Recent Advances in Collective Behaviors of Micro/Nanomotor Swarms

Abstract

Collective motion, exemplified by swarming insects, flocking birds, and bacterial colonies, emerges from the synchronized actions and velocity adjustments of individual units. Inspired by these natural phenomena, researchers have sought to replicate and harness collective behavior in swarms of self-propelled micro/nanomotors. This endeavor is of great importance for the development of multicomponent adaptive systems. Comprising numerous interacting elements, collective swarms exhibit emergent behaviors that capitalize on multi-motor cooperation, enabling highly efficient, flexible, and robust group performance. Understanding and engineering these behaviors are essential for translating them into practical applications. This review examines the driving forces underlying collective motion, outlines various modes of swarm formation across different dimensions, and highlights representative applications. By linking driving forces, system dimensionality, and functional implementation, it provides a comprehensive perspective on this field.

Keywords: collective behavior; driving forces; functional applications; multi‐dimensional collective behavior; swarm manipulation.

FIGURE 1

Chemical signal‐driven and electrostatic forces‐driven collective motion. (A) Urease‐powered nanomotors are employed to analyze the biodistribution of nanomotor swarms following intravenous injection in female mice, as visualized by PET‐CT imaging. Reproduced with permission [29]. Copyright 2021, American Association for the Advancement of Science. (B) An ion‐exchange interaction between ZnO nanorods and PS microbeads lead to collective behavior on a hierarchical scale. Reproduced with permission [48]. Copyright 2021, Springer Nature. (C) Au‐Pt nanorods dynamically assemble into staggered doublets and triplets in the presence of the substrate H₂O₂, facilitating collective motion in a unified direction. Reproduced with permission [50]. Copyright 2013, National Academy of Sciences. (D) Upon exposure to an external electric field, directrons initially exhibit random motion but eventually self‐organize into flocks, synchronizing their movements. Reproduced with permission [51]. Copyright 2020, Wiley‐VCH.

FIGURE 2

Light‐driven and acoustic field‐driven collective motion. (A) Swarming of Fe₃O₄@poly(glycidyl methacrylate)/polystyrene (Fe₃O₄@PGS) core–shell motors is reversibly and remotely manipulated based on the position of irradiation, on/off switching, and light intensity. Reproduced with permission [59]. Copyright 2020, American Chemical Society. (B) Under exposure to a gradient light field, MoS₂ colloidal motors undergo photochemical reactions that generate local chemical gradients, driving their motion in a positive phototactic direction. When illuminated with a rectangularly patterned UV light gradient, these colloidal motors self‐organize into dynamic, rectangular swarms. Reproduced with permission [55]. Copyright 2021, Wiley‐VCH. (C) The formation of swarms composed of microbubbles and they adhere to the walls of venules under an acoustic field. Swarms navigate in mouse brain vasculature under an acoustic field. Reproduced under terms of the CC‐BY license [62]. Copyright 2023, Del Campo Fonseca et al., published by Springer Nature. (D) The experimental setup of checking motion of the system, includes a signal generator, power amplifier, ultrasonic platform, and microscope. The collective behavior of the nanomotors changes with ultrasound frequency under the ultrasonic field, forming three distinct patterns: vortex‐like at 1.3 MHz, stripe‐like chains at 1.4 MHz, and clusters at 2.8 MHz. Reproduced under terms of the CC‐BY license [63]. Copyright 2024, Zhao et al., published by the Multidisciplinary Digital Publishing Institute (MDPI).

FIGURE 3

Magnetic‐driven collective motion. (A) A magnetic swarm comprising porous Fe₃O₄ particles for biofilm disruption. Reproduced with permission [69]. Copyright 2021, American Chemical Society. (B) Reconfigurable magnetic micromotor swarm composed of hematite colloidal particles under alternating magnetic fields, programming them into various configurations such as liquid, chain, vortex, and ribbon‐like structures. Reproduced with permission [20]. Copyright 2019, American Association for the Advancement of Science. (C) Bio‐inspired rolling motion by introducing superparamagnetic particles in magnetic and acoustic fields, inspired by a neutrophil rolling on a wall. Reproduced under terms of the CC‐BY license [70]. Copyright 2017, Ahmed et al., published by Springer Nature. (D) A schematic illustration showing the imaging and navigation of a magnetic swarm within a blood vessel. Reproduced with permission [63]. Copyright 2024, American Association for the Advancement of Science.

FIGURE 4

Biohybrid swarms. (A) Combining magnetic guidance with a synthesized protein‐based hyaluronic acid (HA) microflake for the in situ selection, transport, and release of motile sperm cells. Reproduced with permission [76]. Copyright 2020, Wiley‐VCH. (B) Magnetic nanoparticles‐loaded bacteria achieve magnetic‐driven collective motion by a rotating magnetic field. Reproduced with permission [78]. Copyright 2022, American Chemical Society. (C) Magnetotactic bacteria act as biohybrid motors that naturally contain magnetosome magnetite crystals, exhibit swarm behavior and move in a circular direction under a programed clockwise magnetic field. Reproduced under terms of the CC‐BY license [72]. Copyright 2023, Song et al., published by American Chemical Society. (D) Targeted motion of red blood cells based micromotors containing Fe₃O₄ nanoparticles toward HeLa cells in a microfluidic channel under magnetic navigation. Reproduced with permission [80]. Copyright 2019, American Chemical Society. (E) Magnetic navigation of collective stem cell micromotors in blood under ultrasound doppler imaging. Reproduced with permission [82]. Copyright 2021, Institute of Electrical and Electronics Engineers (IEEE).

