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, CH, and C 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 HNO. 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.

The surface properties of electrospun scaffolds can greatly influence protein adsorption and thus strongly dictate cell-material interactions. In this study, we aim to investigate possible correlations between the surface properties of argon, nitrogen and ammonia/helium plasma-functionalized polycaprolactone (PCL) nanofibers (NFs) and their cellular interactions by examining the protein corona patterns of the plasma-treated NFs as well as the cell membrane proteins involved in cell proliferation. As a result of the performed plasma treatments, PCL NFs morphology was preserved while wettability was improved profoundly after all treatments because of the incorporation of polar surface groups. Depending on the discharge gas, different types of groups are incorporated which influenced the resultant cell-material interactions. Argon plasma-functionalized PCL NFs, only enriched by oxygen-containing functional groups, were found to show the best cell-material interactions, followed by N2 and He/NH3 plasma-treated samples. SDS-PAGE and LC-MS clearly indicated an increased protein retention compared to non-treated PCL NFs. The nine proteins best retained on plasma-treated NF are important mediators of extracellular matrix interaction, illustrating the importance thereof for cell proliferation and viability of cells. Finally, 92 proteins that can be used to differentiate the different plasma treatments are clustered and subjected to a gene ontology study, illustrating the importance of keratinization and extracellular matrix organization.

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In this work, space-resolved analysis of polyethylene terephthalate surface functionalization induced by an atmospheric pressure argon plasma jet has been conducted. In particular, the plasma jet footprint has been determined by examining radial water contact angle profiles. For the first time, space-resolved X-ray photoelectron measurements have also been carried out and have been correlated with the results of the water contact angle profiles. Different plasma treatment conditions, like discharge power, exposure time, sample distance and gas flow, have been varied to observe their effect on the plasma jet radial profiles. From this investigation, it has become clear that variations in exposure time and sample distance can strongly influence the radial hydrophilic region, while changes in gas flow rate and discharge power only result in small differences. Figure 4. Optical emission spectra at different distances from the center of the plasma jet on PET surface. Treatment parameters: distance between the bottom of the grounded electrode and sample -22 mm, power -4.0 W, gas flow -1 slm.