Swimmer-microrheology

TL;DR

This paper investigates the locomotion of a three-sphere microswimmer in viscoelastic media, deriving a relation between swimming velocity and medium viscosity, revealing symmetry-breaking conditions, and challenging Purcell's scallop theorem.

Contribution

It introduces a new active microrheology method and derives a relation linking swimmer velocity to viscoelastic properties, highlighting symmetry-breaking effects.

Findings

Viscous contribution requires broken time-reversal symmetry.

Elastic contribution requires broken structural symmetry.

Purcell's scallop theorem does not hold in viscoelastic media.

Abstract

We discuss a locomotion of a three-sphere microswimmer in a viscoelastic medium and propose a new type of active microrheology. We derive a relation which connects average swimming velocity and frequency-dependent viscosity of the surrounding medium. In this relation, the viscous contribution can exist only when the time-reversal symmetry is broken, whereas the elastic contribution is present only when the structural symmetry of the swimmer is broken. The Purcell's scallop theorem breaks down for a three-sphere swimmer in a viscoelastic medium.