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International audience; The potential beneficial impact of plasma is being investigated for many biotechnological and medical applications. However, translating promising in vitro results to in vivo (bio)medical outcomes remains a challenging task. One of the major challenges in the translation of plasma technologies to in vivo, and ultimately clinical use, is the lack in the fine control necessary for an efficient and safe use of plasma sources in medical applications; this we attribute to the mutual interaction between plasma and target [1]. Many key fundamental questions on the mechanisms taking place at the interface between plasma and (bio) targets still need to be addressed. While there is an abundance of literature on the biological effects of plasma treatment, there are only a few reports on the physico-chemical characterization of the plasma during the treatment process. Even considering a very simple scenario 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 biological effects of the plasma. Recent research has reported how the geometry of the multi-well plate, as well as the electrical characteristics of the support on which it stands, can have a significant impact on the experiment and its reproducibility [1, 2]. Furthermore, the presence or absence of a liquid and small variations in its depth/volume can completely change the nature and the distribution of the bioactive plasma-generated RONS reaching the bottom of the well [3].As it will be presented, surprisingly, even in small liquid volumes (e.g. 0.2–2 ml) typical of biomedical in vitro experiments, the impinging plasma jet on the biological liquid can induce the formation of fast and complex electro fluid dynamic (EFD) flows. These flows are affected by plasma parameters and can lead to vortex recirculation. Whereas biological effects will always be the focus of plasma medicine, it is important for the advancement of this field to achieve a deeper understanding and a greater awareness of the physico-chemical processes taking place during our plasma biomedical experiments.Acknowledgements: PLASCANCER (INCa-PlanCancer N°17CP087-00), GdR 2025 HAPPYBIO and and ERC APACHE Nº714793).References[1] A. Stancampiano, T.-H. Chung, S. Dozias, J.-M. Pouvesle, L. M. Mir, and E. Robert, IEEE Trans. Radiat. Plasma Med. Sci., Early Acess, 10.1109/TRPMS.2019.2936667 (2019)[2] S. Mohades, A. Lietz, J. Kruszelnicki and M. Kushner, Plasma Process. Polym, e1900179 (2019)[3] S. Sasaki, R. Honda, Y. Hokari, K. Takashima, M. Kanzaki and T. Kaneko, J. Phys. D: Appl. Phys, 49, 334002 (2016)

International audience; Following in vitro assessment of cancer cells and the benefit of a combined treatment based on incubation with plasma treated solution and application of Pulsed Electric Field in the context of reversible cell membrane permeabilization, this work reports on the in vivo evaluation of such combined innovative antitumor approach. Three independent studies, dealing with immunocompetent mice bearing fibrosarcoma tumors and involving control groups, PEF treated group (Bleomycine Electro Chemo Therapy (ECT) and combined plasma treated PBS (p-PBS) and PEF treatments, were performed. A single-shot treatment was applied 12 days after tumor cell injection, and follow up of tumor volume was performed for more than two months. The main conclusions of these studies indicate that (i) p-PBS production and storage was highly reproducible and allow for in vivo studies requiring large volume of such solutions; (ii) Bleomycin, p-PBS, and their combined injection has no antitumor action; (iii) ECT as a reference therapy is efficient, especially for fast growing tumors; (iv) combined p-PBS and ECT treatment allow for a slower tumor growthrate, for fast growing tumors, and lead to a significant increase of the number of tumor regressions; and (v) composition of p-PBS solution for different plasma exposures might be a unique parameter for a fine tuning of the efficiency of the combined antitumor treatment.

International audience; Plasma jets are being intensively researched for cancer therapy with encouraging initial clinical outcomes already realised. However, the fine control of plasma jets remains challenging due to the mutual interaction between plasma and target [1]. Even considering perhaps one of the simplest scenarios 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. This study aims to shed light into 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 conductive biologically-relevant liquid (i.e. PBS) in a standard tissue culture grade 24-well plate [2]. 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 (Fig. 1a). 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. 1b). Experimental results indicate that electric charge accumulation on the liquid surface and plasma induced gas swirling could be the causes of the liquid motions. Furthermore, the liquid depth and the voltage polarity were found to be critical parameters in controlling the delivery of the RONS to the bottom of the well. A multijet plasma source was, then, used for the treatment of PBS (pPBS), which was combined with a pulsed electric field (PEF) to permeabilise B16-F10 murine melanoma cells. Compared to PEF alone, the combined treatment with pPBS (applied before and after PEF exposure) can greatly increase the number of permeabilised cells and the uptake of a model non-permeant molecule (Yo-Pro®-1) to confirm the permeability of the cell membrane (Fig. 1c). This synergistic effect of plasma treated PBS and PEF could open new opportunities for the application of plasma jets in electrochemotherapy

National audience; Plasma jets are intensively studied for biomedicine applications but their fine control remains challenging due to the mutual interactions between plasma and target. Even considering the simplest scenario in a research laboratory, a plasma jet treating a 2D culture of cells, it is not known in detail how the physical environment of the micro-well may influence the treatment. This study aims to shed light on this topic by investigating how electro fluid dynamic (EFD) flows influence the delivery of the bioactive plasmagenerated reactive species when a plasma jet is used to treat a biologicallyrelevant 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 species. Shortly after the ignition of the plasma jet a fast stream can reach the bottom of the well, whereas a stable toroidal vortex mixing is observed few seconds later. 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.

International audience; The majority of atmospheric pressure plasma jet (APPJ) applications involves the interaction between the plasma and a target. The understanding of the mechanisms underlining this interaction is a key step for the future development of APPJ technology. Nevertheless, many widely adopted target configuration, such as those encountered in in vitro biomedical studies have barely been investigated from a physical point of view. The present study shows how APPJ can induce vortex formation and lead to strongly non-uniform distribution of plasma-generated long-lived reactive species in a vessel with the characteristic length scale of the wells commonly adopted for in vitro biomedical studies

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 one of the simplest scenario in a research laboratory, using a plasma jet to treat a 2D cells culture 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. This study aims to shed light by investigating for the first time the liquid flows induced by the plasma treating a biologically-relevant liquid (e.g. PBS) in standard tissue culture grade multi well plates (i.e. 96, 24, 12 and 6 wells). Evaporation, induced by the anhydrous gas flow, is demonstrated to govern the thermal effect and be at the origin of the observed liquid cooling. Moreover, the formation of stable vortexes in the liquid induces a non-uniform distribution of plasma generated reactive species. This phenomenon, reported for various vessels and volumes of liquid, does not originate from thermal gradients but is instead the likely result of a combination of electrohydrodynamic forces and gas flow tangential components induced by the plasma impinging on the liquid surface.