News – Page 3 – ActiveMatter ITN

Collective response of microrobotic swarms to external threats published in New Journal of Physics

A swarm of microrobots, consist of active Janus colloids (middle right, not to scale), can form stationary swirl (upper) and respond to a threat as a whole (lower) when each individual follows cohesive “social rules”. Such rules are inspired by living animals and enable the swarm collective benefits, e.g. enhanced robustness of the response. *(Image by C-J Chen.)*

Collective response of microrobotic swarms to external threats

Chun-Jen Chen and Clemens Bechinger
New J. Phys. 24 033001 (2022)
doi: 10.1088/1367-2630/ac5374
repository: KOPS:56911

Many animal species organize within groups to achieve advantages compared to being isolated. Such advantages can be found e.g. in collective responses which are less prone to individual failures or noise and thus provide better group performance. Inspired by social animals, here we demonstrate with a swarm of microrobots made from programmable active colloidal particles (APs) that their escape from a hazardous area can originate from a cooperative group formation. As a consequence, the escape efficiency remains almost unchanged even when half of the APs are not responding to the threat. Our results not only confirm that incomplete or missing individual information in robotic swarms can be compensated by other group members but also suggest strategies to increase the responsiveness and fault-tolerance of robotic swarms when performing tasks in complex environments.

Press release at Universität Konstanz website:
How animal swarms respond to threats: With the help of microrobots, Konstanz physicists decode how swarms of animals respond effectively to danger [in English]

Brownian particles driven by spatially periodic noise published in EPJE

Brownian particles driven by spatially periodic noise
Davide Breoni, Ralf Blossey, Hartmut Löwen
The European Physical Journal E 45, 18 (2022)
arXiv: 2111.10220
DOI:10.1140/epje/s10189-022-00176-4

We discuss the dynamics of a Brownian particle under the influence of a spatially periodic noise strength in one dimension using analytical theory and computer simulations. In the absence of a deterministic force, the Langevin equation can be integrated formally exactly. We determine the short- and long-time behaviour of the mean displacement (MD) and mean-squared displacement (MSD). In particular we find a very slow dynamics for the mean displacement, scaling as t^(-1/2) with time t. Placed under an additional external periodic force near the critical tilt value we compute the stationary current obtained from the corresponding Fokker-Planck equation and identify an essential singularity if the minimum of the noise strength is zero. Finally, in order to further elucidate the effect of the random periodic driving on the diffusion process, we introduce a phase factor in the spatial noise with respect to the external periodic force and identify the value of the phase shift for which the random force exerts its strongest effect on the long-time drift velocity and diffusion coefficient.

A platform for stop flow gradient generation to investigate chemotaxis published in Angewandte Chemie

A controlled gradient of hydrogen peroxide is generated in a microfluidic chip where a precise pressure retroactive loop prevents any external flow to interfere with the chemotaxis response of catalytic microswimmers. *(Image by A. Nsamela.)*

A platform for stop flow gradient generation to investigate chemotaxis
Z. Xiao, A. Nsamela, B. Garlan, and J. Simmchen
Angew. Chemie Int. Ed., Feb. 2022
chemRxiv: 10.26434/chemrxiv-2021-sxqm1
DOI: 10.1002/anie.202117768

The ability of artificial microswimmers to respond to external stimuli and the mechanistical details of their origins belong to the most disputed challenges in interdisciplinary science. Therein, the creation of chemical gradients is technically challenging, because they quickly level out due to diffusion. Inspired by pivotal stopped ow experiments in chemical kinetics, we show that microfluidics gradient generation combined with a pressure feedback loop for precisely controlling the stop of the flows, can enable us to study mechanistical details of chemotaxis of artificial Janus micromotors, based on a catalytic reaction. We find that these copper Janus particles display a chemotactic motion along the concentration gradient in both, positive and negative direction and we demonstrate the mechanical reaction of the particles to unbalanced drag forces, explaining this behaviour.

David presented an oral contribution at PHOTOPTICS 2022

Snapshot of the motion of an ellipsoid in a double beam optical trap. *(Image by D. Bronte Ciriza)*

Optical systems are ubiquitous in modern society, with an ever-increasing number of applications covering medical sciences, spatial exploration, information processing and industry, to name but a few examples. In this context, David presented his work on machine learning enhanced optical forces calculations at PHOTOPTICS 2022 between the 10th and the 11th of February. The conference took place online and it was the perfect opportunity to learn from other scientists and discuss the relevance of optics for the study of active matter systems.

Jesús Domínguez presents a poster at NanoBioTech in Montreux, Switzerland, 15-17 November 2021

The ESR Jesus Manuel Antunez Dominguez presenting his poster at the NanoBioTech Conference. *Image by J. Domínguez.*

Jesús Domínguez attended the NanoBioTech Conference in Montreaux, Switzerland, 15-17th November 2021.
He presented the poster “A microfluidic platform for the study of bacterial biofilms” showing his advances in the development of a droplet-based microfluidic platform for in situ observation of bacterial behavior and biofilms.