FIGURE 5

Multi‐mode driven swarms. (A) Light‐magnetic stimuli‐responsive nanoactuators that consist of a magnetized Au nanorod encapsulated in a thermoresponsive hydrogel. Magnetic manipulation drove the reversible assembly of nanoactuators into chains, while photothermal effect enabled the collective manipulation of nanoactuators to form permanent assemblies. Reproduced under terms of the CC‐BY license [86]. Copyright 2020, Parreira et al., published by Wiley‐VCH. (B) Light‐stimulated micromotor swarms in an electric field with accurate spatial, temporal, and mode control. Reproduced under terms of the CC‐BY license [87]. Copyright 2023, Liang et al., published by American Association for the Advancement of Science. (C) A weak ion‐exchange based swarm which self‐organizes and reconfigures by chemical, light, and magnetic fields, showing crystals, amorphous glasses, liquids, chains, and wheel‐like structures. Reproduced with permission [85]. Copyright 2024, Wiley‐VCH.

FIGURE 6

(a) Dynamically moving hard boundaries enable the confinement of magnetic motors into reprogrammable 2D self‐assembled structures. Reproduced under terms of the CC‐BY license [92]. Copyright 2020, Culha et al., published by National Academy of Sciences. (b) A centrally actuated Chladni plate applies a sequence of vibration‐induced displacement fields, assembling the motors into a desired shape. Reproduced under terms of the CC‐BY license [93]. Copyright 2021, Kopitca et al., published by the American Association for the Advancement of Science.

FIGURE 7

(A) Micromotor swarms for intracellular measurement with enhanced signal‐to‐noise ratio. Reproduced with permission [98]. Copyright 2022, American Chemical Society. (B) An acoustically controlled swarm is developed based on the self‐assembly of clinically‐approved microbubbles. Reproduced under terms of the CC‐BY license [65]. Copyright 2022, Del Campo Fonseca et al., published by Wiley‐VCH. (C) TiO_2–Au microbowls swarm behavior is dynamically repeated by switching UV light on and off under an acoustic field. Reproduced with permission [102]. Copyright 2019, Wiley‐VCH. (D) Chemical field and uniform magnetic field induce assembly and disassembly process, an ion‐exchange reaction enables hierarchical swarm formation composed of cationic ion exchange resin and magnetic microspheres. Reproduced with permission [96]. Copyright 2024, Wiley‐VCH. (E) The swarming/dispersion effect of B‐TiO₂@N/Au nanomotors programmed by on and off switching of a near‐infrared light source. Reproduced with permission [103]. Copyright 2023, American Chemical Society.

FIGURE 8

(A) Dispersed paramagnetic micromotors are actuated with a precessing magnetic field, self‐assembled into linear chains simultaneously, and interact with multipolar magnetic forces. Reproduced under terms of the CC‐BY license [108]. Copyright 2020, Yigit et al., published by Royal Society of Chemistry. (B) The reversible formation of pearl‐like coacervate droplet chains when turning on/off the electric field. Reproduced under terms of the CC‐BY license [110]. Copyright 2020, Agrawal et al., published by National Academy of Sciences. (C) Chain‐shaped swarms rolling along acoustic virtual walls. Reproduced under terms of the CC‐BY license [111]. Copyright 2022, Zhang et al., published by Springer Nature.

FIGURE 9

(A) A swarm system mimics the structure and function of an ant bridge. Reproduced with permission [112]. Copyright 2019, American Chemical Society. (B) Autonomous environment‐adaptive micromotor swarm navigation enabled by deep learning‐based real‐time distribution planning. Reproduced with permission [114]. Copyright 2022, Springer Nature. (C) Ion‐exchange enabled synthetic swarm achieves quorum sensing aggregation with different confined geometries. Reproduced with permission [48]. Copyright 2021, Springer Nature. (D) Nanowires ‘write’ images and translate, rotate and align under full computer control. Reproduced with permission [116]. Copyright 2023, Springer Nature. (E) Two panda sketches obtained by optothermal liquid painting. Reproduced with permission [117]. Copyright 2022, Wiley‐VCH. (F) Dynamic assembly and disassembly of “runners” composed of MoS₂ colloidal motors. Reproduced with permission [55]. Copyright 2021, Wiley‐VCH.

FIGURE 10

(A) Binary phases and crystals are assembled from active and passive colloids. Reproduced with permission [120]. Copyright 2022, American Chemical Society. (B) A photochromic colloidal swarm, capable of autonomously adjusting its appearance in response to incident light by inducing layered phase segregation. Reproduced under terms of the CC‐BY license [121]. Copyright 2023, Zheng et al., published by Springer Nature. (C) Swarm‐based micromanipulator, utilizing its bending deformation behavior to grab and release microspheres. Reproduced with permission [106]. Copyright 2021, Wiley‐VCH. (D) SMARS demonstrate a temperature‐dependent closed‐loop process for dynamically trapping and manipulating AuNPs, progressing from the initial colloidal nanomotor solution (I) through stages of small clusters (II), large clusters (III), alignment (IV), microscale disassembly (V), nanoscale disassembly (VI), and finally, a recovery stage. Reproduced under terms of the CC‐BY license [125]. Copyright 2021, Li et al., published by The American Association for the Advancement of Science.

FIGURE 11

(A) The preparation of enzymatic nanomotors and solutal buoyancy–induced collective behavior and the trajectory tracking of collective behaviors. Reproduced under terms of the CC‐BY license [132]. Copyright 2024, Chen et al., published by Springer Nature. (B) The reconfigurable collective behavior of a swarm from a 2D pattern to 3D tornado‐like structure, consists of rising, hovering, oscillation, and landing stages. Reproduced with permission [129]. Copyright 2020, American Chemical Society.

FIGURE 12

Schematic showing the connection between driving force, system dimensionality, and related application. Thicker arrows represent that the connection between the modules is strong.