Rheotaxis of Bimetallic Micromotors Driven by Chemical–Acoustic Hybrid Power

Abstract

Rheotaxis is a common phenomenon in nature that refers to the directed movement of micro-organisms as a result of shear flow. The ability to mimic natural rheotaxis using synthetic micro/nanomotors adds functionality to enable their applications in biomedicine and chemistry. Here, we present a hybrid strategy that can achieve both positive and negative rheotaxis of synthetic bimetallic micromotors by employing a combination of chemical fuel and acoustic force. An acoustofluidic device is developed for the integration of the two propulsion mechanisms. Using acoustic force alone, bimetallic microrods are propelled along the bottom surface in the center of a fluid channel. The leading end of the microrod is always the less dense end, as established in earlier experiments. With chemical fuel (HO) alone, the microrods orient themselves with their anode end against the flow when shear flow is present. Numerical simulations confirm that this orientation results from tilting of the microrods relative to the bottom surface of the channel, which is caused by catalytically driven electro-osmotic flow. By combining this catalytic orientation effect with more powerful, density-dependent acoustic propulsion, both positive and negative rheotaxis can be achieved. The ability to respond to flow stimuli and collectively propel synthetic microswimmers in a directed manner indicates an important step toward practical applications.

Self‐Propelled Micro/Nanomotors for Sensing and Environmental Remediation

“…Inspired by motion of biological motors, man‐made nanomotors revolutionized the nanotechnology, medicine, and environmental sciences. The field of micro/nanomotors has grown exponentially from understanding the mechanism of motion to diverse applications in various fields of science and engineering . The micro/nanomotors are nanoscale materials which convert chemical energy into force and movement .…”

“…The field of micro/nanomotors has grown exponentially from understanding the mechanism of motion to diverse applications in various fields of science and engineering. [7][8][9][10][11] The micro/nanomotors are nanoscale materials which convert chemical energy into force and movement. [12] Generally, they have been used in approaches which focused on biomedical sciences, [8,[13][14][15] but micro/nanomotors exhibited unique potentials for environmental remediation and water purification.…”

Fabrication of Self‐Propelled Micro‐ and Nanomotors Based on Janus Structures

“…The second metal segment could form into flat or convex tips depending on different surfacei nteractions with the alumina pore walls (Figure6D). [70] Moreover, the nanorod-based motor system could spontaneously assemble into di-, tri-, and tetramers through ultrasound-induced levitation. With increasing rod length, the speed of motion decreased.…”

Dynamic Coupling at Low Reynolds Number

“…Thea bility to impart motion to small molecules and particle assemblies in colloidal suspensions by self-propelled swimmers opens up unique opportunities to manipulate the flow of information and energy at the molecular scale and create new technologies with capabilities rivaling those of living systems.M oreover,o ne of the major incentives of soft matter research in recent years has been to develop ac omprehensive understanding of the interactions among selfpropelled swimmers at various length scales and their communication with the surroundings under complex conditions. [211][212][213][214][215][216][217][218] Success in such an endeavor will enable us to control their organization inside fluidic media and bestow them with rapid and reversible assembly capabilities without any external interventions.M odel systems containing interacting swimmers and tracers offer ideal platforms to observe the nontrivial behavior of systems driven away from equilibrium. Localized energy transduction in an active assembly, apart from leading to their self-propulsion, has been proposed to create fluctuating force fields around themselves that are…”