Local Acoustic Fields Powered Assembly of Microparticles and Applications

Abstract

Controllable assembly in nano-/microscale holds considerable promise for bioengineering, intracellular manipulation, diagnostic sensing, and biomedical applications. However, up to now, micro-/nanoscopic assembly methods are severely limited by the fabrication materials, as well as energy sources to achieve the effective propulsion. In particular, reproductive manipulation and customized structure is quite essential for assemblies to accomplish a variety of on-demand tasks at small scales. Here, we present an attractive assembly strategy to collect microparticles, based on local acoustic forces nearby microstructures. The micro-manipulation chip is built based on an enhanced acoustic field, which could tightly trap microparticles to the boundaries of the microstructure by tuning the applied driving frequency and voltage. Numerical simulations and experimental demonstrations illustrate that the capturing and assembly of microparticles is closely related to the size of particles, owing to the vibration-induced locally enhanced acoustic field and resultant propulsion force. This acoustic assembly strategy can open extensive opportunities for lab-on-chip systems, microfactories, and micro-manipulators, among others.

Ultrasonic Steering Wheels: Turning Micromotors by Localized Acoustic Microstreaming

“…In the past few years, there have also been reports of localized microstreaming flows circulating a micropillar fixed on a vibrating substrate. − An example of such streaming flows is given in Figure . Here, a piezoelectric transducer is glued onto a piece of glass slide and next to a sealed, water-filled experimental chamber made of silicone.…”

“…Here, the tracer moved clockwise, while the center Janus sphere spun counterclockwise. The circular acoustic streaming flows around a Janus microsphere are suspected to arise from the same physical reasons as those around a fixed pillar: − as sound waves propagate across the solid–water interface, momentum is transferred from a vibrating sphere to the fluid, imparting torques that leads to vortices. Following the Newton’s third law, the sphere (fixed to the substrate or not) reciprocally and simultaneously receives a torque from the fluid.…”

Fabrication of Magnetic Microrobots by Assembly

“…Shen et al proposed a method for assembling microparticles based on local acoustic forces nearby microstructures, as shown in Figure 7B. [ 144 ] This method utilizes the local sound field near the V‐shaped micropillars to assemble microspheres. Figure 7B shows a flexible finger acoustically assembled from 5 μm magnetic particles, and it can swing periodically after applying a rotating magnetic field.…”

“…B) Schematic illustration of a micromanipulation chip powered by the acoustic field, second-order acoustic streaming fields excited by the clockwise elliptical motions of the micropillar, and images showing the swing motion of a flexible finger. Reproduced with permission [144]. Copyright 2019, MDPI.…”

Reversible Design of Dynamic Assemblies at Small Scales

“…Topographical features of the substrate interact with the traveling wave generating a localized microstreaming flows capable of trapping nearby objects. [121][122][123] Application of this technique was carried out by building arrays of acoustic microstreaming traps that enabled the enrichment of cancer cells from whole blood around the traps. Interestingly, this methodology could also be used to generate organoids, as the cells can be released upon turning off the acoustic field (Figure 5d).…”