388 results
Search Results
Now showing 1 - 10 of 388
- ItemSpontaneous fluctuations in a plasma ion assisted deposition – correlation between deposition conditions and vanadium oxide thin film growth(Amsterdam [u.a.] : Elsevier, 2021) Frank, Anna; Dias, Miguel; Hieke, Stefan; Kruth, Angela; Scheu, ChristinaIn this work correlations between thin film crystallinity of plasma ion assisted electron beam evaporated vanadium oxide (VOx) and fluctuations of the deposition parameters during the growth process could be observed by in situ monitoring deposition conditions and electron microscopy studies. In the presented case, unintentional fluctuations in the gas flow at the plasma source caused by inhomogeneous melting of the target material lead to an increase in discharge current and therefore a decrease of the oxygen flow in the plasma source, resulting in the formation of highly crystalline bands due to a temporary increase in energy flux. The major part of the VOx thin film consists of a large number of nanocrystals embedded in an amorphous phase. In-depth structural analysis confirms a mixture of V2O5, in different modifications, VO2, as well as the mixed-valence oxides V4O9 and V6O13, for nanocrystalline parts and crystalline bands. These differ mainly in the degree of crystallinity being influenced by variations in discharge current, and partly in the amount of higher oxidized vanadium oxides. In future, precisely controlled variation of plasma source conditions will open up pathways to control and tailor crystallinity of electron beam evaporated thin films, allowing for production methods for patterned thin films or layers with graduated crystallinity. This may give rise to a new class of coatings of nanohybrids combining amorphous VOx with low electrical conductivity and crystalline domains providing a higher electrical conductivity which is useful for electrochromic displays, smart windows, and solar cells.
- ItemNonspherical Nanoparticle Shape Stability Is Affected by Complex Manufacturing Aspects: Its Implications for Drug Delivery and Targeting(Weinheim : Wiley-VCH, 2019) Haryadi, Bernard Manuel; Hafner, Daniel; Amin, Ihsan; Schubel, Rene; Jordan, Rainer; Winter, Gerhard; Engert, JuliaThe shape of nanoparticles is known recently as an important design parameter influencing considerably the fate of nanoparticles with and in biological systems. Several manufacturing techniques to generate nonspherical nanoparticles as well as studies on in vitro and in vivo effects thereof have been described. However, nonspherical nanoparticle shape stability in physiological-related conditions and the impact of formulation parameters on nonspherical nanoparticle resistance still need to be investigated. To address these issues, different nanoparticle fabrication methods using biodegradable polymers are explored to produce nonspherical nanoparticles via the prevailing film-stretching method. In addition, systematic comparisons to other nanoparticle systems prepared by different manufacturing techniques and less biodegradable materials (but still commonly utilized for drug delivery and targeting) are conducted. The study evinces that the strong interplay from multiple nanoparticle properties (i.e., internal structure, Young's modulus, surface roughness, liquefaction temperature [glass transition (Tg) or melting (Tm)], porosity, and surface hydrophobicity) is present. It is not possible to predict the nonsphericity longevity by merely one or two factor(s). The most influential features in preserving the nonsphericity of nanoparticles are existence of internal structure and low surface hydrophobicity (i.e., surface-free energy (SFE) > ≈55 mN m−1, material–water interfacial tension <6 mN m−1), especially if the nanoparticles are soft (<1 GPa), rough (Rrms > 10 nm), porous (>1 m2 g−1), and in possession of low bulk liquefaction temperature (<100 °C). Interestingly, low surface hydrophobicity of nanoparticles can be obtained indirectly by the significant presence of residual stabilizers. Therefore, it is strongly suggested that nonsphericity of particle systems is highly dependent on surface chemistry but cannot be appraised separately from other factors. These results and reviews allot valuable guidelines for the design and manufacturing of nonspherical nanoparticles having adequate shape stability, thereby appropriate with their usage purposes. Furthermore, they can assist in understanding and explaining the possible mechanisms of nonspherical nanoparticles effectivity loss and distinctive material behavior at the nanoscale. © 2019 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
- ItemInfluence of redox stress on crosstalk between fibroblasts and keratinocytes(Basel : MDPI, 2021) Bhartiya, Pradeep; Masur, Kai; Shome, Debarati; Kaushik, Neha; Nguyen, Linh N.; Kaushik, Nagendra Kumar; Choi, Eun HaAlthough the skin is constantly subjected to endogenous and exogenous stress, it maintains a homeostatic state through wound repair and regeneration pathways. Treatment for skin diseases and injury requires a significant understanding of the various mechanisms and interactions that occur within skin cells. Keratinocytes and fibroblasts interact with each other and act as key players in the repair process. Although fibroblasts and keratinocytes are widely studied in wound healing and skin remodeling under different conditions, the influence of redox stress on keratinocyte-fibroblast crosstalk has not been thoroughly investigated. In this study, we used cold atmospheric plasma (CAP) to generate and deliver oxidative stress to keratinocytes and fibroblasts and to assess its impact on their interactions. To this end, we used a well-established in vitro 3D co-culture model imitating a realistic scenario. Our study shows that low CAP exposure is biocompatible and does not affect the viability or energetics of fibroblasts and keratinocytes. Exposure to low doses of CAP enhanced the proliferation rate of cells and stimulated the expression of key genes (KGF, MMP2, GMCSF, IL-6, and IL-8) in fibroblasts, indicating the activation and initiation of the skin repair process. Additionally, enhanced migration was observed under co-culture conditions under the given redox stress conditions, and expression of the upstream regulator and the effectors of the Hippo pathway (YAP and CYR61, respectively), which are associated with enhanced migration, were elevated. Overall, this study reinforces the application of CAP and redox stress in skin repair physiology.
