Self-mixing in microtubule-kinesin active fluid from nonuniform to uniform distribution of activity

TL;DR

This study investigates how spatiotemporal variations in activity influence mixing in microtubule-kinesin active fluids, revealing different transport regimes and informing microfluidic mixing applications.

Contribution

It introduces a controlled activation method to study mixing dynamics in active fluids with variable activity distribution, combining experimental observations with theoretical models.

Findings

Diffusive regime shows diffusion-like interface progression at low Péclet numbers.

Superdiffusive behavior observed at high Péclet numbers with hydrodynamic modeling.

Active stress and ATP transport coupling reduces mixing time and lessens initial component distribution effects.

Abstract

Active fluids have applications in micromixing, but little is known about the mixing kinematics of systems with spatiotemporally-varying activity. To investigate, UV-activated caged ATP was used to activate controlled regions of microtubule-kinesin active fluid and the mixing process was observed with fluorescent tracers and molecular dyes. At low P\'eclet numbers (diffusive transport), the active-inactive interface progressed toward the inactive area in a diffusion-like manner that was described by a simple model combining diffusion with Michaelis-Menten kinetics. At high P\'eclet numbers (convective transport), the active-inactive interface progressed in a superdiffusion-like manner that was qualitatively captured by an active-fluid hydrodynamic model coupled to ATP transport. Results showed that active fluid mixing involves complex coupling between distribution of active stress and active transport of ATP and reduces mixing time for suspended components with decreased impact of initial component distribution. This work will inform application of active fluids to promote micromixing in microfluidic devices.