On-demand cold plasma activation of acetyl donors for bacteria and virus decontamination

Antibiotics are commonly used as the first line of defense in the treatment of infectious diseases. However, the rise of antimicrobial resistance (AMR) is rendering many antibiotics less effective. Consequently, effective non-antibiotic antimicrobial strategies are urgently needed to combat AMR. This paper presents a strategy utilizing cold plasma for the "on-demand"activation of acetyl donor molecules. The process generates an aqueous-based antimicrobial formulation comprising a rich mixture of highly oxidizing molecules: peracetic acid, hydrogen peroxide, and other reactive oxygen and nitrogen species. The synergistic potent oxidative action between these molecules is shown to be highly effective at eradicating common wound pathogenic bacteria (Pseudomonas aeruginosa and Staphylococcus aureus) and at inactivating a virus (SARS-CoV-2)

How membrane lipids influence plasma delivery of reactive oxygen species into cells and subsequent DNA damage:an experimental and computational study

The mechanisms of plasma in medicine are broadly attributed to plasma-derived reactive oxygen and nitrogen species (RONS). In order to exert any intracellular effects, these plasma-derived RONS must first traverse a major barrier in the cell membrane. The cell membrane lipid composition, and thereby the magnitude of this barrier, is highly variable between cells depending on type and state (e.g. it is widely accepted that healthy and cancerous cells have different membrane lipid compositions). In this study, we investigate how plasma-derived RONS interactions with lipid membrane components can potentially be exploited in the future for treatment of diseases. We couple phospholipid vesicle experiments, used as simple cell models, with molecular dynamics (MD) simulations of the lipid membrane to provide new insights into how the interplay between phospholipids and cholesterol may influence the response of healthy and diseased cell membranes to plasma-derived RONS. We focus on the (i) lipid tail saturation degree, (ii) lipid head group type, and (iii) membrane cholesterol fraction. Using encapsulated molecular probes, we study the influence of the above membrane components on the ingress of RONS into the vesicles, and subsequent DNA damage. Our results indicate that all of the above membrane components can enhance or suppress RONS uptake, depending on their relative concentration within the membrane. Further, we show that higher RONS uptake into the vesicles does not always correlate with increased DNA damage, which is attributed to ROS reactivity and lifetime. The MD simulations indicate the multifactorial chemical and physical processes at play, including (i) lipid oxidation, (ii) lipid packing, and (iii) lipid rafts formation. The methods and findings presented here provide a platform of knowledge that could be leveraged in the development of therapies relying on the action of plasma, in which the cell membrane and oxidative stress response in cells is targeted

The role of UV photolysis and molecular transport in the generation of reactive species in a tissue model with a cold atmospheric pressure plasma jet

Cold atmospheric pressure plasma jets (plasma) operated in ambient air provide a rich source of reactive oxygen and nitrogen species (RONS), which are known to influence biological processes important in disease. In the plasma treatment of diseased tissue such as subcutaneous cancer tumors, plasma RONS need to first traverse an interface between the plasma-skin surface and second be transported to millimeter depths in order to reach deep-seated diseased cells. However, the mechanisms in the plasma generation of RONS within soft tissues are not understood. In this study, we track the plasma jet delivery of RONS into a tissue model target and we delineate two processes: through target delivery of RONS generated (primarily) in the plasma jet and in situ RONS generation by UV photolysis within the target. We demonstrate that UV photolysis promotes the rapid generation of RONS in the tissue model target's surface after which the RONS are transported to millimeter depths via a slower molecular process. Our results imply that the flux of UV photons from plasma jets is important for delivering RONS through seemingly impenetrable barriers such as skin. The findings have implications not only in treatments of living tissues but also in the functionalization of soft hydrated biomaterials such as hydrogels and extracellular matrix derived tissue scaffolds

Modulating the concentrations of reactive oxygen and nitrogen species and oxygen in water with helium and argon gas and plasma jets

We employed UV-vis spectroscopy to monitor real-time changes in the oxygen tension and concentration of reactive oxygen and nitrogen species (RONS) in deionized (DI) water during treatments with helium (He) and argon (Ar) gas plasma jets. He and Ar gas jets are both shown to de-oxygenate DI water with He being more efficient than Ar, whilst the plasma jets deliver and regulate the concentrations of hydrogen peroxide (H 2 O 2 ), nitrite (NO 2 - ) and nitrate (NO 3 - ) in DI water. The H 2 O 2 and NO 3 - production efficiency varied between He and Ar plasma jets, but was similar for NO 2 - . Whilst DI water fully equilibrated with ambient air prior to treatment (de-oxygenated by both plasma jets) when DI water was first de-oxygenated by an inert gas jet treatment, both plasma jets were found to be capable of oxygenating DI water. These insights were then used to show how different combinations of plasma jet and inert gas jet treatments can be used to modulate O 2 tension and RONS chemistry. Finally, potential further improvements to improve control in the use of plasma jets in regulating O 2 and RONS are discussed. © 2018 The Japan Society of Applied Physics

Investigation of helium plasma jet-treated serum and cell media on the viability of skin cells

This study compares the differences in the viability of skin cells after culturing in cell medium supplemented with helium (He) plasma jet-treated serum and Dulbecco's Modified Eagle Medium (DMEM). HaCaT and HDFa cells were used as surrogates for the two major cell types of skin, i.e., keratinocytes and fibroblasts, respectively. A reduction in cell viability was observed for cells cultured in cell media supplemented with He plasma jet-treated serum and DMEM; however, cells were more sensitive to the He plasma jet-treated serum. HaCaT cells were more sensitive to He plasma jet-treated serum compared to HDFa cells. The decrease in the viability of HaCaT cells was not directly attributed to excessive oxidative stress (i.e., from reactive oxygen species generated by the He plasma jet). A possible explanation for the decrease in cell viability is that the He plasma jet treatment results in modification of the serum or DMEM, which decreases the bioavailability and/or bioefficacy of their essential components. In response to nutrient-deficiency, the cells may undergo autophagy, which can lead to a different form of cell death compared to apoptosis and necrosis. It will be important in the future to elucidate what essential components in cell media/serum are modified by plasma jets or other plasma sources utilised in biology and medicine research, and how these modifications alter cellular response.Rishabh Bhatia, Xanthe Strudwick, Allison J. Cowin, Endre J. Szil

