ActiveMatter and Scholarship Opportunities: A Day of Learning at Ozyeğin University

On January 4, 2024, engineering students at Ozyeğin University were treated to an insightful session on active matter, exploring its journey from theoretical concepts to real-world applications. This event, led by Alireza Khoshzaban, was an eye-opener for students, demonstrating how active matter plays a key role in modern engineering innovations.
During the session at Ozyegin University, the theory and history of active matter were briefly covered, emphasizing its evolution from early physics concepts to modern engineering marvels. This discussion connected theoretical foundations to practical applications in soft robotics, biomedical devices, and smart materials, showcasing how significant active matter has impacted contemporary engineering solutions.

Transition from scattering to orbiting upon increasing the fuel concentration for an active Janus colloid moving at an obstacle–decorated interface published in Soft Matter

Transition from scattering to orbiting upon increasing the fuel concentration for an active Janus colloid moving at an obstacle–decorated interface
Carolina van Baalen, William E. Uspal, Mihail N. Popescu, and Lucio Isa
Soft Matter, 19, 8790-8801 (2023)
doi: 10.1039/D3SM01079A

Efficient exploration of space is a paramount motive for active colloids in practical applications. Yet, introducing activity may lead to surface-bound states, hindering efficient space exploration. Here, we show that the interplay between self-motility and fuel-dependent affinity for surfaces affects how efficiently catalytically-active Janus microswimmers explore both liquid–solid and liquid–fluid interfaces decorated with arrays of similarly-sized obstacles. In a regime of constant velocity vs. fuel concentration, we find that microswimmer–obstacle interactions strongly depend on fuel concentration, leading to a counter-intuitive decrease in space exploration efficiency with increased available fuel for all interfaces. Using experiments and theoretical predictions, we attribute this phenomenon to a largely overlooked change in the surface properties of the microswimmers’ catalytic cap upon H2O2 exposure. Our findings have implications in the interpretation of experimental studies of catalytically active colloids, as well as in providing new handles to control their dynamics in complex environments.

The Active Matter Game

We have been working on an active matter game! If you want to challenge your colleagues or family members to a game and have them learn about active matter look no further!
The active matter game has been designed over the course of the ITN as a new outreach activity that everyone can print at home. It has been rigorously tested at almost every Active Matter Meeting. It took a few revisions but we have made a fun game for all ages. You can read all about it in the supplementary info of the new Active Matter book.
The game has been developed and finalised by Alireza Khoshzaban, Carolina van Baalen, David Bronte Ciriza, Davide Breoni, Jesús Manuel Antúnez Domínguez, Laura Natali and Sandrine Heijnen.
You only have to wait until the release date till everything will be online! We can’t wait to share it with you!

Patchy landscapes promote stability of small groups on arXiv

Patchy landscapes promote stability of small groups

Gianni Jacucci, Davide Breoni, Sandrine Heijnen, José Palomo, Philip Jones, Hartmut Löwen, Giorgio Volpe, Sylvain Gigan


Abstract: Group formation and coordination are fundamental characteristics of living systems, essential for performing tasks and ensuring survival. Interactions between individuals play a key role in group formation, and the impact of resource distributions is a vibrant area of research. Using active particles in a tuneable optical environment as a model system, we demonstrate that heterogeneous energy source distributions result in smaller, more stable groups with reduced individual exchange between clusters compared to homogeneous conditions. Reduced group sizes can be beneficial to optimise resources in heterogeneous environments and to control information flow within populations. Devoid of biological complications, our system provides insights into the importance of patchy landscapes in ecological dynamics and holds implications for refining swarm intelligence algorithms and enhancing crowd control techniques.

The ActiveMatter project leads to a startup creation: Inside Therapeutics

Audrey Nsamela, co-founder of InsideTx, applied her research to nanomedicine formulation with microfluidics. (Image from InsideTx.)
Leveraging the work of Audrey Nsamela during the Active Matter project, a new company named Inside Therapeutics (Inside Tx) has been created.

