Zwicker Group

Congratulations, Anna! Welcome to this great program 🎉

Wow, congratulations!

📢 Paper alert 📢

Chirality is known to be important for the movement of microorganisms and active matter. In our new paper out today in @natphys.nature.com, we show that chirality is used by malaria parasites to control their motion patterns:

doi.org/10.1038/s415...

Here comes a 🧵 ... (1/9)

Four simulation snapshots showing various possible configurations in phase separating systems with short-range interactions.

In contrast, short-range interactions (e.g., non-local elasticity and Riccardo's system discussed above) show various patterns, which can be explained by a mapping to the Swift-Hohenberg model. These results demonstrates that various processes arresting droplet coarsening fall into two categories.

Simulation snapshot showing a patterned phase with many small droplets in a hexagonal arrangement.

Filipe's work (in collaboration with Yicheng and Oliver) puts these results in context by generally studying the influence of non-local interactions onto phase separation. We find that long-range interactions (e.g., electrostatics and also chemical reactions) generally suppress phase separation.

Simulation snapshot showing a single large droplet coexisting with a patterned phase comprising multiple smaller droplets.

Active processes can further control the droplet dynamics. They can either accelerate coarsening, or they can suppress it completely. In the latter case, we also find interesting states where a macroscopic droplet coexists with a patterned phase comprising many smaller spots.

Top: Schematic of our model describing interacting solutes that phase separate in a 2D surface and exchanges with a 3D bulk. Bottom: Snapshots of numerical simulations with and without passive exchange.

Riccardo and Gerrit looked at condensates embedded in membranes, using polarity spots of yeast as an example. They showed that exchange with the bulk can strongly accelerate coarsening, allowing cells to form one spot quickly.

Two more pre-prints from the group 🎉 Riccardo explored how cells could control surface condensates by regulating bulk exchange (arxiv.org/abs/2511.03619). Filipe studied the impact of non-local interactions onto phase separation (arxiv.org/abs/2511.05214). Some more details in the thread:

No, I don’t agree with such a blanket statement. Equilibrium concepts can also be useful in non-equilibrium situations. For instance, phase coexistence may hold at the interface, while active processes modulate the bulk phases. I propose a more nuanced view, depending on the concrete system.

I don’t know the details of this paper, but one generally needs to be cautious. Phase separation can be a useful conceptual framework, but since cells are complex, it can rarely be „proven“.

Our review on the physics of phase separation in cells has been published by Rep. Prog. Phys. 🎉 doi.org/10.1088/1361...

We hope that the text and citations are helpful for anyone interested in physical descriptions of condensates in cells!

Another pre-print from our group see's the light of day! 🎉 This time we how the coarsening of droplets is affected by advection and reactions: arxiv.org/abs/2510.00827 @stefankoestler2025.bsky.social describes our surprising findings in the thread below ⤵️

Our latest work from a stimulating collaboration with @jerelleaj.bsky.social and @nathanieldhess.bsky.social is out now!

A great example of a totally unplanned discovery in our group, spearheaded by a Bachelor and a PhD student! Curiosity wins 🥳

New preprint 🎉
What began as Frieder Johannsen’s bachelor thesis in the @zwickergroup.bsky.social (which I had the pleasure to supervise) evolved into our latest paper: “Chemically Active Liquid Bridges Generate Repulsive Forces” — unlike passive ones, which attract.
📄 arxiv.org/abs/2509.18777

It was fun to do a little interview and think about the relevance of our work for a more experimental and engineering inclined community.

We have developed a new workflow to map whole human organs at single-cell resolution, while integrating spatial transcriptomics, proteomics, and metabolomics.

We applied this workflow to map precancerous lesions of the fallopian tubes.

More here: www.biorxiv.org/content/10.1...

In other news, we welcome Mengmeng Wu 🇨🇳 and Lukas Kristensen 🇩🇰 to our group! 🥳 Mengmeng is a postdoc who will combine particle-based simulations with analytical theory to study chemically active droplets. Lukas visits us for three months and will work on anchored active droplets. Welcome aboard! 🎉

Marcel developed and analyzed a generalized coarsening model to explain chromosomal crossover placements during meiosis (arxiv.org/abs/2509.09521). This model provides a coherent explanation of experimental data across mutants and species!

Cathelijne discovered that the energy required to maintain Turing patterns can be reduced substantially if the involved molecules repel each other (arxiv.org/abs/2509.05093). This work permits a thermodynamic analysis of this classical reaction-diffusion system!

Oliver looked at the dynamics of phase separation in elastic networks, where non-local effects arrest coarsening and lead to patterns with a well-defined length scale (arxiv.org/abs/2508.09829). These patterns can be realized experimentally to make materials with interesting optical properties!

Yicheng discovered that driven chemical reactions between solvent components can induce a pressure difference at interfaces (arxiv.org/abs/2508.09816). This can lead to fun effects, including self-propulsion, and showcases the surprising versatility of chemically active emulsions.

We were exceptionally effective at finishing manuscripts in the last weeks and couldn't keep up with describing pre-prints here. This thread summarizes the main results of our recent works:

This is a great opportunity to start an independent group in one of the best research environments you could think of!

Interested in doing a PhD in my group? I have an opening for a PhD student to work on understanding and designing nanomedicine-membrane interactions! Apply here:
careers.universiteitleiden.nl/job/Leiden-P...

Looking forward to discussing our little active droplet theories with students!

Congratulations, Anna!

Congratulations! This is very well deserved

Join my team for a PhD in Learning in living adaptive networks (Theory). Apply by October 7th through www.portal.graduatecenter.lmu.de/ocgc/qmb

It was a lot of fun to write this little piece on using phase transitions to process cellular information! We probably pose more questions than we give answers, but that’s exciting.