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- ItemNeutrophil extracellular trap formation is elicited in response to cold physical plasma(Hoboken, NJ : Wiley, 2016) Bekeschus, Sander; Winterbourn, VChristine C.; Kolata, Julia; Masur, Kai; Hasse, Sybille; Bröker, Barbara M.; Parker, Heather A.Cold physical plasma is an ionized gas with a multitude of components, including hydrogen peroxide and other reactive oxygen and nitrogen species. Recent studies suggest that exposure of wounds to cold plasma may accelerate healing. Upon wounding, neutrophils are the first line of defense against invading microorganisms but have also been identified to play a role in delayed healing. In this study, we examined how plasma treatment affects the functions of peripheral blood neutrophils. Plasma treatment induced oxidative stress, as assessed by the oxidation of intracellular fluorescent redox probes; reduced metabolic activity; but did not induce early apoptosis. Neutrophil oxidative burst was only modestly affected after plasma treatment, and the killing of Pseudomonas aeruginosa and Staphylococcus aureus was not significantly affected. Intriguingly, we found that plasma induced profound extracellular trap formation. This was inhibited by the presence of catalase during plasma treatment but was not replicated by adding an equivalent concentration of hydrogen peroxide. Plasma-induced neutrophil extracellular trap formation was not dependent on the activity of myeloperoxidase or NADPH oxidase 2 but seemed to involve short-lived molecules. The amount of DNA release and the time course after plasma treatment were similar to that with the common neutrophil extracellular trap inducer PMA. After neutrophil extracellular traps had formed, concentrations of IL-8 were also significantly increased in supernatants of plasma-treated neutrophils. Both neutrophil extracellular traps and IL-8 release may aid antimicrobial activity and spur inflammation at the wound site. Whether this aids or exacerbates wound healing needs to be tested.
- ItemPoly (hexamethylene biguanide), adsorbed onto Ti-Al-V alloys, kills slime-producing Staphylococci and Pseudomonas aeruginosa without inhibiting SaOs-2 cell differentiation(Hoboken, NJ : Wiley, 2020) Hornschuh, Melanie; Zwicker, Paula; Schmidt, Thomas; Finke, Birgit; Kramer, Axel; Müller, GeraldAntimicrobial coating of implant material with poly(hexamethylene biguanide) hydrochloride (PHMB) may be an eligible method for preventing implant-associated infections. In the present study, an antibacterial effective amount of PHMB is adsorbed on the surface of titanium alloy after simple chemical pretreatment. Either oxidation with 5% H2O2 for 24 hr or processing for 2 hr in 5 M NaOH provides the base for the subsequent formation of a relatively stable self-assembled PHMB layer. Compared with an untreated control group, adsorbed PHMB produces no adverse effects on SaOs-2 cells within 48 hr cell culture, but promotes the initial attachment and spreading of the osteoblasts within 15 min. Specimens were inoculated with slime-producing bacteria to simulate a perioperative infection. Adsorbed PHMB reacts bactericidally against Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa after surface contact. Adhered SaOs-2 cells differentiate and produce alkaline phosphatase and deposit calcium within 4 days in a mineralization medium on PHMB-coated Ti6Al4V surfaces, which have been precontaminated with S. epidermidis. The presented procedures provide a simple method for generating biocompatibly and antimicrobially effective implant surfaces that may be clinically important. © 2019 The Authors. Journal of Biomedical Materials Research Part B: Applied Biomaterials published by Wiley Periodicals, Inc.
- ItemFirst‐mode of negative streamers: Inception at liquid/solid interfaces(Hoboken, NJ : Wiley, 2021) Ariza, David; Beroual, Abderrahmane; Methling, Ralf; Gortschakow, Sergey; Chamorro, Harold R.An experimental study of the inception of the first-mode negative streamer at liquid/solid interfaces is presented in this article. The study is performed with a point-plane configuration under square high voltage pulses. The electrode configuration is immersed in mineral oil and the liquid/solid interface is assembled in contact with the point electrode or in its vicinity. Four polymers and two impregnated papers have been tested as solids of the liquid/solid interface. Thus, it is possible to compare the influence of different parameter of the solid and the interface on the streamer inception. For example: Permittivity, solid surface roughness, chemical composition, etc. It has been observed that streamer inception voltages at interfaces with solids of higher permittivity to that of the mineral oil are statistically similar. Additionally, streamer inception voltages of streamer initiated free in the oil (no liquid/solid interface) are similar to that of the inception voltage of cases with solids with high permittivity. In contrast, the inception voltage of streamers initiated at permittivity matched interfaces are shown to be highest of the cases. The streamer inception voltage is also studied for different distances between the liquid/solid interface and the point electrode with a permittivity matched interface. The results show a dependency of the inception voltage and the distance between the point electrode and the interface. Finally, an analysis of the observation is performed to show that the Townsend-Meek criterion cannot predict the obtained results.
- ItemAtmospheric-pressure pulsed discharges and plasmas: Mechanism, characteristics and applications(Hoboken, NJ : Wiley, 2018) Shao, Tao; Wang, Ruixue; Zhang, Cheng; Yan, PingPulsed discharge plasma and its application is one of the promising directions in civilian areas of pulsed power technology. In order to promote the research and development of the theory and application technology for pulsed discharge plasma, in this paper, recent progress on the mechanism of nanosecond-pulse gas discharge and the characteristics and applications of typical pulsed plasma at the Institute of Electrical Engineering, Chinese Academy of Sciences is reviewed. Firstly, progress on mechanism of nanosecond-pulse discharge based on runaway electrons and measurement technology of runaway electrons is introduced. Then, the characteristics of three typical discharges, including direct-driven pulsed discharge, pulsed dielectric barrier discharge and pulsed plasma jet, are reviewed. Furthermore, typical plasma applications of pulsed plasma on surface modification and methane conversion are presented.
