Iuliia Onyshchenko

Atmospheric Pressure Plasma Jet Treatment of Poly-ε-caprolactone Polymer Solutions To Improve Electrospinning

An atmospheric pressure plasma jet (APPJ) specifically designed for liquid treatment has been used in this work to improve the electrospinnability of a 5 w/v % solution of poly-ε-caprolactone (PCL) in a mixture of chloroform and N,N-dimethylformamide. Untreated PCL solutions were found to result in nonuniform fibers containing a large number of beads, whereas plasma-treated solutions (exposure time of 2-5 min) enabled the generation of beadless, uniform nanofibers with an average diameter of 450 nm. This enhanced electrospinnability was found to be mainly due to the highly increased conductivity of the plasma-modified PCL solutions. Consequently, more stretching of the polymer jet occurred during electrospinning, leading to the generation of bead-free fibers. Plasma treatment also results in an increased viscosity and decreased pH values. To explain these observed changes, optical emission spectroscopy (OES) has been used to examine the excited species present in the APPJ in contact with the PCL solution. This study revealed that the peaks attributed to H, CH, CH2, and C2 species could be responsible for the degradation of solvent molecules and/or PCL structures during the plasma treatment. Size exclusion chromatography and X-ray photoelectron spectroscopy results showed that the molecular weight and the chemical composition of PCL were not significantly affected by the APPJ treatment. Plasma exposure mainly results in the degradation of the solvent molecules instead of modifying the PCL macromolecules, preserving the original polymer as much as possible. A hypothesis for the observed macroscopic changes in viscosity and pH values could be the generation of new chemical species such as HCl and/or HNO3. These species are characterized by their high conductivity, low pH values, and strong polarity and could enhance the solvent quality for PCL, leading to the expansion of the polymer coil, which could in turn explain the observed enhanced viscosity after plasma modification.

Effects of a dielectric barrier discharge (DBD) treatment on chitosan/polyethylene oxide nanofibers and their cellular interactions

In this study, chitosan (CS)/polyethylene oxide (PEO) nanofibrous mats (Ø: 166 ± 43 nm) were fabricated by electrospinning and subsequently surface-modified by a dielectric barrier discharge (DBD) sustained in argon, ammonia/helium or nitrogen. The surface properties of the CS/PEO nanofibers (NFs) before and after plasma treatment were characterized using contact angle measurements, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Additionally, the mechanical properties and PEO leaching in aqueous conditions of the different NFs under study were examined by tensile tests and nuclear magnetic resonance (1H NMR) spectroscopy respectively. Finally, cell behavior and cell morphology of human foreskin fibroblasts (HFFs) on the CS/PEO NFs were evaluated via live/dead fluorescence microscopy, MTT assays and SEM. The obtained results revealed that the surface free energy of the CS/PEO NFs was significantly increased after plasma modification, which was correlated to an enrichment in surface oxygen (Ar, N2, NH3/He) and nitrogen (N2, NH3/He) functional groups. All performed plasma treatments also led to an increase in ultimate tensile strength, most likely due to an increased fiber-to-fiber friction. Additionally, it was also observed that N2 plasma treatment resulted in a decrease in PEO release, which could be attributed to more pronounced surface cross-linking. Cellular interactions on the CS/PEO NFs also significantly increased due to the performed plasma treatments. The best cellular response was noted for the Ar plasma modification although the surface hydrophilicity was the lowest in this case. These observations thus suggest that not only the wettability characteristics but also the presence of distinct functional groups on plasma-treated CS/PEO NFs have a significant influence on the observed enhanced cellular interactions.