structured light, and which self-propel by means of travelling-wave body deformations similar to those exhibited by swimming protozoa.

Enzymatic nanomotors exhibit collective behaviour in fuel-rich environments, forming swarms with enhanced propulsion and coverage. This study investigates the factors affecting swarm movement, revealing that solutal buoyancy drives their motion, with potential biomedical applications like targeted drug delivery.

A suspension of magnetic colloidal particles confined at a liquid–liquid interface and energized by an external periodic magnetic field self-assembles into star-shaped structures that can be magnetically manipulated to capture and transport smaller non-magnetic particles.

Dielectric colloids suspended in a weak electrolyte and energized by a static electric field called Quincke rollers are the model system to study active matter. Zhang et al. report the formation of spontaneous shockwaves in the colloidal Quincke rollers under the temporal activity modulations.

The communication in active systems plays an important role in their self-organization, yet the detail is not fully understood. Here, Ziepke et al. show the formation of complex structures at multiple scales amongst interactive agents that locally process information transmitted by chemical signals.

The control of microswimmers such as bacteria is important for emerging applications of active bioinspired materials. Here, the authors demonstrate the use of vortical shear to expel suspended motile bacteria from the vicinity of a rotating microparticle.

A wide diversity of surfaces patterned with microfibres is highly desirable for various applications as electrode materials. Demortière et al.develop a facile approach of producing polymer microfibres with controlled architectures via dynamic self-assembly under an alternating electric field.

The relationship between the dynamics and spatial order of active matter gives rise to a rich phenomenology that is not fully understood. A study of bacteria swimming in a patterned liquid crystalline environment is a case in point, and provides a way to streamline the chaotic movements of swimming bacteria into polar jets.

Sokolov et al. have previously shown how bacteria are expelled in response to a rotating microparticle. Here the authors find that when the microparticle is spun at much higher rotation rates bacteria are trapped around it and then are expelled radially upon rotation cessation in an explosion-like manner.

Geometrically confined suspensions of swimming bacteria can self-organize into an ordered state. Here, the authors use tiny pillars to trigger organization of bacterial motion into a stable lattice of vortices with a long-range antiferromagnetic order and control vortex direction through pillar chirality.

While there are many demonstrations of self-propelled synthetic particles, there are fewer realisations of multimode swimming for the same particle. Here the authors demonstrate two swimming behaviours in magnetically manipulated microtori and show that these can manipulate other active particles.

Interacting self-propelled particles exhibit phase separation or collective motion depending on particle shape. A unified theory connecting these paradigms represents a major challenge in active matter, which the authors address here by modeling active particles as continuum fields.

Exciton-polariton Bose-Einstein condensates in semiconductor microcavities are a unique manifestation of quantum coherence on a macroscopic scale. By examining the relationship between pumping intensity and polariton spectral properties, the authors demonstrate the cavity parameter space collapse and fundamental limit on the minimal power required for Bose-Einstein condensation.

Understanding the bacteria-phage competition is crucial for horizontal gene transfer and treatment of antibiotic-resistant bacterial infections. This work investigates the interaction between common rod-shaped bacteria such as Escherichia coli or Pseudomonas aeruginosa and lytic phages to provide insights into their proliferating active dynamics in 2D and 3D environments.

The study of topological defects in matter is a topic of extensive interest, but it remains challenging when it concerns non-equilibrium active matter. The authors experimentally and computationally demonstrate that obstacles immersed in a two-dimensional active liquid crystal can pin a type of defects and slow down the dynamics of nearby defects.

Bacterial collective behavior in visco-elastic media is an open area of research. The authors computationally study a viscoelastic environment to look at the trajectories of microswimmers and their interaction, finding that a second swimmer is influenced by the first and that a swimmer changes speed when going backwards along the same track.

Interaction of active matter with geometrical constraints is an emerging topic of research due to its potential for design and control of flow patterns. By exploring various modes of swimming and strength of cell-liquid crystal interaction, the authors present a computational model of a microswimmer propulsion in a liquid crystal probing a range of non-trivial swimming dynamics.

Lamellipodial waves are a very general phenomenon observed in many cell types and is a typical phenomenon for animal cells to adhere and move along substrates. The authors present a model showing that the dynamics of these waves can be reproduced with a minimal, well-defined set of parameters.

The presence of a constraining environment exerts an influence on the behavior of self-propelled synthetic microswimmers, challenging the prediction and control of their individual and collective behaviour in realistic situations. Here, the authors use multiparticle collision dynamics to simulate self-propelled Janus toroidal particles near a wall and study how various contributions, such as thermal fluctuations, hydrodynamic and electrostatic interactions, chemical reactions, and gravity govern their collective behaviour.

Asymmetric nanotopography biases unidirectional cell migration, yet the underpinning molecular determinants are still unclear. The authors use a three-dimensional model to demonstrate that nanosawteeth induce actin-mediated migration directionality, which is dependent on the cell velocity.

Emergent collective behaviour has recently been addressed in systems of self-rotating particles, where motion, in particular, is an emergent phenomenon rather than a basic ingredient. Here, the authors derive a continuum model for mixtures of clockwise and counterclockwise Quincke spinners, demonstrating the emergence of same-spin phase separation, traffic lanes, sustained turbulent-like motion, and a chirality breaking transition depending on the fluid inertia of the system.

During development, wound healing, differentiation or cancer metastasis, cells move continuously in heterogeneous environments, hence understanding how cell migration is controlled by confinement and by different substrate shapes is crucial to begin to build a first conceptual framework for cell motility. Here the authors develop a computational approach to systematically investigate the effect that a complex environment has on cell motion and speed.

Recent experiments showed that weak geometrical constraints can organize topological defects in turbulent bacterial suspensions. Here, the authors use a continuum model to study the connection between symmetry and stability of emergent vortex patterns and the geometry of constraining pillar arrays.