Low Temperature Atmospheric Pressure Plasma Research Articles

Mechanism study of atmospheric-pressure plasma treatment of carbon fiber reinforced polymers for adhesion improvement

Adhesive bonding is widely employed to join structural components. To improve the load resistance of joints, atmospheric-pressure plasma surface treatments are commonly performed to increase the adhesion of the bonding layers. It is known that the surface decontamination, roughness change and surface activation induced by plasma are main factors to increase the surface free energy and improve the adhesion. In this work, a large-area and low-temperature atmospheric-pressure plasma is used to improve the adhesion between carbon fiber reinforced polymers (CFRPs). It is found that the adhesion between CFRPs measured by lap-shear strength test seems to increase by increasing the plasma power and treatment time but start to reach a limit for excessive power and long treatment time as a result of the selective ablation of the resin covering the carbon fibers. Based on physical and chemical analyses of surfaces and plasmas, the effects of plasma treatment on CFRPs are discussed.

Kinetics Analysis of the Reactions between Peroxynitric Acid and Amino Acids.

Plasma disinfection using low-temperature atmospheric pressure plasma is widely studied in many applications, and the use of plasma-treated water (PTW) for disinfection is being developed by many researchers. Exposing plasma to water supplies and preserves reactive oxygen and nitrogen species (RONS) in the water, and this PTW exhibits bactericidal activity. In our previous study, it was revealed that peroxynitric acid (O2NOOH, PNA) was the dominant bactericidal component in PTW. PNA can be easily synthesized without plasma treatment, and the physicochemical properties of PNA have been well-analyzed. As the application of PNA in fields related to medicine and biology has not been reported, a basic study on the behavior of PNA is required. In this study, the bactericidal activity of PNA and its reactivities with 20 naturally occurring amino acids were evaluated to understand its reaction mechanism with biomolecules. Interestingly, PNA exhibited 10-6 times lower reactivities with amino acids when compared with hypochlorous acid and other RONS, although its bactericidal activity was 310 times higher than that of sodium hypochlorite. In addition, the reactivity of PNA with methionine was over 100 times higher than that with other amino acids, indicating that the reactions of PNA with amino acids are highly specific. No other oxidants have been reported to react selectively with only methionine. As methionine is involved in specific activities in cells, the unique reaction profile of PNA was examined in the context of biological systems.

Stop Bleeding Mobile Device "Plasmamed" Based on Low-temperature Gas Plasma

Creation of a mobile device to stop bleeding, sterilize biological tissues and other surfaces (bandages), disinfect food, beverages, air, and stimulate rapid healing of wound surfaces is observed in this article. Plasmomed is based on the current (available) technologies of medical application of low-temperature atmospheric pressure plasma. The multi-digit combined plasma gun is created as part of the developed mobile device which is designed to achieve a coagulation effect, to stimulate accelerated healing of wound surfaces based on the use of low-temperature gas plasma of atmospheric pressure, which allows for effective hemostasis of wound surfaces with simultaneous sterilization of surrounding tissues and dressing materials. In addition, due to the using several types of high-frequency electromagnetic plasma production in one device, it was possible to significantly simplify the final product, to automate its operation modes, which provides mass-dimensional characteristics for its mobile use.
 Keywords: plasma, medical device, stopping bleeding, low-temperature atmospheric pressure plasma.

Surface Dielectric Barrier Discharge plasma: a suitable measure against fungal plant pathogens

