Hierarchical Microswarms with Leader–Follower‐Like Structures: Electrohydrodynamic Self‐Organization and Multimode Collective Photoresponses

Abstract

Swarming micro/nanomotors can self-organize into cohesive groups to execute cooperative tasks. To date, research work has focused on the construction of egalitarian microswarms composed of similar individuals. The construction and collective behaviors of hierarchical leaderfollower-like microswarms are demonstrated. By inducing converging electrohydrodynamic flows under an AC electric field, dielectric microparticles with different sizes and dielectric properties can hierarchically self-organize into leader-follower-like microswarms under attractive electrohydrodynamic interactions, and show novel emergent collective behaviors. First, different from immobile single constituents or egalitarian clusters, the hierarchical microswarms autonomously move with tunable speed. Second, they exhibit multimode collective photoresponses emerging from different behaviors of the constituents in response to light signals. With a vertical UV signal, the photoresponsive followers tend to surround the leader and stop the microswarm. In response to sidewise UV signals, the constituents with stronger phototaxis would migrate to the position away from light stimuli, and thus the microswarms reorient parallel/antiparallel to the light direction and perform collective positive/negative phototaxis. Due to differential roles and huge design spaces of constituents, the hierarchical microswarms are envisioned to possess merits of high-efficiency, multiresponsiveness, and multifunctions, and may serve as intelligent micro/nanorobot systems for biomedicine and microengineering.

Titania-Based Micro/Nanomotors: Design Principles, Biomimetic Collective Behavior, and Applications

“…Thus, they can exert attractive force on neighboring particles and self-assemble into clusters. In this way, the cluster formation and collective motions with dissimilar colloidal microparticles with different radius and dielectric properties were demonstrated (Figure 5A) [72]. While TiO 2 -based MNMs have inherent photochemical propulsion, they can also respond to additional stimuli by hybridization with other materials.…”

Light‐Powered Microrobots: Challenges and Opportunities for Hard and Soft Responsive Microswimmers

“…[ 48 ] Recently, hierarchical microswarms with leader‐follower‐like structures were also demonstrated: the self‐organization and subsequent behavior of two different microparticle populations was induced by controlling local electrohydrodynamic and diffusiophoretic interactions. [ 187 ] Although the nanoparticles investigated so far in these studies do not possess specific functions, fundamental studies on interacting microrobots would open to potential applications where they will accomplish the same or different tasks independently or triggered by mutual interactions and communication. While at the macroscale robot communication can take advantage of sensors, processors, and cabled or wireless routing, such components are difficult to integrate at the microscale within the tiny body of the microrobots.…”

The Encoding of Light‐Driven Micro/Nanorobots: from Single to Swarming Systems

“…In addition, the same group recently designed a leader–follower‐like active–passive particle system, and multimode swarming behaviors were demonstrated in response to light signals. [ 105 ] As shown in Figure 7f, with vertical UV illumination, the photoresponsive followers tend to surround the leader. The asymmetric assembly then gradually grows into symmetric cluster and stops the migration.…”

“…Reproduced with permission. [ 105 ] Copyright 2020, Wiley‐VCH. g) Schematic diagram of light‐controlled assembly with spiropyran‐modified SiO 2 –Pt Janus micromotors.…”