Inside Therapeutics aims to provide innovative nanoparticle manufacturing platforms to help with the novel generation of RNA-LNP therapeutics development. Based on innovative microfluidic technology developed during the Active Matter project, this novel platform will help unlock the main sticking points of the current RNA-LNP drug development process including:

  • The synthesis of very low volumes during for the drug discovery (or screening) phase.
  • Ensuring a seamless scalability of the RNA-LNP manufacturing.
  • Allowing for continuous production of high quality nanoparticles.

It opens up new perspectives for research and industrial applications were lipid or polymeric-based nanoparticles are required.

Feel free to reach out to Audrey at should you have any questions!

Logo of Inside Therapeutics. (Image from InsideTx.)

Giant Activity-Induced Stress Plateau in Entangled Polymer Solutions on arXiv

Giant Activity-Induced Stress Plateau in Entangled Polymer Solutions

Davide Breoni, Christina Kurzthaler, Benno Liebchen, Hartmut Löwen, Suvendu Mandal
Abstract: We study the viscoelastic properties of highly entangled, flexible, self-propelled polymers using Brownian dynamics simulations. Our results show that the active motion of the polymer increases the height of the stress plateau by orders of magnitude due to the emergence of grip forces at entanglement points. Identifying the activity-induced energy of a single polymer and the ratio of polymer length to self-propulsion velocity as relevant energy and time scales, we find the stress autocorrelation functions collapse across Péclet numbers. We predict that the long-time viscosity scales with polymer length squared L^2, in contrast to equilibrium counterparts L^3. These insights offer prospects for designing new materials with activity-responsive mechanical properties.

Tuning Electrostatic Interactions of Colloidal Particles at Oil-Water Interfaces with Organic Salts published in Physical Review Letters

Tuning Electrostatic Interactions of Colloidal Particles at Oil-Water Interfaces with Organic Salts
Carolina van Baalen, Jacopo Vialetto, and Lucio Isa
Phys. Rev. Lett. 131, 128202 (2023)
doi: 10.1103/PhysRevLett.131.128202
arxiv: 2305.01929

Monolayers of colloidal particles at oil-water interfaces readily crystallize owing to electrostatic repulsion, which is often mediated through the oil. However, little attempts exist to control it using oil-soluble electrolytes. We probe the interactions among charged hydrophobic microspheres confined at a water-hexadecane interface and show that repulsion can be continuously tuned over orders of magnitude upon introducing nanomolar amounts of an organic salt into the oil. Our results are compatible with an associative discharging mechanism of surface groups at the particle-oil interface, similar to the charge regulation observed for charged colloids in nonpolar solvents.

Optical calibration of holographic acoustic tweezers published in IEEE Transactions on Instrumentation and Measurement

Optical calibration of holographic acoustic tweezers
Sonia Marrara, David Bronte Ciriza, Alessandro Magazzù, Roberto Caruso, Giuseppe Lupò, Rosalba Saija, Antonino Foti, Pietro Giuseppe Gucciardi, Andrea Mandanici, Onofrio Maria Maragò, Maria Grazia Donato
EEE Transactions on Instrumentation and Measurement, 72, 9600808-1-8, (2023)
doi: 10.1109/tim.2023.3282303
arxiv: 2403.09286

Recently, acoustic tweezers based on an array of ultrasonic transducers have been reported taking inspiration from holographic optical tweezers. In the latter technique, the calibration of the optical trap is an essential procedure to obtain the trap stiffnesses. On the contrary, in the case of acoustic tweezers the calibration of the acoustic forces is seldom carried out. To cover this gap, in this work, we adapt the calibration protocols employed in optical tweezers to acoustic tweezers based on arrays of ultrasonic transducers. We measure trap stiffnesses in the mN/m range that are consistent with theoretical estimates obtained by calculations of the acoustic radiation forces based on the Gor’kov potential. This work gives a common framework to the optical and acoustic manipulation communities, paving the way to a consistent calibration of hybrid acoustooptical setups.

