From the 2nd to the 9th of November 2020, David Bronte Ciriza and Alessandro Magazzù (Post Doc at the CNR-IPCF Messina) have visited the Soft Matter Lab at the University of Gothenburg, Sweden. During their visit, they have been working on a project related to the use of neural networks to improve optical forces calculations. This visit has also served as networking opportunity with the researchers at the Gothenburg University, including the ones that participate in the ActiveMatter network.
Active Brownian and inertial particles in disordered environments: short-time expansion of the mean-square displacement
Davide Breoni, Michael Schmiedeberg, Hartmut Löwen
We consider an active Brownian particle moving in a disordered two-dimensional energy or motility landscape. The averaged mean-square-displacement (MSD) of the particle is calculated analytically within a systematic short-time expansion. As a result, for overdamped particles, both an external random force field and disorder in the self-propulsion speed induce ballistic behaviour adding to the ballistic regime of an active particle with sharp self-propulsion speed. Spatial correlations in the force and motility landscape contribute only to the cubic and higher order powers in time for the MSD. Finally, for inertial particles two superballistic regimes are found where the scaling exponent of the MSD with time is α = 3 and α = 4. We confirm our theoretical predictions by computer simulations. Moreover they are verifiable in experiments on self-propelled colloids in random environments.
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.
Morphology of active deformable 3D droplets
Liam J. Ruske, Julia M. Yeomans
We numerically investigate the morphology and disclination line dynamics of active nematic droplets in three dimensions. Although our model only incorporates the simplest possible form of achiral active stress, active nematic droplets display an unprecedented range of complex morphologies. For extensile activity finger-like 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 behaviour is explained in terms of an interplay between active anchoring, active flows and the dynamics of the motile dislocation 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.
The first meeting between all PIs and ESRs meeting in our network took place on 10 September 2020. During this meeting, Ayten Gülce Bayram, ESR from Bilkent University, presented herself and her research project through a short video presentation. If you are curious about how her research studies are going as a first-year doctoral student in ActiveMatter ITN, please have a look at her presentation!
The ActiveMatter ESRs + PIs Online Meeting (if you want to know more read the main news here) took place on the 10th of last month. For the first time, the members of the ActiveMatter were in the “same place” also if just online. All the Early Stage Researchers were asked to introduce themselves in a short presentation video.
Laura Natali, ESR at the University of Gothenburg, also presented herself during the meeting.
The video lasts only five minutes and introduces Laura, her current project and the area of research she will study during the PhD. You can find the presentation below, and it is also on the ActiveMatter youtube channel .
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.
As our first event with full participation of both PIs and ESRs took place on the 10th of September 2020, all ESRs had a chance to introduce their PhD projects, and benefit from the collective discussion and feedback from the other members of the network.
Chun-Jen Chen (UKONS) briefly explained the Active Brownian Colloidal (ABC) system with real-time controls to displacements and orientations of each individual ABC particles. He further demonstrated the application of such ABC system in the investigation of spontaneous collective behaviours of living systems (also more detail here by UKONS), and how he would extend the study to higher non-equilibrium and more stimulus-interactive cases, e.g. collective prey-predator interactions.
On the 10th of September, the first online meeting between all the ESRs and PIs took place. During this meeting, David presented himself and introduced his future work at the CNR by means of this short video. The presentation was followed by time for questions and discussion with other members of the ActiveMatter network.
Are you wondering about what David did before joining the network? Do you want to know a little bit more about his project? Take a look at his presentation video!
The first meeting of the Active Matter ITN consortium, including ESRs and PIs, took place virtually on the 10th September. Each ActiveMatter project was briefly introduced through a video presentation. Here you can find the video presentation by Jesús Manuel, a PhD student at Elvesys in collaboration with the University of Gothenburg. This project merges industrial and academic research in order to unveil complex systems like soil through microfluidics.