Fingering Instability of Active Nematic Droplets

Abstract

From the mitotic spindle up to tissues and biofilms, many biological systems behave as active droplets, which often break symmetry and change shape spontaneously. Here, I show that active nematic droplets can experience a fingering instability. I consider an active fluid that acquires nematic order through anchoring at the droplet interface, and I predict its morphological stability in terms of three dimensionless parameters: the anchoring angle, the penetration length of nematic order compared to droplet size, and an active capillary number. Droplets with extensile (contractile) stresses and planar (homeotropic) anchoring are unstable above a critical activity or droplet size. This instability is interfacial in nature: It arises through the coupling of active flows with interface motion, even when the bulk instability of active nematics cannot take place. In contrast to the dynamic states characteristic of active matter, the instability could produce static fingering patterns. The number of fingers increases with activity but varies non-monotonically with the nematic penetration length. Overall, these results can help to understand the self-organized shapes of biological systems, and to design patterns in active materials.

Invited article for the Special Issue "Emerging Talents 2021" of J. Phys. A

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Cited by in corpus (12)

• Morphodynamics of Active Nematic Fluid Surfaces
• Microdomains and Stress Distributions in Bacterial Monolayers on Curved Interfaces
• Asymmetric fluctuations and self-folding of active interfaces
• Spontaneous rotation of active droplets in two and three dimensions
• Tubulation and dispersion of oil by bacterial growth on droplets
• Hydrodynamic Enhancement of $p$-atic Defect Dynamics
• Supramolecular assemblies in active motor-filament systems: micelles, bilayers, and foams
• Active nematic response to a deformable body or boundary: elastic deformations and anchoring-induced flow
• Modeling growing confluent tissues using a lattice Boltzmann method: interface stability and fluctuations
• Interfacial instability of confined 3D active droplets
• Conservation laws and slow dynamics determine the universality class of interfaces in active matter
• What is active wetting?