Aqueous medium-induced micropore formation in plasma polymerized polystyrene: an effective route to inhibit bacteria adhesion.

Plasma polymerized styrene (pPS) films were successfully synthesized by means of an atmospheric pressure plasma technique, using a mixture of argon gas and styrene vapor. The morphology and film thickness of the pPS films, deposited on 1 min argon plasma pre-treated glass substrates, were smooth and uniform without any visible features across the whole length of the substrates, and the films displayed a water contact angle of ∼83°. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared (FTIR) analysis confirmed the presence of oxygen-containing groups and the intact aromatic ring in the pPS coating. The obtained pPS films were stable for at least 30 days in air without any visible morphological degradation or chemical changes. However, the formation of a topographical pattern with micrometer lateral size and nanometer depth level was observed upon immersion in aqueous media for 72 hours. Micropore formation was believed to originate from the solubility of low cross-linked oligomers and their subsequent extraction in aqueous media. The influence of the microstructured pPS surface in mediating the attachment of eukaryotic and prokaryotic cells was further investigated. The micro-structured pPS surface influenced the adhesion and proliferation of mammalian cells. Furthermore, we could demonstrate that these films were efficient in the prevention of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus epidermidis (S. epidermis) adhesion and biofilm formation. Importantly, the viability of non-adherent cells and of planktonic bacteria was not affected. Post-coating of the microstructured pPS with biocompatible polydopamine did not impact on the antibacterial properties of the surface, suggesting that the polymer topography was the dominant factor. The non-biocidal pPS coating can be useful in applications where micro-organism colonization and biofilm formation need to be prevented, such as food packaging and medical equipment.

Effects of air transient spark discharge and helium plasma jet on water, bacteria, cells, and biomolecules.

Atmospheric pressure DC-driven self-pulsing transient spark (TS) discharge operated in air and pulse-driven dielectric barrier discharge plasma jet (PJ) operated in helium in contact with water solutions were used for inducing chemical effects in water solutions, and the treatment of bacteria (Escherichia coli), mammalian cells (Vero line normal cells, HeLa line cancerous cells), deoxyribonucleic acid (dsDNA), and protein (bovine serum albumin). Two different methods of water solution supply were used in the TS: water electrode system and water spray system. The effects of both TS systems and the PJ were compared, as well as a direct exposure of the solution to the discharge with an indirect exposure to the discharge activated gas flow. The chemical analysis of water solutions was performed by using colorimetric methods of UV-VIS absorption spectrophotometry. The bactericidal effects of the discharges on bacteria were evaluated by standard microbiological plate count method. Viability, apoptosis and cell cycle were assessed in normal and cancerous cells. Viability of cells was evaluated by trypan blue exclusion test, apoptosis by Annexin V-FITC/propidium iodide assay, and cell cycle progression by propidium iodide/RNase test. The effect of the discharges on deoxyribonucleic acid and protein were evaluated by fluorescence and UV absorption spectroscopy. The results of bacterial and mammalian cell viability, apoptosis, and cell cycle clearly show that cold plasma can inactivate bacteria and selectively target cancerous cells, which is very important for possible future development of new plasma therapeutic strategies in biomedicine. The authors found that all investigated bio-effects were stronger with the air TS discharge than with the He PJ, even in indirect exposure.

Properties and control of anode double layer oscillations and related phenomena.

An experimental investigation is presented on oscillations excited by the dynamics of an anode double layer or fireball in a double plasma (DP) machine. The fireball is created by additional ionization processes in front of a small circular anode, which is inserted into the diffusive DP plasma and biased positively. An annular (ring) electrode, usually biased negatively, surrounds the anode. The extension of the ion sheath in front of this ring controls the anode current by varying the effective diameter of the anode during the fireball oscillations. The ring voltage affects not only the oscillation frequency of the anode current but also other characteristics of the instability. Related phenomena consisting of ion-acoustic waves and almost synchronous oscillations of the plasma potential in the chamber where the fireball is formed are also presented.