Publikationen

Understanding how nanoparticles form stable colloids is fundamental to their practical applications. Nonlinear ligands are known to increase the stability of nanoparticles in apolar solvents compared to shells of linear alkyl chains. Here, we reveal the molecular origin of this colloidal stability. We observe that even a single methyl side chain can suppress disorder–order transitions in the ligand shell, with double bonds or branches leading to drastic decreases in agglomeration temperature in such dispersions. Through a combination of temperature-dependent X-ray scattering and molecular dynamics simulations, we show that these simple structural modifications prevent ligand molecules from forming ordered bundles, maintaining shell disorder even at temperatures approaching solvent freezing. The absence of ligand order enhances colloidal stability by weakening attraction between the ligand shells via a combination of energetic and entropic factors. This mechanism extends dispersion stability by more than 100 K compared to linear ligands of equivalent length. Our findings provide a molecular-level explanation for the enhanced stability previously observed with branched and unsaturated ligands, offering an effective strategy for engineering nanoparticle dispersions that remain stable across broad temperature ranges.

Focal adhesions (FAs) are dynamic structures central to cell migration, serving as mechanotransduction sites linking the extracellular matrix (ECM) to intracellular signaling pathways such as FA kinase (FAK). How FAK becomes activated in response to cell-ECM adhesive forces at single FAs to facilitate directional motion is poorly understood. Using micropillar-based force microscopy and FA-targeted FRET biosensors, we monitored real-time traction forces and FAK activity at individual FAs during assembly and disassembly. Our results demonstrate oscillatory temporal coupling of traction force and FAK activity in high-tension FAs before FA disassembly. Cross-correlation analyses revealed that force precedes FAK activation, guiding FA turnover. Atomistic molecular simulations unveiled a force-induced mechanism where traction forces disrupt autoinhibitory FERM-kinase interactions in FAK, enabling catalytic activity without structural unfolding. Our findings provide mechanistic insights into the spatiotemporal integration of mechanical forces and biochemical signaling in cell migration.

Previous studies have successfully elicited a wide range of emotional responses by stimulating the hand region. The purpose of the current study was to test whether tactile stimuli applied to the torso could elicit similar emotional responses. To this end, we created 45 custom vibrotactile patterns that were presented through a vibrotactile vest to the front, back, and both sides of the torso. The patterns covered a wide range of physical variables such as amplitude, trajectory, and continuity. In an exploratory experiment, participants rated the arousal and valence of these patterns. Emotional responses differed between the patterns, and detailed analyses suggested that vibration amplitude and intensity where these vibrations were applied influenced both valence and arousal judgments. In a follow-up experiment, we systematically varied the amplitude and location of the vibrations. Our results showed that lower amplitudes were less arousing and more pleasant than higher amplitudes. Similarly, vibrations to the back torso were less arousing and more pleasant than those applied to the front or both sides of the torso, which can be explained by the lower sensitivity on the back. Taken together, we suggest that perceived intensity partially explains the relationship between the emotionality of vibration patterns on the torso.

We report the successful synthesis of nanocomposites between the MXene Ti3C2Tx and polyaniline (PAni), achieved via an innovative approach starting from the intercalation of anilinium ions into non-exfoliated Ti3C2Tx, and followed by a liquid/liquid interfacial polymerization. This approach produces transparent films with beneficial optical quality. The spectroscopic analysis confirmed the formation of PAni in its conductive form, emeraldine salt. The absence of TiO2 bands in the Raman spectra indicated that the organic polymer protected Ti3C2Tx from degradation, even in acidic media. Electrochemical characterization revealed that the nanocomposites exhibited promising performance as supercapacitors, with specific capacity dependent on the amount of polymer. The combination of the conductive Ti3C2Tx and the redox activity of PAni, as well as the specific nanoarchitecture in which the materials are organized, significantly improved the electrochemical response, facilitating ion diffusion. These transparent films demonstrated specific capacity values up to 89 mAh g-1 at 0.1 mAh g-1, with the potential for further enhancement through current collector optimization, positioning them as strong candidates for miniaturized energy storage applications and transparent devices.

Carbon allotropes are crucial to advanced interfaces to control friction and wear because of their unique range of mechanical properties: from diamond's hardness to graphite's lubricity. Friction force microscopy (FFM) is reported for diamond tips sliding on SiC(0001)-supported epitaxial graphene. A sharp friction increase is observed at a threshold normal force, linked to an intermittent graphene rehybridization. Comparing the FFM response of a diamond tip to that of a previously studied silicon tip with a comparable radius reveals a similar abrupt friction increase, though at roughly half the threshold force. Atomistic simulations of SiC(0001)-supported graphene sliding against hydroxylated amorphous carbon (a-C) and silicon oxide show low shear stress at low pressures for both systems. The shear stress increases at higher pressures due to bond formation between graphene and the counterbody. For a-C, the transition threshold shifts to higher pressures, consistent with FFM results. In simulations with high normal pressures, epitaxial graphene undergoes a structural transformation into single-layer diamond, contributing to the abrupt increase in friction. The graphene structure recovers after lifting the a-C counterbody, demonstrating structural robustness under tribological stress. These findings provide insights into the stability of low-friction interfaces between epitaxial graphene and key materials for current micro-electro-mechanical systems (MEMS)

Friction between fingertip and surface is a key contribution to tactile perception during active exploration of materials. We explore the role of skin factors such as stratum corneum thickness and hydration, deformability, elasticity, or density of sweat glands and of Meissner corpuscles in friction and tactile perception. The skin parameters were determined non-invasively for the glabrous skin at the index finger pad of 60 participants. Sets of randomly rough plastic surfaces and of micro-structured fibrillar rubber surfaces were explored as model materials with well-defined parameterized textures. Friction varies greatly between participants, and this variation can be explained to 70% by skin factors for the randomly rough plastic surfaces. The predictability of friction by skin factors is much lower for micro-structured rubber surfaces with bendable fibrils, where 50% of variance is explained for the stiffest fibrils but only 20% for the most bendable fibrils. The participants’ age is the key predictor for their tactile sensitivity to perceive the fibrils, where age is negatively correlated to the density of Meissner corpuscles. The results suggest that stratum corneum hydration, skin deformability, and age are important factors for friction and perception in active tactile exploration of materials.

