Showing papers in "Plasma Processes and Polymers in 2008"

Applied Plasma Medicine

Abstract: An emerging field of plasma medicine is discussed, where non-equilibrium plasmas are shown to be able to initiate, promote, control, and catalyze various complex behaviors and responses in biological systems. More importantly, it will be shown that plasma can be tuned to achieve the desired medical effect, especially in medical sterilization and treatment of different kind of skin diseases. Wound healing and tissue regeneration can be achieved following various types of plasma treatment in a multitude of wound pathologies. Non-equilibrium plasmas will be shown to be non-destructive to tissue, safe, and effective in inactivation of various parasites and foreign organisms.

Microplasmas: sources, particle kinetics, and biomedical applications

Abstract: Thanks to their portability and the non-equilibrium character of the discharges, microplasmas are finding application in many scientific disciplines. Although microplasma research has traditionally been application driven, microplasmas represent a new realm in plasma physics that still is not fully understood. This paper reviews existing microplasma sources and discusses charged particle kinetics in various microdischarges. The non-equilibrium character highlighted in this manuscript raises concerns about the accuracy of fluid models and should trigger further kinetic studies of high-pressure microdischarges. Finally, an outlook is presented on the biomedical application of microplasmas.

Nitrogen-Rich Plasma-Polymer Films for Biomedical Applications

Abstract: Low-pressure plasma co-polymerisation of binary gas mixtures of ethylene and ammonia was investigated in order to deposit N-rich plasma polymer coatings for biomedical applications. Deposition kinetics and relevant surface characteristics were investigated as a function of r.f. power, gas pressure, and NH 3 /C 2 H 4 ratio. Physico-chemical properties of the coatings were determined by surface-sensitive techniques: for example, total nitrogen concentrations up to 40 at.-% were measured by XPS, while those of primary amines were determined by chemical derivatisation followed by XPS analysis. L-PPE:N films were further characterised by UV-vis and IR spectroscopic ellipsometry and by CAG.

Characterization of microwave plasma torch for decontamination

Abstract: An atmospheric low-temperature microwave plasma torch has been developed and applied to disinfection. The size of the plasma output is relatively large (35 mm in diameter). Ar gas at a flow rate of 2.2 slm and 85 W microwave power are used. Plasma discharges are produced between the tip of each electrode and the inner surface of the cylinder. When an Escherichia coli culture is placed for 2 min at 20 mm below the torch, where the gas temperature is sufficiently cool, the bacteria are almost completely killed within a 40 mm diameter circle. The UV radiation is one of the major players responsible for killing bacteria, others being the reactive species and the charged particles.

Global Model of He/O2 and Ar/O2 Atmospheric Pressure Glow Discharges

Abstract: Atmospheric pressure glow discharges (APGDs) have widespread applications, including sterilization, cancer cell treatment, deposition, and surface modification due to their rather simple configurations, thanks to no need for vacuum system and their great capability to generate reactive species such as radical oxygen species. Helium and argon are widely used as feeding gases, achieving stable operations for wide ranges of parameters in atmospheric pressure, and oxygen is added into these gases to generate more reactive oxygen species (ROS), which play a significant role in sterilization. As the measurements of species densities and electron temperature in APGDs are difficult, we have developed the zero-dimensional global model of He/O 2 and Ar/O 2 APGDs to calculate the densities of several kinds of species and electron temperature. It was shown that even though small fraction of oxygen less than 1% was added to helium or argon, electrons dissipated most of their energy through collisions with oxygen molecules rather than helium or argon atoms. The densities of electron, atomic oxygen, and ozone of Ar/O 2 were higher than those of He/ O 2 ; however, the electron temperature of He/O 2 was higher than that of Ar/O 2 . When the pulsed power is applied, the time-averaged electron temperature for the shorter pulse period and the larger duty ratio increased, and the electron density decreased as the duty ratio increased.

Effect of Dielectric Barrier Discharge Plasma on the Attachment and Proliferation of Osteoblasts Cultured over Poly(ε‐caprolactone) Scaffolds

Abstract: We report the use of DBD plasma to improve the osteoblast cells adhesion and proliferation on PCL scaffolds. The effects of plasma treatment were characterized by surface energy, surface topography, and surface biocompatibility. The PCL film treated for 5 min showed the highest degree of total surface energy, mouse osteoblast cell proliferation and surface roughness. It is demonstrated that the oxygen plasma treatment not only enhances the hydrophilicity and increases solid surface energy, surface roughness of PCL but also improves the initial attachment and the proliferation of osteoblasts on the PCL substrate.

