Advanced Hollow Cathode Discharge Plasma Treatment of Unique Bilayered Fibrous Nerve Guidance Conduits for Enhanced/Oriented Neurite Outgrowth.

Despite all recent progresses in nerve tissue engineering, critical-sized nerve defects are still extremely challenging to repair. Therefore, this study targets the bridging of critical nerve defects and promoting an oriented neuronal outgrowth by engineering innovative nerve guidance conduits (NGCs) synergistically possessing exclusive topographical, chemical, and mechanical cues. To do so, a mechanically adequate mixture of polycaprolactone (PCL) and polylactic-co-glycolic acid (PLGA) was first carefully selected as base material to electrospin nanofibrous NGCs simulating the extracellular matrix. The electrospinning process was performed using a newly designed 2-pole air gap collector that leads to a one-step deposition of seamless NGCs having a bilayered architecture with an inner wall composed of highly aligned fibers and an outer wall consisting of randomly oriented fibers. This architecture is envisaged to afford guidance cues for the extension of long neurites on the underlying inner fiber alignment and to concurrently provide a sufficient nutrient supply through the pores of the outer random fibers. The surface chemistry of the NGCs was then modified making use of a hollow cathode discharge (HCD) plasma reactor purposely designed to allow an effective penetration of the reactive species into the NGCs to eventually treat their inner wall. X-ray photoelectron spectroscopy (XPS) results have indeed revealed a successful O2 plasma modification of the inner wall that exhibited a significantly increased oxygen content (24 → 28%), which led to an enhanced surface wettability. The treatment increased the surface nanoroughness of the fibers forming the NGCs as a result of an etching effect. This effect reduced the ultimate tensile strength of the NGCs while preserving their high flexibility. Finally, pheochromocytoma (PC12) cells were cultured on the NGCs to monitor their ability to extend neurites which is the base of a good nerve regeneration. In addition to remarkably improved cell adhesion and proliferation on the plasma-treated NGCs, an outstanding neural differentiation occurred. In fact, PC12 cells seeded on the treated samples extended numerous long neurites eventually establishing a neural network-like morphology with an overall neurite direction following the alignment of the underlying fibers. Overall, PCL/PLGA NGCs electrospun using the 2-pole air gap collector and O2 plasma-treated using an HCD reactor are promising candidates toward a full repair of critical nerve damage.

Impact of Nonthermal Plasma on Lipid Oxidation from the Perspective of Plasma Treatment Parameters and Plasma Species: Identification of Key Reactive Species.

Nonthermal plasma is a mild processing technology for food preservation. Its impact on lipid oxidation was investigated in this study. Stripped methylesters were considered as a basic lipid model system and were treated by a multihollow surface dielectric barrier discharge. In dry air plasma, O3, ·NO2, ·NO3, and 1O2 were identified as the main reactive species reaching the sample surface. Treatment time was the most prominent parameter affecting lipid oxidation, followed by the (specific) power input and the plasma-sample distance. In humid air plasma, less O3 was detected, but ONOOH and O2NOOH were generated and presumed to play a role in lipid oxidation. Ozone mainly resulted in the formation of carbonyl substances via the trioxolane pathway, while reactive nitrogen species (i.e., ·NO2, ·NO3, ONOOH, and O2NOOH) led to the formation of hydroperoxides. The impact of short-living radicals (e.g., ·O, ·N, ·OH, and ·OOH) was restricted in general, since they dissipated too fast to reach the sample.·NO, HNO3, H2O2, and UV radiation did not induce lipid oxidation. All the reactive species identified in this study were associated with the presence of O2 in the input gas.

Multifaceted polymeric nerve guidance conduits with distinctive double-layered architecture and plasma-induced inner chemistry gradient for the repair of critical-sized defects.

Despite tissue engineering advances, current nerve guidance conduits (NGCs) are still failing in repairing critical-sized defects. This study aims, therefore, at tackling large nerve gaps (2 cm) by designing NGCs possessing refined physicochemical properties enhancing the activity of Schwann cells (SCs) that support nerve regeneration over long distances. As such, a combinatorial strategy adopting novel plasma-induced surface chemistry and architectural heterogeneity was considered. A mechanically suitable copolymer (Polyactive®) was electrospun to produce nanofibrous NGCs mimicking the extracellular matrix. An innovative seamless double-layered architecture consisting of an inner wall comprised of bundles of aligned fibers with intercalated random fibers and an outer wall fully composed of random fibers was conceived to synergistically provide cell guidance cues and sufficient nutrient inflow. NGCs were subjected to argon plasma treatments using a dielectric barrier discharge (DBD) and a plasma jet (PJ). Surface chemical changes were examined by advanced X-ray photoelectron spectroscopy (XPS) micro-mappings. The DBD homogeneously increased the surface oxygen content from 17 % to 28 % on the inner wall. The PJ created a gradient chemistry throughout the inner wall with an oxygen content gradually increasing from 21 % to 30 %. In vitro studies revealed enhanced primary SC adhesion, elongation and proliferation on plasma-treated NGCs. A cell gradient was observed on the PJ-treated NGCs thus underlining the favorable oxygen gradient in promoting cell chemotaxis. A gradual change from circular to highly elongated SC morphologies mimicking the bands of Büngner was visualized along the gradient. Overall, plasma-treated NGCs are promising candidates paving the way towards critical nerve gap repair.

Atmospheric Pressure Microwave Plasma Jet for Organic Thin Film Deposition.

In this work, the potential of a microwave (MW)-induced atmospheric pressure plasma jet (APPJ) in film deposition of styrene and methyl methacrylate (MMA) precursors is investigated. Plasma properties during the deposition and resultant coating characteristics are studied. Optical emission spectroscopy (OES) results indicate a higher degree of monomer dissociation in the APPJ with increasing power and a carrier gas flow rate of up to 250 standard cubic centimeters per minute (sccm). Computational fluid dynamic (CFD) simulations demonstrate non-uniform monomer distribution near the substrate and the dependency of the deposition area on the monomer-containing gas flow rate. A non-homogeneous surface morphology and topography of the deposited coatings is also observed using atomic force microscopy (AFM) and SEM. Coating chemical analysis and wettability are studied by XPS and water contact angle (WCA), respectively. A lower monomer flow rate was found to result in a higher C-O/C-C ratio and a higher wettability of the deposited coatings.

Synthesis of Ag/TiO2 nanocomposite via plasma liquid interactions: Improved performance as photoanode in dye-sensitized solar cell.

Ag/TiO2 nanocomposite was prepared by the atmospheric direct current plasma in aqueous solution to improve its performance in dye-sensitized solar cells (DSSCs) as the photoanode. The fabricated DSSC shows high power conversion efficiency over 6.5% and displays better long-term stability than that of referenced pure TiO2. The comparison of photoluminescence spectra of Ag/TiO2 and pure TiO2 showed that only the Ag containing samples had notable photocurrent under visible light, which was attributed to the highly dispersed Ag, according to the EDS and XRD measurements. The short-circuit current density (Jsc) and open-circuit voltage (Voc) reached 13.43 mA cm-2 and 0.72 V in Ag/TiO2, and 9.44 mA cm-2 and 0.68 V in pure TiO2, respectively. The performance improvement in Ag/TiO2 DSSC may occur due to the declined band-gap energy, retarded charge recombination and greater surface coverage of the sensitizing dye over Ag/TiO2 nanocomposite.