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Item type:Publication, Access status: with files , Lagrangian μ-particle tracking velocimetry analysis of microscale flow over structured surfaces(American Chemical Society (ACS), 2026-10-08); ; ; ; This work aims to provide an experimental basis for the improvement of (bio)reactors by studying flow over micro- and nanostructured surfaces, with a focus on microscale mass transport toward and away from the surface. μ-Particle tracking velocimetry is employed in a microreactor to experimentally obtain Lagrangian trajectories of flow-following tracer particles. The method also resolves three-dimensional, time-dependent velocity fields. The derived mean velocity profiles agree well with the theory of flow over porous walls. Beyond averaged Eulerian velocities, the Lagrangian framework captures near-surface interactions. The Lagrangian analysis of different surfaces indicates that rectangular structured microgrooves increase the wall contact of the tracer particles, especially when the flow is oriented perpendicular to the microgrooves. Particularly, this approach enables resolution of trapping phenomena and localized recirculation dynamics. Nanostructuring by growing a carbon nanotube forest increases surface area and modifies local fluid dynamics, thereby enhancing contact with (bio)catalysts that are potentially functionalized on the nanotubes in future applications.Publicationtype: Journal Article41 15 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Millimeter-scale Lagrangian sensor spheres for local state monitoring in SMART reactors: towards energy-autonomous operation(American Chemical Society (ACS), 2026-09-18); ; ; ; Flow-following sensor particles are a promising route to obtaining spatially resolved measurements in (bio)chemical reactors. However, their practical deployment is limited by miniaturization, power supply, and packaging. This work presents a millimeter-scale Lagrangian sensor-node platform that integrates an inertial measurement unit (IMU) and a low-power microcontroller unit (MCU) on a high-density interconnect (HDI) printed circuit board (PCB), illustrating the evolution from a first demonstrator (V1) toward a reduced-footprint design (V2) intended for spherical encapsulation. The main contribution is a quantitative system-level feasibility boundary that links miniaturized sensor-node design, duty-cycled energy demand, candidate energy-input routes, and spherical packaging constraints at the targeted millimeter scale. We analyze the baseline power demand of the current duty-cycled implementation, including a cycle-based charge and energy budget, and relate this demand to two experimentally investigated energy-input routes: photovoltaic harvesting under controlled optical illumination and resonant inductive power transfer at 13.56 MHz. The harvesting experiments are performed on dedicated evaluation platforms and are used to quantify candidate energy-input routes. A closed energy-autonomous sensor-in-flow demonstration is not yet claimed. The results show that the platform concept, compact HDI integration, low-power duty cycling, optical data transmission, and a glass-based encapsulation route are technically feasible at the targeted size. At the same time, neither harvesting route yet closes the gap to robust energy-autonomous operation under realistic reactor conditions. Photovoltaic powering appears strongly constrained by alignment, optical access, and geometric coupling. Inductive transfer is more promising but remains highly sensitive to orientation, field distribution, and RF-to-DC conversion efficiency. The presented measurements therefore define both the current feasibility range and the remaining engineering requirements for future energy-autonomous sensor spheres.Publicationtype: Journal Article42 22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Advanced micromolding approach toward scaling-up smart hydrogel microvalves(American Chemical Society (ACS), 2026-09-09); ; ; Smart hydrogel valves are a promising technology for autonomous process control. At the macroscale, hydrogel valves offer high flow rates with slow response times, whereas hydrogel microvalves offer low flow rates with fast response times. This contradiction limits the practical applicability of these valves, particularly in industry. Scaling-up refers to the process of transferring the benefits and results of microfluidics from the laboratory scale to the production scale. In this paper, we present advanced fabrication methods and corresponding promising concepts toward scaling-up responsive hydrogel microvalves to achieve higher throughput while maintaining fast response times. Using selective laser-induced etching (SLE), precise three-dimensional (3D) microfluidic structures and corresponding molds can be produced from fused silica, allowing hydrogel to be molded and anchored directly within the microchannel. This method enables the sizing-up of hydrogel microstructures in both horizontal and vertical directions. The influence of this scaling, in the form of various hydrogel dimensions up to 1500 μm, was investigated with regard to their suitability for an autonomous hydrogel valve. As a proof-of-principle, three hydrogel valves with different depths were fabricated using this method, whereby the response time decreases with increasing depth while the flow rate is increased simultaneously.Publicationtype: