Stefan Köstler

Our second Cornell-era preprint is also out!

Kaarthik's paper discusses the gap between cellular and in vitro condensates. In cells, condensates are low-contrast (small partition coefficients), enabling a wide range of responses.

Congrats, Kaarthik and the team!

www.biorxiv.org/content/10.6...

Happy to share our first preprints from work originating at Cornell!

Takumi's paper describes how small molecules shift phase equilibria of condensates by focusing on the dilute-phase response. It shows how metabolites may tune stability and material properties.

www.biorxiv.org/content/10.6...

A great start to the new year! Our paper on how advection and reactions affect the coarsening of droplets got published in Physical Review Research. 🥳
📄 doi.org/10.1103/hdls...

Flyer for the lecture that takes place on January 21st at 3 pm CET

We’re excited to kick off 2026 with a rescheduled talk in the Matter to Life Lecture Series:
“Droplets Come to Life” by MtL Fellow David Zwicker @zwickergroup.bsky.social from the Max Planck Institute for Dynamics and Self-Organization 🙌

Register here: us02web.zoom.us/webinar/regi...

Roadmap for Condensates in Cell Biology Biomolecular condensates govern essential cellular processes yet elude description by traditional equilibrium models. This roadmap, distilled from structured discussions at a workshop and reflecting t...

Our "Roadmap for Condensates in Cell Biology" is now available on arXiv: arxiv.org/abs/2601.03677 🎉 This article summarizes the interdisciplinary weekly discussions we had at our condensate workshop at KITP in the summer of 2025. Feedback is very welcome!

Want to learn about how we use computational approaches at different scales to study biomolecular condensates?
Check out our latest review, out in Advances in Physics X
@juliamaristany.bsky.social @alinaemelianova.bsky.social
@rcollepardo.bsky.social

www.tandfonline.com/doi/epdf/10....

We're looking for a postdoc to strengthen our group! Please apply by January 15, 2026 if you're a fun and motivated person who likes theoretical modeling of biological processes by combining analytics and numerics. There is freedom in choosing projects! Details: www.ds.mpg.de/4110032/job_...

Size control guidelines for chemically active droplets Biological cells and synthetic analogues use liquid-liquid phase separation to dynamically compartmentalize their environment for various applications. In many cases, multiple droplets need to coexist...

Since more than a decade, our group has been exploring chemically active droplets, which are exciting since their size can be controlled. Yet, we still do not fully understand this control even in the simplest models. Until a new preprint (arxiv.org/abs/2512.02542) spearheaded by postdoc Guido...

Biomolecular Phase Boundaries are Described by a Solubility Product That Accounts for Variable Stoichiometry and Soluble Oligomers The solubility product is a rigorous description of the phase boundary for salt precipitation and has previously been shown to qualitatively describe the condensation of biomolecules. Here we present a derivation of the solubility product showing that the solubility product is also a robust description of biomolecule phase boundaries if care is taken to account for soluble oligomers and variable composition within the dense phase. Our calculation describes equilibrium between unbound monomers, the dense phase, and an ensemble of oligomer complexes with significant finite-size contributions to their free energy. The biomolecule phase boundary very nearly resembles the power law predicted by the solubility product when plotted as a function of the monomer concentrations. However, this simple form is concealed by the presence of oligomers in the dilute phase. Accounting for the oligomer ensemble introduces complexities to the power law phase boundary including re-entrant behavior and large shifts for stoichiometrically matched molecules. We show that allowing variable stoichiometry in the dense phase expands the two phase region, which appears as curvature of the phase boundary on a double-logarithmic plot. Furthermore, this curvature can be used to predict variations in the dense phase composition at different points along the phase boundary. Finally, we show how the solubility product power law can be identified in experiments by using dilute phase dissociation constants to account for the oligomer ensemble.

New publication! How to read the curves in biomolecular phase diagrams! A collaboration between the Schmit Group and Jonathon Ditlev, Les Loew, and @ani-chattaraj.bsky.social. 1/7 pubs.acs.org/doi/10.1021/...

