An emerging field of plasma medicine is discussed, where non-equilibrium plasmas are shown to be able to initiate, promote, control, and catalyze various complex behaviors and responses in biological systems. More importantly, it will be shown that plasma can be tuned to achieve the desired medical effect, especially in medical sterilization and treatment of different kind of skin diseases. Wound healing and tissue regeneration can be achieved following various types of plasma treatment in a multitude of wound pathologies. Non-equilibrium plasmas will be shown to be non-destructive to tissue, safe, and effective in inactivation of various parasites and foreign organisms.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/ppap.200700154

Applied Plasma Medicine

Reactive oxygen species (ROS) and the closely related reactive nitrogen species (RNS) are often generated in applications of atmospheric pressure plasmas intended for biomedical purposes. These species are also central players in what is sometimes referred to as ‘redox’ or oxidation‐reduction biology. Oxidation‐reduction biochemistry is fundamental to all of aerobic biology. ROS and RNS are perhaps best known as disease-associated agents, implicated in diabetes, cancer, heart and lung disease, autoimmune disease and a host of other maladies including ageing and various infectious diseases. These species are also known to play active roles in the immune systems of both animals and plants and are key signalling molecules, among many other important roles. Indeed, the latest research has shown that ROS/RNS play a much more complex and nuanced role in health and ageing than previously thought. Some of the most potentially profound therapeutic roles played by ROS and RNS in various medical interventions have emerged only in the last several years. Recent research suggests that ROS/RNS are significant and perhaps even central actors in the actions of antimicrobial and anti-parasite drugs, cancer therapies, wound healing therapies and therapies involving the cardiovascular system. Understanding the ways ROS/RNS act in established therapies may help guide future efforts in exploiting novel plasma medical therapies. The importance of ROS and RNS to plant biology has been relatively little appreciated in the plasma biomedicine community, but these species are just as important in plants. It appears that there are opportunities for useful applications of plasmas in this area as well. (Some figures may appear in colour only in the online journal)

https://iopscience.iop.org/article/10.1088/0022-3727/45/26/263001/pdf

The emerging role of reactive oxygen and nitrogen species in redox biology and some implications for plasma applications to medicine and biology

During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

http://iopscience.iop.org/article/10.1088/0022-3727/42/5/053001/pdf

Non-thermal plasmas in and in contact with liquids

Reactive species in non-equilibrium atmospheric-pressure plasmas: Generation, transport, and biological effects

Reactive oxygen species (ROS) can attack a diverse range of targets to exert antimicrobial activity, which accounts for their versatility in mediating host defense against a broad range of pathogens. Most ROS are formed by the partial reduction in molecular oxygen. Four major ROS are recognized comprising superoxide (O2•-), hydrogen peroxide (H2O2), hydroxyl radical (•OH), and singlet oxygen ((1)O2), but they display very different kinetics and levels of activity. The effects of O2•- and H2O2 are less acute than those of •OH and (1)O2, because the former are much less reactive and can be detoxified by endogenous antioxidants (both enzymatic and nonenzymatic) that are induced by oxidative stress. In contrast, no enzyme can detoxify •OH or (1)O2, making them extremely toxic and acutely lethal. The present review will highlight the various methods of ROS formation and their mechanism of action. Antioxidant defenses against ROS in microbial cells and the use of ROS by antimicrobial host defense systems are covered. Antimicrobial approaches primarily utilizing ROS comprise both bactericidal antibiotics and nonpharmacological methods such as photodynamic therapy, titanium dioxide photocatalysis, cold plasma, and medicinal honey. A brief final section covers reactive nitrogen species and related therapeutics, such as acidified nitrite and nitric oxide-releasing nanoparticles.

Antimicrobial strategies centered around reactive oxygen species - bactericidal antibiotics, photodynamic therapy and beyond

Nonequilibrium plasmas driven by submicrosecond high voltage pulses have been proven to produce high-energy electrons, which in turn lead to enhanced ionization and excitations. Here, we describe a device capable of launching a cold plasma plume in the surrounding air. This device, “the plasma pencil,” is driven by few hundred nanosecond wide pulses at repetition rates of a few kilohertz. Correlation between current-voltage characteristics and fast photography shows that the plasma plume is in fact a small bulletlike volume of plasma traveling at unusually high velocities. A model based on photoionization is used to explain the propagation kinetics of the plasma bullet under low electric field conditions.

