Prof. Dr. Tobias Kraus

Wearable electrochemical biosensors offer a promising alternative to conventional invasive blood-based methods for monitoring biomarkers in diagnostic or therapeutic applications. Microneedle (MN)-based technology provides direct access to the skin's interstitial fluid (ISF), enabling real-time monitoring of biomarkers. Nevertheless, current micro- and nanofabrication techniques do not adequately support the development of MN-based wearable technology that can utilize soft hybrid conductive inks, limiting its use in transdermal biosensing. Herein, an MN-based biosensing platform is developed by integrating 3D printing, soft lithography, and hybrid conductive ink technology, featuring a fenestrated MN shell (FMNS) that serves as a protective layer for the inner hybrid conductive ink coating and prevents delamination during skin application. This FMNS patch demonstrates a wide pH monitoring range, high selectivity and accurate detection of subtle ISF pH changes, safe integration of hybrid conductive inks, and reduced fabrication time and cost when compared to other microfabrication methods such as lithography and deep reactive ion etching. The biosensor excels in protecting the biosensing layer and demonstrates excellent analytical performance in monitoring changes in pH levels of the skin ISF. This micro- and nanofabrication approach has great potential in integrating hybrid conductive ink technology into transdermal wearable devices for health monitoring and diagnostics.

A solvent-free approach to the formation of freestanding photonic material from amphiphilic polystyrene-block-poly(2-hydroxyethyl methacrylate) (PS-b-PHEMA) is reported, where the application of shear force and pressure induces phase separation. This work demonstrates access to high molecular weight (HMW; >100 kg mol−1) PS-b-PHEMA with PHEMA contents up to 62 vol% using sequential anionic polymerization. By exploring hot pressing, the dependency of microstructure formation on temperature, pressure, and time is demonstrated using transmission electron microscopy and small-angle X-ray scattering measurements. Within 30 min, phase-separated block copolymer (BCP) films are obtained. Although no highly ordered equilibrium structures are formed, photonic properties are observed for PS-b-PHEMA films with molecular weights higher than 140 kg mol−1 and PHEMA contents between 20 and 51 vol%. The photonic properties are investigated by ultraviolet–visible (UV–vis) and fluorescence spectroscopy as well as confocal fluorescence microscopy. The BCP films exhibit tailored transmittance that is dependent on molecular weight and microstructure, making them suitable for UV and blue light filter applications. Also, structure-dependent reflection and fluorescence are demonstrated. Finally, the application in the field of sensors is addressed by demonstrating a reversible color change of BCP films with a co-continuous microstructure, achieved through polar solvent infiltration and evaporation.

Inks of gold nanoparticles with stabilizing and conducting polymer shells are promising materials for printed electronics. Local measurements of their electrical properties at the single-particle scale are required to understand the relationship between the particle network and electrical functionality. Herein, we report on conductive atomic force microscopy (cAFM) on films produced from hybrid Au nanoparticles that carry a covalently bound shell of the conducting polymer poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) and are distributed in a non-conductive matrix of polyvinyl alcohol (PVA). Current maps reveal the clustering of particles into electrically well-connected local networks and allow us to quantify the contact resistance between particles or clusters of particles. We find that the contact resistance between particles inside clusters is lower than those between clusters, indicating a hierarchical layer structure. By comparing inkjet-printed thicker bulk films and drop-cast films of single- or few-layer thickness, the experimental results offer valuable insights into the relationship between the structure of nanoparticle networks and the electrical conductance in these hybrid systems.

