Morphodynamics of surface-attached active drops

TL;DR

This paper explores the complex shapes and internal flows of surface-attached active suspension drops, revealing new stable states and providing principles for controlling active material behaviors.

Contribution

It introduces a comprehensive analysis of active drops beyond thin limits, uncovering diverse stable shapes and flows, and offers predictive principles for active material design.

Findings

Active drops exhibit a variety of stable shapes and internal flows.

Boundary conditions and active stress strength determine the states.

The study provides quantitative principles for controlling active suspension behaviors.

Abstract

Many biological and synthetic systems are suspensions of oriented, actively-moving components. Unlike in passive suspensions, the interplay between orientational order, active flows, and interactions with boundaries gives rise to fascinating new phenomena in such active suspensions. Here, we examine the paradigmatic example of a surface-attached drop of an active suspension (an "active drop"), which has so far only been studied in the idealized limit of thin drops. We find that such surface-attached active drops can exhibit a wide array of stable steady-state shapes and internal flows that are far richer than those documented previously, depending on boundary conditions and the strength of active stresses. Our analysis uncovers quantitative principles to predict and even rationally control the conditions under which these different states arise -- yielding design principles for next-generation active materials.