Kaloian Koynov

Many tumours release lactate as a major metabolic product and signalling molecule. Here we use lactate flux as an endogenous trigger for covalent hydrogel formation. Phenol-functionalised alginate remains soluble until cell-derived lactate is oxidised by lactate oxidase; the generated hydrogen peroxide is used by horseradish peroxidase to crosslink phenols and form a matrix at metabolically active sites. Hydrogels form within minutes and reach storage moduli from approximately 10 Pa to 5 kPa. In tumour-spheroid models, including a patient-derived glioblastoma spheroid model, local lactate production generates spatially confined gelation that extended up to around 1 mm from the spheroid surface. Nanoindentation and fluorescence correlation spectroscopy reveal radial stiffness and polymer-density gradients, while proteome profiling and imaging indicate reduced proliferative signalling and increased markers associated with migration and matrix remodelling. These findings establish metabolite-gated hydrogelation as a strategy to couple cellular metabolism to covalent matrix assembly, mechanics and transport, providing a bio-synthetic platform for modelling cell–matrix reciprocity and tumour confinement.

ZUSAMMENFASSUNG: Dynamische dreidimensionale (3D) Muster weisen gegenüber ihren statischen Gegenstücken überlegene Fähigkeiten auf und spielen eine entscheidende Rolle in Anwendungen wie wiederbeschreibbarer Datenspeicherung und aktualisierbarer Informationsverschlüsselung. Die effiziente Herstellung und Rekonfiguration von 3D‐Mustern erfordert jedoch geeignete Methoden und Materialien. In dieser Arbeit untersuchen wir die Herstellung und Rekonfiguration dynamischer 3D‐Muster durch Laserdirektschreiben mittels Hochkonversion in Kombination NIR‐lichtempfindlichen Nanokompositen. Wir haben ein System entwickelt, das einen kostengünstigen kontinuierlich betriebenen NIR‐Laser nutzt, um reversible Photoreaktionen im Laserfokus auszulösen, und so durch Bewegung des Laserfokus dynamische 3D‐Muster zu erzeugen. Durch die Integration von Hochkonversions‐Nanopartikeln (UCNPs) mit photoschaltbaren Materialien in eine Polymermatrix, einschließlich Spiropyran, Diarylethen und Azobenzol, ermöglichen wir eine lokalisierte Photoisomerisierung durch fokussierte Laserbestrahlung. Die Reversibilität des Photoschaltprozesses macht die resultierenden 3D‐Muster löschbar, wiederbeschreibbar und dynamisch. Diese Technik stellt eine universelle und wirtschaftliche Methode für die dynamische 3D‐Photostrukturierung dar und ist besonders vielversprechend für den Fortschritt in den Bereichen Informationsverschlüsselung, optische Speicherung und Datensicherheit.

Dynamic three‐dimensional (3D) patterns exhibit superior capabilities compared to their static counterparts, playing crucial roles in applications such as rewritable data storage and updatable information encryption. However, the efficient fabrication and reconfiguration of 3D patterns require suitable methods and materials. In this work, we explore the fabrication and reconfiguration of dynamic 3D patterns using upconversion laser direct writing in combination with near‐infrared (NIR) light‐responsive nanocomposites. We have developed a system that utilizes a cost‐effective continuous‐wave (CW) NIR laser to induce reversible photoreactions at the laser focus, thereby fabricating dynamic 3D patterns by moving the laser focus. By integrating upconversion nanoparticles (UCNPs) with photoswitchable materials, including spiropyran (SP), diarylethene (DTE), and azobenzene (AZO), within a polymer matrix, we enable localized photoisomerization through focused laser irradiation. The reversibility of the photoswitching process renders the resulting 3D patterns erasable, rewritable, and dynamic. This technique represents a universal and economical method for dynamic 3D photopatterning, particularly promising for advancing information encryption, optical storage, and data security technologies.

Controlling the motion of non-Newtonian drops on surfaces is crucial for applications ranging from inkjet printing to biomedical devices and food processing. While the macroscopic behavior of viscoelastic drops sliding on tilted hydrophobic surfaces has been characterized—showing reduced velocities and elongation compared to Newtonian fluids—the underlying microscopic mechanisms remain poorly understood. To address this gap, we developed a high-speed, high-resolution reflection microscope that enables direct visualization of the contact line of sliding drops. We used water-soluble polyelectrolyte solutions based on polyacrylamide and allowed drops to slide on hydrophobic substrates composed of Teflon amorphous fluoropolymer and polydimethylsiloxane-coated glass slides. The substrate tilting angle was varied between 20° and 45°. We reveal how viscoelasticity influences the dynamics of the receding contact line and drop motion. Our experiments demonstrate that viscoelasticity can destabilize the receding contact line, triggering filament formation. This instability previously observed in the coating of thin viscoelastic films is reported here for sliding drops, for the first time on smooth surfaces. We further highlight the critical role of polymer charge in this process: while cationic and nonionic polymers promote filament formation, anionic polymers do not, a difference we attribute to the distinct wetting properties of the solutions. In conclusion, we clarify the interplay between rheology, surface interactions, and drop dynamics.

