Magnetically Driven Elastic Microswimmers: Exploiting Hysteretic Collapse for Autonomous Propulsion and Independent Control

TL;DR

This paper presents a novel magnetically actuated microswimmer that uses hysteretic collapse for autonomous propulsion and can be independently controlled with a single magnetic field.

Contribution

It introduces a new microswimmer design exploiting hysteretic magnetic collapse for propulsion and demonstrates independent control via magnetic field tuning.

Findings

Hysteretic collapse enables nonreciprocal motion for net propulsion.

Microswimmers can be tuned for different speeds by adjusting magnetic field parameters.

The design is optimized for maximum speed using evolutionary algorithms.

Abstract

When swimming at low Reynolds numbers, inertial effects are negligible and reciprocal movements cannot induce net motion. Instead, symmetry breaking is necessary to achieve net propulsion. Directed swimming can be supported by magnetic fields, which simultaneously provide a versatile means of remote actuation. Thus, we analyze the motion of a straight microswimmer composed of three magnetizable beads connected by two elastic links. The swimming mechanism is based on oriented external magnetic fields that oscillate in magnitude. Through induced reversible hysteretic collapse of the two segments of the swimmer, the two pairs of beads jump into contact and separate nonreciprocally. Due to higher-order hydrodynamic interactions, net displacement results after each cycle. Different microswimmers can be tuned to different driving amplitudes and frequencies, allowing for simultaneous independent control by just one external magnetic field. The swimmer geometry and magnetic field shape are optimized for maximum swimming speed using an evolutionary optimization strategy. Thanks to the simple working principle, an experimental realization of such a microrobot seems feasible and may open new approaches for microinvasive medical interventions such as targeted drug delivery.