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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; This work reports on the interaction of so-called plasma jet with or within liquid solutions. The use ofthe Plasma Gun as an archetypical setup for processing liquid samples or humid tissues in thecontext on plasma biomedical applications but also in a more innovative configuration where plasmajet is immersed in solution to generate plasma in gas bubbles will be discussed. In the "abovesolution" setup, recent experiments have shown that reactive species generation and delivery in theliquid could be very non intuitive, revealing the existence of steady state vortexes, surfaceaccumulation zones, needle-like transient patterns, ... depending on various operating conditionssuch as gas flow, pulse repetition rate, distance to the sample, while being quite universal for variousliquid containers typically used for biomedical applications. Conversely, the in-bubble plasmageneration while being very dependent on the operating conditions as well and on the liquid electricalconductivity, is shown to allow for a, at a first glance surprising, very fast and very homogenousdelivery of reactive species in liquid samples. Plasma generation is gas bubbles will be documented,together with the reactive species generation efficiency versus gas flow rate, number of plasma pulsedelivery in a single bubble. It is shown that plasma generation in gas bubble has drastic impact on thebubble expansion dynamics and that synchronization of plasma pulse generation during the bubblelifetime could be a key parameter to optimize the reactive species generation and balance.Perspectives for multi bubble plasma reactors delivered in large liquid volume processing will bediscussed.

International audience; The last decade has seen an impressive increase of the research dedicated to the biological applications of low temperature atmospheric pressure plasmas. Medical appli-cations are tacking an increasing place underlined by many clinical trials. They now concern numerous domains, including blood coagulation, dental care, skin decontamination and hygiene, wound and ulcer treatment, dermatology, cancer treatment. Biological applications are also now extended to agriculture and, more recently, to cosmetic. Despite the huge number of in vitro and in vivo experiments, there are still numerous challenges to overcome linked to the nature of the encountered target (biological tissues and materials, organs and their direct environment, liquids) that have a direct effect on the produced plasma itself and on the generated species. That must therefore be taken into account in the applied treatments and complicates the definition of a "plasma dose" expected by many.

International audience; Non-thermal plasmas, produced from dielectric barrier discharges in air or from rare gas plasma jet devices, generate at room temperature, long and short lifetime reactive species (RS) in gaseous phase or in the liquid solution on which they impinge, ionic species, UV photons and intense transient electric fields (EF). In the last decade, the main focus was drawn on the RS to understand and optimize their action in the frame of the broad topic of “Plasma medicine”. More recently, the characterization and implication of EF in biomedical applications is studied, considering the generation of ns to μs duration, kV/cm amplitude features of plasma EF. Plasma have been shown to be a potential alternative to more “conventional technologies” for gene transfer, cell permeabilization, drug delivery in various applications including for cancer therapy. Quite recently, the concepts of reversible electroporation, especially the models of so called pore formation in cell membranes were broaden and detailed involving not only the key role of EF but also the oxidation of cell membrane associated with RS. Thus it appears we attend to a unique opportunity to reach more insights and achieve cell manipulation process optimization with considering the potential complementary or synergistic delivery of pulsed electric fields and plasma for in vitro and in vivo protocols.Besides a quick overview of some significant works focused on the use of non-thermal plasmas in interaction with cell membranes, the lecture will document the results obtained so far with the Plasma Gun developed at GREMI for first, cancer cell permeabilization with various plasma delivery protocols, and second on the first demonstrations of the positive combined action of pulsed electric fields (PEF) and plasma for antitumor action. Cell permeabilization has been performed in vitro for different adherent cell lines, exposed to plasma jet delivered at various pulse repetition rates for short duration and followed with cell incubation in plasma treated solution. The combination of plasma and PEF is studied in vitro and with murine models considering the delivery of pulsed voltage and current pulses (electroporation) together with plasma treated solutions in contact with biological targets (suspended cancer cells in electroporation cuvettes or tumors) at different delays with respect to the electroporation step.AcknowledgmentsWork supported by PLASCANCER project INCa-PlanCancer-n°17CP087-00 and GDR CNRS 2025 HAPPYBIO