Cold Plasma Generation of Peracetic Acid for Antimicrobial Applications

This study compares how a helium plasma jet activates peracetic acid (PAA) from tetraacetylethylenediamine (TAED) and acetic acid (AA). Hydrogen peroxide (H 2 O 2 ) generated from the plasma jets reacts with TAED resulting in the formation of PAA which further dissoci-ates into AA. The by-product AA can also react with H 2 O 2 to form PAA, which might also be use-ful for antimicrobial applications when coupled with plasma. Equivalent concentrations of TAED and AA solutions are used to compare the formation of PAA after activation with a helium plasma jet. Our results showed that the concentrations of both H 2 O 2 and PAA in plasma-activated TAED (PAT) are higher than plasma-activated AA (PAAA), and that PAT is more efficient in reducing the growth of Pseudomonas aeruginosa and Staphylococcus aureus; the pathogens commonly found in wounds. The results are attributed to the presence of more acetyl donor groups in TAED, resulting in the formation of higher concentrations of PAA and H 2 O 2

The influence of a second ground electrode on hydrogen peroxide production from an atmospheric pressure argon plasma jet and correlation to antibacterial efficacy and mammalian cell cytotoxicity

This study investigates how addition of a 2nd ground electrode in an argon plasma jet influences the production of hydrogen peroxide (H2O2) in deionised water (DIW). Briefly, plasma is ignited by purging argon gas through a quartz tube at 1 l min-1 and applying a sinusoidal voltage of 7 kV (peak-peak) at 23.5 kHz to a high voltage stainless steel needle electrode sealed inside the quartz tube surrounded by one or two copper ring(s) that served as the ground electrode(s) situated downstream of the high voltage electrode. The mechanisms of H2O2 production are investigated through the electrical and optical plasma properties and chemical analysis of the treated DIW. We discover that the addition of a 2nd ground electrode results in higher accumulation of charges on the inner wall surface of the quartz tube of the plasma jet assembly resulting in an increase in the discharge current and dissipated power. This further leads to an increase in the electron temperature that more than doubles the H2O2 production through dissociative recombination of water vapour molecules, whilst still maintaining a biological tissue tolerable gas temperature. The double ground electrode plasma jet is shown to be highly effective at reducing the growth of common wound pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) in both planktonic and biofilm states whilst inducing a low level of cytotoxicity in HaCaT keratinocyte skin-like cells under certain conditions. The information provided in this study is useful in understanding the complex physicochemical processes that influence H2O2 production in plasma jets, which is needed to optimise the development of plasma sources for clinical applications

On cold atmospheric-pressure plasma jet induced DNA damage in cells

To investigate the potential role of the hydroxyl radical (•OH) in cold atmospheric plasma (CAP) jet treatment, two fluorescence-based methodologies are utilised to measure DNA strand breaks. The first comprises a model system of a double-stranded DNA oligomer, where the respective strand ends are tagged with fluorophore and quencher molecules; and the second, a cell culture system reporting DNA strand breaks using the γ-H2AX assay. During the various CAP jet treatments, optical emission spectroscopy is used to detect the •OH in the gas phase and electron spin resonance is used to detect the •OH in solution. The CAP jet production of the •OH is shown to correlate to CAP jet induced DNA damage both with the DNA model and in biological cells. Results indicate that the CAP jet induces a higher degree of DNA damage when the CAP plume is in contact with the target solution. The potential of a 'plasma screen' based upon a hydrogel film, as a method to remove the DNA-damaging •OH species from reaching skin cells, is shown to significantly reduce DNA damage whilst facilitating the delivery of hydrogen peroxide. These findings could aid in the development of CAP jet-based applications where DNA damage is the objective (e.g. in cancer treatment) and others where it is to be avoided, e.g. in open-wound treatment and dermatology. © 2020 The Author(s). Published by IOP Publishing Ltd

Electrochemically enhanced antimicrobial action of plasma‐activated poly(vinyl alcohol) hydrogel dressings

This paper presents and explains the principle behind anelectrochemical method to enhance the antimicrobial action of plasma-activated hydrogel therapy (PAHT) in the context of wound decontamination. The process involves grounding and hydratingpoly(vinyl alcohol) (PVA) hydrogel films during treatment with a helium (He) plasma jet. This electrochemically enhances production of hydrogen peroxide (H2O2), which is amajor antibacterial agent produced in the PVA hydrogel. Production of H2O2 is shownto be electrically enhanced through electron dissociation reactions, and through reactions associated with excited state species, metastables and ultra-violet (UV) photolysis. H2O2 production is chemically enhanced through the He flow of the plasma jet dehydrating the PVA hydrogel, which fuels the electrochemical dependent reactions associated with H2O2 production. The electrochemical process produces an unprecedented 3.4 mM of H2O2 in the PVA hydrogel. Production of other molecules such as reactive nitrogen species (RNS) are also enhanced by the same method. The electrochemically enhanced PAHT is highly effective ateradicating common wound pathogens Escherichia coli and Pseudomonas aeruginosa and mildly effective against Staphylococcus aureus. Overall, this study shows that the new PAHT dressing offers a promising alternative to antibiotics and silver-based dressings for controlling infection and stimulating healing in wounds