New Plasma Techniques for Polymer Surface Modification with Monotype Functional Groups

Abstract: The production of chemically-defined plasma polymers and the introduction of monotype functional groups onto polymer surfaces are described. One method is to lower the energetic level of low-pressure plasmas. Pressure- and plasma-pulsed plasmas were successfully tested for the production of chemically-defined plasma polymers by increasing the monomer supply during the plasma-off period. Well-defined ultra-thin polymer films with regular structure were deposited from atmospheric plasmas by electrospray techniques. Post-plasma wet-chemical processing was also applied, as were gas/liquid-based aerosols and underwater plasmas.

Chemical Characterisation of Nitrogen-Rich Plasma-Polymer Films Deposited in Dielectric Barrier Discharges at Atmospheric Pressure

Abstract: We have used an atmospheric pressure DBD apparatus to deposit novel families of N-rich plasma polymers (PP:N), using mixtures of three different hydrocarbon precursors in nitrogen at varying respective gas flow ratios. This research focuses on the overall chemical characterisation of those materials, with specific attention to (semi)-quantitative analysis of functional groups. Well-established and some lesser-known analytical techniques have been combined to provide the best possible chemical and structural characterisations of these three families of PP:N thin films, namely XPS, NEXAFS and FT-IR spectroscopy.

Sublethal and Killing Effects of Atmospheric-Pressure, Nonthermal Plasma on Eukaryotic Microalgae in Aqueous Media

Abstract: In-depth studies on the interaction of nonthermal plasmas with microorganisms usually focus on bacteria; only little attention has been given to their effects on more complex eukaryotic cells. We report here nonthermal plasma's effects on cell motility, viability staining, and morphology of eukaryotic microalgae, with three marine dinoflagellates and a marine diatom as major targets. The effects on motility and viability staining depended on the time of exposure to plasma and the species of microalgae. We observed a strong pH decrease in aqueous samples (marine and freshwater algal cultures, their culture media, and deionized water) after exposure to plasma, and hypothesized this decreased pH as the principal mechanism by which plasma exerts its deleterious effects on cells in aqueous media. The hypothesis was supported by results of experiments in which decreasing the pH of algal samples (effected by addition of acid) caused the same morphological damage (as determined with scanning-electron microscopy) as did exposure to plasma.

Delayed Effects of Cold Atmospheric Plasma on Vascular Cells

Abstract: We investigated the long-term behaviour of vascular cells (endothelial and smooth muscle) after exposure to a cold atmospheric plasma source. The cells were treated through a gas-permeable membrane, in order to simulate intravenous treatment with a gas plasma-filled catheter. Such indirect treatment resulted in (dose-dependent) apoptosis and necrosis in smooth muscle cells; these effects were visible 6-10 h after exposure. We ascribed cell damage to poisoning by active nitrogen species. A not yet resolved phenomenon of total (irreversible) cell inactivation without necrosis was observed in endothelial cells. Conditions for non-inflammatory plasma treatment (no cell necrosis) can be realized. Furthermore the current experiments have brought new insights in the mechanism of cell detachment, which was observed in many previous studies.

Plasma Sterilization: What are the Conditions to Meet this Claim?

Abstract: Plasma-based processes to inactivate micro-organisms are usually called 'plasma sterilization'. Based on the debatable assumption of exponential first-order micro-organism inactivation kinetics, sterilization process validation is realizable by a combination of experimental tests and data extrapolation. In this article, an alternative concept for a solid and reproducible process qualification is proposed to guarantee reliable microbiological safety on a sufficient level for products that must be sterilized by alternative procedures like plasma processes. A proof of antimicrobial efficacy on the highest experimentally accessible level under experimentally realizable, reproducible, and statistically evaluable conditions is demanded.

States of Biological Components in Bacteria and Bacteriophages during Inactivation by Atmospheric Dielectric Barrier Discharges

Abstract: Atmospheric DBD has been applied to the wet state of Escherichia coli and bacteriophage-2. Upon DBD treatment, both E.coli and 2phage were immediately inactivated. The states of different biological components were monitored during the course of inactivation. Only minor and slow degradation of proteins, DNA, and membranes was observed, a remarkable degradation was seen only after the completion of sterilization. Analysis of GFP recombinantly introduced into E.coli cells proved that the DBD has a prominent protein denaturation activity without affecting peptide bonds. The irreversible denaturation of proteins, seen in the early stage of DBD application, may play a central role in inactivation of both the bacteria and bacteriophages.