- ItemX-ray Emissions in a Multiscale Fluid Model of a Streamer Discharge(Hoboken, NJ : Wiley, 2018) Lehtinen, Nikolai G.; Østgaard, NikolaiWe use a three-specie fluid model of electric discharge in air to simulate streamer evolution from the avalanche-to-streamer transition to the collision of opposite-polarity streamers. We estimate the upper limit on the production of thermal runaway electrons, which is dominant during the second of these processes. More thermal runaways are produced if the ionization due to natural background and photoionization is reduced, due to possibility of creation of higher electric fields at streamer tips. The test-particle simulation shows, however, that these thermal runaway electrons have insufficient energies to become relativistic runaways. The simulations are done in constant uniform background fields of E0=4 and 6 MV/m. A simulation was also performed in E0=2 MV/m after formation of streamers in 4-MV/m field, in order to approximate the average background field created by ∼1-MV voltage over a ∼1-m electrode gap used in laboratory spark experiments. We conclude that the used fluid model is insufficient to explain X-ray observations during such experiments. We discuss the possible role of mechanisms which were not included in this or previous modeling but may play the deciding role in the electron acceleration and X-ray production during a streamer collision.
- ItemPositive and negative streamers in air and nitrogen in a sharply inhomogeneous electric field under conditions of runaway electron generation(Hoboken, NJ : Wiley, 2023) Beloplotov, Dmitry; Tarasenko, Victor; Sorokin, Dmitry; Zhang, Cheng; Shao, TaoThe development of positive and negative streamers in a point-to-plane gap filled with air and nitrogen at various pressures (50–200 kPa) and voltages (8–25 kV) was studied. A four-channel intensified charge-coupled device (ICCD) and a streak-camera were used. Electrical parameters were measured with high resolution (10 GHz). An original method of measuring a displacement current caused by a streamer was applied. As was expected, positive streamer branches in nitrogen at low voltages and/or elevated pressures while a large-diameter streamer is formed in air. However, at high voltages or negative polarity, the large-diameter streamer is formed both in nitrogen and air in the entire pressure range. It was found that runaway electrons (REs) are generated in the very first picoseconds of gas ionisation near the pointed cathode. It was assumed that REs can be generated near the pointed anode and produce bremsstrahlung radiation due to a sharply inhomogeneous distribution of electrical potential. It was found that in the final stage of negative streamer development in air and nitrogen, the gas between the streamer front and the opposite electrode is ionised almost simultaneously in the entire volume when the streamer diameter is almost equal to the interelectrode gap.
- ItemIonization waves in nanosecond pulsed atmospheric pressure plasma jets in argon(Hoboken, NJ : Wiley, 2021) Huang, Bangdou; Zhang, Cheng; Zhu, Wenchao; Lu, Xinpei; Shao, TaoTypical ionization waves (IWs) are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets (APPJs) with argon flow, combining both the measurement of the axial electric field (Ez) and the temporal resolved optical imaging. The movement of the luminous APPJ head is recognized as the development of the IW front, accompanied with the propagation of the peak electric field. Especially, the radial distribution of Ez transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front. As for the temporal Ez trend, there is a mode transition from the single-peak feature under a low peak voltage to the double-peak feature under a higher peak voltage, indicating the existence of both primary and secondary IWs. The effect of target conditions on the IWs in APPJs is also explored. With a metal target, no residual electric field is observed before imposing the high-voltage pulses. However, with a dielectric target, the residual surface charges generate a background electric field in the opposite direction to that during IW propagation. In the free APPJ (with no target), on the voltage falling edge, a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propagation on the voltage rising edge.
- ItemRadio Frequency Electromagnetic Radiation From Streamer Collisions(Hoboken, NJ : Wiley, 2017) Luque, AlejandroWe present a full electromagnetic model of streamer propagation where the Maxwell equations are solved self-consistently together with electron transport and reactions including photoionization. We apply this model to the collision of counter-propagating streamers in gaps tens of centimeters wide and with large potential differences of hundreds of kilovolts. Our results show that streamer collisions emit electromagnetic pulses that, at atmospheric pressure, dominate the radio frequency spectrum of an extended corona in the range from about 100 MHz to a few gigahertz. We also investigate the fast penetration, after a collision, of electromagnetic fields into the streamer heads and show that these fields are capable of accelerating electrons up to about 100 keV. By substantiating the link between X-rays and high-frequency radio emissions and by describing a mechanism for the early acceleration of runaway electrons, our results support the hypothesis that streamer collisions are essential precursors of high-energy processes in electric discharges.
- ItemTranslational plasma stomatology: Applications of cold atmospheric plasmas in dentistry and their extension(Hoboken, NJ : Wiley, 2017) Li, He‐Ping; Zhang, Xiao‐Fei; Zhu, Xiao‐Ming; Zheng, Miao; Liu, Shu‐Fang; Qi, Xuan; Wang, Kai‐Peng; Chen, Jian; Xi, Xiao‐Qing; Tan, Jian‐Guo; Ostrikov, Kostya (Ken)In recent years, translational plasma medicine (TPM), as a novel application area of plasmas, has attracted much attention of experts from both academic and clinical fields. State-of-the-art of the lab-scale research and clinical trials of the cold atmospheric plasmas (CAPs) in the stomatology are reviewed in detail from the direct and indirect applications of the CAPs. Based on the discussions concerning the relationship between the plasma stomatology and the plasma medicine, it is indicated that it would be an important reference for promoting the TPM starting from the fundamental and application studies in the field of dentistry, which is also one of the most three promising application fields of plasma medicine.