Active Micro/Nanoparticles in Colloidal Microswarms

Abstract

Colloidal microswarms have attracted increasing attention in the last decade due to their unique capabilities in various complex tasks. Thousands or even millions of tiny active agents are gathered with distinctive features and emerging behaviors, demonstrating fascinating equilibrium and non-equilibrium collective states. In recent studies, with the development of materials design, remote control strategies, and the understanding of pair interactions between building blocks, microswarms have shown advantages in manipulation and targeted delivery tasks with high adaptability and on-demand pattern transformation. This review focuses on the recent progress in active micro/nanoparticles (MNPs) in colloidal microswarms under the input of an external field, including the response of MNPs to external fields, MNP-MNP interactions, and MNP-environment interactions. A fundamental understanding of how building blocks behave in a collective system provides the foundation for designing microswarm systems with autonomy and intelligence, aiming for practical application in diverse environments. It is envisioned that colloidal microswarms will significantly impact active delivery and manipulation applications on small scales.

Keywords: active micro/nanoparticle; collective behavior; micro/nanorobot; microswarm; swarm control; wireless actuation.

Figure 1

Schematic illustration of active micro/nanoparticles (MNPs) in microswarms under external fields. The insets were reproduced from the following references. Magnetic: (a) Adapted from [50], copyright 2018 SAGE Publications. (b) Reproduced from [51] under a Creative Commons CC-BY license. (c) Adapted from [52] under a Creative Commons CC-BY license. Light: (d) Adapted from [53], copyright 2014 Wiley. (e) Adapted from [54], copyright 2017 Wiley. (f) Adapted from [55], copyright 2018 Springer Nature. Acoustic: (g) Adapted from [56], copyright 2020 Wiley. (h) Adapted from [57], copyright 2015 American Chemical Society. Electric: (i) Adapted from [58], copyright 2015 National Academy of Sciences. (j) Adapted from [59], copyright 2016 Springer Nature. Multiple: (k) Adapted from [60] under a Creative Commons CC-BY license. (l) Adapted from [61], copyright 2019 Wiley. (m) Reproduced from [62], copyright 2020 American Chemical Society.

Figure 2

Paramagnetic ${\mathrm{Fe}}_3{\mathrm{O}}_4$ nanoparticles in microswarms. (a) Vortex microswarm formed under a rotating magnetic field, governed by hydrodynamic interactions among nanoparticle chains. Reproduced from [50], copyright 2018 SAGE Publications. (b) Bio-inspired ribbon microswarms formed under an oscillating field. Reproduced from [64], copyright 2022 American Chemistry Society. (c) Spreading and disassembly of nanoparticle chains on a flat surface. Reproduced from [67], copyright 2017 IEEE. (d) Reversible spreading–disassembly and gathering of nanoparticle clusters on uneven surfaces. Reproduced from [43], copyright 2020 Elsevier.

Figure 3

Paramagnetic polymer microparticles in microswarms. (a) Dispersion of dense magnetic microparticles by interfacial rotaphoresis. Reproduced from [68], copyright 2015 Royal Society of Chemistry. (b) Magnetic control of a microswarm under precessing magnetic fields. Adapted from [69] under a Creative Commons CC-BY license. (c) Microswarm navigates through an array of obstacles. Adapted from [70] under a Creative Commons CC-BY license. (d) Self-organization of a microswarm under dynamic magnetic fields. Adapted from [51] under a Creative Commons CC-BY license. (e) Microswarm moves against an immobile obstacle. Reproduced from [71], copyright 2015 American Physics Society.

Figure 4

Anisotropic magnetic microparticles in microswarms. (a) Formation of a dipolar ring by ellipsoids. Reproduced from [75], copyright 2016 American Physics Society. (b) Pattern formation by magnetic microdisks. Adapted from [52] under a Creative Commons CC-BY license. (c) Hydrodynamic-interaction-governed microswarms by magnetic rollers. Adapted from [76], copyright 2017 Springer Nature.

Figure 5

UV light-driven particles in microswarms. (a) AgCl particles exposed to on–off-controlled UV light. Adapted from [77], copyright 2009 Wiley. (b) Assembly of UV light-activated self-propelled Janus particles. Adapted from [54], copyright 2017 Wiley. (c) Reversible collective behavior of ${\mathrm{TiO}}_2$ microparticles under different light intensities. Adapted from [78], copyright 2020 Wiley. (d) Navigation of a ${\mathrm{TiO}}_2$ microswarm under UV light. Adapted from [79] under the Creative Commons CC-BY-NC-ND license.

Figure 6

Light-driven active particles in microswarms. (a) Prey and predator particles in light-driven hierarchical microswarms. Reproduced from [80], copyright 2019 American Chemical Society. (b) Janus particles under NIR light for tissue welding. Adapted from [81] under the Creative Commons CC-BY license. (c) Pear-shaped polystyrene microparticles in UV/blue light-driven microswarms. Reproduced from [53], copyright 2014 Wiley. (d) Haematite cube polymer beads in a laser-driven microswarm. Adapted from [55], copyright 2018 Springer Nature.

Figure 7

Acoustic-field-driven active particles in microswarms. (a) Formation of EGaIn nanorod microswarms under an acoustic field. Adapted from [56], copyright 2020 Wiley. (b) Formation and navigation of Au-Pt Janus microswarms under an acoustic field. Adapted from [57], copyright 2015 American Chemical Society.

Figure 8

Electric-field-driven active particles in microswarms. (a) Janus colloidal spheres in microswarms with imbalanced, off-centered charges. Adapted from [59], copyright 2016 Springer Nature. (b) Collective motion of rolling particles. Adapted from [84], copyright 2013 Springer Nature. (c) Asymmetric dimers in a collective system. Adapted from [58], copyright 2015 National Academy of Sciences.

Figure 9

Multiple-field-actuated particles in microswarms. (a) Rotating acoustic–magnetic microparticle microswarms near a boundary. Adapted from [60] under a Creative Commons CC-BY license. (b) Collective behavior of magneto–acoustic nanorods. Adapted from [85], copyright 2015 American Chemical Society. (c) Collective behavior of Janus microbowls under light modulation and magnetic actuation. Adapted from [61], copyright 2019 Wiley. (d) Hovering ${\mathrm{Fe}}_3{\mathrm{O}}_4@{\mathrm{SiO}}_2$ nanoparticle microswarms. Reproduced from [62], copyright 2020 American Chemical Society.