TY - JOUR A1 - Hornberger, Helga A1 - Kissel, Hannah A1 - Striegl, Birgit A1 - Kronseder, Matthias A1 - Vollnhals, Florian A1 - Christiansen, Silke H. T1 - Bioactivity and corrosion behavior of magnesium barrier membranes JF - Materials and Corrosion N2 - In the current research, magnesium and its alloys have been intensively studied as resorbable implant materials. Magnesium materials combine their good mechanical properties with bioactivity, which make them interesting for guided bone regeneration and for the application as barrier membranes. In this study, the in vitro degradation behavior of thin magnesium films was investigated in cell medium and simulated body fluid. Three methods were applied to evaluate corrosion rates: measurements of (i) the gaseous volume evolved during immersion, (ii) volume change after immersion, and (iii) polarization curves. In this comparison, measurements of H2 development in Dulbecco's modified Eagle's medium showed to be the most appropriate method, exhibiting a corrosion rate of 0.5 mm·year−1. Observed oxide and carbon contamination have a high impact on controlled degradation, suggesting that surface treatment of thin foils is necessary. The bioactivity test showed positive results; more detailed tests in this area are of interest. Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-24499 N1 - Corresponding author: Helga Hornberger VL - 73 IS - 1 SP - 8 EP - 19 PB - Wiley ER - TY - JOUR A1 - Stelzer, Vera A1 - Krenkel, Lars T1 - 2D numerical investigations derived from a 3D dragonfly wing captured with a high-resolution micro-CT JF - Technology and health care : official journal of the European Society for Engineering and Medicine N2 - BACKGROUND: Due to their corrugated profile, dragonfly wings have special aerodynamic characteristics during flying and gliding. OBJECTIVE: The aim of this study was to create a realistic 3D model of a dragonfly wing captured with a high-resolution micro-CT. To represent geometry changes in span and chord length and their aerodynamic effects, numerical investigations are carried out at different wing positions. METHODS: The forewing of a Camacinia gigantea was captured using a micro-CT. After the wing was adapted an error-free 3D model resulted. The wing was cut every 5 mm and 2D numerical analyses were conducted in Fluent® 2020 R2 (ANSYS, Inc., Canonsburg, PA, USA). RESULTS: The highest lift coefficient, as well as the highest lift-to-drag ratio, resulted at 0 mm and an angle of attack (AOA) of 5∘. At AOAs of 10∘ or 15∘, the flow around the wing stalled and a Kármán vortex street behind the wing becomes CONCLUSIONS: The velocity is higher on the upper side of the wing compared to the lower side. The pressure acts vice versa. Due to the recirculation zones that are formed in valleys of the corrugation pattern the wing resembles the form of an airfoil. KW - aerodynamics KW - computational fluid dynamics KW - Dragonfly wing KW - gliding flight KW - insect flight Y1 - 2022 U6 - https://doi.org/10.3233/THC-219010 N1 - Corresponding author: Vera Stelzer VL - 30 IS - 1 SP - 283 EP - 289 PB - IOS Press ER - TY - JOUR A1 - Tauwald, Sandra Melina A1 - Michel, Johanna A1 - Brandt, Marie A1 - Vielsmeier, Veronika A1 - Stemmer, Christian A1 - Krenkel, Lars T1 - Experimental studies and mathematical modeling of the viscoelastic rheology of tracheobronchial mucus from respiratory healthy patients JF - Multidisciplinary Respiratory Medicine N2 - BACKGROUND: Tracheobronchial mucus plays a crucial role in pulmonary function by providing protection against inhaled pathogens. Due to its composition of water, mucins, and other biomolecules, it has a complex viscoelastic rheological behavior. This interplay of both viscous and elastic properties has not been fully described yet. In this study, we characterize the rheology of human mucus using oscillatory and transient tests. Based on the transient tests, we describe the material behavior of mucus under stress and strain loading by mathematical models. METHODS: Mucus samples were collected from clinically used endotracheal tubes. For rheological characterization, oscillatory amplitude-sweep and frequency-sweep tests, and transient creep-recovery and stress-relaxation tests were performed. The results of the transient test were approximated using the Burgers model, the Weibull distribution, and the