Fungal diseases seriously affect agricultural production and the food industry. Crop protection is usually achieved by synthetic fungicides, therefore more sustainable and innovative technologies are increasingly required. The atmospheric pressure low-temperature plasma is a novel suitable measure. We report on the effect of plasma treatment on phytopathogenic fungi causing quantitative and qualitative losses of products both in the field and postharvest. We focus our attention on the in vitro direct inhibitory effect of non-contact Surface Dielectric Barrier Discharge on conidia germination of Botrytis cinerea, Monilinia fructicola, Aspergillus carbonarius and Alternaria alternata. A few minutes of treatment was required to completely inactivate the fungi on an artificial medium. Morphological analysis of spores by Scanning Electron Microscopy suggests that the main mechanism is plasma etching due to Reactive Oxygen Species or UV radiation. Spectroscopic analysis of plasma generated in humid air gives the hint that the rotational temperature of gas should not play a relevant role being very close to room temperature. In vivo experiments on artificially inoculated cherry fruits demonstrated that inactivation of fungal spores by the direct inhibitory effect of plasma extend their shelf life. Pre-treatment of fruits before inoculation improve the resistance to infections maybe by activating defense responses in plant tissues.

Wound healing improvement in large animals using an indirect helium plasma treatment

BackgroundTo optimize wound healing, the use of low-temperature atmospheric pressure plasma (ionized gas) has been proposed as an innovative therapeutic method for treating extensive and chronic wound. The aim of this study was to evaluate the specific effects of an indirect helium plasma treatment in a sheep surgical wound model based on clinical, histopathological and molecular analyses. This study was part of a larger study aimed at assessing five different wound healing improvement methods. MethodsSix sheep were used in this study. Six square wounds were performed on the back of each sheep. Five of the lesions were used to analyze the effect of five different treatments, one of which was the plasma treatment. The sixth lesions was used as control. A 2-min plasma treatment was daily performed, using a radiofrequency helium plasma source for indirect treatments, until complete wound healing was obtained. Biopsies were performed at two and six weeks. The plasma effects were tested through clinical evaluation, histopathological and immunohistological evaluation, real time PCR analysis, bacteriological evaluation and intracellular ROS evaluation. ResultsWound closure time for the plasma-treated wounds was quicker than that of the control group. Plasma treatment drastically reduced the bacterial load in the wounds. A strong increase in intracellular ROS was observed. After six weeks, the inflammatory process was significantly reduced in the plasma-treated case with respect to the control. The plasma treatment was found to lead to an anticipated induction of blood vessel formation, as detected through mRNA expression of VEGF. The high Ki67-positivity at two weeks indicated a strong stimulation of cell proliferation induced by the plasma treatment. The expression of the hair keratine (hKER) at six weeks indicated that the plasma was promoting hair regrowth. The plasma treatment induced an increased rate of reformation of cutaneous adnexa at six weeks. ConclusionsThe obtained results suggest that the plasma action, at the used dose, induces an increase in cell proliferation, a reduction of inflammation, a reduction of the bacterial load, a stimulation of blood vessel formation, and an improvement in the formation of cutaneous adnexa with a positive consequence on hair regrowth.

Analysis of Hydroxyl Radical and Hydrogen Peroxide Generated in Helium-Based Atmospheric-Pressure Plasma Jet and in Different Solutions Treated by Plasma for Bioapplications

This study systematically analyzed reactive species generated with self-built helium-based low-temperature atmospheric-pressure plasma jet (He-APPJ); we measured the hydroxyl radical (·OH) and hydrogen peroxide (H2O2) above surfaces of plasma–treating solutions and in plasma-treated medium (PTM) of different solutions, including deionized water, phosphate buffered saline, and Dulbecco’s modified Eagle medium. The effects of adding O2 into He working gas on ·OH and H2O2 generation were discussed. The MCF7 cell responses to plasma treatment were also observed. The ·OH emission (309 nm) in He-APPJ and above surfaces of plasma–treating solutions were analyzed through optical emission spectroscopy, and concentrations of ·OH and H2O2 in different solutions were measured using terephthalic acid and Amplex Red, respectively. In our plasma system, it was observed that higher conductivity of solutions may cause stronger ·OH emission above solution. The ingredients of the solution may affect the concentrations of ·OH and H2O2. Addition of 0.1% O2 generates strongest ·OH emission above surfaces of plasma–treating solution with our He-APPJ, and thus, the highest H2O2 concentration in PTM. The MCF7 cell viability is influenced by the H2O2 concentration in PTM. The results of this study can facilitate further study of plasma effects on PTM and cell culture.