Different Ways to Plasma‐Polymerize HMDSO in DBD Configuration at Atmospheric Pressure for Corrosion Protection

Abstract: Organosilicon layers were deposited on galvanized steel to give a protective coating against corrosion. HMDSO was atomized and injected into a DBD plasma at atmospheric pressure. Plasma-polymerized HMDSO layers were different when HMDSO nanodroplets reacted directly in the plasma area or when such droplets reacted with the plasma once deposited on the surface. Addition of a plasma curing step was also studied. Influence of the deposition method on the properties of ppHMDSO layers was also studied. Layer structure was measured by SEM and interferometry, and its chemical structure was analyzed by FTIR and XPS. Corrosion resistance, which was measured by electrochemistry, was significantly increased when a plasma curing step was performed.

Nano-Structured Cell-Adhesive and Cell-Repulsive Plasma-Deposited Coatings : Chemical and Topographical Effects on Keratinocyte Adhesion

Abstract: Cell-adhesive and cell-repulsive coatings have been plasma-deposited on poly(ethylene terephthalate) surfaces previously structured with nano-metric conical features by means of colloidal lithography. Surface analysis revealed that both coatings are conformal on mono-structured substrates, with their wettability depending on the substrate morphology. The effect of surface chemistry and surface topography on cell adhesion has been investigated and clarified. The adhesion of a human keratinocyte cell-line was found to be strongly dependent on the surface topography for plasma-deposited acrylic acid (cell-adhesive), and on the surface chemistry for poly(ethylene oxide)-like (cell-repulsive) coatings.

Carbon Nanotube Synthesis in Atmospheric Pressure Glow Discharge: A Review

Abstract: This review presents recent developments of formation techniques related to atmospheric pressure glow discharge. The description specifically emphasizes their application to carbon nanotube (CNT) synthesis based on our recent work. High-purity vertically aligned single-walled CNTs are producible only when an atmospheric pressure glow discharge is applied: even moderate pressure such as 20 kPa preferentially synthesizes multi-walled CNTs. Lower operating pressures are known to produce carbon nanofibers exclusively. A tentative reaction mechanism is discussed based on plasma-induced substrate heating and on-line gas analysis in the plasma sheath. Finally, concluding and prospective remarks are presented briefly.

Plasma-Modified PTFE for Biological Applications: Correlation between Protein-Resistant Properties and Surface Characteristics

Abstract: PTFE samples were treated by low-pressure, O2 RF plasmas. The adsorption of BSA was used as a probe for the protein resistant properties. The exposure of PTFE to an O2 plasma leads to an increase in the chamber pressure. OES reveals the presence of CO, CO2 and F in the gas phase, indicating a strong etching of the PTFE surface by the O2 plasma. Furthermore, the high resolution C1s spectrum shows the appearance of CF3, CF and C-CF components in addition to the CF2 component, which is consistent with etching of the PTFE surface. WCA as high as 160° were observed, indicating a superhydrophobic behaviour. AFM Images of surfaces treated at high plasma power showed a increase in roughness. Lower amounts of BSA adsorption were detected on high power, O2 plasma-modified PTFE samples compared to low power, oxygen plasma-modified ones.

Nitrogen Atmospheric Pressure Post Discharges for Surface Biological Decontamination inside Small Diameter Tubes

Abstract: A nitrogen afterglow at atmospheric pressure has recently been described as able to transport active species over long distances in small diameter tubes, with a biocidal effect. For a discharge gas composed of nitrogen, either of high purity or with some controlled ppm of oxygen, survival curves are presented. The afterglow, flowing at 40 slm in a cylindrical quartz tube with 8 mm internal diameter is studied using emission spectroscopy. Fundamental or excited states of atomic or molecular species of parent gases are detected and evaluated. Their absolute concentration is measured along the tube axis. Correlated to transport equations, results give information on the creation and destruction reactions of these species, especially of the O(1S) metastable state of O, the species that has been shown to boost the biocidal effect.

Carbon Nanowalls Growth by Radiofrequency Plasma‐Beam‐Enhanced Chemical Vapor Deposition

Abstract: We report the remote growth of carbon nanowalls in a plasma beam sustained by an expanding argon radiofrequency discharge and injected with a small amount of acetylene in the presence of hydrogen as active gas. The growth process was investigated by varying the mass flow rates, ratio and nature of gases (argon, ammonia/hydrogen, and acetylene), the substrate temperature, and the radiofrequency power. Scanning and transmission electron microscopy, Raman spectroscopy, and electron diffraction methods were used for the investigation of the deposited material. We found that although materials with various morphologies can be generally obtained, nanostructured carbon material with a 2D morphology is obtained within a specific range of parameter values.

