image: Light emitted by the plasma generated in the electrode unit when no solution has been infused. Scale bar, 3 mm.
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Credit: Daisuke Yoshino, Tokyo University of Agriculture and Technology

Plasma medicine, a therapeutic technology that uses atmospheric pressure plasma, is gaining attention as an innovative tool in medicine. It has potential in applications ranging from wound healing to cancer treatment. Most current plasma biomedical tools use direct effects, such as heat, optical stimulation and reactive chemical species, applied to the patient’s body. Although current tools are useful for treating lesions or wounds on the surface of the body, there are many challenges before the technology can be used safely inside the human body.

A research team from Tokyo University of Agriculture and Technology has developed a method to directly generate plasma in the form of a nano-sized mist. Posted in Scientific reports on June 22, their method has great potential for medical applications.

Where plasma is currently used in medicine, its applications are mainly limited to the treatment of burns, skin diseases and wounds, where the lesion is exposed. For plasma to be used in the treatment of a patient’s internal organs, researchers must find new ways to administer the plasma.

To solve this challenge, the research team developed a method to directly generate a nano-sized mist by passing a solution through the dielectric barrier discharge. They were able to generate fog for three types of solutions, including water-based and oil-based solutions. Next, they studied the changes in the physical and chemical characteristics of each solution by plasma treatment. Their results suggest that the electrical conductivity of the solution influenced the efficiency of fog generation.

Using this new method, they were able to atomize different types of solutions without the need to ground the target to be sprayed. The current electrostatic spraying method presents the risk of currents flowing through the target. Since the research team’s new method does not require the sputtered target to be grounded, it is a much safer option.

Plasma is sometimes called the fourth state of matter, along with solid, liquid, and gas. With its interesting properties and behavior, researchers have already found many applications for plasma in the electronics, aerospace, textile and automotive industries. In recent years, researchers have begun to explore ways to use plasma systems in the fields of medicine and biology.

Where plasma is currently used in medicine, it works like a very precise scalpel. These current plasma applications rely primarily on the action of plasma-derived physical and chemical stimuli, such as heat, optical stimulation, and reactive oxygen and nitrogen species. Like traditional surgeries, these plasma applications are demanding on the patient’s body.

Newer technologies include transdermal absorption systems where plasma is irradiated onto living tissue. The skin can be easily irradiated directly by the plasma. But if drug penetration could be accelerated by allowing plasma to act on the drug itself, the technology could be extended beyond use on the skin to include treatment of the respiratory and digestive organs.

To deliver drugs in this way, a nanotechnology delivery system is required. Then, the plasma-generated nanoparticles could enable drugs to cross the skin barrier and reach the target area stably with long-lasting efficacy. The transdermal drug delivery process could be taken even further if nanoparticles could be produced directly from aqueous or oil-based solutions where the drug is dissolved by a simple process.

Electrostatic spraying, where electrical effects are used, is a technique for generating a nano-sized mist. This technique is already used in a range of applications, including pesticide spraying, water purification and seawater desalination. However, the electrostatic spray technique is not safe for applications biological as it requires high voltage and grounding of the sputtered target. As an alternative, a dielectric barrier discharge method could be used. However, it is difficult to generate liquid particles by this method because another fog generation mechanism, such as an ultrasonic transducer, must also be used. This method of dielectric barrier discharge, where plasma is produced by two electrodes with a dielectric (or insulator) between them, is often used in manufacturing applications.

The research team’s new method overcomes these challenges and makes plasma more useful in the medical field. “We have successfully developed a technology to generate a nano-sized mist by passing a liquid through a low velocity dielectric barrier discharge. This technology is safer than conventional electrostatic spraying, which is used in the industrial field,” said Daisuke Yoshino, associate professor at Tokyo University of Agriculture and Technology. “Ultimately, we aim to apply our technology to biomedical areas, such as transdermal drug delivery systems.”

The Tokyo University of Agriculture and Technology research team includes Ryosuke Watanabe, Shiori Tanaka, Godai Miyaji and Daisuke Yoshino.

The research is supported by JSPS KAKENHI grant numbers JP18K19894, JP21K19893.

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For more information about the Daisuke Yoshino Research Group, please visit https://sites.google.com/go.tuat.ac.jp/dyoshino-research-group/home.

About Tokyo University of Agriculture and Technology (TUAT)

TUAT is a distinguished university in Japan dedicated to science and technology. TUAT focuses on agriculture and engineering which form the foundation of the industry and promotes fields of education and research which integrate them. Boasting a history of more than 140 years since its founding in 1874, TUAT continues to boldly take on new challenges and steadily promote areas. With high ethics, TUAT assumes social responsibility in the ability to transmit scientific and technological information towards the construction of a sustainable society where human beings and nature can prosper in a symbiotic relationship. For more information, please visit http://www.tuat.ac.jp/en/.

Contact

Daisuke Yoshino, Ph.D.
Associate Professor, Division of Advanced Applied Physics, Institute of Engineering, TUAT, Japan
[email protected]


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