Protocol to evaluate the viscoelastic response of a polymer suspension to an active agent via oscillatory shear rheometry

TL;DR

This paper introduces a systematic protocol to measure how active microorganisms deform viscoelastic polymer environments using oscillatory shear rheometry, linking swimming activity to rheological responses.

Contribution

It presents a novel method to quantify swimmer-induced viscoelasticity by mapping swimming effects to oscillatory rheometry parameters, validated through simulations.

Findings

Protocol effectively maps swimming effects to rheometry parameters.

Validated with lattice Boltzmann simulations of a squirmer.

Framework extends to active microrheology applications.

Abstract

Microorganisms inhabit viscoelastic environments, where their locomotion can deform polymers and trigger local complex viscoelastic responses. However, a systematic approach to quantify such responses remains lacking. Here, we propose a protocol that maps the shear effect induced by an active agent to oscillatory shear rheometry. The central idea is to establish a correspondence between the mean shear rate generated by swimming and that produced by an oscillating plate. In this mapping, the swimming velocity and active stress are translated into an effective oscillation frequency and strain amplitude. The resulting viscoelastic response can then be evaluated by standard oscillatory rheometry. The protocol is validated using lattice Boltzmann simulations of a squirmer embedded in polymer solutions. Our framework is generic and can be naturally extended to active microrheology, providing a pathway to quantify swimmer-induced viscoelasticity.