/pdf/dynamics-of-an-atmospheric-pressure-plasma-plume-generated-3lh9e6swlk.pdf

Dynamics of an atmospheric pressure plasma plume generated by submicrosecond voltage pulses

Summary: A device capable of generating a relatively long cold plasma plume has recently been developed. The advantages of this device are: plasma controllability and stability, room temperature and atmospheric pressure operation, and low power consumption. These features are what is required from a plasma source to be used reliably in material processing applications, including the biomedical applications. In this communication we describe the device and we present evidence that it can be used successfully to inactivate Escherechia coli in a targeted fashion. More recent experiments have shown that this device inactivates other bacteria also, but these will be reported in the future.

Photograph of a He plasma plume launched out of the plasma pencil.

Inactivation of bacteria by the plasma pencil

An AC-driven, non-equilibrium, atmospheric pressure air plasma is generated within the gap separating a disc-shaped metal electrode and a water electrode. The typical OH emission intensity distribution is recorded by high-speed CCD camera. The temporal emission behaviour of OH(A–X) shows that the OH emission intensity stays relatively constant during most of the current cycle but decreases abruptly when the current is close to zero. The N2 rotational and vibrational temperatures are obtained by comparison of the simulated spectra of C 3 � u–B 3 � g (�v =− 2) band transition of nitrogen with the experimental results. They are about 1800 K and 2600 K, respectively. The electron density in the plasma is measured utilizing the electrical conductivity. It is found to be 7 × 10 12 cm −3 in the centre of the discharge during the peak current of Ipeak = 40 mA. The electron density follows a Gaussian radial distribution with a typical width of 0.35 mm.

Optical and electrical diagnostics of a non-equilibrium air plasma

An atmospheric pressure glow discharge in air is generated between the surface of a water electrode and a metal electrode with a high alternating current (60 Hz) voltage (<20 kV). The gap distance between the two electrodes can be adjusted from 3 mm to a few centimeters. The diameter of the plasma column is in the 3-10 mm range. Photographs taken with a high-speed charge coupled device camera clearly show a cathode fall region, negative glow, positive column, and anode dark space; a structure consistent with that of a normal glow discharge. The initial breakdown process shows that the plasma ignites at the water surface and terminates at the metal electrode. The N/sub 2/ rotational and vibrational temperatures were spectroscopically measured to be about 1800 and 2600 K, respectively.

Atmospheric pressure glow discharge in air using a water electrode

Polar liquids are characterized by high permittivity and high dielectric strength. These properties make them appealing dielectrics for use in high-energy storage systems and as high-power switching media. Most of the studies on electrical breakdown and recovery have focused on water as a switch medium in pulsed-power systems. As an alternative to water, the authors have studied the breakdown and dielectric recovery of propylene carbonate (C4H6O 3). One advantage of propylene carbonate over water is its relatively low freezing temperature of -55degC, which allows its use at a high altitude. The permittivity of propylene carbonate is 65, somewhat less than water (81). Its dielectric strength for pulses of 200-ns duration was measured as 2.2 MV/cm, higher than that of water (1.5 MV/cm). A nonlinear increase in conductivity above electric fields of 1.225 MV/cm, assumed to be due to field-enhanced dissociation, was recorded in both cases. The recovery of propylene carbonate is similar to that of water, with plasma decay, shock-wave emission, and vapor bubble formation, except for the very last phase, which is determined by chemical reactions: the generation and decay of polypropylene polymers. This limits the time for dielectric recovery of propylene carbonate switches to values of more than 10 ms

XinPei Lu

Papers

Dynamics of an atmospheric pressure plasma plume generated by submicrosecond voltage pulses

Inactivation of bacteria by the plasma pencil

Optical and electrical diagnostics of a non-equilibrium air plasma

Atmospheric pressure glow discharge in air using a water electrode

Electrical Breakdown and Dielectric Recovery of Propylene Carbonate