Augusto Stancampiano

Characterization of a Cold Atmospheric Pressure Plasma Jet Device Driven by Nanosecond Voltage Pulses

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 107-108 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 (N2, N2+ , OH, and NO emission bands); total UV irradiance was lower than 1 μW/cm2 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.

Cold Atmospheric Plasma Induces Apoptosis and Oxidative Stress Pathway Regulation in T-Lymphoblastoid Leukemia Cells

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.

Practical and theoretical considerations on the use of ICCD imaging for the characterization of non-equilibrium plasmas

Over the past decade the use of ICCD cameras as a means for characterizing non-equilibrium plasmas has been steadily increasing. Due to their high sensitivity and high speed gateability, ICCD cameras enable time-resolved studies of the anatomy and, when adopted in conjunction with filters, monochromators, spectrometers or laser systems, time-resolved investigation of physical and chemical properties of non-equilibrium plasma discharges. This paper is meant as an introduction to ICCD technology and its use as a plasma diagnostic technique, discussing the experimental problems typically associated with its use and providing the readers with practical examples and suggestions on how to address them. In particular, the issues of ICCD camera synchronization with the voltage pulse driving the plasma discharge and of investigating small volume discharges are addressed, focusing mainly on the case of non-equilibrium atmospheric pressure plasma jets. Finally, a possible way to achieve absolute calibration of plasma discharge emission is presented and discussed. A wide range of data, mostly unpublished, is provided here to illustrate the points.

Investigation of the antimicrobial activity at safe levels for eukaryotic cells of a low power atmospheric pressure inductively coupled plasma source

Low power atmospheric pressure inductively coupled thermal plasma sources integrated with a quenching device (cold ICP) for the efficient production of biologically active agents have been recently developed for potential biomedical applications. In the present work, in vitro experiments aimed at assessing the decontamination potential of a cold ICP source were carried out on bacteria typically associated with chronic wounds and designed to represent a realistic wound environment; further in vitro experiments were performed to investigate the effects of plasma-irradiated physiological saline solution on eukaryotic cells viability. A thorough characterization of the plasma source and process, for what concerns ultraviolet (UV) radiation and nitric oxide production as well as the variation of pH and the generation of nitrates and nitrites in the treated liquid media, was carried out to garner fundamental insights that could help the interpretation of biological experiments. Direct plasma treatment of bacterial cells, performed at safe level of UV radiation, induces a relevant decontamination, both on agar plate and in physiological saline solution, after just 2 min of treatment. Furthermore, the indirect treatment of eukaryotic cells, carried out by covering them with physiological saline solution irradiated by plasma, in the same conditions selected for the direct treatment of bacterial cells does not show any noticeable adverse effect to their viability. Some considerations regarding the role of the UV radiation on the decontamination potential of bacterial cells and the viability of the eukaryotic ones will be presented. Moreover, the effects of pH variation, nitrate and nitrite concentrations of the plasma-irradiated physiological saline solution on the decontamination of bacterial suspension and on the viability of eukaryotic cells subjected to the indirect treatment will be discussed. The obtained results will be used to optimize the design of the ICP source for an effective production of reactive species, while keeping effluent temperature and UV radiation at values compatible with biomedical treatments.

High-Speed and Schlieren Imaging of a Low Power Inductively Coupled Plasma Source for Potential Biomedical Applications

High-speed and Schlieren imaging have been used to visualize ignition transients, discharge behavior and flow fields of a plasma device integrating a low-power inductively coupled plasma torch, generating a high temperature thermal plasma, with a quenching device, able to cool the gaseous effluent down to biocompatible temperatures for effective use in biomedical applications.

Comparing the effect of different atmospheric pressure non-equilibrium plasma sources on PLA oxygen permeability

Plasma technology is widely adopted for polymer surface modification. In this work polylactide (PLA) samples have been exposed to the plasma region generated by three different plasma sources operating at atmospheric pressure: a floating electrode dielectric barrier discharge (FE-DBD), a novel linear corona discharge and a DBD roller. The sources have been supplied with a high voltage generator capable of producing pulses with a rise rate in the order of several kV/ns in order to obtain diffuse plasma and avoid local damage to the membrane; air and argon have been used as working gases. Pure oxygen permeation tests in PLA films have been carried out by means of a closed-volume manometric apparatus working at 35°C with a pressure difference of pure O2 of about 1 bar applied across the membrane. Tests have been performed shortly after the plasma treatment and also replicated at different times in order to investigate the durability of surface modification. The effects of voltage, pulse repetition frequency (PRF) and exposure time on the membrane surface characteristics and barrier property have been studied.