Roadmap for Optical Tweezers published in Journal of Physics: Photonics

Roadmap for optical tweezers
Giovanni Volpe, Onofrio M Maragò, Halina Rubinsztein-Dunlop, Giuseppe Pesce, Alexander B Stilgoe, Giorgio Volpe, Georgiy Tkachenko, Viet Giang Truong, Síle Nic Chormaic, Fatemeh Kalantarifard, Parviz Elahi, Mikael Käll, Agnese Callegari, Manuel I Marqués, Antonio A R Neves, Wendel L Moreira, Adriana Fontes, Carlos L Cesar, Rosalba Saija, Abir Saidi, Paul Beck, Jörg S Eismann, Peter Banzer, Thales F D Fernandes, Francesco Pedaci, Warwick P Bowen, Rahul Vaippully, Muruga Lokesh, Basudev Roy, Gregor Thalhammer-Thurner, Monika Ritsch-Marte, Laura Pérez García, Alejandro V Arzola, Isaac Pérez Castillo, Aykut Argun, Till M Muenker, Bart E Vos, Timo Betz, Ilaria Cristiani, Paolo Minzioni, Peter J Reece, Fan Wang, David McGloin, Justus C Ndukaife, Romain Quidant, Reece P Roberts, Cyril Laplane, Thomas Volz, Reuven Gordon, Dag Hanstorp, Javier Tello Marmolejo, Graham D Bruce, Kishan Dholakia, Tongcang Li, Oto Brzobohatý, Stephen H Simpson, Pavel Zemánek, Felix Ritort, Yael Roichman, Valeriia Bobkova, Raphael Wittkowski, Cornelia Denz, G V Pavan Kumar, Antonino Foti, Maria Grazia Donato, Pietro G Gucciardi, Lucia Gardini, Giulio Bianchi, Anatolii V Kashchuk, Marco Capitanio, Lynn Paterson, Philip H Jones, Kirstine Berg-Sørensen, Younes F Barooji, Lene B Oddershede, Pegah Pouladian, Daryl Preece, Caroline Beck Adiels, Anna Chiara De Luca, Alessandro Magazzù, David Bronte Ciriza, Maria Antonia Iatì, Grover A Swartzlander Jr
Journal of Physics: Photonics 2(2), 022501 (2023)
arXiv: 2206.13789
doi: 110.1088/2515-7647/acb57b

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects, ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in the life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nano-particle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration.

3-D rotation tracking from 2-D images of spherical colloids with textured surfaces published in Soft Matter

3-D rotation tracking from 2-D images of spherical colloids with textured surfaces
Vincent Niggel, Maximilian R. Bailey, Carolina van Baalen, Nino Zosso, and Lucio Isa
Soft Matter, 19, 8790-8801 (2023)
doi: 10.1039/d3sm00076a

Tracking the three-dimensional rotation of colloidal particles is essential to elucidate many open questions, e.g. concerning the contact interactions between particles under flow, or the way in which obstacles and neighboring particles affect self-propulsion in active suspensions. In order to achieve rotational tracking, optically anisotropic particles are required. We synthesise here rough spherical colloids that present randomly distributed fluorescent asperities and track their motion under different experimental conditions. Specifically, we propose a new algorithm based on a 3-D rotation registration, which enables us to track the 3-D rotation of our rough colloids at short time-scales, using time series of 2-D images acquired at high frame rates with a conventional wide-field microscope. The method is based on the image correlation between a reference image and rotated 3-D prospective images to identify the most likely angular displacements between frames. We first validate our approach against simulated data and then apply it to the cases of: particles flowing through a capillary, freely diffusing at solid–liquid and liquid–liquid interfaces, and self-propelling above a substrate. By demonstrating the applicability of our algorithm and sharing the code, we hope to encourage further investigations in the rotational dynamics of colloidal systems.