Anna Liguori

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.

Atmospheric Pressure Non-Equilibrium Plasma as a Green Tool to Crosslink Gelatin Nanofibers

Electrospun gelatin nanofibers attract great interest as a natural biomaterial for cartilage and tendon repair despite their high solubility in aqueous solution, which makes them also difficult to crosslink by means of chemical agents. In this work, we explore the efficiency of non-equilibrium atmospheric pressure plasma in stabilizing gelatin nanofibers. We demonstrate that plasma represents an innovative, easy and environmentally friendly approach to successfully crosslink gelatin electrospun mats directly in the solid state. Plasma treated gelatin mats display increased structural stability and excellent retention of fibrous morphology after immersion in aqueous solution. This method can be successfully applied to induce crosslinking both in pure gelatin and genipin-containing gelatin electrospun nanofibers, the latter requiring an even shorter plasma exposure time. A complete characterization of the crosslinked nanofibres, including mechanical properties, morphological observations, stability in physiological solution and structural modifications, has been carried out in order to get insights on the occurring reactions triggered by plasma.

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.

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.

Non-equilibrium atmospheric pressure plasma as innovative method to crosslink and enhance mucoadhesion of econazole-loaded gelatin films for buccal drug delivery

In this paper we developed an innovative, effective and rapid one-step approach to crosslink mucoadhesive gelatin films for buccal drug delivery. The method, which involves the application of non-equilibrium pressure plasma for 3 or 5 minutes/side, was compared with a classical approach based on the use of a chemical crosslinking agent, namely genipin. Econazole nitrate (ECN), an imidazole antifungal agent used for the treatment of skin infections and mucosal candidiasis, was selected as model drug. X-Ray Diffraction characterization performed on the drug-containing gelatin films revealed that ECN undergoes to a topotactic transformation into Econazole (EC) immediately after mixing with gelatin suggesting the occurrence of an acid-base reaction between drug and gelatin during film processing. Plasma treatment, as well as genipin crosslinking, did not provoke any further variation of EC structure. However, plasma exposure significantly improved films adhesiveness and allowed to reach mucoadhesive strength values more than double with respect to those obtained with genipin, ascribable to the presence of polar and hydrophilic groups on the plasma treated films surface. A residence time of at least 48 h was obtained by properly selecting the plasma exposure times. These results, together with the in-vitro data showing retention of antifungal efficacy against a strain of Candida albicans, demonstrated that plasma treatment was a valid and rapid alternative, easy to scale-up, to chemical crosslinking methods for the production of highly mucoadhesive gelatin-based films.

Antibody immobilization on poly(L-lactic acid) nanofibers advantageously carried out by means of a non-equilibrium atmospheric plasma process

In the present study, the comparison between a conventional wet-chemical method and a non-equilibrium atmospheric pressure plasma process for the conjugation of biomolecules on the surface of poly(L-lactic acid) (PLLA) electrospun fibers is reported. Physico-chemical and morphological characteristics of chemically and plasma functionalized mats are studied and compared with those of pristine mats. The efficiency in biomolecules immobilization is assessed by the covalent conjugation of an antibody (anti-CD10) on the functionalized PLLA fibers. The achieved results highlight that the proposed plasma process enables antibodies to be successfully immobilized on the surface of PLLA fibers, demonstrating that non-equilibrium atmospheric pressure plasma can be an effective, highly flexible and environmentally friendly alternative to the still widely employed wet-chemical methods for the conjugation of biomolecules onto biomaterials.

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.

Synthesis of Copper-Based Nanostructures in Liquid Environments by Means of a Non-equilibrium Atmospheric Pressure Nanopulsed Plasma Jet

The influence of the liquid composition on the chemical and morphological properties of copper-based nanostructures synthesized by a non-equilibrium atmospheric plasma treatment is investigated and discussed. The synthesis approach is simple and environmentally friendly, employs a non-equilibrium nanopulsed atmospheric pressure plasma jet as a contactless cathode and a Cu foil as immersed anode. The process was studied using four distinct electrolyte solutions composed of distilled water and either NaCl + NaOH, NaCl only or NaOH only at two different concentrations, without the addition of any copper salts. CuO crystalline structures with limited impurities (e.g. Cu and Cu(OH)2 phases) were produced from NaCl + NaOH containing solutions, mainly CuO and CuCl2 structures were synthesized in the electrolyte solution containing only NaCl and no synthesis occurred in solutions containing only NaOH. Both aggregated and dispersed nanostructures were produced in the NaCl + NaOH and NaCl containing solutions. Reaction pathways leading to the formation of the nanostructures are proposed and discussed.