six-element Maxwell model. The three-dimensional microstructure of the tracheobronchial mucus was visualized using scanning electron microscope imaging. RESULTS: Amplitude-sweep tests showed storage moduli ranging from 0.1 Pa to 10000 Pa and a median critical strain of 4 %. In frequency-sweep tests, storage and loss moduli increased with frequency, with the median of the storage modulus ranging from 10 Pa to 30 Pa, and the median of the loss modulus from 5 Pa to 14 Pa. The Burgers model approximates the viscoelastic behavior of tracheobronchial mucus during a constant load of stress appropriately (R2 of 0.99), and the Weibull distribution is suitable to predict the recovery of the sample after the removal of this stress (R2 of 0.99). The approximation of the stress-relaxation test data by a six-element Maxwell model shows a larger fit error (R2 of 0.91). CONCLUSIONS: This study provides a detailed description of all process steps of characterizing the rheology of tracheobronchial mucus, including sample collection, microstructure visualization, and rheological investigation. Based on this characterization, we provide mathematical models of the rheological behavior of tracheobronchial mucus. These can now be used to simulate mucus flow in the respiratory system through numerical approaches. KW - tracheobronchial mucus KW - rheological model KW - viscoelasticity Y1 - 2023 U6 - https://doi.org/10.4081/mrm.2023.923 SN - 2049-6958 N1 - Corresponding author: Sandra Melina Tauwald VL - 18 IS - 1 PB - PAGEPress CY - Pavia, Italy ER - TY - JOUR A1 - Kriegl, Raphael A1 - Krenkel, Lars A1 - Shamonin (Chamonine), Mikhail T1 - Preservation of wetting ridges using field-induced plasticity of magnetoactive elastomers JF - Journal of Colloid and Interface Science N2 - Hypothesis. The presence of a wetting ridge is crucial for many wetting phenomena on soft substrates. Conventional experimental observations of a wetting ridge require permanent presence of a droplet. The magnetic field-induced plasticity effect (FIPE) of soft magnetoative elastomers (MAEs) allows one to overcome this limitation. Depositing a droplet onto an MAE surface and applying a magnetic field fixes the wetting ridge in place due to the FIPE. The droplet can be removed to investigate the ridge with ease using conventional optical methods. Experiments. The wetting ridge is observed on MAEs with different shear moduli and different material thicknesses by confocal laser scanning microscopy (LSM). The preservation quality of the ridge is analyzed for several values of magnetic field from 10 mT to 270 mT. To verify the plausibilty of results obtained, the measured shape is compared to a theoretical model by Style & Dufresne. Findings. Upon removal of the sessile droplet, the deformation remains embossed onto the MAE surface as long as the magnetic field remains applied. The height of the ridge peak on soft samples (effective shear modulus kPa) is close to the theoretical prediction for a magnetic flux density of 50 mT. The magnitude of the external magnetic field magnifies the height of the wetting ridge. KW - Wetting ridge KW - Droplet KW - Magnetoactive elastomer KW - Magnetorheological elastomer KW - Field-induced plasticity KW - Confocal laser scanning microscopy Y1 - 2025 U6 - https://doi.org/10.1016/j.jcis.2024.12.132 SN - 0021-9797 N1 - Corresponding author der OTH Regensburg: Raphael Kriegl VL - 683 SP - 1019 EP - 1027 PB - Elsevier ER - TY - JOUR A1 - Kloiber, Jessica A1 - Anetsberger, Viktoria A1 - Schultheiß, Ulrich A1 - Hornberger, Helga T1 - High quality surfaces of magnesium alloy AZ31 by adjusting appropriate electropolishing parameters JF - Electrochimica Acta Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-79298 N1 - Corresponding author der OTH Regensburg: Jessica Kloiber VL - 513 PB - Elsevier ER - TY - JOUR A1 - Kloiber, Jessica A1 - Schultheiß, Ulrich A1 - Hornberger, Helga T1 - Impact of heat treatment on the surface quality of electropolished WE43 alloy JF - Materials Letters N2 - In this study, the Mg alloy WE43 was solution annealed and precipitation hardened prior to electropolishing to evaluate the effects of different microstructures on the electropolishing result. While coarsely distributed precipitates led to surfaces showing wavy structures and dents after electropolishing, a uniform microstructure resulted in an even