Atmospheric pressure low-temperature plasma and its applications to biotechnologies

Atmospheric pressure low-temperature plasma and its applications to biotechnologies

Application of persulfate in low-temperature atmospheric-pressure plasma jet for enhanced treatment of onychomycosis

Fungal infection of human nails, or onychomycosis, affects 10% of the world’s adult population, but current therapies have various drawbacks. In this work, we employed a self-made low-temperature plasma (LTP) device, namely, an atmospheric-pressure plasma jet (APPJ) device to treat the nails infected with Trichophyton rubrum (T. rubrum) with the aid of persulfate solution. We found that persulfate solution had a promoting effect on plasma treatment of onychomycosis. With addition of sodium persulfate, the APPJ therapy could cure onychomycosis after several times of treatment. As such, this work has demonstrated a novel and effective approach which makes good use of LTP technique in the treatment of onychomycosis.

Influence of low-temperature atmospheric pressure plasma on the vital functions of microorganisms

Experimental research on inactivating various types of microorganisms with low-temperature plasma at atmospheric pressure demonstrates great advantages of this method. It is shown that when treating the cells with cold plasma for 3 minutes by using a compact plasma source (plasmatron) a partial or complete disruption of the functional activity of Paramecium caudatum cells occurs. We have found out that plasma treatment for 5 minutes suppresses completely the vital functions of pathogenic microorganisms such as Mucor, Fusarium, Aspergillus and Bacillus mesentericus cells.

Optical properties of fluorocarbon coatings obtained by ion-plasma method at atmospheric pressure in dynamic mode of deposition

This paper presents the results of a study of the formation of fluorocarbon coatings obtained by using a low-frequency plasmatron of a low-temperature atmospheric pressure plasma in a dynamic mode of deposition. The main dependences of chemical vapor deposition (CVD) are investigated. The absorption spectra in the UV range was studied, and the band gap was determined by the Tauc method.

Improved de-inking of inkjet-printed paper using environmentally friendly atmospheric pressure low temperature plasma for paper recycling

Nowadays, due to environmental pollution and natural energy consumption caused by waste paper, many researches are being conducted on the reuse of printed-paper. To recycle the paper, de-inking has to be performed. In this article, in order to reduce the use of the commonly used de-inking chemicals, the effect of an atmospheric pressure helium plasma treatment on the de-inking enhancement of printed-paper is studied. Through colorimeter and UV-visible spectrometer measurements the plasma treatment is shown to speed up the de-inking. While SEM observations and FTIR measurements suggest that the paper quality is retained upon plasma treatment, the increase of surface hydrophilicity measured by water contact angle measurements, compared to non-treated paper, is believed to enhance the fiber swelling of the paper and lead to a faster ink removal.

SOLUTION PLASMA PROCESSING OF NATURAL POLYMER-BASED MATERIALS

Non-equilibrium low-temperature atmospheric pressure plasma is a highly reactive medium that allows for the ecofriendly modification of nature-derived materials. This work reviews the field of liquid phase plasma modification of polymer-based materials derived from natural sources. Types of solution plasma systems are considered with respect to the efficiency of the generation of active species, their transport to and interaction with macromolecules. Tunable modification of plants (birch, willow, bamboo and vine shoots; barley, rice and rapeseed straw; perennial grasses), algae, plant-derived by-products and wastes (sawdust, bast fibers, nutshells, seeds, peels, press-cake and pomace), plant-derived polymers (cellulose, hemicellulose, lignin, starch, sodium alginate) and animal-derived polymer-based materials (chitosan, collagen, gelatin) by solution plasma treatment is compared to conventional wet chemistry methods. Synthesis of nano-biocomposites with advanced functionalities is also considered.
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A high efficiency low-temperature microwave-driven atmospheric pressure plasma jet

