Tubular Micro/Nanomachines: From the Basics to Recent Advances

Abstract

Inspired by the machines that have changed the world through their autonomous functions, scientists have focused their attention on performing similar functions at the micro/nanoscale. The motility of these micro/nanomachines (micro/nanomotors) offers enormous opportunities for cargo delivery, biodetection, and environmental and biomedical applications. Among the various geometries of micro/nanomotors, a tubular shape provides asymmetric inner and outer surfaces, where the inner wall hosts chemical reactions that supply the moving power and the outer wall can be modified for specific chemical and biological functions. This review describes the concept of tubular micro/nanomotors, including their basic principles, fabrication methods and control over their motion. With the assistance of catalytic reactions, tubular micro/nanomotors can generate a powerful thrust force to navigate in complex natural and in vitro environments. Modification of the tubular micro/nanomotors allows the motors to capture, transport, and release selected cargos on demand. In addition, their application in sensing and decontamination benefits from their collection behavior and self‐mixing effect. Furthermore, noncatalytic reaction‐driven tubular micro/nanomotors, such as redox‐based and biohybrid tubular micro/nanomotors, provide new possibilities for practical in vivo applications. The state‐of‐the‐art tubular micro/nanomotors could offer a promising platform for various applications, e.g., lab‐on‐chip devices and in vivo theranostics.

Biohybrid and Bioinspired Magnetic Microswimmers

“…In a similar fashion, rolled‐up multilayers with a magnetic material like iron oxide together with Pt or silver (Ag) inside the formed tube produced gas bubbles that are released at one end of the tubes, resulting in a forward movement in the opposite direction . Recently, more general advances of tubular micro‐ and nanomachines are given elsewhere …”

“…[122][123][124] Recently, more general advances of tubular micro-and nanomachines are given elsewhere. [125,126] While Janus particles are prominent for catalytic diffusiophoresis, their movement is nondirectional, and they are subject to the rotational diffusion of a sphere. Due to the high symmetry of the sphere, a simple coating with a material that has an in-plane easy axis for the magnetization, covering one hemisphere would not result in an effective magnetic moment, since all contributions would cancel each other out.…”

A Review on Artificial Micro/Nanomotors for Cancer-Targeted Delivery, Diagnosis, and Therapy

“…To meet these demands of efficient energy harvesting and conversion, a wide variety of fabrication strategies have been developed, such as metallic thin films deposition, templateassistant metal electroplating, rolling-up methods, and selfassembly techniques [31,32]. With these techniques, a broad array of micro/nanomotors have been fabricated, such as nanowires [33][34][35], microtubular microrockets [36][37][38], Janus microspheres [39][40][41], and supermolecule-based nanomotors [42][43][44]. They can efficiently be moved by harnessing various fuels and various driving modes [45][46][47].…”

Light-controlled two-dimensional TiO2 plate micromotors

“…[1][2][3][4][5][6][7][8][9][10] In such cases, micro-/nano-motor-based catalytic micro-/nano-machines can efficiently convert chemical energy into kinetic energy of motion. Usually, in order to power the micro-/nano-motors, extra fuels are required, including well studied H 2 O 2 , [11][12][13] hydrazine, 14 acidic, 15 and alkaline-based fuels. 15 From the viewpoint of practical applications of micromotors, steering them in a precise and controllable way, e.g., controllable activation, directionality and speed, is of great advantage.…”