Acoustic actuation of bioinspired microswimmers

Abstract

Acoustic actuation of bioinspired microswimmers is experimentally demonstrated. Microswimmers are fabricated in situ in a microchannel. Upon acoustic excitation, the flagellum of the microswimmer oscillates, which in turn generates linear or rotary movement depending on the swimmer design. The speed of these bioinspired microswimmers is tuned by adjusting the voltage amplitude applied to the acoustic transducer. Simple microfabrication and remote actuation are promising for biomedical applications.

Fig. 1

Fabrication and acoustic actuation of microswimmers. (a) Fabrication and actuation setup. UV light is patterned and focused by photomask and objective lens. (b) Schematic of microswimmer which is in situ fabricated and moves freely. (c) Schematic of microstreaming at the tip of flagellated tail. The microstreaming, which originates from oscillation of the flagellated tail, propels the microswimmer.

Fig. 2

Design of different microswimmers. (a) and (b): image and schematic of a microstructure which is not able to rotate. (c) and (d): microswimmer moves directionally due to acoustic streaming. (e) and (f): the oscillation of flagella creates clockwise rotation due to unsymmetrical design. (g) and (h): microswimmer rotates counter-clockwise.

Fig. 3

Opposing movement of microswimmers under the same conditions. (a) Both microswimmers are at rest, absent any oscillations of their flagella due to the lack of acoustic actuation. (b), (c), (d) and (e) Microswimmers move in opposite directions under 140 V_PP acoustic excitation. (See supplementary video).

Fig. 4

Characterization of microswimmers’ directional movement. (a) Microswimmer is stationary in the absence of acoustic oscillation. (b) Actuating the PZT transducer at 140 VPP, the microswimmer’s flagella oscillates and it moves directionally. (c) and (d): Under constant excitation voltage (140 VPP), the microswimmer moves at a constant velocity. (e) The terminal velocity of a microswimmer as a function of voltage, increasing from 220 μm/s at 20 VPP to 1200 μm/s at 140 VPP.

Fig. 5

Microswimmer’s rotational movement. (a)–(f): A full revolution divided into six frames, at 140 V_PP excitation. (e) The angular speed as a function of voltage, increasing from 25 RPM at 20 V_PP to 200 RPM at 140 V_PP.