Romolo Laurita

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.

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.

Plasma assisted nanoparticle dispersion in polymeric solutions for the production of electrospun lithium battery separators

Electrospun nanofibrous mats loaded with inorganic nanoparticles can find application as separators for lithium-ion batteries. A good disaggregation of nanoadditive in the starting polymeric solution is a necessary condition to obtain fibers with homogeneous dispersion of nanoparticles, thus with improved mechanical, thermal and electrical properties. In this work atmospheric pressure non-equilibrium plasma was applied to polymeric solutions to evaluate its effects on nanoparticle dispersion for obtaining electrospun fibers loaded with homogeneously dispersed nanoparticles. To this aim, different kinds of plasma treatments and procedures were implemented and their effect on particle distribution in electrospun fibers was investigated. We demonstrated that plasma is a valuable and effective way to favour nanoparticles dispersion in polymeric solutions.

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.

Poly-l-Lactic Acid Nanofiber-Polyamidoamine Hydrogel Composites: Preparation, Properties, and Preliminary Evaluation as Scaffolds for Human Pluripotent Stem Cell Culturing

Electrospun poly-l-lactic acid (PLLA) nanofiber mats carrying surface amine groups, previously introduced by nitrogen atmospheric pressure nonequilibrium plasma, are embedded into aqueous solutions of oligomeric acrylamide-end capped AGMA1, a biocompatible polyamidoamine with arg-gly-asp (RGD)-reminiscent repeating units. The resultant mixture is finally cured giving PLLA-AGMA1 hydrogel composites that absorb large amounts of water and, in the swollen state, are translucent, soft, and pliable, yet as strong as the parent PLLA mat. They do not split apart from each other when swollen in water and remain highly flexible and resistant, since the hydrogel portion is covalently grafted onto the PLLA nanofibers via the addition reaction of the surface amine groups to a part of the terminal acrylic double bonds of AGMA1 oligomers. Preliminary tested as scaffolds, the composites prove capable of maintaining short-term undifferentiated cultures of human pluripotent stem cells in feeder-free conditions.

Study of the effect of atmospheric pressure plasma treatment on electrospinnability of poly-L-lactic acid solutions: Voltage waveform effect

Polymeric nanofibrous mats are currently used for biomedical applications as tissue engineering scaffolds. Electrospinning is an innovative and efficient technology to produce scaffolds starting from a polymeric solution. However, toxic organic solvents must be frequently used to produce fibers with good morphology. In particular, high boiling solvents are often helpful for improving polymer electrospinnability. Nevertheless, toxic traces may be found in the final electrospun mat. In order to minimize the use of organic solvents, particularly the high boiling point ones, while maintaining good electrospinnability of the polymeric solution, the latter can be exposed to plasma. In this work we investigate the use of a novel treatment enabling the production of good quality nanofibers starting from a polymer dissolved in 100% of a low boiling point solvent. This treatment consists in the exposure of the polymeric solution to an atmospheric pressure non-thermal plasma before the electrospinning process. Plasma can be driven by several bias showing different waveforms. In this study the waveform influence on the electrospinnability of the plasma treated solution is investigated.

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.

Interaction between cold atmospheric plasma and phytoplasmas in micropropagated infected periwinkle shoots

Plasma activated water (PAW) was employed to treat phytoplasma infected micropropagated periwinkle shoots to verify effects on symptomatology and phytoplasma presence. The preliminary results indicate that PAW do not induce shoot toxicity, and allow an improved detection of phytoplasma presence in shoots and also in liquid phytoplasma isolation medium. The reduced symptomatology and the lack of colony formation from liquid isolation medium induce to speculate that PAW interact with phytoplasmas and/or endophytes viability. Research to verify these aspects are in progress.

Atmospheric plasma surface modification of electrospun poly(L-lactic acid): Effect on mat properties and cell culturing

Summary form only given.Material science applied to regenerative medicine and tissue engineering study the achievement of biocompatible artificial tissues to improve, self-repair or favour cellular therapies. Various studies prove plasma ability to modify polymeric scaffold surface, with an improvement of hydrophilicity and surface roughness demonstrated by a reduction of contact angle and by an increase of surface energy without altering bulk properties. Furthermore, it was demonstrated that cell cultures on plasma modified scaffolds display better proliferation and viability compared to pristine materials. In this work we focus on the use of atmospheric pressure non-thermal plasma for surface modification of electrospun poly(L-lactic acid) (PLLA) non-woven mats. The electrospinning technology allows to fabricate scaffolds of polymeric materials with highly porous structure, interconnected pores and large specific surface area, that mimic extracellular matrix (ECM). In this work results will be presented concerning the process of exposure of electrospun scaffolds to the plasma region generated by three different plasma sources operated at atmospheric pressure: a floating electrode dielectric barrier discharge (FE-DBD), a linear corona discharge and a DBD roller. A high voltage generator capable of producing pulses with a rise rate in the order of some kV/ns has been used. All the sources are easily scaled-up in the frame of a “large area treatment” approach. Plasma sources characterization has been carried out through a wide set of measurements, changing operating conditions, geometry and plasma gas composition, as the fundamental stage in a multi-step approach for process optimization. In this work, results on the effect of plasma treatment on morphology, thermo-mechanical and surface properties of PLLA electrospun nanofibrous mats will be presented. Results for the introduction of COOH functional group on PLLA electrospun scaffold and for the proliferation of rat embryonic stem cells (RESCs) grown on plasma treated and untreated PLLA electrospun scaffolds will be presented and discussed.

Fluid-dynamic characterization of atmospheric pressure non-equilibrium plasma sources for biomedical applications

Summary form only given. The complexity of plasma interaction with biological material and the stiff requisites imposed by biomedical treatments put a premium on diagnostics as a means to investigate process feasibility and to develop plasma sources tailored for specific applications. Among the several diagnostic techniques adopted in the field of cold non-equilibrium atmospheric pressure plasmas, optical emission spectroscopy (OES), high speed imaging (HSI) and Fourier transform infrared spectroscopy (FTIR) are widely used.