Giant polymersomes are widely used as artificial cells due to their resemblance to natural cells; however, their intrinsically low membrane permeability remains a major limitation for applications such as drug delivery and bioreactors. Here, we report a microfluidic approach to fabricate permeable polymersomes using PB-b-PEO as a macromolecular surfactant and oleyl alcohol as a cosurfactant. Incorporation of the cosurfactant into the membrane induces membrane structural disorder in polymer packing, leading to enhanced membrane permeability. Using advanced nuclear magnetic resonance (NMR) spectroscopy, we directly probe the heterogeneity within polymersome membranes, representing membrane-level investigation in giant polymersomes. Comparison with polymersomes exhibiting tightly packed polymer assemblies reveals pronounced differences in the lateral mobility and permeability of the membrane. Our results demonstrate how subtle changes in formulation translate into distinct membrane structures, establishing a molecular basis for the rational design of polymersomes with tailored permeability.

The motion of contact line plays a crucial role in both natural phenomena and industrial processes. While it is well known that surface defects influence contact line dynamics, we demonstrate that their impact depends not only on geometry, size, and composition, but also on the history of fluid interaction with the surface. Using ultrafast, high‐resolution reflection microscopy, we visualized the dynamics of the three‐phase contact line as successive water droplets slid across a hydrophobic surface patterned with protrusions. We observed a growing attraction between the contact line and surface defects with increasing drop number. This effect arises from the spontaneous electrification that occurs during sliding: the droplets and the surface acquire opposite charges, generating electrostatic forces that significantly influence both advancing and receding contact lines. These forces contribute more than half of the total pinning force. Our findings reveal a previously overlooked factor in drop sliding and offer new insights into the dynamics of the contact line.

Cylindrical polymer brushes (CPBs) enable remarkable control over nanoparticle properties solely through sequential polymerization. The spatial dimensions and functionality of the resulting polymeric nanoparticles can be adjusted by the ratio of backbone to side chain length and the chemical nature of both parts. In this work, we present a convenient and straightforward synthetic pathway to polypept(o)ide-based CPBs using a "grafting-from" strategy utilizing poly-l-lysine (pLys) as the macroinitiator backbone and polysarcosine (pSar) as the side chain. End-capping of pSar chains with azido-butyric acid pentafluorophenyl ester enables facile surface functionalization by click chemistry (e.g., dye labeling). This strategy allows for straightforward control over nanoparticle size (R_h from 12 to 41 nm), shape (aspect ratio from 1.7 to 8.3), and molecular weights (from 350 to 2980 kg mol^-1). Despite the high grafting density of pSar side chains from the pLys backbone (>85%), enzymatic degradation is feasible by the natural protease B fromStreptomyces griseusand enables the analysis of pSar side chains upon cleavage (Đ = 1.03-1.04). Interestingly, these CPBs exhibit thermal stability in phosphate-buffered saline at elevated temperatures (60 °C for 24 h) and display notable circulation in zebrafish embryos (up to 3 days). Therefore, CPBs based on polypept(o)ides not only allow for precise tuning of size, shape, and surface functionality but also display high biocompatibility and extended circulation time in zebrafish, leveraging the stealth-like properties of pSar.

Functionalized silica-based surfaces are widely used across industries, from semiconductors to pharmaceuticals. Aminosilanes are commonly employed as coupling agents during surface functionalization to anchor diverse functional molecules. However, the surface modifications perturb interfacial physicochemical properties, resulting in a significant shift in interfacial pH compared to the bulk solution. This shift complicates direct measurement and accurate monitoring of interfacial conditions. To overcome this challenge, we functionalized glass surfaces with aminosilane-coupled pH-sensitive fluorescent dyes and utilized confocal microscopy to measure their fluorescence response to changes in bulk pH. Complementing these experiments, we developed a theoretical model describing equilibrium surface chemistry taking into account electrostatic interactions at aminosilane-functionalized glass interfaces. It revealed a linear relationship between interfacial and bulk pH, with the interfacial pH varying over a narrowed range compared to the bulk pH. Building upon these insights, we calibrate the fluorescence response of the grafted pH-sensitive dyes. This integrated approach enables precise and reliable in situ monitoring of interfacial pH under various conditions, demonstrating significant potential for environmental sensing and advanced material characterization.

A versatile method for image-based determination of a particle size distribution, based on a 2D classification approach.

It has been discovered during the last decade that when water drops slide on hydrophobic surfaces, they spontaneously leave negative charges along the drop path. The drops become positively charged with a potential of 1 kV. This process, called slide electrification, influences drop motion and alters contact angles. Here, a third effect of slide electrification is demonstrated: the preferential deposition of dissolved solutes with positive charges. To illustrate this, water drops containing dissolved charged fluorophore ions are allowed to slide down a tilted hydrophobic surface, and their track is imaged. Two perylene derivatives are applied as fluorophores, one chromophore carrying positive charges, PDI⁺, and one carrying negative charges, PDI^─. PDI⁺ is deposited at a concentration as low as 0.5 µm. In contrast, PDI^─ is only deposited above 5 µm. Experiments using grounded drops or a hydrophobic coating on a conducting substrate indicate that the electric field generated from the negative surface charges behind the drop causes a preferential deposition of the dissolved ions near the interface. This hypothesis also agrees with Kelvin probe measurements. Complex biomolecules deposition e.g. DNA can be also affected by this. These findings contribute to a better understanding of mass transfer processes at interfaces.