Protein Immobilization Using Atmospheric-Pressure Dielectric-Barrier Discharges : A Route to a Straightforward Manufacture of Bioactive Films

Abstract: An alternative single-step method for biomolecule entrapment in atmospheric plasma polymers is described. Relying on our experience to fabricate organic coatings at mild plasma conditions, fluorescent proteins and an organic coating precursor were simultaneously introduced to the DBD. Fluorescence microscopy and spectrum analysis unambiguously illustrate the single-step protein immobilization procedure using DBD. Moreover, in contrast to covalent immobilization procedures, the developed technique showed a homogeneous protein distribution in the coating.

Selective Surface Modification of Poly(propylene) with OH and COOH Groups Using Liquid-Plasma Systems

Abstract: Underwater plasma and glow discharge electrolysis are interesting new methods for polymer surface functionalization. The achievable content of O-containing functional groups exceeds that of oxygen glow discharge gas plasmas by a factor of two (up to ca. 56 O/100 C). The percentage of OH groups among all O-containing groups can reach 25 to 40%, whereas it is about 10% in the gas plasmas. Addition of hydrogen peroxide increases the fraction of OH groups to at most 70% (27 OH/100 C). The liquid plasma systems are also able to polymerize acrylic acid and deposit the polymer as very thin film on substrate surfaces or membranes, thereby retaining about 80% of all COOH functional groups (27 COOH/ 100 C).

Low‐Temperature Internal Sterilization of Medical Plastic Tubes Using a Linear Dielectric Barrier Discharge

Abstract: The use of a linear DBD for the internal sterilization of thin plastic tubes used in medical facilities is studied. We demonstrated that flexible, long, linear DBD plasmas were produced with a diameter of 0.2-3 mm and a length longer than 1 m. The internal sterilization experiments of medical plastic tubes were carried out using a thin, linear DBD. We confirmed that 10 6 Geobacillus stearothermophilus spores were killed inside the tube at room temperature after 12 min DBD irradiation under atmospheric conditions. The sterilization was attributed to UV radiation of the nitrogen molecules' second positive system, the ozone generated in the air, and/or their synergetic effect.

Modelling the Low‐Pressure N2 ? O2 Plasma Afterglow to Determine the Kinetic Mechanisms Controlling the UV Emission Intensity and Its Spatial Distribution for Achieving an Efficient Sterilization Process

Abstract: The flowing afterglow of a N 2 -O 2 microwave discharge intended to provide intense and spatially uniform UV emission for an efficient inactivation of bacterial spores is modelled with a 3-D hydrodynamic model leading to the spatial density distribution of the species in the reactor. The agreement of the calculated densities of the NO(A) and NO(B) UV emitting species with the corresponding measured emission intensities strongly supports the choice of the kinetic reactions retained in the ; model. In that respect, the specific contribution of N and O atoms to the spatial distribution of the NO(A) density ; (generating the NOy system) in the late afterglow is, for the first time, brought into relief.

Generation and Transportation Mechanisms of Chemically Active Species by Dielectric Barrier Discharge in a Tube for Catheter Sterilization

Abstract: The mechanisms of generation and transportation of a chemically active species in a tube generated by dielectric barrier discharge have been analyzed by experimental and computational methods to elucidate the sterilization mechanism. The obtained results are: i) Nitrogen oxide is an important sterilization factor. ii) Two-dimensional profiles of emission intensities that expand between the wire and ground in a cross section of the tube were generated by streamer propagation and relaxation processes. iii) A twin vortex was induced in the cross section of the tube by the discharge. Chemically active species, probably transported from the discharge region to the upper region of the tube by the twin vortex, were concentrated by the circular flow.

Stability of Ionic Liquids under the Influence of Glow Discharge Plasmas

Abstract: The combination of cold plasma and ionic liquids is very promising for many applications in chemical syntheses and nano material fabrication. Using NMR and FTIR analyses, we confirmed for the first time that imidazolium ionic liquids remain stable under the influence of a glow discharge plasma. Reduction of HAuCl 4 and PdCl 2 using an argon glow discharge was performed at room temperature for the formation of metal nano particles in 1-butyl-3-methylimidazolium tetrafluoroborate. TEM and XRD showed that the Au particles were hexagonal with average sizes of 32.7 nm, while the Pd particles were spherical with average size of 5.0 nm.