- ItemOn the fundamental relation of laser schlieren deflectometry for temperature measurements in filamentary plasmas(Les Ulis : EDP Sciences, 2015) Schäfer, Jan; Bonaventura, Zdeněk; Foest, RüdigerRecently, laser schlieren deflectometry (LSD) had been successfully employed as a temperature measurement method to reveal the heat convection generated by micro filaments of a self-organized non-thermal atmospheric plasma jet. Based on the theory of the temperature measurements using LSD, in this work, three approaches for an application of the method are introduced: (i) a hyperbolic-like model of refractive index is applied which allows an analytical theory for the evaluation of the deflection angle to be developed, (ii) a Gaussian shape model for the filament temperature is implemented which is analyzed numerically and (iii) an experimental calibration of the laser deflection with a gas mixture of helium and argon is performed. Thus, these approaches demonstrate that a universal relation between the relative maximum temperature of the filament core (T1/T0) and a the maximum deflection angle δ1 of the laser beam can be written as T1/T0=(1 − δ1/δ0)−1, where δ0 is a parameter that is defined by the configuration of the experiment and by the assumed model for the shape of the temperature profile.
- ItemPlasma-derived reactive species shape a differentiation profile in human monocytes(Basel : MDPI, 2019) Freund, Eric; Moritz, Juliane; Stope, Matthias; Seebauer, Christian; Schmidt, Anke; Bekeschus, SanderBackground: Monocyte-derived macrophages are key regulators and producers of reactive oxygen and nitrogen species (ROS/RNS). Pre-clinical and clinical studies suggest that cold physical plasma may be beneficial in the treatment of inflammatory conditions via the release of ROS/RNS. However, it is unknown how plasma treatment affects monocytes and their differentiation profile. Methods: Naïve or phorbol-12-myristate-13-acetate (PMA)-pulsed THP-1 monocytes were exposed to cold physical plasma. The cells were analyzed regarding their metabolic activity as well as flow cytometry (analysis of viability, oxidation, surface marker expression and cytokine secretion) and high content imaging (quantitative analysis of morphology. Results: The plasma treatment affected THP-1 metabolisms, viability, and morphology. Furthermore, a significant modulation CD55, CD69, CD271 surface-expression and increase of inflammatory IL1β, IL6, IL8, and MCP1 secretion was observed upon plasma treatment. Distinct phenotypical changes in THP-1 cells arguing for a differentiation profile were validated in primary monocytes from donor blood. As a functional outcome, plasma-treated monocytes decreased the viability of co-cultured melanoma cells to a greater extent than their non-treated counterparts. Conclusions: Our results suggest plasma-derived ROS/RNS shaped a differentiation profile in human monocytes as evidenced by their increased inflammatory profile (surface marker and cytokines) as well as functional outcome (tumor toxicity). © 2019 by the authors.
- ItemPlasma-oxidative degradation of polyphenolics – Influence of non-thermal gas discharges with respect to fresh produce processing(Prague : ČSAZV, 2009) Grzegorzewski, F.; Schlüter, O.; Ehlbeck, J.; Weltmann, K.-D.; Geyer, M.; Kroh, L.W.; Rohn, S.Non-thermal plasma treatment is a promising technology to enhance the shelf-life of fresh or minimaly processed food. An efficient inactivation of microorganisms comes along with a moderate heating of the treated surface. To elucidate the influence of highly reactive plasma-immanent species on the stability and chemical behaviour of phytochemicals, several polyphenolics were exposed to an atmospheric pressure plasma jet (APPJ). The selected flavonoids are ideal target compounds due to their antioxidant activity protecting cells against the damaging effects of reactive oxygen species such as singlet oxygen, superoxide, peroxyl radicals, hydroxyl radicals and peroxynitrite. Reactions were carried out at various radio-frequency voltages, using Ar as a feeding gas. Degradation was followed by reversed-phase high-performance liquid chromatography.
- ItemEnhanced reliability of drift-diffusion approximation for electrons in fluid models for nonthermal plasmas(New York, NY : American Inst. of Physics, 2013) Becker, M.M.; Loffhagen, D.Common fluid models used for the description of electron transport in nonthermal discharge plasmas are subject to substantial restrictions if the electron energy transport significantly influences the discharge behaviour. A drift-diffusion approach is presented which is based on a multiterm approximation of the electron velocity distribution function and overcomes some of these restrictions. It is validated using a benchmark model and applied for the analysis of argon discharge plasmas at low and atmospheric pressure. The results are compared to those of common drift-diffusion models as well as to experimental data. It is pointed out that fluid models are able to describe nonlocal phenomena caused by electron energy transport, if the energy transport is consistently described. Numerical difficulties that frequently occur when the conventional drift-diffusion model is consistently applied are avoided by the proposed method.
