In this work we report the surface modification of different engineering polymers, such as, polyethylene terephthalate (PET), polyethylene (PE) and polypropylene (PP) by an atmospheric pressure plasma jet (APPJ). It was operated with Ar gas using 10 kV, 37 kHz, sine wave as an excitation source. The aim of this study is to determine the optimal treatment conditions and also to compare the polymer surface modification induced by plasma jet with the one obtained by another atmospheric pressure plasma sourcethe dielectric barrier discharge (DBD). The samples were exposed to the plasma jet effluent using a scanning procedure, which allowed achieving a uniform surface modification. The wettability assessments of all polymers reveal that the treatment leads to reduction of more than 40• in the water contact angle (WCA). Changes in surface composition and chemical bonding were analyzed by x-ray photoelectron spectroscopy (XPS) and Fourier-Transformed Infrared spectroscopy (FTIR) that both detected incorporation of oxygen-related functional groups. Surface morphology of polymer samples was investigated by Atomic Force Microscopy (AFM) and an increase of polymer roughness after the APPJ treatment was found.The plasma-treated polymers exhibited hydrophobic recovery expressed in reduction of the O-content of the surface upon rinsing with water. This process was caused by the dissolution of low molecular weight oxidized materials (LMWOMs) formed on the surface as a result of the plasma exposure.

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Non-thermal atmospheric pressure plasma jets (APPJs) are capable of generating cold plasma plumes that are not confined by electrodes, which makes them very attractive for bio-medical applications. In the present work, the inactivation efficiency of cold APPJ was evaluated against three pathogenic microorganisms with different cell wall characteristics. The Gram-positive bacterium Enterococcus faecalis (ATCC 29212), the Gram-negative bacterium Pseudomonas aeruginosa (ATCC 15442) and the fungus Candida albicans (SC 5314) were plated on standard Petri dishes filled with specific culture media. The plasma jet with mean power of 1.8 W was directed perpendicularly on agar plates and the system was flushed with pure helium at two different flows, 2.0 and 4.0 SLM. During the treatments, time and distance between nozzle and agar were varied. The presence of excited reactive species was confirmed by optical emission spectroscopy. Scanning electron microscopy (SEM) was applied for investigation of cell morphology. The microbicidal efficiency was evaluated by measuring the area of inhibition zone (where there was no cell growth). For different flows of helium, no significant difference of inhibition zone size was noted for the same microbial species. However, high flows led to formation of non-homogenous inhibition zones, presenting microcolonies distributed through the inactivated region. The Gram-positive bacterium was more susceptible to the plasma antimicrobial effects than the other microorganisms.

The aim of this study was to establish an effective and safe protocol for in vivo oral candidiasis treatment with atmospheric plasma jets. A novel amplitude-modulated cold atmospheric pressure plasma jet (AM-CAPPJ) device, operating with Helium, was tested. In vitro assays with Candida albicans biofilms and Vero cells were performed in order to determine the effective parameters with low cytotoxicity. After the determination of such parameters, the protocol was evaluated in experimentally induced oral candidiasis in mice. AM-CAPPJ could significantly reduce the viability of C. albicans biofilms after 5 minutes of plasma exposure when compared to the non-exposed group (p = 0.0033). After this period of exposure, high viability of Vero cells was maintained (86.33 ± 10.45%). Also, no late effects on these cells were observed after 24 and 48 hours (83.24±15.23% and 88.96±18.65%, respectively). Histological analyses revealed significantly lower occurrence of inflammatory alterations in the AM-CAPPJ group when compared to non-treated and nystatin-treated groups (p < 0.0001). Although no significant differences among the values of CFU/tongue were observed among the non-treated group and the groups treated with AM-CAPPJ or nystatin (p = 0.3201), histological analyses revealed marked reduction in candidal tissue invasion. In conclusion, these results point out to a clinical applicability of this protocol, due to the simultaneous anti-inflammatory and inhibitory effects of AM-CAPPJ with low cytotoxicity.

Recently, cold atmospheric plasmas have demonstrated very promising antimicrobial activity in vitro and in vivo including selective destruction of tumor cells. However, the size and the rigidity of most plasma systems limit the clinical application for treatments in internal organs or regions with difficult access (e.g., mouth). Here, we report a device that allows ignition of cold He plasma jet at the tip of 1 m long, 3.5 mm diameter, flexible plastic tube. It is connected to a dielectric enclosure where dielectric barrier discharge (DBD) is generated by a low‐frequency AC power supply. A thin wire at floating potential put inside the plastic tube assists the formation of plasma jet at the downstream tube end. The flexible tube can be kept and manipulated by hand without electric shock and thus the plasma jet can be easily directed to a target. Variation of duty cycle of the applied voltage signal allows precise adjustment of the discharge power. The anti‐microbial efficiency of plasma jet system with flexible tube was tested against fungus Candida albicans seeded on agar.