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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 demonstrated recently to possess selective properties on killing cancer cells and attract attention towards 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 2between 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 Sarcoma Osteogenic (SaOS-2) cell line exposed to plasma-treated gelatin lead to timedependent increasing cytotoxicity with the longer plasma treatment time of gelatin. While SaOS-2 cell viability decreased down to 12%-23% after 72 hours for cells exposed to 3-min treated gelatin, viability of healthy cells (hMSC) was preserved (around 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.

Cold atmospheric plasma (CAP) has shown its antitumor activity in both in vitro and in vivo systems. However, the mechanisms at the basis of CAP-cell interaction are not yet completely understood. The aim of this study is to investigate CAP proapoptotic effect and identify some of the molecular mechanisms triggered by CAP in human T-lymphoblastoid leukemia cells. CAP treatment was performed by means of a wand electrode DBD source driven by nanosecond high-voltage pulses under different operating conditions. The biological endpoints were assessed through flow cytometry and real-time PCR. CAP caused apoptosis in Jurkat cells mediated by p53 upregulation. To test the involvement of intrinsic and/or extrinsic pathway, the expression of Bax/Bcl-2 and caspase-8 was analyzed. The activation of caspase-8 and the upregulation of Bax and Bcl-2 were observed. Moreover, CAP treatment increased ROS intracellular level. The situation reverts after a longer time of treatment. This is probably due to compensatory cellular mechanisms such as the posttranscriptional upregulation of SOD1, CAT, and GSR2. According to ROS increase, CAP induced a significant increase in DNA damage at all treatment conditions. In conclusion, our results provide a deeper understanding of CAP potential in the oncological field and pose the basis for the evaluation of its toxicological profile.

Non-thermal plasma (NTP) medical applications are now well established but the translation from in vitro plasma effects to in vivo effects remains far from being intuitive. Among various possible reasons, the translation may be disturbed by a loose control over the electrical characteristics of the different targets (e.g. cell culture dish, animal models) met during the development process, a parameter generally neglected and often unmentioned in papers. The aim of this study is to raise consciousness on how target electrical parameters (e.g. conductivity, electric potential…) play a major role in determining plasma treatment conditions. This effect is of particular relevance in plasma medicine where we move from treating small in vitro samples to humans, passing by animal models. The plasma conditions on targets with different electrical characteristics are compared by means of electrical measurements, optical emission spectroscopy and basic liquid analysis. Commonly tested in vitro targets induce the generation of a plasma significantly different from that produced in contact with a human body. We demonstrate how by means of a basic and easy to implement electrical circuit it is possible to "compensate" the electrical differences between in vitro models, mice and human body and in such a way to reach more reproducible treatment conditions between in vitro and in vivo targets. The proposed method for the control of the target electrical parameters could greatly favor the transition from in vitro and in vivo models to patients for many plasma devices developed for biomedical applications.

The structure, fluid-dynamic behavior, temperature, and radiation emission of a cold atmospheric pressure plasma jet driven by high-voltage pulses with rise time and duration of a few nanoseconds have been investigated. Intensified charge-coupled device (iCCD) imaging revealed that the discharge starts when voltage values of 5-10 kV are reached on the rising front of the applied voltage pulse; the discharge then propagates downstream the source outlet with a velocity around 10 7 -10 8 cm/s. Light emission was observed to increase and decrease periodically and repetitively during discharge propagation. The structure of the plasma plume presents a single front or either several branched subfronts, depending on the operating conditions; merging results of investigations by means of Schlieren and iCCD imaging suggests that branching of the discharge front occurs in spatial regions where the flow is turbulent. By means of optical emission spectroscopy, discharge emission was observed in the ultraviolet-visible (UV-VIS) spectral range (N 2 , N + 2 , OH, and NO emission bands); total UV irradiance was lower than 1 µW/cm 2 even at short distances from the device outlet (<15 mm). Plasma plume temperature does not exceed 45 °C for all the tested operating conditions and values close to ambient temperature were measured around 10 mm downstream the source outlet.

The interaction of plasmas and liquid aerosols offers special advantages and opens new perspectives for plasma–liquid applications. The paper focuses on the key research challenges and potential of plasma-aerosol interaction at atmospheric pressure in several fields, outlining opportunities and benefits in terms of process tuning and throughputs. After a short overview of the recent achievements in plasma–liquid field, the possible application benefits from aerosol injection in combination with plasma discharge are listed and discussed. Since the nature of the chemicophysical plasma-droplet interactions is still unclear, a multidisciplinary approach is recommended to overcome the current lack of knowledge and to open the plasma communities to scientists from other fields, already active in biphasic systems diagnostic. In this perspective, a better understanding of the high chemical reactivity of gas–liquid reactions will bring new opportunities for plasma assisted in-situ and on-demand reactive species production and material processing.

Successful plasma-polymerization of acrylic acid (AA), aimed at depositing plasmapolymerized polyacrylic acid (pPAA) coatings stable upon water contact with a high amount of carboxyl groups, using a non-equilibrium atmospheric pressure nanopulsed plasma jet is reported. Special attention is devoted to the surface chemical characterization of the pPAA coatings deposited on pristine and plasma pretreated polymeric substrates. The investigation of the pPAA chemical structure is performed by means of attenuated total reflectance-Fourier transform infrared and X-ray photoelectron spectroscopies. Insights on the morphological characteristics of the coatings are also provided by optical microscopy.

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