Spontaneous rotation and propulsion of suspended capsules in active nematics

TL;DR

This study explores how elastic capsules in active nematic fluids exhibit rotation and movement driven by internal defects, with their behavior influenced by shape and flexibility, revealing mechanisms for designing microswimmers.

Contribution

The paper demonstrates how capsule shape and deformability affect active nematic-induced rotation and motility, highlighting defect dynamics as a key factor.

Findings

Circular capsules with active interiors rotate persistently due to internal defects.

Axisymmetric capsules move along their symmetry axis because of defect-induced forces.

Flexibility reduces motility and rotation by dissipating active stresses into shape changes.

Abstract

We investigate the dynamics of elastic capsules suspended in two-dimensional active nematic fluids using lattice Boltzmann simulations. The capsules, modeled as flexible membranes enclosing active internal regions, exhibit a rich variety of behaviors shaped by their geometry and the interplay between internal and external activity. Circular capsules with active interiors undergo persistent rotation driven by internally confined +1/2 topological defects. Axisymmetric capsules, such as boomerangs, develop directed motion along their axis of symmetry due to unbalanced active forces generated by defect distributions near their boundaries. We further show that capsule flexibility suppresses motility and rotation, as active stresses are dissipated into shape deformations. These findings reveal how shape, deformability, and defect dynamics cooperate to produce emergent motility in soft active matter, with potential applications in the design of microswimmers and drug delivery vehicles.