Carbon black (CB)-elastomer composites can serve as low-cost, highly deformable sensor materials. We report on the flow-induced anisotropy of CB-silicone films generated via doctor blade coating. Cured films exhibited larger conductivity perpendicular to the coating direction (R II / R > 1). The piezoresistive sensitivity was 2-3 times larger when stretching perpendicular than parallel to the coating direction, with relative resistance increases of 100–200 %. In contrast, the mechanical stress response to strain was isotropic within the measurement uncertainties. Structural analyses at length scales up to the CB agglomerate level (< 1µm) m) yielded only weak structural anisotropy and excluded alignment of small, primary CB aggregates (<150 nm) in flow direction. Small structural anisotropy apparently suffices to induce significant (piezo-)electric anisotropy. Atomistic molecular dynamics simulations of CB in a viscous medium under strong shear indicate that the CB aggregates have a weak tendency to align with the flow. This generally leads to increased conductivity parallel to the coating R II / R <1. Affine deformation in response to small tensile strain reduces conductivity uniformly. Our results show that shear can induce the formation of electrically anisotropic composites but excludes shear alignment as dominating mechanism. We propose that anisotropy is caused by an interplay of extensional flow and weak alignment in the flow-vorticity plane that varies under tensile strain.

In this work, we present a proof-of-concept demonstration of inkjet-printed resistive temperature sensors based on nanoparticle platinum ink on flexible polyimide substrates. The resistive temperature sensors are designed as meander structures with a target nominal resistance of 100 and 1000 Ω to be compared to conventional bulk Pt100 and Pt1000 resistors. Thermogravimetric analysis and in situ resistance measurements identified 250°C as the optimal sintering temperature, enabling sufficient solvent removal for conductive structure formation while avoiding Pt surface oxidation and polyimide substrate degradation. Electrical characterization in the 20°C–80°C range revealed a linear relationship between resistance and temperature with effective temperature coefficients of resistance (~48%/57%) and sensitivities (~72%/87%) compared to Pt100/Pt1000 standards, respectively. Mechanical testing over 400 bending cycles showed less than 1% change in electrical resistance, confirming robust flexibility. This study demonstrates the feasibility of translating nanoparticle Pt-based resistive temperature sensors into flexible and automotive sensing applications, offering low-temperature processability, stable temperature coefficients of resistance, linear sensitivity, mechanical robustness, and chemical stability across 20°C–80°C range.

Antimicrobial resistance is a global crisis driven by a scarce pipeline of new antibiotics. A major contributor is the intrinsic resistance conferred by the bacterial envelope, highlighting the need for innovative molecules for improved therapies. In this study, TAT–ArgBD, a conjugate of the cell-penetrating TAT peptide and arginine biodynamer (ArgBD), serves in vitro as a multivalent macromolecular antibiotic and synergist. TAT–ArgBD rapidly kills 99.9% of Pseudomonas aeruginosa at 32 µg/mL within 1 h, outperforming colistin, and shows minimum inhibitory concentrations (MICs) of 2–8 µg/mL against Acinetobacter baumannii and Staphylococcus aureus. Notably, it potentiates antibiotics such as novobiocin, chloramphenicol, and imipenem, leading to lowered MICs up to 256-fold. Notably, novobiocin, typically active only against Gram-positive bacteria, showed activity against Gram-negative bacteria when combined with TAT–ArgBD. Mechanistic studies suggest TAT–ArgBD antimicrobial and synergistic actions result from preferential binding to POPG and cardiolipin. This interaction induces bacterial membrane pore formation by adopting an α-helical conformation in the presence of bacterial lipids. With a favorable in vitro safety profile, a membranolytic index > 64 and low mammalian cell toxicity at effective bactericidal concentrations, TAT–ArgBD’s potential to enhance antibiotic efficacy, as well as function as a stand-alone treatment, supports further preclinical evaluation as an antimicrobial adjuvant.

