Morphology of active deformable 3D droplets published in Physical Review X

3D droplets composed of active matter change their shape in response to a continuous influx of energy. Active droplets display an unprecedented range of complex morphologies, from cup-shaped droplet invagination, run-and-tumble motion or surface wrinkles caused by contractile activity, to the continuous formation and retraction of finger-like protrusions driven by extensile activity.
Morphology of active deformable 3D droplets
Liam J. Ruske, Julia M. Yeomans
Phys. Rev. X 11, 021001 (2021)

Abstract:
We numerically investigate the morphology and disclination line dynamics of active nematic droplets in three dimensions. Although our model incorporates only the simplest possible form of achiral active stress, active nematic droplets display an unprecedented range of complex morphologies. For extensile activity, fingerlike protrusions grow at points where disclination lines intersect the droplet surface. For contractile activity, however, the activity field drives cup-shaped droplet invagination, run-and-tumble motion, or the formation of surface wrinkles. This diversity of behavior is explained in terms of an interplay between active anchoring, active flows, and the dynamics of the motile disclination lines. We discuss our findings in the light of biological processes such as morphogenesis, collective cancer invasion, and the shape control of biomembranes, suggesting that some biological systems may share the same underlying mechanisms as active nematic droplets.

Presentation by Liam Ruske at CECAM Mixed-Gen and Fundamentals of Growing Active Matter Workshop

3D droplets composed of active matter change their shape in response to a continuous influx of energy. Active droplets display an unprecedented range of complex morphologies, from cup-shaped droplet invagination, run-and-tumble motion or surface wrinkles caused by contractile activity, to the continuous formation and retraction of finger-like protrusions driven by extensile activity.
Liam Ruske has taken the opportunity to present and discuss his work on three-dimensional organisation and morphology of active droplets at the CECAM Mixed-Gen series on March 4 and the Fundamental of Growing Active Matter workshop on March 25.

A lot is understood about the ways in which single cells move, but there are still many questions about the motion and organisation of cell aggregates where cells coupled through intercellular junctions show a range of collective behaviours.

This work, which has been recently published Phys. Rev. X 11, 021001 (2021), shows the potential of active nematic continuum models to describe collective cell motion in a three dimensional environment.

Popular Summary:

Active matter describes systems—living and synthetic—where a continuous influx of energy at the level of individual components leads to striking collective behavior among the individual components, such as self-organizing bacteria colonies, bird flocks, or polymers in the cytoskeleton of cells. Understanding their behavior has attracted interest for studies of biological systems—from the spread of cancer to the development of organisms—as well the development of mesoscopic engines. Here, we numerically investigate 3D droplets composed of active matter and the ways in which their shapes change in response to the continuous input of energy.

One striking observation is the continuous formation of fingerlike protrusions, reminiscent of the collective motion of invading cancer cells. By changing the mechanical properties of the drop or the activity level, we find several different dynamical responses: For example, the droplet surface can wrinkle in a way that resembles a walnut or the active forces can drive a dimple in the droplet to grow, leading to a cup shape. Such invagination is reminiscent of patterns seen during morphogenesis.

Understanding the behavior of model systems, here a continuum model of active material, is an important step toward the goal of understanding the role of physical theories in the life sciences.

On the Morphology of Active Deformable 3D Droplets

It is increasingly becoming apparent that the physical concepts of forces and flows play an important role in understanding biological processes, from the spread of cancers to morphogenesis, thedevelopment of organisms. However, biological systems, such as cells, probe new ideas in that theyoperate out of thermodynamic equilibrium continually taking chemical energy from their surroundings, and using it to move and self-organise.

The term active matter has come to describe models of living systems where such a continuous influx of energy leads to striking collective behaviour like the chaotic flow patterns of active turbulence seen in collections of bacteria and self-propelled topological defects which are now thought to be relevant to some modes of biofilm formation. This paper is a numerical investigation of three-dimensional droplets composed of active matter and the ways in which their shapes change in response to the continuous input of energy. One striking observation is the continuous formation of finger-like protrusions, reminiscent of the collective motion of invading cancer cells. By changing the mechanical properties of the drop or the activity level, we find several different dynamical responses: for example the droplet surface can wrinkle in a way that resembles a walnut or the active forces can drive a dimple in the droplet to grow, leading to a cup-shape: such invagination is reminiscent of patterns seen during morphogenesis.

Understanding the behaviour of model systems, here a continuum model of active material, is an important step towards the goal of understanding the role of physical theories in the life sciences.

Links: https://arxiv.org/abs/2010.10427

Morphology of active deformable 3D droplets

Morphology of active deformable 3D droplets.

Liam Ruske presents his PhD project at the ActiveMatter online meeting, 10 September 2020

The first major meeting between the ESRs and PIs in our network took place on 10 September. On that occasion Liam Ruske, ESR from the University of Oxford, gave a brief introduction to the field of active fluids in the form of a short presentation.

Why not take a moment to learn about why active liquid crystals surprisingly exhibit turbulence at small Reynolds numbers and how the study of active nematics can help us to better understand collective dynamics in biological systems.