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:

Condensation and activator/repressor control of a transcription-regulated biomolecular liquid Cells operate in part by compartmentalizing chemical reactions. For example, recent work has shown that chromatin, the material that contains the cell's genome, can auto-regulate its structure by util...

We’re excited to share our new work in Soft Matter: doi.org/10.1039/D5SM...
We demonstrate how in vitro transcription can drive biomolecular phase separation — and how that phase separation in turn regulates transcription.

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!

New pre-print with Jacqueline Janssen and Frank Jülicher! We extend the Lifshitz-Slyozov-Wagner (LSW) theory by matter supply, and find a novel universal law governing coarsening kinetics, valid for any constant matter supply in the interface-resistance-limited regime.

📄: arxiv.org/abs/2510.21552

Good news in rough times:
Our work on generalising Lifshitz-Slyosov-Wagner (LSW) theory to active systems, led by the all-mighty Jonathan Bauermann, is out on PRL!! Special thanks to Christoph Weber @m-pol.bsky.social and Frank Jülicher.

doi-org.sire.ub.edu/10.1103/f5x9...

Many thanks to my colleagues @zwickergroup.bsky.social!
📄 arxiv.org/abs/2510.00827

🔬 This mechanism could be vital in biological cells to control condensates. Similarly, this method could allow creating micro-reactors for chemical assembly in synthetic applications or facilitate localized enzymatic activity for biomedical applications.

Taken together, advection modulates the initial dynamics — essentially independent of reactions — and biases the overall system toward a particular configuration, which is then maintained by reactions.

Interestingly, we find that multiple pattern sizes around the predicted one are stable!
Linear stability analysis reveals that emulsions become stable against Ostwald ripening from a minimal pattern size onwards.

Reactions arrest coarsening (left)
Advection accelerates early coarsening (right)

👉 We numerically and analytically determine the final equilibrium pattern size using a mapping to an equilibrium system.
👉 Looking at dissipation, we observe that advection peaks in early stages of coarsening.

New preprint 🥳
In our new paper, we show that “Advection selects pattern in multi-stable emulsions of active droplets” — which provides a path toward controlling regular arrangements of droplets. 🧵
📄 arxiv.org/abs/2510.00827

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

“Journals and peer review are unlikely to change for the better if the companies that operate scientific indexes and citation databases continue to stifle innovation.”

Read our guest post in DORA: buff.ly/EGDbskH

Our institute turned 100 years today! We had a fantastic celebration with scientific talks by Howard Stone and Christina Marchetti. 🎉

And that concludes our #kitp program on biomolecular condensates 😢 Wow, what an *incredible* experience, and unique place to learn and think and grow! 🤓

Can't say enough about the Condensates program at @kitp-ucsb.bsky.social. Invigorating discussions, fantastic facilities, and a beautiful location (a place I consider "home"). Thanks to @weber-lab.bsky.social, @jerelleaj.bsky.social, @zwickergroup.bsky.social, and Frank Julicher for organizing!

Just leaving Paris after 3 weeks of summer school on combining maths and physics to tackle #ActiveMatter.
I gained new perspectives, met wonderful people and had fascinating discussions. It was great to communicate my research to so many interested people!
And of course, Paris was just wonderful!

@jerelleaj.bsky.social, master painter 👩🏽‍🎨 of the blackboard 👩🏽‍🏫, in action! 🤩 She is amazing at capturing the essence of our complex, meandering (and sometimes contentious) discussions @kitp-ucsb.bsky.social

It’s been a lot of fun talking about chemically active condensates to such an attentive and motivated crowd!

We updated our pre-print on equilibria in multicomponent mixtures: arxiv.org/abs/2405.01138 In particular, we added the figure below, which shows that such mixtures exhibit countless metastable states between a metastable homogeneous state and the equilibrium with many phases.

Huge thanks to all the incredible speakers who have shared their research at the Young Biophysicists Meeting so far!

Here's a glimpse.

See you in the next session!