iCCD Imaging of the Transition From Uncoupled to Coupled Mode in a Plasma Source for Biomedical and Materials Treatment Applications

Intense and energetic atmospheric plasma was achieved by jet-to-jet coupling using an array of plasma jets arranged in an axisymmetric structure. To highlight the effects of pulse repetition frequency, peak voltage and mass flow rate on the transition from a coupled mode to an uncoupled one, qualitative results coming from iCCD imaging of a nanopulsed Gatling machine gun-like plasma source will be shown. Moreover, results on surface modifications and bacterial inactivation will be presented.

Cold Atmospheric Plasma Treatment of Infected Skin Tissue: Evaluation of Sterility, Viability, and Integrity

Sterilization of equipment and tissues is a common clinical practice: there are different chemical, mechanical, and electromagnetic aseptic techniques for inactivating microorganisms. In particular, skin tissue banks are investigating new methods to efficiently decolonize skin tissues, while preserving their structural features. In recent years, cold atmospheric plasma (CAP) has demonstrated bactericidal, virucidal, and fungicidal properties, due to the generation of reactive species and charged particles. For this reason, the aim of this paper is to demonstrate that the implementation of a dielectric barrier discharge (DBD) treatment in air can effectively decontaminate skin tissue from Staphylococcus aureus, retaining cell viability and skin integrity. Fresh skin samples, taken from multitissue donors, were contaminated with Staphylococcus aureus and treated with a DBD source, to verify the level of bacterial decontamination induced by plasma. Cell viability and structural properties of skin tissue were investigated using MTT assay and hematoxylin-eosin staining, respectively. Our results show that CAP can sterilize skin tissue with a bacterial load up to 103 CFU/cm2; moreover, it does not affect cell viability, and no loss of skin structural properties was observed. Thus, CAP treatment could be considered an innovative method for decolonization of human skin, without inducing any microscopic tissue damage, while keeping good cell viability.

High-Speed Multi-Imaging of Repetitive Unipolar Nanosecond-Pulsed DBDs

Dielectric barrier discharges (DBDs) are being studied for a wide range of biomedical and industrial applications. In this paper, qualitative results coming from synchronized high-speed and Schlieren multi-imaging of a unipolar nanosecond-pulsed DBD are presented, with the final aim of showing plasma structure, filament movement, and refractive index gradients in different interelectrode gaps and counter electrode materials.

Parametric study on the effectiveness of treatment of polyethylene (PE) foils for pharmaceutical packaging with a large area atmospheric pressure plasma source

Atmospheric pressure plasmas have been developed in the last decades for many material treatment applications such as cleaning and activation of surfaces, interaction with in-vivo and in vitro tissues and, as such, they play an increasing role in disinfection and sterilization of surfaces. Heat sensitive polymers can be plasma treated with the final aim of microbial inactivation: given for granted such a capability for many different atmospheric pressure plasma sources, in this work, we focus on the investigation of the effectiveness of the treatment of a polyethylene (PE) polymer foil commonly used for pharmaceutical packaging by means of a Dielectric Barrier Discharge (DBD) operated on a “large area” at atmospheric pressure in ambient air. For effectiveness of the treatment we considered the uniformity of the variation of water contact angle (WC) induced by the plasma on different positions of the treated area (for example, 160×300 mm) and the capability not to affect negatively the properties of the plasma treated packaging material in terms of weldability (for example, hot plate weldability). The surface of the polymer foil has been characterized by measuring the variation of water contact angle (WCA) in different position on the treated sample; Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR-FTIR) has been used to investigate the surface oxidation of the treated samples; moreover, polymer weldability after plasma treatment has been tested on a packaging machine that includes a contact hot plate. This procedure allowed correlating surface oxidation with polymer weldability and with plasma treatment parameters. Results show that it is possibile to select geometrical (DBD gap width; for example, 2mm) and generator operating conditions (for example, 12kV, 100Hz) suitable to obtain uniform change in WCA (for example from 98.2° to 55°) while maintaining good weldability for the treated material. Aging of the treated polymer for what concerns WCA has also been considered, together with treatment time compatible with the final industrial on-line treatment, forming and welding process.