Snapping elastic disks as microswimmers: swimming at low Reynolds numbers by shape hysteresis

TL;DR

This paper demonstrates how a shape-hysteresis-driven elastic disk can swim in viscous fluids at low Reynolds numbers by cyclically swelling and shrinking, exploiting hysteresis to achieve net motion despite time-reversible actuation.

Contribution

It introduces a novel microswimming mechanism based on hysteretic shape transitions of elastic disks driven by localized swelling, validated through simulations and a simple model.

Findings

The elastic disk achieves net propulsion via hysteretic shape change.

Swimmer moves in the direction of the dome opening during cyclic swelling.

A simple 9-bead model qualitatively reproduces the swimming mechanism.

Abstract

We illustrate a concept for shape-changing microswimmers, which exploits the hysteresis of a shape transition of an elastic object, by an elastic disk undergoing cyclic localized swelling. Driving the control parameter of a hysteretic shape transition in a completely time-reversible manner gives rise to a non-time-reversible shape sequence and a net swimming motion if the elastic object is immersed into a viscous fluid. We prove this concept with a microswimmer which is a flat circular elastic disk that undergoes a transition into a dome-like shape by localized swelling of an inner disk. The control parameter of this shape transition is a scalar swelling factor of the disk material. With a fixed outer frame with an additional attractive interaction in the central region, the shape transition between flat and dome-like shape becomes hysteretic and resembles a hysteretic opening and closing of a scallop. Employing Stokesian dynamics simulations of a discretized version of the disk we show that the swimmer is effectively moving into the direction of the opening of the dome in a viscous fluid if the swelling parameter is changed in a time-reversible manner. The swimming mechanism can be qualitatively reproduced by a simple 9-bead model.