Silver microflakes and -spheres are common fillers for electrically conductive screen-printing pastes. Here, we report on the effects of filler shapes and sizes on conductivity, sintering, and recyclability. We printed pastes based on flakes and spheres, treated them at 110 °C to 300 °C, and evaluated the electrical conductivity of the resulting layers. The electrical conductivity of the layers treated at 110 °C was dominated by particle–particle contact resistances; flakes yielded layers that were five times more conductive than sphere-based layers due to differences in the particle–particle contact area. Increasing temperature led to a reduction of the resistivity of all layers through sintering. At 300 °C, prints based on spheres were 4 times more conductive than those from flakes. Tomography of the sintered structures showed that the difference was caused by a lower tortuosity factor for spheres. In a final study, we showed that silver flakes and spheres could be recycled after sintering and reused for a new generation of prints without losing electrical performance. The more porous structure of sintered flakes allowed for higher recycling yields compared to spheres. At 140 °C, 91.6% of the flakes and 69.7% of the spheres were recovered as reusable dispersions.

Bispecific T cell engagers (TcEs) link T cell receptors to tumor-associated antigens on cancer cells, forming cytotoxic immunological synapses (IS). Close membrane-to-membrane contact (≤13 nm) has been proposed as a key mechanism of TcE function. To investigate this and identify potential additional mechanisms, we compared four immunoglobulin G1-based (IgG1) TcE Formats (A–D) targeting CD3ε and Her2, designed to create varying intermembrane distances (A < B < C < D). Small-angle X-ray scattering (SAXS) and modeling of the conformational states of isolated TcEs and TcE–antigen complexes predicted close contacts (≤13 nm) for Formats A and B and far contacts (≥18 nm) for Formats C and D. In supported lipid bilayer (SLB) model interfaces, Formats A and B recruited, whereas Formats C and D repelled, CD2–CD58 interactions. Formats A and B also excluded bulky Quantum dots more effectively. SAXS also revealed that TcE–antigen complexes formed by Formats A and C were less flexible than complexes formed by Formats B and D. Functional data with Her2-expressing tumor cells showed cytotoxicity, surface marker expression, and cytokine release following the order A > B = C > D. In a minimal system for IS formation on SLBs, TcE performance followed the trend A = B = C > D. Addition of close contact requiring CD58 costimulation revealed phospholipase C-γ activation matching cytotoxicity with A > B = C > D. Our findings suggest that when adhesion is equivalent, TcE potency is determined by two parameters: contact distance and flexibility. Both the close/far-contact formation axis and the low/ high flexibility axis significantly impact TcE potency, explaining the similar potency of Format B (close contact/high flexibility) and C (far contact/low flexibility). Copyright © 2025 the Author(s).

The development is proposed of a specific non-enzymatic amperometric sensor based on electrodeposited copper nanoparticles (Cu-NPs) for the determination of uric acid (UA) in fermentation samples. Through optimization of the Cu-NPs-containing sensing layer, it was demonstrated that copper(II)-induced oxidation (catalytic effect) in the presence of molecular oxygen is more effective for determining UA than the adsorption of UA on Cu and Cu-oxide surfaces. More importantly, simply changing the sensing layer’s surface chemistry by increasing the defect CuxOy on the surface of Cu-NPs after heating at 70 °C for only 20 min significantly improved the specificity of UA determination in both model and real fermentation samples (viz. supernatants of S. cerevisiae and E. coli). This study can be used as a guideline for the future assembly of functional electrodeposited sensing layers for the specific determination of target electroactive bioanalyte(s).

The synthesis of an amphiphilic three-arm block copolymer (AB)3-BCP, which consists of poly(methyl methacrylate) (PMMA) and poly(butyl methacrylate) (PBMA) in the hydrophobic inner block, is reported. The hydrophilic block segment is based on poly(2-hydroxyethyl methacrylate) (PHEMA) originating from 2-(trimethylsiloxyl)ethyl methacrylate (HEMA-TMS). The preparation is carried out in two steps using a core-first approach. Using atom transfer radical polymerization (ATRP) as a controlled polymerization technique, three (AB)3-BPCs with HEMA contents of 15 to 38 mol−1 % are prepared, applying different reaction conditions. Porous structures are generated from these BCPs by applying a self-assembly and nonsolvent-induced phase separation (SNIPS) protocol. Complex surface structures are observed using scanning electron microscopy (SEM). Bulk morphologies are investigated for a better understanding of the underlying self-assembly. For PHEMA-rich (AB)3-BCPs, non-regular lamellar microphases are observed in transmission electron microscopy (TEM) and confirmed by small-angle X-ray scattering (SAXS). The porous structures and their expected swelling characteristics are analyzed using atomic force microscopy (AFM) in air and water. Time-resolved measurements in water indicate a rapid swelling after immersion into the water bath. The present study paves the way for exciting porous materials based on the herein synthesized amphiphilic three-arm block copolymers useful for applications as absorber materials and coatings.