International audience; The last decade has seen an impressive increase of the research dedicated to the biomedical applications of low temperature plasmas, especially with plasma sources working at atmospheric pressure. In this new trend, beside decontamination/sterilization and surface treatment that have already a quite long story through low-pressure plasma research and developments, medical applications are tacking an increasing place underlined by the actual numerous clinical trials. Medical applications of low temperature plasmas now concern a very wide range of domains, including primary haemostasis and blood coagulation, dental care, skin decontamination and hygiene, wound and ulcer treatment, dermatology, cancer treatment. Biological applications are also now extended to agriculture and, more recently, to cosmetic. Despite the huge number of in vitro and in vivo experiments there are still numerous challenges to overcome linked to the nature of the encountered target (biological tissues and materials, organs and their direct environment, liquids) that have a direct effect on the produced plasma itself and on the generated species. It is clear that the extremely strong coupling between the characteristics of the plasma and those of the target, as already shown, will play a very important role in the results observed during the treatments. A variation in the chemical or physical characteristics of the target will involve significant differences in the gas flow, the local temperature, or the induced electric field, resulting de facto in variations in the production of the reactive species. It also concerns the transposition of the results between the in vitro and the in vivo experiments that are carried out under extremely different conditions, especially concerning the equivalent electric circuit of the reactor / plasma / biological target assembly. These problems directly affect the identification of the processes involved and currently limit the possibility of a definition of a "dose" in plasma treatments. Recently, study reported led to reflections on non-sustainable tumor response. The loss of effectiveness under long-term plasma treatment of cancer tissue opens questions about plasma application and protocol. It must be considered that the treated area is morphologically and chemically changing over the time, from activated surrounding to more normal tissues that are less humid and bacteriologically cleaner. This aspect is particularly important for the development of efficient systems and protocols in plasma cancer treatment but also for any other plasma therapeutically approaches. It induce a in real-time in situ control of plasma production and at longer term a protocol adaptation taking into account the biological target evolution. Some progress are already done in that domain

International audience; The parameters needed for helium plasma jet to induce a cell membrane permeabilization on cancerous cells for drug delivery purposes have been investigated. Using our optimal settings, different fluorescent molecular markers were used in order to determine pore size, opening kinetics and the importance of endocytosis in the process. It is shown that plasma induced chemistry but also electric field play a role in drug uptake and that endocytosis is one of the mode of membrane permeabilzation.

International audience; Single plasma jets have allowed significant advances in in vivo or directly on human experiments(e.g. [1], [2]). The results are particularly promising, but, ultimately, they couldbe limited in thefuture due to the fact that the treatment times are rather long due to the very small surface areatreated by the produced plasma. There is a real challenge to develop sources that allow treatmentover larger areas while remaining practical and at a reasonable cost. To this end, there arealready flexible or rigid surface DBDs but they require an extremely small distance between thereactor and the treated tissues, which limits their use in many situations (particularly when thetreated surfaces exhibit large variations in the surface morphology leading to points ofattachment of streamers and therefore to a very inhomogeneous treatment). "Ideal" sources aretherefore sources with the flexibility of a jet and treatment surfaces comparable to large DBDs. Itis in this spirit that we have developed a new generation of applicators based on a single PlasmaGun system and able to generate a multitude of jets (from tens up to few hundreds) fromtheprimary plasma jet, as shown in Fig. 1.Fig. 1: Multijet plasma source from single Plasma GunBefore proceeding to in vivo treatments, we qualified the sourcesthrough in vitro experiments ofdecontamination on colonies grown on agar plates in traditional Petri dishes, to check theequivalence of each of the jets generated, as well as on colonies grown onvery large agarsurfacesscanned with our system,to check large surface treatment feasibility. The results are extremelyencouraging and demonstrate the effectiveness of the multijet system, which allows both theprocessing of large-scale targets as well as the reductionof the processing times that otherwisecan be prohibitive with single-jet systems.We will present experimental results obtained on thegeneration of different types of multijets, as well as results obtained with one multijet plasmasource on the decontamination of multi-resistant bacterial colonies grown from hospital inpatientsamples.AcknowledgementsThis work was supported by the CNRS PEPS project ACUMULTIPLAS and the ITMO Cancerin the frame of the Plan Cancer, project N°17CP086-00.References[1] L. Brulé et al, Plos One 7, 0052653 (2012)[2] H R Metelmannet al, CPM, 9, 6(2018)