Sponges are simple metazoans that build hierarchical mineral-organic architectures under ambient conditions, offering bioinspiration for lightweight, damage-tolerant structural materials. Yet the multiscale mechanics of freshwater sponges remain unexplored compared with well-studied marine species. Here we report the first quantitative investigation of an Amazonian freshwater sponge (Cauxi), linking its biogenic silica spicules and a double-shell, spicule-reinforced gemmule capsule to survival under alternating aquatic and subaerial conditions. Multiscale structural characterization combined with micro-/nanomechanical testing reveals that the silica spicules in Cauxi exhibit lower stiffness and toughness than fused glass, consistent with their amorphous, nanoporous structure. Micropillar tests show no statistically significant orientation dependence within experimental uncertainty, reflecting the spicules’ amorphous character. The gemmule architecture—two shells separated by a lightweight foam and reinforced by short spicules with star-like outer tips and disk-like inner bases—resists localized loading and suggests shell-buckling and rib-stiffening as operative protection principles. Building on these observations, we provide simple scaling arguments and testable predictions for buoyancy, dispersal by damage tolerance, positioning Cauxi as a model for lightweight, damage-tolerant capsules and short-fiber-reinforced composites formed under ambient conditions. These results articulate environment-specific structure–property trade-offs and offer generalizable cues for architected structural materials.

A low-temperature sintering mechanism of silver microparticles is established and used to enable the design-for-recycling of printed electronics. The formation of necks during the initial phase sintering of precipitated and atomized silver microparticles is studied. Temperature- and time-dependent in-situ analyses indicate the existence of a mobile silver species that provides efficient mass transport. The activation energy of neck formation identifies silver ion formation as the rate-limiting step of low-temperature silver sintering. It is demonstrated that resistivities of 271 times that of bulk silver can be attained after 40 minutes at 150°C. Low-temperature sintering not only reduces the energy required during thermal treatment but it yields layers that are suitable for recycling, too. The resulting layers have conductive necks that are mechanically weak enough to be broken during recycling. Printed layers are redispersed and the recycled silver powder is reused without loss of the electrical performance in new prints. Their conductivities are industrially relevant, which makes this recyclability-by-design approach promising for manufacturing more sustainable printed electronics.

Materials science research faces challenges due to diverse and evolving measurements, materials, and methods. Managing research data in a way that is understandable, comparable, and reproducible is essential for high data quality, particularly for data science and machine learning applications. In Li-ion batteries research data storage concepts and structures vary widely between institutions and researchers, leading to difficulties in data comparison and understanding. To address the issue of data structuring, battery production and characterization ontology (BPCO) is developed. The ontology builds on existing ontologies like the Platform MaterialDigital core ontology and quantities, units, dimensions, and types ontology to model standard battery production processes, characterization methods, and materials. The BPCO is based on a workflow structure to be accessible to nonexperts and, unlike highly specialized existing ontologies, models the whole production process removing the need for separate data structures and enabling the identification of dependencies between parameters. This work builds upon a previously published paper in which the taxonomy and fundamental strategies for ontology development are established. The article presents the developed ontology and its use for structuring research data in three key use cases, that is, different experiments performed to validate the ontology's capabilities, provide feedback, and ensure its applicability.

The significant demand for energy storage systems has spurred innovative designs and extensive research on lithium-ion batteries (LIBs). To that end, an in-depth examination of utilized materials and relevant methods in conjunction with comparing electrochemical mechanisms is required. Lithium titanate (LTO) anode materials have received substantial interest in high-performance LIBs for numerous applications. Nevertheless, LTO is limited due to capacity fading at high rates, especially in the extended potential range of 0.01–3.00 V versus Li+/Li, while delivering the theoretical capacity of 293 mAh g−1. This study demonstrates how the performance of the LTO anode can be improved by modifying the manufacturing process. Altering the dry and wet mixing duration and speeds throughout the manufacturing process leads to differences in particle sizes and homogeneity of dispersion and structure. The optimized anode at 5 A g−1 (≈17C) and 10 A g−1 (≈34C) yielded 188 and 153 mAh g−1 and retained 73% and 68% of their initial capacity after 1000 cycles, respectively. The following findings offer valuable information regarding the empirical modifications required during electrode fabrication. Additionally, it sheds light on the potential to produce efficient anodes using commercial LTO powder.