Significance: The exploration of chiral active matter composed of self-spinning objects, which breaks both parity and time-reversal symmetries, is an exciting and rapidly developing area. A particularly interesting phenomenon of chiral active matter is the emergence of a spontaneous unidirectional collective edge flow in confinement, with potentials for robust material transport. This unique feature has generally been discussed in the context of incompressible and structureless homogeneous fluid. Here, we show that confinement-induced nonuniform distribution of spinners greatly influences the edge flow, causing a spatially oscillatory pattern. Moreover, as the structure of the active media varies, different collective modes emerge. These findings significantly advance our understanding of collective behavior of chiral active matter in confinement.

The discovery of topological edge states that unidirectionally propagate along the boundary of system without backscattering has enabled the development of new design principles for material or information transport. Here, we show that the topological edge flow supported by the chiral active fluid composed of spinners can even robustly transport an immersed intruder with the aid of the spinner-mediated depletion interaction between the intruder and boundary. Importantly, the effective interaction significantly depends on the dissipationless odd viscosity of the chiral active fluid, which originates from the spinning-induced breaking of time-reversal and parity symmetries, rendering the transport controllable. Our findings propose a novel avenue for robust cargo transport and could open a range of new possibilities throughout biological and microfluidic systems.

Exploiting the energy of randomly moving active agents such as bacteria is a fascinating way to power a microdevice. Here we show, by simulations, that a chain-grafted disk-like colloidal particle can rotate unidirectionally and hence output work when immersed in a thin film of active particle suspension. The collective spontaneous symmetry breaking of chain configurations is the origin of the unidirectional rotation. Long persistence time, large propelling force and/or small rotating friction are keys to sustaining the collective broken symmetry and realizing the rotation. In the rotating state, we find very simple linear relations, e.g. between the mean angular speed and the propelling force. The time-evolving asymmetry of chain configurations reveals that there are two types of non-rotating state. The basic phenomena are also observed in the macroscopic granular experiments, implying the generic nature of these phenomena. Our findings provide new insights into the collective spontaneous symmetry breaking in active systems with flexible objects and also open the way to conceive new soft/deformable microdevices.

Computational imaging makes it possible to reconstruct hidden objects through random media and around corners, which is of fundamental importance in various fields. Despite recent advances, computational imaging has not been studied in certain types of random scenarios, such as tortuous corridors filled with random media. We refer to this category of complex environment as a ’random corridor’, and propose a reduced spatial- and ensemble-speckle intensity correlation (RSESIC) method to image a moving object obscured by a random corridor. Experimental results show that the method can reconstruct the image of a centimeter-sized hidden object with a sub-millimeter resolution by a low-cost digital camera. The imaging capability depends on three system parameters and can be characterized by the correlation fidelity (CF). Furthermore, the RSESIC method is able to recover the image of objects even for a single pixel containing the contribution of about 10² speckle grains, which overcomes the theoretical limitation of traditional speckle imaging methods. Last but not least, when the power attenuation of speckle intensity leads to serious deterioration of CF, the image of hidden objects can still be reconstructed by the corrected intensity correlation.

Artificial active matter with a macroscopic scale, including vibrating particles, robots, and camphor boats, have attracted increasing attentions due to their uniform properties, rich and easily controllable parameters, convenient observation, and the independence of biochemical processes from physical processes, especially providing these unique advantages for researching the collective behaviors under strong confinement and crowded surroundings. \red{In this review, we present an overview of motion models, mechanisms, and dynamic characteristics of various active particles, both in free and complex media. Additionally, we delve into the collective behaviors of ``dry'' active matter, covering structural and dynamic properties observed in experiments and theoretical models. We summarize the impact of hydrodynamic interactions on the dynamics and structure of these active particles within hydrodynamic environments. Lastly, we discuss emerging opportunities and challenges for the future advancement of macroscopic artificial active matter.