The design, performance, and characteristics of a low-temperature microwave-driven atmospheric pressure plasma jet (MAPPJ) are presented. The MAPPJ is based on a complex coaxial transmission line structure, and the gas is discharged by a continuous-wave microwave. By inputting two channel gas through inner and outer coaxial transmission lines, respectively, the gas flow can be restricted and the plasma jet open to atmospheric air could be long and straight without quartz tube. A 28.6 mm long straight low-temperature plasma jet is observed in the experiment. This MAPPJ device shows high efficiency in a wide operation range, and a maximum efficiency of 89.6% is measured in the experiment without a microwave matching network. This approach can be an initiation toward the commercialization of low-temperature MAPPJs.

Low-temperature plasma treatment of polylactic acid and PLA/HA composite material

Investigations of the surface physicochemical properties of polylactic acid and polylactic acid/hydroxyapatite composite in a 70/30 ratio modified by atmospheric pressure low-temperature glow discharge argon plasma with the pulse duration of 1 μs and 5 μs and repetition rate of 100 kHz are described. Plasma modification of such materials may significantly affect physicochemical properties of surface. The polymerization of l-lactide was carried out at a temperature of 155 °C for 6 h. X-ray diffraction analysis shows that the degree of crystallinity of polylactic acid and composites based on polylactic acid/hydroxyapatite composite increases after plasma treatment due to polymer chain disruption. Infrared spectroscopy indicates that the –C=O absorption band intensity increases with plasma pulse duration, in turn indicating oxidation processes occurring in the polylactic acid surface layers. The wettability characteristics of the materials are improved by the plasma treatment, resulting in decreased water, glycerol, and ethylene glycol contact angle, and enhanced free surface energy.

Plasma disinfection via the reduced-pH method using an ex vivo porcine contaminated skin model

Plasma disinfection has been developed as a medical application using low temperature atmospheric pressure plasma. We identified an enhancement effect of the bactericidal activity of plasma treatment against a bacterial suspension by the acidification of the solution (the reduced-pH method). The key efficacy factor of the reduced-pH method was shown to be hydroperoxy radicals (HOO•). However, in the case of medical application, the efficacy of plasma disinfection on living body should be evaluated, because it have complicated surface structure and rich organic matter which can inhibit disinfection. Here, we demonstrated the efficacy of the reduced-pH method on the skin surface by using a porcine skin model. The bactericidal activity of plasma treatment at pH 3.7 and 6.6 was 3.7 and 0.8 log reduction, respectively. The enhancement effect of bactericidal activity was confirmed to be 4.6 on the skin at the tested pH conditions. The method for providing pH control on the skin surface was very simple, involving spreading of the pH buffer solution on the skin. The reduced-pH method may therefore serve as an essential technique for plasma disinfection on the human body, as one of the most important concerns for such treatment is to ensure low levels of thermal damage by the plasma jet. The reduced-pH method thus enables enhancement of the bactericidal activity of plasma treatment without increasing the plasma power.

Design and characteristics investigation of a miniature low-temperature plasma spark discharge device

Atmospheric pressure low-temperature plasma is a promising tool in biomedicine applications including blood coagulation, bacterial inactivation, sterilization, and cancer treatment, due to its high chemical activity and limited thermal damage. It is of great importance to develop portable plasma sources that are safe to human touch and suitable for outdoor and household operation. In this work, a portable and rechargeable low-temperature plasma spark discharge device (130 mm × 80 mm × 35 mm, 300 g) was designed. The discharge frequency and plume length were optimized by the selection of resistance, capacitance, electrode gap, and ground electrode aperture. Results show that the spark plasma plume is generated with a length of 12 mm and a frequency of 10 Hz at a capacitance of 0.33 μF, resistance of 1 MΩ, electrode gap of 2 mm, and ground electrode aperture of 1.5 mm. Biological tests indicate that the plasma produced by this device contains abundant reactive species, which can be applied in plasma biomedicine, including daily sterilization and wound healing.

