Density Asymmetry Driven Propulsion of Ultrasound‐Powered Janus Micromotors

Abstract

The ability of acoustically propelled micro and nanoscale motors to perform diverse tasks while moving in solutions can open up new applications in diverse fields such as medicine, biotechnology, and materials science. However, the current understanding of the underlying propulsion mechanisms of ultrasound-driven structures is limited for translating their motion and operation to practical applications. Here, the behavior of Janus microparticles displaying acoustically driven propulsion is demonstrated. A new approach to harness the acoustically-induced vibration and oscillation of a density asymmetric Janus microstructure into translational motion is presented, based on fixing the micromotor orientation with an external magnetic field. Such acoustic propulsion of Janus microparticles is realized through a judicious material selection based primarily on density and asymmetry considerations. Experimental data and theoretical models indicate that the density asymmetry provides an acoustic propulsive force for translational motion. The Janus structure presented here is also able to propel using chemical and magnetic actuations, paving the way for different hybrid nanovehicles. The new approach to harvest acoustic energy leads to a robust motile platform and expands the horizons of ultrasound-propelled micro/nanomotors, offering new possibilities for their design and applications.

Acoustically propelled nano- and microcones: fast forward and backward motion

“…There exist two different types of acoustically propelled particles: rigid particles [26][27][28][31][32][33][34]37,38,40,41,43,44,46,51,[55][56][57][60][61][62][63][64][65] and particles with movable components. 23,40,45,50,53,54,58,59,66 The rigid particles are easier to produce in large numbers and thus of special relevance with respect to future applications, where usually a large number of particles is required.…”

“…57,62,64,65,67,68 In recent years, ultrasound-propelled nanoand microparticles have been intensively investigated. [26][27][28]30,32,34,[37][38][39][40][43][44][45][46][51][52][53][54][55][57][58][59][60][61][63][64][65][69][70][71] Besides two articles that are based on analytical approaches 61,63 and an article that relies on direct computational fluid dynamics simulations, 51 a large number of experimental studies have been published so far. [26][27][28]30,32,[38][39][40]44,45,49,50,…”

Magnetically Driven Micro and Nanorobots

“…(C) ON–OFF feature and direction control capacity of the magnetic field for ultrasound-powered Janus micromotors: (a) Propulsion of a single microrobot without and with the application of a static magnetic field; (b) Magnetic navigation of a single acoustic-powered microrobot. Reproduced with permission from ref ( 181 ). Copyright 2020 WILEY-VCH GmbH and Co. KGaA, Weinheim.…”

Recent progress in actuation technologies of micro/nanorobots

“…Valdez-Garduño et al [36] proposed a new method that uses an external magnetic field to fix the direction of a micromotor and converts the ultrasound-induced oscillation motion of a Janus microstructure with asymmetric density into a translational motion. The acoustic movement of the Janus microstructure is based on the selection of materials with different densities and shapes.…”