Effect of Plasma Exposure on the Chemistry and Morphology of Aerosol‐Assisted, Plasma‐Deposited Coatings

Abstract: This study reports on the effect on the morphology and chemistry of atmospheric pressure plasma deposited nm-thick coatings (21 � 3 nm) as the level of exposure to the plasma is systematically altered. Coatings were deposited by directly injecting hexamethyldisiloxane, polydimethylsiloxane or tetramethyldisiloxane liquid precursors through a nebulizer into a helium/oxygen atmospheric pressure plasma. An increase in the level of the precursor was found to be associated with a decrease in the concentration of methyl functional groups in the coating and to an increase of the Si–O crosslinking, as demonstrated using surface energy and XPS analysis. This resulted in an increase in the coating refractive index, and in a reduction of the number of surface particulates, as well as of surface roughness.

Electromechanical Behavior of Nanoscale Silver Coatings on PET Fibers

Abstract: Plasma-assisted deposition of silver films on PET mono- and multifilament fibers provides conductive fibers for wearable electronics. The nanoscale films were prepared in a continuously running low pressure plasma process using an ICM design for sputtering from a silver target combined with a prior RF cleaning step. The electrical resistance of the as-deposited layers was measured in situ enabling an immediate feedback of the electrical properties, the film quality, applied Ag mass, and film thickness. The deposited quantity of Ag mass on the PET fibers was investigated by ICP-OES and was correlated with the electrical resistance of the film. The metallized fibers showed excellent mechanical properties for wearable electronics as demonstrated by tensile properties measurement.

Colloid Probe AFM and XPS Study of Time-Dependent Aging of Amine Plasma Polymer Coatings in Aqueous Media

Abstract: Effects of surface oxidation on the properties of amine plasma polymer (pp) films in aqueous media have not been widely studied, despite their use to control bio-interfacial properties. Changes in the surface composition of allylamine and heptylamine pp films, on water exposure, were followed by XPS. The surface potential was monitored via AFM measurements and comparison to DLVO theory. Analysis of XPS data implied high initial oxidation rates (rapid quenching of surface radicals). Oxidation of the pp films followed evolution of carbon-based rather than nitrogen-based species. Analysis of AFM force data showed changes in the sign of the surface potential with aging from positive to negative. Implications, for example for surface immobilization of molecules in aqueous environments, are also discussed.

Plasma Amination of Low-Density Polyethylene by DBD Afterglows at Atmospheric Pressure

Abstract: Surfaces of LDPE can be functionalized with primary amino groups using the afterglows from dielectric barrier discharges in N 2 , N 2 + H 2 , and N 2 + NH 3 mixtures at atmospheric pressure. Quantitative analysis by a recently developed ATR FT-IR spectroscopic method allows calculation of the number of NH 2 groups generated per unit area. Treatment in N 2 + H 2 afterglows was found to be most efficient in terms of area densities of primary amines achieved (more than is nm -2 ), but appreciable quantities of -NH 2 , up to about 3 nm -2 , are also obtained in pure N 2 . Possible mechanisms of the amination reaction and the roles of gas additives are discussed.

Surface Modification of Poly(propylene) Microporous Membrane to Improve Its Antifouling Characteristics in an SMBR: O2 Plasma Treatment

Abstract: Fouling is the major obstacle in membrane processes applied in water and wastewater treatment. To improve the antifouling characteristics of PPHFMMs in an SMBR for wastewater treatment, the PPHFMMs were surface-modified by O 2 low temperature plasma treatment. Structural and morphological changes on the membrane surface were characterized by XPS and FE-SEM. The change of surface wettability was monitored by contact angle measurements. Results of XPS clearly indicated that the plasma treatment introduced oxygen containing polar groups on the membrane surface. The static water contact angle of the modified membrane reduced obviously with the increase of plasma treatment time. The relative pure water flux for the modified membranes increased with plasma treatment time up to 1 min, then it decreased with further increase of plasma treatment time. Decreases in the tensile strength and the tensile elongation at break of the modified membranes were also observed. To assess the relation between the plasma treatment and the membrane fouling in an SMBR, filtration for activated sludge was carried out by using synthetic wastewater. After continuous operation in the SMBR for about 75 h, flux recovery were 8.7 and 12.3%, reduction of flux were 91.6 and 87.4% for the nascent and O 2 plasma treated PPHFMM for 1 min, relative flux ratio for O 2 plasma treated PPHFMM for 1 min was 49.9% higher than that of the nascent PPHFMM.