Toshihiro Takamatsu

Investigation of reactive species using various gas plasmas

In this study, atmospheric nonequilibrium plasmas were generated with six gas species using a multi-gas plasma jet. Singlet oxygen, OH radicals, H radicals, and NO radicals, in reaction with a solution interface, were measured using electron spin resonance. Carbon dioxide plasma generated the largest amount (90 μM) of singlet oxygen at 30 s, and argon-containing vapor gas plasma generated the largest amount (210 μM) of OH radicals. Among the homo-atomic gas species, nitrogen plasma generated the largest amount (130 μM) of OH radicals. In addition, H radicals were generated with argon, helium, and nitrogen plasmas. NO radicals were generated with nitrogen–oxygen plasma, and the largest amount of NO radicals was generated at a 1 : 1 volume ratio. These measurement results of the reactive species generated by individual gas plasmas permit identification of the production processes of reactive species.

Surface Hydrophilization of Polyimide Films Using Atmospheric Damage-Free Multigas Plasma Jet Source

Atmospheric-pressure plasma jet sources have proven useful for surface treatments; however, conventional plasma and near-plasma sources have limitations in the number of different plasma gas species that they can handle. We previously developed a damage-free multigas plasma jet source that can generate stable atmospheric-pressure plasma using various gas species without thermal/electrical discharge damage. Herein, we investigate the fundamental characteristics of the generated plasma such as gas temperature (<;57°C) and emission properties. In addition, we evaluate the industrial potential of the jet source by using it with various gas species to induce surface hydrophilization in a polyimide film. The jet source proved useful, and carbon dioxide proved the most effective of the studied gas species for the purpose with the hydrophilized surface maintaining a contact angle of about 30° for over 32 days after plasma irradiation.

Microbial Inactivation in the Liquid Phase Induced by Multigas Plasma Jet.

Various gas atmospheric nonthermal plasmas were generated using a multigas plasma jet to treat microbial suspensions. Results indicated that carbon dioxide and nitrogen plasma had high sterilization effects. Carbon dioxide plasma, which generated the greatest amount of singlet oxygen than other gas plasmas, killed general bacteria and some fungi. On the other hand, nitrogen plasma, which generated the largest amount of OH radical, killed ≥6 log of 11 species of microorganisms, including general bacteria, fungi, acid-fast bacteria, spores, and viruses in 1–15 min. To identify reactive species responsible for bacterial inactivation, antioxidants were added to bacterial suspensions, which revealed that singlet oxygen and OH radicals had greatest inactivation effects.

Temperature Controllable Atmospheric Plasma Source

An atmospheric pressure plasma source in which the gas temperature can be accurately controlled from below freezing point up to a high temperature has been developed. In general plasma devices, an electrical discharge is passed through a gas at about room temperature to generate plasma, so the plasma is at a temperature higher than room temperature; moreover, the gas temperature is determined by the discharge condition such as discharge power and plasma gas flow rate, so accurate temperature control is difficult. In the plasma source that has been developed in this research, the gas that is to be supplied to the discharge unit is first cooled using a gas cooler and then heated by a heater. The gas temperature of the produced plasma is measured, and feedback is sent to the heater. Thus, plasma at a desired temperature can be generated. Gas temperature control of the plasma over a range from -54 °C to +160 °C with a standard deviation of 1 °C was realized. Spectroscopic characteristics of generated plasma were investigated. This plasma source/technique will realize that effective plasma is applicable for heat-sensitive materials such as paper, textile, polymer, and especially human tissue. Furthermore, it enables us to generate the plasma at optimal gas temperature for chemical reaction of each plasma treatment.

Atmospheric nonequilibrium mini-plasma jet created by a 3D printer

In this study, a small-sized plasma jet source with a 3.7 mm head diameter was created via a 3D printer. The jet’s emission properties and OH radical concentrations (generated by argon, helium, and nitrogen plasmas) were investigated using optical emission spectrometry (OES) and electron spin resonance (ESR). As such, for OES, each individual gas plasma propagates emission lines that derive from gases and ambient air inserted into the measurement system. For the case of ESR, a spin adduct of the OH radical is typically observed for all gas plasma treatment scenarios with a 10 s treatment by helium plasma generating the largest amount of OH radicals at 110 μM. Therefore, it was confirmed that a plasma jet source made by a 3D printer can generate stable plasmas using each of the aforementioned three gases.

