Guiding isotropic active fluids with anisotropic friction

TL;DR

This paper investigates how anisotropic friction patterns influence the behavior of active fluids, revealing mechanisms for controlled accumulation and directed motion of clusters, with potential applications in material design.

Contribution

It introduces a model showing how anisotropic friction patterns can steer active fluid clusters, including analytical insights and substrate design for directed motion.

Findings

Anisotropic friction patterns can cause active fluid accumulation or circular motion.

Pattern asymmetry influences the robustness of fluid clustering behavior.

Designed substrate patterns enable directed movement of fluid clusters.

Abstract

Inspired by recent experiments of cells accumulating on anisotropic substrates, we study a two-dimensional, compressible, isotropic, active fluid in the presence of anisotropic friction. We find that regions of anisotropic friction that are patterned as positive topological defects may drive accumulation of an active fluid into a clump, but the robustness of this behavior depends on the initial configuration. If the initial azimuthal symmetry is sufficiently broken, we find that patterning asymmetry can instead lead to circular motion of accumulated clumps. We develop an approximate analytical model to qualitatively explain the motion. Finally, we use our simplified model to design a substrate pattern that creates directed motion of accumulated clusters along a given path.