Horizontal and Vertical Coalescent Microrobotic Collectives Using Ferrofluid Droplets

Abstract

Many artificial miniature robotic collectives have been developed to overcome the inherent limitations of inadequate individual capabilities. However, the basic building blocks of the reported collectives are mainly in the solid state, where the morphological boundaries of internal individuals are clear and cannot genuinely merge. Miniature robotic collectives based on liquid units still need to be explored; such on‐demand mergeable swarm systems are advantageous for adapting to the changing external environment. Here, a strategy to achieve a coalescent collective system we presented that exploits the ferrofluid droplets' splitting and coalescence properties to trigger the formation of horizontal multimodal and vertical gravity‐resistant collectives and unveil pattern‐enabled robotic functionalities. When subjected to a time‐varying magnetic field, the droplet swarm exhibits a variety of morphologies ranging from horizontal collectives, including vortex‐like, chain‐like, and crystal‐like patterns to vertical layer‐upon‐layer patterns. Using experiments and simulations, the formation and transformation of different morphological collectives are shown and their robust environmental adaptability are demonstrated. Potential applications of the multimodal droplet collectives are presented, including exploring an unknown environment, targeted object delivery, and fluid flow filtration in a lab‐on‐a‐chip. This work may facilitate the design of microrobotic swarm systems and expand the range of materials for miniature robots.

Micro/Nanorobotic Swarms: From Fundamentals to Functionalities

“…They were also capable of inclination, height reconfiguration, and navigated motion in complex environments when the interaction between the composing chains was tuned via changing of the strength and pitch angle of the magnetic fields. Similar swarm behaviors were also observed in a group of ferrofluid droplets …”

“…Similar swarm behaviors were also observed in a group of ferrofluid droplets. 181 Depending on the geometrical confinement, the dipole− dipole interaction between self-propelled ferromagnetic particles has been found to induce swarming phenomenon on a concave substrate. 182 The particles were powered by outof-plane uniaxial oscillating magnetic fields, and the particle oscillation broke the symmetry on the boundary and led to self-propulsion.…”

Magnetic Soft Matter toward Programmable and Multifunctional Miniature Machines

“…Soft machines utilizing liquid media, such as liquid metal or ferrofluid, possess dramatic deformation capabilities. , Ferrofluids are stable colloidal suspensions consisting of magnetic nanoparticles, carrier fluid, and surfactant . When subjected to an external magnetic field, ferrofluids exhibit a variety of deformation behaviors, including stretching, fission, and fusion.…”

Millirobot Based on a Phase-Transformable Magnetorheological Liquid Metal

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