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PublicationComparison of Electronic Resistance Measurement Methods and Influencing Parameters for LMFP and High-Nickel NCM Cathodes( 2024)
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PublicationEuropean Hydrogen Infrastructure Planning( 2024)
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PublicationDesign of Laser Activated Antimicrobial Porous Tricalcium Phosphate-Hydroxyapatite Scaffolds for Orthopedic Applications( 2024)The field of bone tissue engineering is steadily being improved by novel experimental approaches. Nevertheless, microbial adhesion after scaffold implantation remains a limitation that could lead to the impairment of the regeneration process, or scaffold rejection. The present study introduces a methodology that employs laser-based strategies for the development of antimicrobial interfaces on tricalcium phosphate–hydroxyapatite (TCP-HA) scaffolds. The outer surfaces of the ceramic scaffolds with inner porosity were structured using a femtosecond laser (λ = 800 nm; τ = 70 fs) for developing micropatterns and altering local surface roughness. The pulsed laser deposition of ZnO was used for the subsequent functionalization of both laser-structured and unmodified surfaces. The impact of the fs irradiation was investigated by Raman spectroscopy and X-ray diffraction. The effects of the ZnO-layered ceramic surfaces on initial bacterial adherence were assessed by culturing Staphylococcus aureus on both functionalized and non-functionalized scaffolds. Bacterial metabolic activity and morphology were monitored via the Resazurin assay and microscopic approaches. The presence of ZnO evidently decreased the metabolic activity of bacteria and led to impaired cell morphology. The results from this study have led to the conclusion that the combination of fs laser-structured surface topography and ZnO could yield a potential antimicrobial interface for implants in bone tissue engineering.
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PublicationDynamische Modellierung und Regelung eines Festoxid-BrennstoffzellensystemsDie Anstrengungen zur Reduktion von Treibhausgasemissionen durch fossile Energieträger erfordern innovative Lösungsansätze. Neben dem Einsatz von effizienteren Energiewandlungstechnologien spielt Wasserstoff in der Planung auf nationaler Ebene eine wichtige Rolle. Er kann in einer möglichen Anwendung eingeschränkt in der bestehenden Erdgasinfrastruktur zwischengespeichert werden. In diesem Kontext können Festoxid-Brennstoffzellensysteme einen wesentlichen Beitrag leisten. Sie sind in der Lage, neben Wasserstoff auch fossile Energieträger mit einem hohen Wirkungsgrad umzusetzen. Insbesondere die Betriebsfähigkeit unter Erdgas mit schwankenden H2-Konzentrationen macht die Technologie zu einem potenziellen Baustein zukünftiger Energiesysteme. Ein störungsfreier und optimierter Anlagenbetrieb unter zeitlich fluktuierender Brenngaszusammensetzung bringt jedoch große Herausforderungen für das Regelkonzept mit sich. In der vorliegenden Arbeit wird eine vielversprechende Regelkreisarchitektur entwickelt, die ohne zusätzliche Messtechnik einen effizienten Systembetrieb selbst bei schwankender Gaszusammensetzung ermöglicht und somit einen Beitrag zur Markteinführung der Systeme leisten kann.
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Publication60 years open‐celled ceramics based on replica technique - Applications, obstacles and opportunities( 2024)Open-celled ceramics look back on a remarkable history of development and innovation spanning around 60 years. Starting with the first patents to produce ceramic foams in the 1960s, the Schwartzwalder process became established industrially for manufacturing molten metal filters. Since then, a wide range of potential applications for these specific structured materials has been identified and discussed in the literature, such as porous burners, direct heaters, structured catalyst supports, filters, bone substitute materials, energy absorbers, preforms, and lightweight or acoustic construction components. For such high-performance applications, ceramic foams require high quality in terms of purity, mechanical strength, high temperature and chemical resistance or structural design. On this account, production technologies and material variety of ceramic foams have developed rapidly over the past few decades, and there are numerous applications in the industrial sector. This paper gives an overview of the current state of development of open-celled ceramic foams for various applications. Based on selected examples, it is demonstrated for which applications an industrial implementation has been successfully realized and why some applications will never get beyond the proof-of-concept stage in research.