- ItemMolecular mechanisms of the efficacy of cold atmospheric pressure plasma (CAP) in cancer treatment(Basel : MDPI AG, 2020) Semmler, Marie Luise; Bekeschus, Sander; Schäfer, Mirijam; Bernhardt, Thoralf; Fischer, Tobias; Witzke, Katharina; Seebauer, Christian; Rebl, Henrike; Grambow, Eberhard; Vollmar, Brigitte; Nebe, J. Barbara; Metelmann, Hans-Robert; Woedtke, Thomas von; Emmert, Steffen; Boeckmann, LarsRecently, the potential use of cold atmospheric pressure plasma (CAP) in cancer treatment has gained increasing interest. Especially the enhanced selective killing of tumor cells compared to normal cells has prompted researchers to elucidate the molecular mechanisms for the efficacy of CAP in cancer treatment. This review summarizes the current understanding of how CAP triggers intracellular pathways that induce growth inhibition or cell death. We discuss what factors may contribute to the potential selectivity of CAP towards cancer cells compared to their non-malignant counterparts. Furthermore, the potential of CAP to trigger an immune response is briefly discussed. Finally, this overview demonstrates how these concepts bear first fruits in clinical applications applying CAP treatment in head and neck squamous cell cancer as well as actinic keratosis. Although significant progress towards understanding the underlying mechanisms regarding the efficacy of CAP in cancer treatment has been made, much still needs to be done with respect to different treatment conditions and comparison of malignant and non-malignant cells of the same cell type and same donor. Furthermore, clinical pilot studies and the assessment of systemic effects will be of tremendous importance towards bringing this innovative technology into clinical practice. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- ItemNumerical analysis of the effect of nitrogen and oxygen admixtures on the chemistry of an argon plasma jet operating at atmospheric pressure([London] : IOP, 2015) Van Gaens, W.; Iseni, S.; Schmidt-Bleker, A.; Weltmann, K.-D.; Reuter, S.; Bogaerts, A.In this paper we study the cold atmospheric pressure plasma jet, called kinpen, operating in Ar with different admixture fractions up to 1% pure ${{{\rm N}}_{2}}$, ${{{\rm O}}_{2}}$ and ${{{\rm N}}_{2}}$ + ${{{\rm O}}_{2}}$. Moreover, the device is operating with a gas curtain of dry air. The absolute net production rates of the biologically active ozone (${{{\rm O}}_{3}}$) and nitrogen dioxide (${\rm N}{{{\rm O}}_{2}}$) species are measured in the far effluent by quantum cascade laser absorption spectroscopy in the mid-infrared. Additionally, a zero-dimensional semi-empirical reaction kinetics model is used to calculate the net production rates of these reactive molecules, which are compared to the experimental data. The latter model is applied throughout the entire plasma jet, starting already within the device itself. Very good qualitative and even quantitative agreement between the calculated and measured data is demonstrated. The numerical model thus yields very useful information about the chemical pathways of both the ${{{\rm O}}_{3}}$ and the ${\rm N}{{{\rm O}}_{2}}$ generation. It is shown that the production of these species can be manipulated by up to one order of magnitude by varying the amount of admixture or the admixture type, since this affects the electron kinetics significantly at these low concentration levels.
- ItemAntimicrobial effects of microwave-induced plasma torch (MiniMIP) treatment on Candida albicans biofilms(Oxford : Wiley-Blackwell, 2019) Handorf, Oliver; Schnabel, Uta; Bösel, André; Weihe, Thomas; Bekeschus, Sander; Graf, Alexander Christian; Riedel, Katharina; Ehlbeck, JörgThe susceptibility of Candida albicans biofilms to a non-thermal plasma treatment has been investigated in terms of growth, survival and cell viability by a series of in vitro experiments. For different time periods, the C. albicans strain SC5314 was treated with a microwave-induced plasma torch (MiniMIP). The MiniMIP treatment had a strong effect (reduction factor (RF) = 2.97 after 50 s treatment) at a distance of 3 cm between the nozzle and the superior regions of the biofilms. In addition, a viability reduction of 77% after a 20 s plasma treatment and a metabolism reduction of 90% after a 40 s plasma treatment time were observed for C. albicans. After such a treatment, the biofilms revealed an altered morphology of their cells by atomic force microscopy (AFM). Additionally, fluorescence microscopy and confocal laser scanning microscopy (CLSM) analyses of plasma-treated biofilms showed that an inactivation of cells mainly appeared on the bottom side of the biofilms. Thus, the plasma inactivation of the overgrown surface reveals a new possibility to combat biofilms. © 2019 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.