Sterilization effect of various gas non-thermal plasma

Summary form only given. In recent years, atmospheric non-thermal plasma have been attracted attention in medical field because of its effectiveness for sterilization and wound treatment. However, conventional plasma sources have a limitation in plasma gas species. Plasma can be generated with specific gas such as helium, argon, nitrogen, or air. In our group, the damage-free multi-gas plasma jet source was developed in 2010. This plasma source is free from thermal or electric discharge damage to target materials. Therefore, the plasma treatment is applicable for various materials such as semiconductor, metal, plastic, paper, textile, living body and tissue. And it can generate stable atmospheric plasma jet with helium, argon, oxygen, neon, nitrogen, carbon dioxide, air, and their mixture gas. In surface treatment using the damage-free multi-gas plasma jet, obvious difference of hydrophilization effect by plasma gas species was observed. So, in this study, we examined some biological effects of various gas plasmas. 5 L/min of argon, oxygen, nitrogen, air and oxygen mixed argon plasma were irradiated to E. Coli in agar medium. A clear difference was seen by plasma gas species in the bactericidal effect. Oxygen mixed argon plasma was most effective for sterilization of E. Coli. E. Coli in 90 mm agar medium was sterilized in 10 seconds plasma irradiation. This plasma showed good sterilization effect for other bacteria such as B. subtilis, S. aures, A. niger, and G. stearo. Shape change of bacteria was observed using electron microscope after plasma irradiation. To explore the possibility of plasma irradiation for therapeutic application, its effect on cultured human cell line was investigated. As a result, 90 % of HeLa cells were killed in 40 seconds by irradiation of oxygen mixed argon plasma. The details of the plasma source and the results of these experiments will be presented.

Imaging of the Staphylococcus aureus Inactivation Process Induced by a Multigas Plasma Jet.

To identify mechanisms underlying the bacterial inactivation process by atmospheric nonthermal plasma using a unique plasma jet that can generate various gas plasmas, Staphylococcus aureus were irradiated with carbon dioxide plasma, which produces a large amount of singlet oxygens, and nitrogen plasma, which produces a large amount of OH radicals. And damaged areas of plasma-treated bacteria were observed by field emission scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. As a result, bacteria were damaged by both gas plasmas, but the site of damage differed according to gas species. Therefore, it suggests that singlet oxygen generated by carbon dioxide plasma or other reactive species caused by singlet oxygen contributes to the damage of internal structures of bacteria through the cell wall and membrane, and OH radicals generated by nitrogen plasma or other reactive species derived from OH radicals contribute to damage of the cell wall and membrane.

Indigo Naturalis Ameliorates Oxazolone-Induced Dermatitis but Aggravates Colitis by Changing the Composition of Gut Microflora

Background: Indigo naturalis (IND) is an herbal medicine that has been used as an anti-inflammatory agent to treat diseases including dermatitis and inflammatory bowel disease in China. However, the mechanism by which IND exerts its immunomodulatory effect is not well understood. Methods: A murine model of dermatitis and inflammatory bowel disease, both induced by oxazolone (OXA), was treated with IND. The severity of dermatitis was evaluated based on ear thickness measurements and histological scoring. The severity of colitis was evaluated by measuring body weight, histological scoring, and endoscopic scoring. The expression of inflammatory cytokines in ear and colon tissue was evaluated using real-time PCR. 16S rRNA DNA sequencing of feces from OXA-induced colitis mice was performed before and after IND treatment. The effects of IND on OXA-induced colitis were also evaluated after depleting the gut flora with antibiotics to test whether alteration of the gut flora by IND influenced the course of intestinal inflammation in this model. Results: IND treatment ameliorated OXA dermatitis with a reduction in IL-4 and eosinophil recruitment. However, OXA colitis was significantly aggravated in spite of a reduction in intestinal IL-13, a pivotal cytokine in the induction of the colitis. It was found that IND dramatically altered the gut flora and IND no longer exacerbated colitis when colitis was induced after gut flora depletion. Conclusions: Our data suggest that IND could modify the inflammatory immune response in multiple ways, either directly (i.e., modification of the allergic immune cell activity) or indirectly (i.e., alteration of commensal compositions).

Measurement of sterilization ability and reactive species of various gas plasma bubbled-up water

Recently, various sterilization methods using atmospheric non-thermal plasma have been studied. Plasma generates reactive species that contributes to the sterilization. Most of the previous studies were reported that water treated by plasma irradiation (plasma treated water) shows sterilization ability. In these experiments, plasma is irradiated to the water surface from above. Therefore, this method is inefficient because the contact area between the plasma and the water is limited. Additionally, a lot of reactive species such as hydroxyl radical (HO·), singlet oxygen (1O2) are not generated by helium or argon plasma.

Investigation of bacterial inactivation by various gas plasmas and electron microscopic observation of treated bacteria

Our group succeeded in developing a multi-gas plasma jet, which can generate plasma from various gas species. Using this plasma source, reactive species can be investigated in detail, since they can be generated selectively by the supplied gas species. This study aims to investigate the amount of reactive species generated by various gas plasmas, find reactive species that can inactivate bacteria and observe treated bacteria using electron microscope.