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Propulsion of Bubble-Based Acoustic Microswimmers

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A new microfabrication technique creates bubble-based acoustic swimmers at the 10-µm scale—the size of a red blood cell. The authors use experiments and a three-dimensional analytical model to analyze the efficient propulsion mechanism of these artificial microswimmers. Such active matter could be used to transport a payload within the bloodstream, or to mix fluids in a lab-on-chip device.

Acoustic microswimmers present a great potential for microfluidic applications and targeted drug delivery. Here, we introduce armored microbubbles (size range, 10–20  μm) made by three-dimensional microfabrication, which allows the bubbles to last for hours even under forced oscillations. The acoustic resonance of the armored microbubbles is found to be dictated by capillary forces and not by gas volume, and its measurements agree with a theoretical calculation. We further measure experimentally and predict theoretically the net propulsive flow generated by the bubble vibration. This flow, due to steady streaming in the fluid, can reach 100  mm/s, and is affected by the presence of nearby walls. Finally, microswimmers in motion are shown, either as spinning devices or free swimmers.

The article has appeared in Physical Review Applied.