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Current methods for tattoo removal are long, costly and have drawbacks such as scarring among others. Looking for alternatives, here we assess the feasibility of non-thermal plasma (NTP) as a standalone method for the removal of tattoos. We report the results of atmospheric pressure plasma jet treatment of real tattoo inks suspensions in water and in gelatin (liquid or as a solid film), selected as a model of skin. Analysis of the residual color and the temperature effect in all the samples after plasma treatment reveals significant differences between water and the skin model. Kinetic considerations and the extension of our results to more realistic scenarios allow us to conclude that NTP cannot compete with the current laser technology in a real application.

Hydrogels have been recently proposed as suitable materials to generate reactive oxygen and nitrogen species (RONS) upon gas-plasma treatment, and postulated as promising alternatives to conventional cancer therapies. Acting as delivery vehicles that allow a controlled release of RONS to the diseased site, plasma-treated hydrogels can overcome some of the limitations presented by plasma-treated liquids in in vivo therapies. In this work, we optimized the composition of a methylcellulose (MC) hydrogel to confer it with the ability to form a gel at physiological temperatures while remaining in the liquid phase at room temperature to allow gas-plasma treatment with suitable formation of plasma-generated RONS. MC hydrogels demonstrated the capacity for generation, prolonged storage and release of RONS. This release induced cytotoxic effects on the osteosarcoma cancer cell line MG-63, reducing its cell viability in a dose-response manner. These promising results postulate plasma-treated thermosensitive hydrogels as good candidates to provide local anticancer therapies.

Plasma medicine is a multidisciplinary field of science that uses cold atmospheric pressure plasmas for biomedical purposes. Several applications have been proposed in the last years, including disinfection of bacteria and fungi, wound healing, dermatological diseases and selective killing of cancer cells. Several plasma production schemes and plasma source designs have been proposed, most of which have obtained interesting therapeutic effects on biological samples. However, an overall understanding of the mechanisms that induce such benefices is still missing. Such an understanding is not trivial, considering the multiplicity of possible interactions between complex systems, such as cold plasmas and biological tissues.

HO radicals are the most important reactive species generated during water treatment by non-thermal plasma devices. In this letter, we report the first quantification of the steady-state concentration and lifetime of plasma-produced hydroxyl radicals in water solutions at pH 3 and 7, and we discuss the differences based on their reactivity with other plasma-generated species. Finally, we show to what extent the use of chemical probes to quantify short-lived reactive species has an influence on the results and that it should be taken into account.

Cold atmospheric plasma (CAP) is a potential anticancer therapy. CAP has cytotoxic effects when applied either directly to cancer cell cultures or indirectly through plasma-conditioned liquids. This protocol describes how to treat adherent cultures of human cancer cell lines with CAP or plasma-conditioned medium and determine cell viability following treatment. The protocol also includes details on how to quantify the reactive oxygen and nitrogen species present in medium following CAP treatment, using chemical probes using UV-visible or fluorescence spectroscopy. CAP treatment takes ~30 min, and 3 h are required to complete quantification of reactive oxygen and nitrogen species. By providing a standardized protocol for evaluation of the effects of CAP and plasma-conditioned medium, we hope to facilitate the comparison and interpretation of results seen across different laboratories.

