Propulsion and far-field hydrodynamics of linked-sphere microswimmers with viscoelastic deformability

TL;DR

This study explores how viscoelastic deformability enables linked-sphere microswimmers to achieve propulsion and flow patterns under reciprocal actuation, revealing optimal and critical frequencies for different designs.

Contribution

It introduces two linked-sphere microswimmer models with viscoelastic deformability, analyzing their propulsion performance and flow fields under reciprocal actuation.

Findings

The 3-sphere swimmer has an optimal actuation frequency for propulsion.

The 4-sphere swimmer exhibits a critical frequency where direction reverses.

Flow fields are dominated by dipolar and quadrupolar contributions, sensitive to design parameters.

Abstract

Viscoelasticity governs the locomotion strategies of deformable microorganisms, rendering it a fundamental mechanical property of microbial motility and an integral component in the design of envisioned microbots. Recent studies have shown that it can enable effective propulsion through non-reciprocal body deformations, even under time-reversible actuation. In this work, we investigate the dynamics of model microswimmers driven by reciprocal actuation, wherein the passive body exhibits viscoelastic deformability. We consider two linked-sphere designs, distinguished by the location of actuation: applied at one end (3-sphere design) or at the midpoint of the swimmer body (4-sphere design). Adopting Kelvin-Voigt deformability, we characterize the kinematic performance of both designs: the three-sphere swimmer possesses an optimal actuation frequency, while the four-sphere swimmer exhibits a critical frequency at which the locomotion direction reverses. We examine the swimmer's far-field hydrodynamic signature and find that resulting flow field is characterized by dominant dipolar and quadrupolar contributions, whose magnitudes are sensitive to the relative length of the actuator segment.