Light-stimulated micromotor swarms in an electric field with accurate spatial, temporal, and mode control

Modular Micromotor Fabrication with Self-Focusing Lithography

Synthetic Janus micro/nanomotors can efficiently convert ambient energy into asymmetrical self-propulsive force, overcoming random thermal fluctuations and enabling autonomous migration. Further modifications to the motors can equip them with different functional modules to meet different needs. However, developing a versatile and high-yield fabrication method for multifunctional Janus micromotors remains challenging. In this study, a modular fabrication approach for micromotors with a particle-tip structure based on the self-focusing lithography induced by an array of TiO2 microspheres is presented. By adjusting the tip composition or loading, precise programming of motor functionality is achieved, allowing for various capabilities such as photoredox reaction-induced propulsion, fluorescent imaging, electric and magnetic navigation. Furthermore, the flexibility of this fabrication method by selectively loading materials onto two tips is demonstrated to achieve multifunctionality within a micromotor unit. This study proposes a straightforward and versatile approach for modular functional micromotors.

Photo-controlled order-to-order host-guest self-assembly transfer for an afterglow effect with water resistance

Due to the general incompleteness of photochemical reactions, the photostationary structure in traditional photo-controlled host-guest self-assembly transfer is usually disordered or irregular. This fact readily affects the photoregulation or improvement of related material properties. Herein, a photoexcitation-induced aggregation molecule, hydroxyl hexa(thioaryl)benzene (HB), was grafted into β-cyclodextrin to form a host-guest system. Upon irradiation, the excited state conformational change of HB can drive an order-to-order phase transition of the system, enabling the transfer of the initial linear nanostructure to a photostationary worm-like nanostructure with orderliness and crystallinity capability. Along with the photoexcitation-controlled phase transition, an afterglow effect was obtained from the films prepared by doping the host-guest system into poly(vinyl alcohol). The afterglow effect had a superior water resistance, which successfully overcame the general sensitivity of doped materials with the afterglow effect to water vapor. These results are expected to provide new insights for pushing forward chemical self-assembly from the light perspective, towards materials with superior and stable properties under light treatment.

Magnetic-actuated hydrogel microrobots with multimodal motion and collective behavior

Magnetic-actuated miniature robots have sparked growing interest owing to their promising potential in biomedical applications, such as noninvasive diagnosis, cargo delivery, and microsurgery. Innovations are required to combine biodegradable materials with flexible mobility to promote the translation of magnetic robots towards in vivo application. This study proposes a biodegradable magnetic hydrogel robot (MHR) with multimodal locomotion and collective behavior through magnetic-assisted fabrication. The MHRs with aligned magnetic chains inside their structures have more significant maximum motion speeds under rotating magnetic fields than the robots without magnetic alignment. By reconfiguring the external magnetic fields, three types of stable motion modes (tumbling, spinning, and wobbling modes) of the individual MHRs can be triggered, while flexible conversion can be achieved between each motion mode. The motion mechanism of each motion mode under diverse rotating magnetic fields has been analyzed. The collective behavior of the MHRs, which is triggered by the magnetic dipole force, can enhance the motion performance and pass through sophisticated terrains. Furthermore, the experimental results demonstrate that the assembled MHRs can execute complicated tasks such as targeted cargo delivery. The proposed MHRs with multimodal locomotion and assembled behavior show effective motion efficiency, flexible maneuverability, and remarkable targeting ability, providing a new choice for magnetic robots in biomedical applications.

Swarm Autonomy: From Agent Functionalization to Machine Intelligence

Swarm behaviors are common in nature, where individual organisms collaborate via perception, communication, and adaptation. Emulating these dynamics, large groups of active agents can self-organize through localized interactions, giving rise to complex swarm behaviors, which exhibit potential for applications across various domains. This review presents a comprehensive summary and perspective of synthetic swarms, to bridge the gap between the microscale individual agents and potential applications of synthetic swarms. It is begun by examining active agents, the fundamental units of synthetic swarms, to understand the origins of their motility and functionality in the presence of external stimuli. Then inter-agent communications and agent-environment communications that contribute to the swarm generation are summarized. Furthermore, the swarm behaviors reported to date and the emergence of machine intelligence within these behaviors are reviewed. Eventually, the applications enabled by distinct synthetic swarms are summarized. By discussing the emergent machine intelligence in swarm behaviors, insights are offered into the design and deployment of autonomous synthetic swarms for real-world applications.

Colloidal Self-Assembly: From Passive to Active Systems

Self-assembly fundamentally implies the organization of small sub-units into large structures or patterns without the intervention of specific local interactions. This process is commonly observed in nature, occurring at various scales ranging from atomic/molecular assembly to the formation of complex biological structures. Colloidal particles may serve as micrometer-scale surrogates for studying assembly, particularly for the poorly understood kinetic and dynamic processes at the atomic scale. Recent advances in colloidal self-assembly have enabled the programmable creation of novel materials with tailored properties. We here provide an overview and comparison of both passive and active colloidal self-assembly, with a discussion on the energy landscape and interactions governing both types. In the realm of passive colloidal assembly, many impressive and important structures have been realized, including colloidal molecules, one-dimensional chains, two-dimensional lattices, and three-dimensional crystals. In contrast, active colloidal self-assembly, driven by optical, electric, chemical, or other fields, involves more intricate dynamic processes, offering more flexibility and potential new applications. A comparative analysis underscores the critical distinctions between passive and active colloidal assemblies, highlighting the unique collective behaviors emerging in active systems. These behaviors encompass collective motion, motility-induced phase segregation, and exotic properties arising from out-of-equilibrium thermodynamics. Through this comparison, we aim to identify the future opportunities in active assembly research, which may suggest new application domains.