Selectively manipulable acoustic-powered microswimmers

Abstract

Selective actuation of a single microswimmer from within a diverse group would be a first step toward collaborative guided action by a group of swimmers. Here we describe a new class of microswimmer that accomplishes this goal. Our swimmer design overcomes the commonly-held design paradigm that microswimmers must use non-reciprocal motion to achieve propulsion; instead, the swimmer is propelled by oscillatory motion of an air bubble trapped within the swimmer's polymer body. This oscillatory motion is driven by the application of a low-power acoustic field, which is biocompatible with biological samples and with the ambient liquid. This acoustically-powered microswimmer accomplishes controllable and rapid translational and rotational motion, even in highly viscous liquids (with viscosity 6,000 times higher than that of water). And by using a group of swimmers each with a unique bubble size (and resulting unique resonance frequencies), selective actuation of a single swimmer from among the group can be readily achieved.

Man-made rotary nanomotors: a review of recent developments

“…156 They fabricated hydrophobic polymer blocks with cavities using photo-curable polyethylene glycol (PEG) mixture. When the blocks were suspended in a liquid medium, tiny bubbles formed inside the cavities.…”

Spiral diffusion of rotating self-propellers with stochastic perturbation

“…In the absence of noise a circle swimmer, confined to a plane with a strong rotational component to its powered motion, travels on a fixed circle with a steady clockwise or counterclockwise chirality [7]. Artificial swimmers of this sort have been fabricated in a variety of forms such as tadpoles [8,9], Janus sphere dimers [10,11], nanorods [12,13], and acoustically-activated swimmers [14]. Stochastic perturbations in the form of unbiased orientational diffusion or random chirality-reversal resulting from flipping about the direction of motion have significant effects on the long term motion: an effective translational diffusion is generated [15][16][17], the infinite-time limit of the mean position conditioned on the initial position and velocity is non-zero and chirality-dependent [5], and the mean approach to the limit is a logarithmic spiral [17,18].…”

Dancing with the Cells: Acoustic Microflows Generated by Oscillating Cells

“…Similarly, the self‐propulsion mechanism of some flagella‐less microorganisms, such as the cyanobacterium Synechococcus, is hypothesized to be acoustic streaming . This hypothesis is also inspiring the development of autonomous microswimmers propelled by acoustic streaming . Other biological systems, such as cells, have viscoelastic properties similar to many materials, such as microbubbles, that produce acoustic microstreaming under acoustic excitation.…”