finish of the surface. The homogenization and refinement of the microstructure by heat treatment is a method to ensure improved electropolished surfaces of Mg materials Y1 - 2025 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-83512 SN - 0167-577X N1 - Corresponding author der OTH Regensburg: Jessica Kloiber VL - 397 PB - Elsevier BV ER - TY - JOUR A1 - Loo, Xuyan A1 - Nagaraju, Bhavana A1 - Pathivada, Sai A1 - Bartsch, Alexander A1 - Schratzenstaller, Thomas A1 - Sattler, Robert A1 - Monkman, Gareth J. T1 - Electrical properties of bisphenol-A-free magnetoactive borosilicate polymers JF - AIP Advances N2 - The recent REACH regulations require the elimination of bisphenol-A and titanium dioxide from commercially available boron-based polymers. This has led to changes in some of the mechanical characteristics, which strongly influence the properties of magnetoactive borosilicate polymers. This work delivers results on the electrical properties and discusses some implications for future research using bisphenol-A and titanium-dioxide-free substitutes. KW - Electrical components KW - Electrical properties and parameters KW - Dielectric properties KW - Electrical resistivity KW - Magnetic materials KW - Viscoelasticity KW - Polymers KW - Non Newtonian fluids KW - Magnetic fluids Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-72936 SN - 2158-3226 N1 - Corresponding author der OTH Regensburg: Gareth J. Monkman VL - 14 IS - 5 PB - AIP Publishing ER - TY - JOUR A1 - Wiesent, Lisa A1 - Schultheiß, Ulrich A1 - Lulla, Philipp A1 - Noster, Ulf A1 - Schratzenstaller, Thomas A1 - Schmid, Christof A1 - Nonn, Aida A1 - Spear, Ashley T1 - Computational analysis of the effects of geometric irregularities and post-processing steps on the mechanical behavior of additively manufactured 316L stainless steel stents JF - PLoS ONE N2 - Advances in additive manufacturing enable the production of tailored lattice structures and thus, in principle, coronary stents. This study investigates the effects of process-related irregularities, heat and surface treatment on the morphology, mechanical response, and expansion behavior of 316L stainless steel stents produced by laser powder bed fusion and provides a methodological approach for their numerical evaluation. A combined experimental and computational framework is used, based on both actual and computationally reconstructed laser powder bed fused stents. Process-related morphological deviations between the as-designed and actual laser powder bed fused stents were observed, resulting in a diameter increase by a factor of 2-2.6 for the stents without surface treatment and 1.3-2 for the electropolished stent compared to the as-designed stent. Thus, due to the increased geometrically induced stiffness, the laser powder bed fused stents in the as-built (7.11 ± 0.63 N) or the heat treated condition (5.87 ± 0.49 N) showed increased radial forces when compressed between two plates. After electropolishing, the heat treated stents exhibited radial forces (2.38 ± 0.23 N) comparable to conventional metallic stents. The laser powder bed fused stents were further affected by the size effect, resulting in a reduced yield strength by 41% in the as-built and by 59% in the heat treated condition compared to the bulk material obtained from tensile tests. The presented numerical approach was successful in predicting the macroscopic mechanical response of the stents under compression. During deformation, increased stiffness and local stress concentration were observed within the laser powder bed fused stents. Subsequent numerical expansion analysis of the derived stent models within a previously verified numerical model of stent expansion showed that electropolished and heat treated laser powder bed fused stents can exhibit comparable expansion behavior to conventional stents. The findings from this work motivate future experimental/numerical studies to quantify threshold values of critical geometric irregularities, which could be used to establish design guidelines for laser powder bed fused stents/lattice structures. KW - Heat treatment KW - Lasers KW - Surface treatments KW - Specimen preparation and treatment KW - Material properties KW - Stiffness KW - Deformation KW - Powders KW - Koronarendoprothese KW - Rapid prototyping KW - Numerische Methode Y1 - 2020 U6 - https://doi.org/10.1371/journal.pone.0244463 