International audience; Over the past decade, there has been a growing interest in the development of cold atmosphericpressure plasmas for new biomedical applications. This so called Plasma Medicine concernsvarious clinical indications, including infectious diseases and recently, cancer treatment [1].Besides encouraging demonstrations, it has been shown that tolerance and safety issues should beconsidered with great care for any therapeutic application [2]. A new generation of applicators,able to generate multiple jets from a single primary plasma jet, has been developed and qualifiedthrough in vitro experiments. Moreover, they have shown multiple interests (cf. the presentation ofTh. Maho and colleagues in this conference).Using one of these multijet plasma sources, we have proceeded to in vivo treatments on healthymice skin. Various assays have been carried, on nude mice (hairless mice) and CBl57/6 mice (hairymice), which skins have different properties. The distance between the nozzle and the skin surfaceof the treated mouse can be adjusted by applying a spacer (in order to guarantee a constant gapduring treatment - spacer not shown). The presence or absence of skin damages caused by theplasma was assessed as a function of time, distance and delivered power.Fig. 1: Assays of multijet plasma source from single Plasma Gunon Nude mouse (left) and CBl57/6 mouse (right)Between the applicator and the target, plasma jets could appear either clearly separated from eachother or as a more diffuse discharge. Depending on the distance set between the nozzle and thetissue, different thermal effects and skin damages have been observed. The experimental resultsobtained from the characterization of these variables and their effects on the healthy mouse skinsurface will be presented. These promising results will be used as guidance for the application ofmultijet plasma on decontamination procedures (cf. the presentation of Th. Maho et al.).AcknowledgementsThis work was supported by the CNRS PEPS project ACUMULTIPLAS and the ITMO Cancer inthe frame of the Plan Cancer, project N°17CP086-00.References[1] M. Vandamme et al, Plasma Medicine 1(1): 27-43 (2011)[2] S. Kos et al, PLoS ONE 12(4), e0174966 (2017)

International audience; The study of plasma jets operating in free jet mode and on conductive targets relevant for biomedical applications is discussed. The simultaneous diagnostics of helium metastable through laser absorption, electric field (EF) with an electro-optic probe and current appears as a unique approach to get deep insights on the mechanisms triggered when primary ionization wave (IW), driving the plasma jet propagation, impacts the target. Secondary IWs, back and forth travelling from the plasma jet powered electrode and the grounded target, is measured and may result, depending on the operating parameters of the device, in the transition to a glow like discharge. In such situation, huge enhancement of reactive species production is triggered in connection with significant increase of current flowing through the target. This study allow for a better analysis of the plasma jet delivery on target relevant for biomedical applications and open up opportunities to control reactive species concentration and current amplitude in such experiments. These experimental results are in good agreement with modeling work recently published by group of M.J. Kushner (University of Michigan) on the plasma jet touching or not targets of various natures. The second aspect of the study deals with the characterization of both the amplitude and the topology of the transient EF generated in the vicinity of the plasma jets. Time resolved longitudinal and radial EF, with respect to the jet propagation axis, having amplitudes ranging from a few to a few tens of kV/cm have been measured. There also a good agreement is achieved with modeling data from the group of A. Bourdon (LPP laboratory) which allow extending this diagnostics to region where experimental analysis is hard or disturbing with our probe. It is probably worth considering such intense EF with respect to their potential impact on biological samples.

International audience; In this preliminary work, we showed that a kHz plasma jet can induce cell membrane permeabilization. Those results have been compared to electropermeabilization and indicate that permeabilization by plasma is less efficient, which is probably due to the fact that in electropermeabilization a current gets through the cells. We also showed that chemistry and/or electric field induced by plasma plays a role in cell permeabilization.

International audience; Compelling evidence suggests that Cold Atmospheric Pressure Plasma (CAPPs) has potential as a new cancer therapy. However, knowledge about cellular signaling events and toxicity subsequent to plasma treatment of is still poorly documented. The aim of this study was to focus on the interaction between 3 different types of plasma (He, He-O2, He-N2) and human epithelial cell lines to gain better insight into plasma-cell interaction. We choose epithelial cell lines (human keratinocytes, human fibroblasts, human colorectal carcinoma and skin melanoma) to gain insight into plasma-cell interaction and to determine which cellular pathways are induced by CAPP treatment in normal and malignant cells. We provide evidence that the proteasome, a major intracellular proteolytic system which is important for tumor cell growth and survival, is a target for (He or He-N2) CAPP. This is accompanied by apoptosis, DNA damage, mitochondrial dysfunction and mild oxidative protein damage. By differential label-free quantitative proteomic analysis we found that CAPP triggers antioxidant and cellular defense but also seen cancerous processes in keratinocytes. Moreover we found that malignant cells are more resistant to CAPP treatment than normal cells. However, reactiveoxygen and nitrogen species (RONS) are not the only actors involved in cell death; electric field and charged particles could play a significant role especially for He-O2 CAPP. Particular attention was paid to the contribution of the electric field (EF) and RONS in cellular response to plasma treatment. Taken together, our findings provide insight into potential mechanisms of CAPP-induced cell death.