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PublicationGiant Blue Energy Harvesting in Two‐Dimensional Polymer Membranes with Spatially Aligned Charges( 2024)Blue energy between seawater and river water is attracting increasing interest, as one of the sustainable and renewable energy resources that can be harvested from water. Within the reverse electrodialysis applied in blue energy conversion, novel membranes with nanoscale confinement that function as selective ion transport mediums are currently in high demand for realizing higher power density. The primary challenge lies in constructing well-defined nanochannels that allow for low-energy barrier transport. This work proposes a concept for nanofluidic channels with a simultaneous dual electrostatic effect that can enhance both ion selectivity and flux. To actualize this, this work has synthesized propidium iodide-based two-dimensional polymer (PI-2DP) membranes possessing both skeleton charge and intrinsic space charge, which are spatially aligned along the ion transport pathway. The dual charge design of PI-2DP significantly enhances the electrostatic interaction between the translocating anions and the cationic polymer framework, and a high anion selectivity coefficient (≈0.8) is reached. When mixing standard artificial seawater and river water, this work achieves a considerable power density of 48.4 W m-2, outperforming most state-of-the-art nanofluidic membranes. Moreover, when applied between the Mediterranean Sea and the Elbe River, an output power density of 42.2 W m-2 is achieved by the PI-2DP. This nanofluidic membrane design with dual-layer charges will inspire more innovative development of ion-selective channels for blue energy conversion that will contribute to global energy consumption.
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PublicationCharacterization of Tannic Acid-Coated AZ31 Mg Alloy for Biomedical Application and Comparison with AZ91( 2024)Magnesium alloys are promising materials for bioresorbable implants that will improve patient life and reduce healthcare costs. However, their clinical use is prevented by the rapid degradation and corrosion of magnesium, which leads to a fast loss of mechanical strength and the formation of by-products that can trigger tissue inflammation. Here, a tannic acid coating is proposed to control the degradation of AZ31 and AZ91 alloys, starting from a previous study by the authors on AZ91. The coatings on the two materials were characterized both by the chemical (EDS, FTIR, XPS) and the morphological (SEM, confocal profilometry) point of view. Static degradation tests in PBS and electrochemical measurements in different solutions showed that the protective performances of the tannic acid coatings are strongly affected by the presence of cracks. The presence of fractures in the protective layer generates galvanic couples between the coating scales and the metal, worsening the corrosion resistance. Although degradation control was not achieved, useful insights on the degradation mechanisms of coated Mg surfaces were obtained, as well as key points for future studies: it resulted that the absence of cracks in protective coatings is of uttermost importance for novel biodegradable implants with proper degradation kinetics.
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PublicationBone regeneration in critical-size defects of the mandible using biomechanically adapted CAD/CAM hybrid scaffolds: An in vivo study in miniature pigs( 2024)Background: Facial cranial defects of critical size, typically resulting from tumor, inflammation, or trauma, lead to both aesthetic and functional limitations in patients, ultimately reducing their quality of life. The current gold standard for addressing these issues in the head and neck region involves autologous bone grafting. However, this approach has limitations relating to fit, availability, and morbidity associated with harvesting. An alternative approach with promise involves bone induction using 3D-engineered scaffolds and growth factors. Recent scaffold materials have exhibited insufficient mechanical properties for postoperative stability and physiological bone remodeling. Our study aimed to analyze bone regeneration in critical-size defects using hybrid scaffolds biomechanically adapted to the specific defect and adding the growth factor rhBMP-2. Materials and methods: For this animal study, ten minipigs underwent bilateral defects in the corpus mandibulae and were subsequently treated with novel cylindrical hybrid scaffolds. These scaffolds were designed digitally to suit the biomechanical requirements of the mandibular defect, utilizing finite element analysis. The scaffolds comprised zirconium dioxide-tricalcium phosphate (ZrO2-TCP) support struts and TCP foam ceramics. One scaffold in each animal was loaded with rhBMP-2 (100 μg/cm³), while the other served as an unloaded negative control. Fluorescent dyes were administered every 2 weeks, and computed tomography (CT) scans were conducted every 4 weeks. Euthanasia was performed after 3 months, and samples were collected for examination using micro-CT and histological evaluation of both hard and soft tissue. Results: Intravital CT examinations revealed minor changes in radiographic density from 4 to 12 weeks postoperatively. In the group treated with rhBMP-2, radiographic density shifted from 2513 ± 128 (mean ± SD) to 2606 ± 115 Hounsfield units (HU), while the group without rhBMP-2 showed a change from 2430 ± 131 to 2601 ± 67 HU. Prior to implantation, the radiological density of samples measured 1508 ± 30 mg HA/cm³, whereas post-mortem densities were 1346 ± 71 mg HA/cm³ in the rhBMP-2 group and 1282 ± 91 mg HA/cm³ in the control group (p = 0.045), as indicated by micro-CT measurements. The histological assessment demonstrated successful ossification in all specimens. The newly formed bone area proportion was significantly greater in the rhBMP-2 group (48 ± 10%) compared with the control group without rhBMP-2 (42 ± 9%, p = 0.03). The mean area proportion of remaining TCP foam was 23 ± 8% with rhBMP-2 and 24 ± 10% without rhBMP-2. Conclusion: Successful bone regeneration was accomplished by implanting hybrid scaffolds into critical-size mandibular defects. Loading these scaffolds with rhBMP-2 led to enhanced bone regeneration and a uniform distribution of new bone formation within the hybrid scaffolds. Further studies are required to determine the adaptability of hybrid scaffolds for larger and potentially segmental defects in the maxillofacial region.
