Active Synthetic Microrotors: Design Strategies and Applications

Abstract

Microrotors are microscopic objects that convert energy stored in the environment into spontaneous rotation, in the form of spinning along an axis, rolling on a surface, or orbiting in circles. Because of its distinct dynamics and the vertical flows around it, a microrotor is potentially useful for applications, including drug delivery, minimally invasive surgery, fluid mixing, and sensing. It is also useful as a model system to probe the collective behaviors among rotating microobjects. In this review article, we comprehensively review the recent experimental progress in designing, synthesizing, and using microrotors. For applications, particular emphasis is placed on microfluidic mixing, biomedicine, and collective behaviors. In the end, we comment on how microrotors can be made more biocompatible and more controllable and rotate in more ways and the challenges therein. A key feature of this review article is to introduce three ways in which to classify a microrotor: the nature of its rotational behavior (spinners, rollers, or orbiters), the cause of its rotation (whether chiral symmetry is broken by shapes, chemical compositions, or the way energy is applied), and its power source (whether powered by chemical reactions, electric or magnetic fields, light, or ultrasound). This review article will help materials scientists and chemists in designing micromachines and microrotors, help engineers in finding appropriate microrotors for a specific application, and help physicists in finding appropriate model systems.

Catalytically Propelled Micro‐ and Nanoswimmers

“…Some studies have demonstrated programmed rotary motion by appropriately designing catalytic swimmers. [96] Previous research has also shown the feasibility of single chemotactic events, enabling swimmers to move toward higher fuel concentrations of the surrounding environment. [52,94,97] To achieve full autonomy, the next step is enabling directional changes in movement by adjusting the propulsion mechanism in response to the surrounding environment, similar to natural microorganisms, which exhibit dual chemotaxis (positive and negative chemotaxis) in response to chemical cues.…”

Electroosmotic flow spin tracers near chemical nano/micromotors

“…Note that we are focusing on the torques exerted by a moving nano/micromotor on its neighbors, rather than on itself, which makes it a rotor that is beyond the scope of this work. [13][14][15] We report in this communication that a chemically powered nano/micromotor spins nearby tracers, so that a tracer moves along with the nanomotor and spins in place (in the co-moving frame), unlike the tracers in ref. 16 and 17 that orbit in large convective loops.…”

“…Note that we are focusing on the torques exerted by a moving nano/micromotor on its neighbors, rather than on itself, which makes it a rotor that is beyond the scope of this work. 13–15…”

Droplet Rolling Transport on Hydrophobic Surfaces Under Rotating Electric Fields: A Molecular Dynamics Study

“…53 MD simulations have confirmed that droplets on a superhydrophobic surface will roll when a body force is applied. 54 Although the concept of microrotor rotation and rolling under a rotating electric field has been reported, 55 the rolling mechanism of nanodroplets under a rotating electric field has still not been investigated in detail, and the effect of the solid surface on the rolling transport of the droplets is still unclear. Here, we studied the rolling transport of nanodroplets on a hydrophobic surface under a rotating electric field by MD simulations.…”