International audience; Cold atmospheric pressure plasmas have demonstrated their ability in biomedical applications thanks to their low gas temperature and their capacity to produce radicals, ions, electrons, UV radiation and electric field. However, the understanding of the interactions between plasma, living cells and tissues is still far from being completely understood. Several studies have shown that plasma could be used to enhance cell permeabilization to deliver chemotherapy [1] or nucleic acids [2].In this work, we investigated the parameters needed for helium plasma to induce a cell membrane permeabilization on cancerous cells for drug delivery purposes. Using our optimal settings, different fluorescent molecular markers were used in order to determine pore size, opening kinetics and the importance of endocytosis in the process. We were able to deliver propidium iodide in almost 30% of HeLa cells 30 minutes after plasma treatment generated at 14kV, a frequency of 100Hz during 100s using 0.5slm of helium. No significant cytotoxicity was measured 24h after treatment. Efficient drug delivery was obtained using molecules up to 70kDa (figure 1). Experiments using plasma activated media were done to understand the contribution of radical formation on cell membrane permeabilization. The influence of plasma-generated electric field has also been investigated. For this purpose, a dielectric barrier was used between the plasma and the biological target. A comparison with and without the barrier will be presented for biological application. In conclusion drug delivery using plasma is dependent of the electric field, endocytosis and plasma-induced chemistry. Figure 1. Fluorescence microscopy of HeLa cells 30 minutes after treatment by helium plasma in the presence of propidium iodide, 70kDa FITC-Dextran or 150kDa FITC-Dextran.References[1] W. Zhu, et al., Scientific Report, 6, 21974 (2016).[2] M. Jinno, et al., Arch. Biochem. Biophys, 605, 59 (2016).

International audience; The antitumor action of Low Temperature Non Thermal Plasma (LTNTP) has been now widely demonstrated both in vitro and in vivo (on animal models and more recently on human [1]) on a large variety of cancer cell lines and tumor types. Nevertheless, due to the great variety of plasma components able to play a role, the precise understanding of the process chain leading to the observed effects is far to be reached. It is not easy to isolate or to measure the plasma component individual action or, in contrast, to evaluate the potential benefit or synergy of combined ones. Up to now, many experiments in vitro have been realized with that intention, but the translation to in vivo results is rather complicated, even, in many cases, impossible due to the complex environment of the cells in vivo, including vascularization (then blood flow and oxygenation/physioxia) and the body response (signaling, recruitment, immune system). Generally, the first step of dedicated studies concerns in vitro cell viability or toxicity in culture media with the analysis of both the induced changes in the cells and in the medium. It must be stressed that the used experimental conditions together with the fact to treat cells in multiwell plates outside their incubation chamber may generate cell stress that can affect their behavior and then leading to biased results. This presentation will show some of the issues and challenges associated with in vitro cancerous cells treatments by a plasma jet (here a Plasma Gun), also in relation with in vivo conditions associated with the hypoxic/physioxic environment.We will present results on direct effect of plasma treatment on both the culture medium and cells, including liquid evaporation, oxygen deprivation, extra and intracellular RONS generation, membrane poration, cell depolarization, with the potential role of electric field in the treated and adjacent wells [2]. We will particularly emphasize the importance of cell oxygenation level which is a key factor in the proliferation/regression of tumors in hypoxic environment. It will be shown that an uncontrolled plasma jet in vitro treatments can lead to drastic changes in the oxygen pressure (and temperature) in cell culture during the experiment with sequences of maxima (leading to normoxia) and minima (potentially leading to strong hypoxia). The latter contrasts with the plasma oxygen pressure and blood flow increases measured in the in vivo conditions [3]. This also means that a great attention must paid in the modeling of interactions of plasma jets with physiological liquid media since the initial concentration of oxygen can be greatly affected. AcknowledgmentsThis work is founded by ARD 2020 Cosmetoscience PLASMACOSM project. X.D. is supported by INEL/Region Centre-Val de Loire fellowship.References[1] Metelmann et al, Clinical Plasma Medicine, 3 17-23 (2015).[2] E. Robert, T. Darny, S. Dozias, S. Iseni, and J. M. Pouvesle, Phys. Plasmas 22, 122007 (2015).[3] G. Collet, E. Robert, A. Lenoir, M. Vandamme, T. Darny, S. Dozias, C. Kieda, and J. M. Pouvesle, Plasma Sources Sci. Technol.23, 012005 (2014).