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PublicationAn experimental investigation into the conversion of nuclear graphite by oxygen and carbon dioxide: Kinetics and change in pore structure( 2024)The study on the thermochemical conversion of release-measured nuclear-grade graphite recovered from the thermal column of a shut-down nuclear research reactor focuses on kinetic processes of gasification and oxidation of this graphite. More specifically, the kinetic parameters were determined and the evolution of the graphite structure during carbon conversion was investigated. For oxidation, the three conversion regimes of heterogeneous reactions in the temperature range of 500 °C to 950 °C were observed. The activation energy is approx. 288 kJ/mol in the kinetic regime limited by the chemical reaction (Regime I), approx. 185 kJ/mol in the pore diffusion regime (Regime II) and approx. 10 kJ/mol in the mass transfer regime (Regime III). With an increase of the partial pressure of oxygen, an increase of the pre-exponential factor in Regime I from 6.6 × 1012 1/s at 0.2 bar to 1.8 × 1013 1/s at 0.5 bar and to 2.0 × 1013 at 0.8 bar of oxygen was determined. A similar effect was observed in Regime II. A reaction order of 0.96 ± 0.16 was obtained for the oxidation reaction. In case of CO2 gasification at temperatures of 900 °C to 1400 °C, two regimes were identified. In Regime I, an activation energy of approx. 294 kJ/mol and a pre-exponential factor of 3.5 × 107 1/s were determined, the corresponding parameters being approx. 156 kJ/mol and 8.3 × 102 1/s for Regime II, respectively. Similar activation energy values for both oxidation and gasification reactions indicate that the structure of the nuclear graphite remains stable with proceeding carbon conversion. From the analysis of the development of the inner surface area and particle size distribution at increasing conversion rates, it can be concluded that the gasification of nuclear graphite mainly takes place on the outer surface. Using the ETV-ICP-OES analysis, it was found that the trace elements, Ca, Fe, S, V and Zn, were evaporated and no longer detectable in partially gasified nuclear graphite, whereas elements such as Ba, Cr or Mn are being accumulated in the solid resiude.
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PublicationAdvances in In Vitro blood-air barrier models and the use of nanoparticles in COVID-19 research( 2024)Respiratory infections caused by coronaviruses (CoVs) have become a major public health concern in the past two decades as revealed by the emergence of SARS-CoV in 2002, MERS-CoV in 2012, and SARS-CoV-2 in 2019. The most severe clinical phenotypes commonly arise from exacerbation of immune response following the infection of alveolar epithelial cells localized at the pulmonary blood-air barrier. Preclinical rodent models do not adequately represent the essential genetic properties of the barrier, thus necessitating the use of humanized transgenic models. However, existing monolayer cell culture models have so far been unable to mimic the complex lung microenvironment. In this respect, air-liquid interface (ALI) models, tissue engineered models, and organ-on-a-chip systems, which aim to better imitate the infection site microenvironment and microphysiology, are being developed to replace the commonly used monolayer cell culture models, and their use is becoming more widespread every day. On the other hand, studies on the development of nanoparticles that mimic respiratory viruses, and those nanoparticles used in therapy are progressing rapidly. The first part of this review describes in vitro models that mimic the blood-air barrier, the tissue interface that plays a central role in COVID-19 progression. In the second part of the review, nanoparticles mimicking the virus and/or designed to carry therapeutic agents are explained and exemplified.