Journal Article84 17 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , NMR relaxometry probes solvent-polarity-dependent molecular interactions in stimuli-responsive lyogels(Royal Society of Chemistry (RSC), 2026-01-14); ; ; ; Stimuli-responsive gels demonstrate macroscopic changes upon exposure to external stimuli, offering potential for the development of adaptive chemical reactors. Early investigations into hydrogels established that crosslinked polymer networks experience reversible volume phase transitions, with temperature, pH, and solvent composition governing swelling and shrinking dynamics. Although hydrogels behavior in aqueous environments has been extensively characterized, lyogels that incorporate organic solvents remain comparatively underexplored, despite their potential for enhanced chemical compatibility and functional versatility. Here, we investigate how solvent polarity and crosslinking density govern the swelling behavior, pore formation, and molecular-scale dynamics of poly(N-isopropylacrylamide)-based lyogels. Using a combination of swelling measurement, scanning electron microscopy, and multiscale NMR relaxometry and diffusometry, we demonstrate that solvent polarity fundamentally alters lyogel structure and dynamics. Lyogels swollen in a high-polarity solvent exhibits macroporous networks and slower solvent exchange rates, whereas a low-polarity solvent induces shrinkage, denser microstructures, faster solvent exchange rates, and stronger surface interactions. These results establish a mechanistic framework linking thermodynamic affinity, solvent dynamics, and microstructural confinement to macroscopic gel responsiveness. This framework provides guidance for tailoring lyogels in dynamic environments, with potential applications in adaptable and tunable chemical reactors.Publicationtype: Journal Article25 52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , NMR Relaxometry for Molecular Structure Analysis of Stimuli-Responsive Lyogels in Varied Solvent PolaritiesIntroduction: Stimuli-responsive lyogels exhibit pronounced macroscopic changes in response to external stimuli, positioning them as promising candidates for applications such as flow control valves and catalyst carriers in SMART reactors [1]. For their effective integration in such systems, it is essential to understand their internal pore structure and diffusion behavior, as these factors directly influence functionality. While several techniques exist to quantify macroscopic swelling and shrinking, few methods provide insight into the microstructural transformations occurring during these processes. Methods: To address this gap, we employed ¹H Nuclear Magnetic Resonance (NMR) relaxometry and diffusometry to study solvent dynamics within lyogels under different environmental conditions. NMR is particularly well-suited for examining molecular mobility within macro-, meso-, and nanoporous systems by detecting changes in relaxation times and self-diffusion coefficients [2, 3]. Using a Spinsolve 60 MHz benchtop NMR spectrometer (Magritek, Germany), we investigated the dynamic swelling and shrinking behavior of lyogels in solvents with differing polarity. Results and discussion: Our measurements revealed significant variations in the relaxation time profiles depending on solvent polarity, reflecting changes in molecular mobility and pore structure during swelling and shrinking (Fig. 1). These relaxation dynamics provide valuable insights into the solvent-polymer interactions at the microstructural level, which are often inaccessible by traditional swelling ratio measurements. The data suggest that solvent polarity play a critical role in modulating the internal morphology and transport behavior of lyogels. Conclusion: ¹H NMR relaxometry proves to be an effective tool for probing the microstructural evolution of stimuli-responsive lyogels. By offering detailed insights into solvent dynamics and polymer-solvent interactions, this method supports the rational design and integration of lyogels in SMART reactor technologies and other responsive material applications. References: [1] Eckert, Fluid Phase Equilibria. (2024). [2] Giussi, Soft Matter. (2015). [3] Gruber, Polymer. (2023).Publicationtype: Conference Poster68 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Development of an oxygen-sensitive hydrogel for monitoring oxygen diffusion in tissue engineeringAdditive manufacturing has revolutionized the development of biomaterials by enabling precise control over structural properties at the microscale. In tissue engineering, oxygen transport remains a major challenge, particularly in the development of vascularized artificial tissues. To address this, we present an oxygen-sensitive hydrogel fabricated using one-photon polymerization and two-photon polymerization (2PP), designed for real-time observation of oxygen diffusion characteristics. The hydrogel, based on polyethylene glycol diacrylate (PEGDA), incorporates oxygen-sensitive dyes to enable a colorimetric response to varying oxygen concentrations. The hydrogel formulation and fabrication were optimized for biocompatibility, tunable permeability, and stable optical readout. Diffusion experiments were conducted to analyze the oxygen transport behavior under different conditions, including variations in hydrogel thickness and environmental oxygen levels. The results demonstrate that the hydrogel allows