Self-organization and shape change by active polarization in nematic droplets

Fabian Jan Schwarzendahl,Pierre Ronceray,Kimberly L Weirich,Kinjal Dasbiswas

doi:10.1103/physrevresearch.3.043061

Abstract

Active forces drive critical biological processes such as spontaneous organization and shape change during cell division. Here, we present a minimal hydrodynamic model leading to a unified description of self-organization and division in nematic droplets through active polarity sorting of cytoskeletal filaments by molecular motors. We find that motors self-organize within droplets while structuring filaments into polarized aster defects. At large activity, motors deform droplets leading to multidroplet chains and droplet division, consistent with experiments on actomyosin tactoids. We predict droplet steady-state phase diagrams that inform programmable shape changes in confined soft materials.

Highlights

Active mechanical forces enable biological cells, to move, change shape, organize components, and divide
Cytoskeletal systems can form active nematic states characterized by large-scale flows and chaotic dynamics, but these can be transient since motors eventually cluster causing localized stresses [20]
We employ numerical simulations to explore the consequences of motor activity on the dynamics and morphology of phase-separating nematic droplets

Summary

INTRODUCTION

Active mechanical forces enable biological cells, to move, change shape, organize components, and divide. The directed “walking” of motors on filaments, along with motorbased filament crosslinking, can lead to polar order, where filaments point in the same direction in local regions Such polar active states, including their defect structures such as asters and vortices [21], are fruitfully described by hydrodynamic theories for bulk systems [22,23,24,25,26,27,28]. Using numerical simulations, complemented by theoretical analysis, we show that the resulting motor-filament self-organization destabilizes droplets This gives rise to a rich array of experimentally observed shapes including deformed, divided, and multidroplet chains that can be generated through tuning motor activity

ONE-DIMENSIONAL POLARITY SORTING MODEL

RESULTS

CONCLUSIONS