From Passive Inorganic Oxides to Active Matters of Micro/Nanomotors

Abstract

Controllable actuation and coordinating motion of artificial self-propelled micro/nanomotors to mimic the motile natural microorganism systems are of great significance for constructing intelligent nanoscale machines. In particular, inorganic oxide particles have shown considerable promise in implementation of synthetic micro/nanomotors, due to their unique features and active response to environmental stimuli. This work critically reviews the recent progress in inorganic oxide-based micro/nanomotors and focuses on their propulsion response to chemical and physical stimuli, especially emphasizing and discussing operating principles in the single engine, adaptive navigation under composite-driven powers, and intriguing collective behaviors. The impact of oxide structure, multiple fields in motion controllability, and interaction between grouped micro/nanomotors are explored. Practical applications of individual and assembled micro/nanomotors in environmental and biomedical fields are demonstrated, including the removal of pollutants, drug delivery, cancer therapy, and in vivo imaging. Finally, current challenges for the development of novel micro/nanomotors and possible constraints toward the defined structure and accumulated toxicity are discussed along with future opportunities and directions. Owing to their facile synthesis, impressive physicochemical performances, high biocompatibility, and versatile actuations, it is expected that the association of inorganic oxides with micro/nanomotors will bring new and unique capabilities to the field of active matter.

Universal Control for Micromotor Swarms with a Hybrid Sonoelectrode

“…To demonstrate the dispersion and aggregation enabled by the hybrid sonoelectrode, 10 µm fluorescent polystyrene (PS) microspheres were selected as the spherical micromotor (SM) models, representing a typical configuration of conventional micromotors. [ 39 ] Figure a clearly shows the sketch of a stainless sonoelectrode and its detailed plain tip with 0.5 mm diameter. Generally, bubbles are generated via water electrolysis when two identical needle electrodes were connected to a 1.5 V battery, as schematically depicted in Figure 4b.…”

Magnetic Microrobotic Swarms in Fluid Suspensions

“…The microrobotic swarms have also been exploited for environmental remediation and pollution control [58]. Compared to the conventional passive diffusion of solutes, the controllable swarms with locomotion capability bright more effective solutions to decontamination [59]. For instance, by triggering larger flow velocity and rotating fluid flow, magnetic biohybrid swarms can adsorb and remove heavy metal ions in contaminated water with enhanced efficiency [60].…”

Vector-Controlled Wheel-Like Magnetic Swarms With Multimodal Locomotion and Reconfigurable Capabilities

“…One of the recent frontiers of micro-/nanorobots researches involves swarms that stem from bacteria colonies ( Felfoul et al, 2016 ), bird flocks ( Colorado and Rodewald, 2015 ) and insect swarms ( Gelblum et al, 2015 ) in nature, exhibit high environmental adaptability and enhanced tasking capabilities for environmental remediation ( Joh and Fan, 2021 ; Liu et al, 2020a ; Liu et al, 2020b ), micromanipulation ( Xu et al, 2020 ; Kagan et al, 2011 ; Solovev et al, 2010 ) and biomedicine ( Servant et al, 2015 ; Melde et al, 2016 ). Swarming micro-/nanorobots could be energized by different external stimuli, such as magnetic fields ( Yu et al, 2018a ; Li et al, 2015 ), chemicals ( Hu et al, 2020 ; Chang et al, 2019 ), electric fields ( Yan et al, 2016 ; Bricard et al, 2015 ), light ( Dong et al, 2018 ; Ibele et al, 2009 ), and ultrasound ( Xu et al, 2019 ; Xu et al, 2015 ).…”