N1 - Corresponding author: Lisa Wiesent VL - 15 IS - 12 SP - 1 EP - 30 PB - PLOS ER - TY - JOUR A1 - Tauwald, Sandra Melina A1 - Erzinger, Florian A1 - Quadrio, Maurizio A1 - Rütten, Markus A1 - Stemmer, Christian A1 - Krenkel, Lars T1 - Tomo-PIV in a patient-specific model of human nasal cavities: a methodological approach JF - Measurement Science and Technology N2 - The human nose serves as the primary gateway for air entering the respiratory system and plays a vital role in breathing. Nasal breathing difficulties are a significant health concern, leading to substantial healthcare costs for patients. Understanding nasal airflow dynamics is crucial for comprehending respiratory mechanisms. This article presents a detailed study using tomo-Particle Image Velocimetry (PIV) to investigate nasal airflow dynamics while addressing its accuracy. Embedded in the OpenNose project, the work described aims to provide a validation basis for different numerical approaches to upper airway flow. The study includes the manufacturing of a transparent silicone model based on a clinical CT scan, refractive index matching to minimize optical distortions, and precise flow rate adjustments based on physiological breathing cycles. This method allows for spatial high-resolution investigations in different regions of interest within the nasopharynx during various phases of the breathing cycle. The results demonstrate the accuracy of the investigations, enabling detailed analysis of flow structures and gradients. This spatial high-resolution tomo-PIV approach provides valuable insights into the complex flow phenomena occurring during the physiological breathing cycle in the nasopharynx. The study's findings contribute to advancements in non-free-of-sight experimental flow investigation of complex cavities under nearly realistic conditions. Furthermore, reliable and accurate experimental data is crucial for properly validating numerical approaches that compute this patient-specific flow for clinical purposes. Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:898-opus4-70393 N1 - Corresponding author: Sandra Melina Tauwald VL - 35 IS - 5 PB - IOP Publishing ER - TY - JOUR A1 - Thema, Martin A1 - Weidlich, Tobias A1 - Hörl, Manuel A1 - Bellack, Annett A1 - Mörs, Friedemann A1 - Hackl, Florian A1 - Kohlmayer, Matthias A1 - Gleich, Jasmin A1 - Stabenau, Carsten A1 - Trabold, Thomas A1 - Neubert, Michael A1 - Ortloff, Felix A1 - Brotsack, Raimund A1 - Schmack, Doris A1 - Huber, Harald A1 - Hafenbradl, Doris A1 - Karl, Jürgen A1 - Sterner, Michael T1 - Biological CO2-Methanation: An Approach to Standardization JF - Energies N2 - Power-to-Methane as one part of Power-to-Gas has been recognized globally as one of the key elements for the transition towards a sustainable energy system. While plants that produce methane catalytically have been in operation for a long time, biological methanation has just reached industrial pilot scale and near-term commercial application. The growing importance of the biological method is reflected by an increasing number of scientific articles describing novel approaches to improve this technology. However, these studies are difficult to compare because they lack a coherent nomenclature. In this article, we present a comprehensive set of parameters allowing the characterization and comparison of various biological methanation processes. To identify relevant parameters needed for a proper description of this technology, we summarized existing literature and defined system boundaries for Power-to-Methane process steps. On this basis, we derive system parameters providing information on the methanation system, its performance, the biology and cost aspects. As a result, three different standards are provided as a blueprint matrix for use in academia and industry applicable to both, biological and catalytic methanation. Hence, this review attempts to set the standards for a comprehensive description of biological and chemical methanation processes. KW - Biological methanation KW - bubble column reactor KW - CO2-methanation KW - CSTR KW - membrane reactor KW - methanation KW - Power-to-Gas KW - Power-to-Methane KW - standardization KW - Trickle-bed reactor Y1 - 2019 U6 - https://doi.org/10.3390/en12091670 N1 - Corresponding author: Martin Thema VL - 12 IS - 9 SP - 1 EP - 32 PB - MDPI ER -