The NanoBioTech Conference brings together international researchers in the fields of Micro- and Nanotechnology and its applications in Biology and Medicine.

Apart from the featured talks and presentations on related topics and techniques of interest, Jesus benefited from the direct contact with international researchers, that promoted an exchange of ideas and opens the door for possible future collaborations.

Talk by Chun-Jen Chen at Institute of Physics, Academia Sinica (Taiwan), 21 January 2022

This talk focused on the social collective response of a group of active particles to a threat, demonstrated in the figure above (the threat appeared at t = 0s). *(Image by C-J Chen.)*

On the 21st of January 2022, Chun-Jen gave a talk at Institute of Physics, Academia Sinica (Taipei, Taiwan) with title “Collective response of microrobotic swarms to external threats”. Chun-Jen shared and discussed about his most recent scientific work, which involves active Janus colloids and animal collective behaviours, with researchers and students of several fields, including biophysics, soft-matter, and surface/nano science.

David’s secondment at UCL

David (right) discussing the results with Phil Jones (left). *(Photos provided by D. Bronte Ciriza)*

Between the 11th of the January and the 14th of April David visited UCL to work together with Giorgio Volpe and Phil Jones. During this time in London he studied elongated active particles in complex optical fields, finding some interesting properties that still need to be further understood. Getting to know other people working with soft and active matter gave rise to new ideas and inspiration. More to come!

David visits the Soft Materials and Interfaces lab at ETH Zurich

Carolina (left) and David (right) in the micro 3D printing room. *(Image by D. Bronte Ciriza.)*

From the 11th to the 19th of December 2021, David Bronte Ciriza visited the Soft Materials and Interfaces lab at ETH Zurich. During this visit, David learnt different techniques to fabricate elongated microparticles, and together with Carolina van Baalen produced the ones that will be tested under different optical landscapes in David’s secondment in UCL London. This visit has also served as an opportunity to meet other early stage researchers at ETH Zurich working in related topics, allowing to discuss different ideas in the fields of microfabrication, optical tweezers, and active matter.

Raman tweezers for tire and road wear micro- and nanoparticles analysis published in Environmental Science: Nano

Raman Tweezers are used to detect tires and road wear particles in water. We analyze samples collected from a brake test platform, highlighting the presence of car tires and brake particles debris with sub-micrometric dimensions. *(Featuring work from Dr Pietro G. Gucciardi, Prof Giovanni Volpe, and Dr Fabienne Lagarde).*

Raman tweezers for tire and road wear micro- and nanoparticles analysis

R. Gillibert, A. Magazzù, A. Callegari, D. Bronte-Ciriza, A. Foti, M. G. Donato, O. M. Maragò, G. Volpe, M. L. de La Chapelle, F. Lagarde and P. G. Gucciardi.

Environmental Science: Nano (2022) doi: 10.1039/D1EN00553G

Abstract:

Tire and road wear particles (TRWP) are non-exhaust particulate matter generated by road transport means during the mechanical abrasion of tires, brakes and roads. TRWP accumulate on the roadsides and are transported into the aquatic ecosystem during stormwater runoffs. Due to their size (sub-millimetric) and rubber content (elastomers), TRWP are considered microplastics (MPs). While the amount of the MPs polluting the water ecosystem with sizes from ∼5 μm to more than 100 μm is known, the fraction of smaller particles is unknown due to the technological gap in the detection and analysis of <5 μm MPs. Here we show that Raman tweezers, a combination of optical tweezers and Raman spectroscopy, can be used to trap and chemically analyze individual TRWPs in a liquid environment, down to the sub-micrometric scale. Using tire particles mechanically grinded from aged car tires in water solutions, we show that it is possible to optically trap individual sub-micron particles, in a so-called 2D trapping configuration, and acquire their Raman spectrum in few tens of seconds. The analysis is then extended to samples collected from a brake test platform, where we highlight the presence of sub-micrometric agglomerates of rubber and brake debris, thanks to the presence of additional spectral features other than carbon. Our results show the potential of Raman tweezers in environmental pollution analysis and highlight the formation of nanosized TRWP during wear.

Laura Natali and Jesús Domínguez participate in the Ämnets dag at the University of Gothenburg

Presentation of Laura Natali and Jesús Domínguez at the Ämnets dag. *Image by L. Natali and J. Domínguez.*

On Tuesday 2 November 2021 the Ämnets dag took place at the university of Gothenburg.

At the Ämnets dag, different high-school teachers of physics and science were given the chance to attend different workshops dealing with lines of research inside the Physics department. Laura Natali and Jesus Manuel Antunez Dominguez joined the initiative and prepared an introductory class to simulations modelling active matter.

The workshop addressed the basic aspects of active matter and some examples of its relevant applications nowadays. Overall, the focus of the workshop was to bring closer some of the main characteristics of active matter through interactive simulations that give a qualitative idea of active behaviour and the effect of different parameters on it.

Stay tuned for more activities like this!