International audience; Plasma jets are being intensively studied for biomedicine applications but their fine control remains challenging due to the mutual interactions between plasma and target. Even considering perhaps one of the simplest scenario in a research laboratory, using a plasma jet to treat a 2D culture of cells in a plastic multi-well plate, it is not known in detail how the physical environment of the micro-well may influence the nature of the plasma jet treatment. [see Mohades 2020 and Stancampiano 2019] This study aims to shed light on this topic by investigating how electro fluid dynamic (EFD) flows influence the delivery of the bioactive plasma-generated RONS when a plasma jet is used to treat a biologically-relevant liquid (i.e. PBS) in a standard tissue culture grade 24-well plate. The results show how the formation of complex EFD flows in the liquid induce a non-uniform distribution of the RONS, especially within the first few seconds of treatment. Shortly after the ignition of the plasma jet an initial rapid liquid stream can reach the bottom of the well, whereas a stable vortex mixing is observed few seconds later (Fig.1). Electric charge accumulation on the liquid surface and plasma induced gas swirling could be the causes of the liquid motions. Furthermore, the liquid depth/volume and the voltage polarity are found to be critical parameters in controlling the delivery of the RONS to the bottom of the well. Mohades, S., Lietz A., Kruszelnicki, J., Kushner, M. J. : 2020, Plasma Processes and Polymers, 17, 3Stancampiano, A., Chung, T.-H., Dozias, S., Pouvesle, J.-M., Mir, L. M., Robert, E. : 2019, IEEE Trans. Radiat. Plasma Med. Sci., 4, 3

Atmospheric pressure plasma jets generate reactive oxygen and nitrogen species (RONS) in liquids and biological media, which find application in the new area of plasma medicine. These plasma-treated liquids were demonstrated recently to possess selective properties on killing cancer cells and attracted attention toward new plasma-based cancer therapies. These allow for local delivery by injection in the tumor but can be quickly washed away by body fluids. By confining these RONS in a suitable biocompatible delivery system, great perspectives can be opened in the design of novel biomaterials aimed for cancer therapies. Gelatin solutions are evaluated here to store RONS generated by atmospheric pressure plasma jets, and their release properties are evaluated. The concentration of RONS was studied in 2% gelatin as a function of different plasma parameters (treatment time, nozzle distance, and gas flow) with two different plasma jets. Much higher production of reactive species (H(2)O(2) and NO(2)(-)) was revealed in the polymer solution than in water after plasma treatment. The amount of RONS generated in gelatin is greatly improved with respect to water, with concentrations of H(2)O(2) and NO(2)(-) between 2 and 12 times higher for the longest plasma treatments. Plasma-treated gelatin exhibited the release of these RONS to a liquid media, which induced an effective killing of bone cancer cells. Indeed, in vitro studies on the sarcoma osteogenic (SaOS-2) cell line exposed to plasma-treated gelatin led to time-dependent increasing cytotoxicity with the longer plasma treatment time of gelatin. While the SaOS-2 cell viability decreased to 12%-23% after 72 h for cells exposed to 3 min of treated gelatin, the viability of healthy cells (hMSC) was preserved (~90%), establishing the selectivity of the plasma-treated gelatin on cancer cells. This sets the basis for designing improved hydrogels with high capacity to deliver RONS locally to tumors.

In the last years, great advances have been made in therapies based in cold atmospheric plasmas (CAP). CAP generate reactive oxygen and nitrogen species (RONS) which can be transferred to liquids. These CAP activated liquids display the same biological efficacy (i.e. on killing cancer cells) as CAP themselves, opening the door for minimally invasive therapies. However, injection of a liquid in the body results in fast diffusion due to extracellular fluids and blood flow. Therefore, the development of efficient vehicles which allow local confinement and delivery of RONS to the diseased site is a fundamental requirement. In this work, we investigate the generation of RONS (H 2 O 2 , NO 2 - , short-lived RONS) in alginate hydrogels by comparing two atmospheric pressure plasma jets: kINPen and a helium needle, at a range of plasma treatment conditions (time, gas flow, distance to the sample). The physic-chemical properties of the hydrogels remain unchanged by the plasma treatment, while the hydrogel shows several-fold larger capacity for generation of RONS than a typical isotonic saline solution. Part of the RONS are quickly released to a receptor media, so special attention has to be put on the design of hydrogels with in-situ crosslinking. Remarkably, the hydrogels show capacity for sustained release of the RONS. The plasma-treated hydrogels remain fully biocompatible (due the fact that the species generated by plasma are previously washed away), indicating that no cytotoxic modifications have occurred on the polymer. Moreover, the RONS generated in alginate solutions showed cytotoxic potential towards bone cancer cells. These results open the door for the use of hydrogel-based biomaterials in CAP-associated therapies.