for controlled oxygen diffusion, provides a measurable response to oxygen gradients and that the hydrogel’s permeability can be tailored via additive manufacturing. This approach offers a valuable tool for studying oxygen supply in engineered tissues and could enhance the design of microfluidic organ-on-a-chip systems. Our findings indicate that oxygen-sensitive hydrogels hold great potential for improving in vitro tissue models by enabling precise monitoring of oxygen distribution, which is essential for cell viability and function. Future research will focus on integrating these hydrogels into microfluidic systems to simulate vascularized environments more accurately.Publicationtype: Journal Article22 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , NMR relaxometry for molecular structure analysis of stimuli-responsive lyogels in varied solvent polaritiesStimuli-responsive lyogels undergo significant macroscopic changes under external stimuli, making them ideal for applications like flow control valves or catalyst carriers in SMART reactors [1]. However, effective integration requires understanding their pore structure and diffusion behavior under various conditions, as this influences functionality. While several methods assess macroscopic swelling/shrinking, few provide microstructural insights into their swelling and shrinking state. Nuclear Magnetic Resonance (NMR) is a suitable tool for the study of solvent dynamics inside macro, meso, and nanopores, through changes in their relaxation times and self-diffusion coefficients. Although 1H NMR relaxometry has been widely used to investigate the in-situ swelling behavior of hydrogels, microgels, and different polymer matrices [2, 3], there is still limited research on the dynamic swelling/shrinking behavior of lyogels in pure and/or mixtures of solvents of varying polarity. In this work, we use 1H NMR relaxometry measurements (Spinsolve 60, Magritek) to investigate the microstructural changes of lyogels under different stimuli. By analyzing relaxation dynamics, we examine how molecular interactions and structural modifications respond to solvents of different polarity. These insights enhance our understanding of the physicochemical behavior of organic systems and their interactions with diverse environments. References: [1] K. M. Eckert, et al., Fluid Phase Equilibria 586 (2024) 114182. [2] J. M. Giussi, et al., Soft Matter 11.45 (2015) 8879-8886. [3] D. M. Gruber, M. S. Ferris, G. Zabow, Polymer 281 (2023) 126108.Publicationtype: Conference Poster34 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enhancing the applicability of femtosecond laser written waveguides in fused silicaFemtosecond laser structuring of transparent materials is becoming increasingly relevant and useful due to its ability to pattern 3D structures, especially when Micro-Electro-Mechanical-Systems (MEMS) are getting more complex. Similarly, the possibility of integrating waveguides into transparent materials increases the potential of this technology and can further enhance the complexity of manufactured systems. This paper examines femtosecond laser written (FLW) waveguides and identifies challenges in their applicability. In addition, strategies and approaches for enhancing the applicability of waveguides are explored.Publicationtype: Conference Paper52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Development of a microfluidic chip with integrated hydrogel membranes for tissue engineering applicationsThe integration of permeable hydrogel membranes into microfluidic glass chips enables novel applications in tissue engineering by mimicking capillary-like mass transport in vitro. This work describes a seamless process for fabricating fused silica chips and directly integrating hydrogel membranes using a single femtosecond laser system. This unification of Selective Laser-Induced Etching (SLE) and Two-Photon Polymerization (2PP) in one workflow eliminates system changes and enables precise alignment between rigid chip structures and soft functional membranes. The membranes are polymerized directly within structured microchannels sealed by a laser-welded glass lid. This allows for tunable and mechanically stable membrane structures embedded in a biocompatible, rigid substrate. The work focuses on the process development, material behavior during integration, and membrane positioning within the chip.Publicationtype: Conference Paper68 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Enhancing the 3D patterning of MEMS : an extended toolbox(2023-10-23); ; Micro-Electro-Mechanical-Systems (MEMS) are nowadays indispensable and typically fabricated using semiconductor technology methods. As the systems are getting more complex, methods for 3D patterning in MEMS become more relevant and useful. At the same time, established methods from 3D printing getting more precise and gaining ground in the fabrication of MEMS. Within this work, an approach for an extended toolbox is presented, which integrates the often one-step processes of 3D patterning into thetypically iterative process flows composed of the traditional semiconductor technology methods and thus improves the capabilities for the fabrication of 3D MEMS. For this, methods of 3D printing and 3D patterning in-volume and on surface are investigated with regard to compatibility with methods of the traditional semiconductor technology.Publicationtype: Conference Paper29