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Micro plasma jets operating at atmospheric pressure in free atmosphere have recently attracted great attention because of their numerous advantages. In fact, micro plasma jets can be operated stably at atmospheric pressure and propagated over some centimeters in a free atmosphere. Moreover, these jets are non-thermal plasmas and create numerous reactive species. These properties allow to use this kind of plasma in many applications, such as surface treatment, decontamination, and plasma medicine.In this work it is shown that these micro plasma jets correspond to the fast propagation of an ionization front with no displacement of matter. A characterization of the plasma proprieties (e.g. distance and velocity of propagation) has been done as a function of the applied voltage, gas flow, gas composition and discharge geometry. The spatiotemporal distribution of the reactive species created by the plasma has been measured, with a special focus on the helium metastable atoms which have been measured by absorption laser spectroscopy. The helium metastable atom densities obtained are in the range of 1.10¹² to 5.10¹³ cm-³. Thanks to a very good spatiotemporal resolution, we have done a time-resolved full cartography of the plasma. This allowed us to show that the helium metastable atom distribution is annular near the nozzle and becomes circular as the plasma propagates. The maximum helium metastable atoms density has been measured at about half of the distance where the helium metastable atoms are present. This observation is in contradiction with results reported by numerical models. To gain further insight into the physical processes of the plasma, we have placed two micro plasma jets face to face. This study showed that both plasmas interact in such a way that they never come into contact, letting a space free of plasma between them. Moreover, we revealed that after the extinction of the plasmas, a second discharge is ignited in the previously free space. Fast imaging, spectroscopy diagnostics and electrical measurements showed that this second discharge is due to a polarity reversal, which creates an electron trap. Aiming the study of the application of micro plasma jets in the plasma medicine field, we have studied the degradation of plasmid DNA by our plasma jet. We observed that the plasma treatment leads mostly to single and double strands breaks, and to very little base oxidation and abasite site, even when oxygen is added into the gas mixture., Ces dernières années un nouveau type de décharges hors équilibre thermodynamique, aptes à générer des micro jets de plasma se propageant en atmosphère libre, a suscité beaucoup d’intérêt dans la communauté scientifique. Ces micro jets, produits dans des structures type décharge à barrière diélectrique, ont des propriétés particulièrement intéressantes, tant sur le plan de la physique des plasmas que sur celui des applications, en particulier pour des applications biomédicales ou de traitement de surface.Dans ce travail de thèse il est démontré que ces jets de plasma correspondent à la propagation à grande vitesse d'un front d'ionisation sans déplacement de matière. Une caractérisation des propriétés des jets (vitesse et distance de propagation) a été effectuée en fonction de la tension appliquée, du débit, de la composition du gaz, et de la géométrie de la décharge. La distribution spatio-temporelle des espèces réactives produites par le jet a été mesurée, et en particulier celle de l'état métastable He (2³S) mesuré par absorption laser. Des densités comprises entre 1.10¹² et 5.10¹³ cm-³ ont été obtenues pour l’état He (2³S). Sa distribution est annulaire à la sortie de la structure de la décharge et se referme le long du jet. La densité maximale est obtenue à une distance correspondant à la moitié de la zone où les atomes métastables sont présents, ce qui est en contradiction avec les modèles actuels. De plus, afin de mieux comprendre la physique des jets de plasma, nous avons fait interagir deux jets placés l’un en face de l’autre. L'étude de la contre propagation de deux jets révèle qu’il existe une distance minimale d'approche laissant entre eux une zone exempte de plasma. Après l’extinction des deux plasmas, une seconde décharge s’amorce exactement dans cette zone. Une étude détaillée couplant diagnostics électrique, imagerie ultra-rapide et spectroscopie d'émission nous a permis de montrer que cette décharge secondaire est due à une inversion de polarité conduisant à la création transitoire d'un piège à électrons.Dans le but d'aborder l'étude des applications des jets de plasma au domaine biologique, nous avons également étudié la dégradation de l’ADN plasmidique par un jet de plasma. Nous avons mis en évidence que ce type de plasma induit majoritairement des cassures simples et doubles brins, alors que très peu d’oxydations de base ou de sites abasiques sont observés, ceci même avec l’ajout de quelques pourcents d’oxygène dans le gaz.