Dynamics of Fluid Vesicles in Flow through Structured Microchannels

TL;DR

This paper investigates the complex behaviors of fluid vesicles in microchannels with varying widths, revealing flow-induced shape and orientation oscillations through theoretical, experimental, and simulation approaches.

Contribution

It introduces a combined theoretical, experimental, and simulation study of vesicle dynamics in structured microchannels, identifying new flow instability modes and shape oscillations.

Findings

Prolate vesicles exhibit orientational and shape oscillations with increasing flow velocity.

Large vesicles show symmetric shape oscillations at high reduced volume.

Non-spherical vesicles develop tails and asymmetric shapes at lower reduced volumes.

Abstract

The dynamics of fluid vesicles is studied under flow in microchannels, in which the width varies periodically along the channel. Three types of flow instabilities of prolate vesicles are found. For small quasi-spherical vesicles -- compared to the average channel width -- perturbation theory predicts a transition from a state with orientational oscillations of a fixed prolate shape to a state with shape oscillations of symmetrical ellipsoidal or bullet-like shapes with increasing flow velocity. Experimentally, such orientational oscillations are observed during the slow migration of a vesicle towards the centerline of the channel. For larger vesicles, mesoscale hydrodynamics simulations and experiments show similar symmetric shape oscillation at reduced volumes $V^* \gtrsim 0.9$. However, for non-spherical vesicles with $V^* \lesssim 0.9$, shapes are found with two symmetric or a single asymmetric tail.