Generators of Atmospheric Pressure Diffuse Discharge Plasma and Their Use for Surface Modification

Studies of the properties of runaway electron preionized diffuse discharges (REP DDs) and their possible use have been carried out for more than 15 years. Three experimental setups generating a low-temperature atmospheric-pressure plasma and differing in the geometry of a discharge gap were developed. They allow the treatment of surfaces of different materials with an area of several tens of square centimeters. A diffuse discharge plasma was formed in the pulse–periodic mode by applying negative voltage pulses with an amplitude of several tens of kilovolts and a duration of 4 ns to a discharge gap with sharply non-uniform electric field strength distribution. This paper presents experimental results of the study of the surface layer microstructure of copper and steel specimens of different sizes after treatment with the REP DD plasma in nitrogen flow mode and nitrogen circulation mode in the discharge chamber. It was shown that after 105 discharge pulses, the carbon concentration decreases and a disoriented surface layer with a depth of up to 200 nm is formed. Moreover, the results of X-ray phase analysis did not reveal changes in the phase composition of the surface of copper specimens. However, as a result of surface treatment with the REP DD plasma, the copper lattice becomes larger and the microstress increases.

Systematic diagnostics of the electrical, optical, and physicochemical characteristics of low-temperature atmospheric-pressure helium plasma sources

The performance characteristics of two plasma sources, based on different types of discharge, were assessed. Three primary aspects of these sources were examined. These were electrical parameters (voltage and current flowing through a target), plasma parameters (gas temperature and electron density, determined using optical emission spectroscopy), and levels of gas-phase oxygen atoms (measured by vacuum ultraviolet absorption spectroscopy) and liquid-phase ▪OH radicals (generated by plasma treatment of water and detected using an electron spin resonance spin-trapping technique). As a result, there were few significant differences such as electron density, oxygen atom density, and gas temperature between the two plasma sources. However, the time-averaged electrical currents flowing to the target and the amount of liquid-phase ▪OH radicals showed a large difference, especially when the plume made contact with the target. Thus, many points of similarity but some differences in the two devices were found by the benchmarking study. These shall contribute to our understanding of the mechanisms for each consequence in medical applications.

Thin film deposition method for ZnO nanosheets using low-temperature microwave-excited atmospheric pressure plasma jet

Electronic devices such as solar cells and thin-film transistors can be fabricated using thin-film deposition. Low-cost, low-temperature and high-speed deposition methods are required to ensure that the production of devices using thin-film deposition is affordable. Herein, we report the development of a low-cost and simple thin-film deposition method using microwave-excited atmospheric pressure plasma jet (MWAPPJ). MWAPPJ produces a low-temperature (several hundred degrees) plasma under atmospheric conditions, does not require expensive vacuum equipment, and it enables high-speed deposition of thin-films. Zinc acetylacetonate sol-gel precursors that were adhered to stainless steel mesh targets were irradiated by MWAPPJ with oxygen, which resulted in zinc oxide (ZnO) nanosheet thin-films with diameters of 100–200 nm on silicon substrates. We used 50-nm-thick ZnO thin-films that were processed using MWAPPJ as the electron collection layer in organic photovoltaic (OPV) cells. This work represents an important contribution to the design and production of low-cost OPV solar cells.

Development of an Ambient Air Flow Rotating Arc Jet for Low-Temperature Treatment

For low-temperature atmospheric pressure plasma treatment applications, we developed a novel rotating arc jet operated using various gases, including ambient air. We demonstrate the operation of plasma via the injection of various gas mixtures and tune operation parameters to achieve a low-temperature gas output from the arc jet. The rotating arc jet has an efficiency two orders of magnitude higher in the generation of reactive oxygen and nitrogen species than commercially available conventional nonequilibrium atmospheric pressure plasma jets operated with He or Ar gases. The high concentration of reactive species and use of ambient air as a process gas is promising for biomedical and agriculture applications. This work is a step toward the commercial use of plasma jets operated with ambient air.