Non-thermal Oxygen Plasma Research Articles

Enhanced Hemocompatibility and Cytocompatibility of Stainless Steel.

The present study introduces an advanced surface modification approach combining electrochemical anodization and non-thermal plasma treatment, tailored for biomedical applications on stainless steel grade 316L (SS316L) surfaces. Nanopores with various diameters (100-300 nm) were synthesized with electrochemical anodization, and samples were further modified with non-thermal oxygen plasma. The surface properties of SS316L surfaces were examined by scanning electron microscopy, atomic force microscopy, X-ray photoemission spectroscopy, and Water contact angle measurements. It has been shown that a combination of electrochemical anodization and plasma treatment significantly alters the surface properties of SS316L and affects its interactions with blood platelets and human coronary cells. Optimal performance is attained on the anodized specimen featuring pores within the 150-300 nm diameter range, subjected to subsequent oxygen plasma treatment; the absence of platelet adhesion was observed. At the same time, the sample demonstrated good endothelialization and a reduction in smooth muscle cell adhesion compared to the untreated SS316L and the sample with smaller pores (100-150 nm). This novel surface modification strategy has significant implications for improving biocompatibility and performance of SS316L in biomedical applications.

Plasma Oxidation of Copper: Molecular Dynamics Study with Neural Network Potentials.

The formation of thin oxide films is of significant scientific and practical interest. In particular, the semiconductor industry is interested in developing a plasma atomic layer etching process to pattern copper, replacing the dual Damascene process. Using a nonthermal oxygen plasma to convert the metallic copper into copper oxide, followed by a formic acid organometallic reaction to etch the copper oxide, this process has shown great promise. However, the current process is not optimal because the plasma oxidation step is not self-limiting, hampering the degree of thickness control. In the present study, a neural network potential for the binary interaction between copper and oxygen is developed and validated against first-principles calculations. This potential covers the entire range of potential energy surfaces of metallic copper, copper oxides, atomic oxygen, and molecular oxygen. The usable kinetic energy ranges from 0 to 20 eV. Using this potential, the plasma oxidation of copper surfaces was studied with large-scale molecular dynamics at atomic resolution, with an accuracy approaching that of the first principle calculations. An amorphous layer of CuO is formed on Cu, with thicknesses reaching 2.5 nm. Plasma is found to create an intense local heating effect that rapidly dissipates across the thickness of the film. The range of this heating effect depends on the kinetic energy of the ions. A higher ion energy leads to a longer range, which sustains faster-than-thermal rates for longer periods of time for the oxide growth. Beyond the range of this agitation, the growth is expected to be limited to the thermally activated rate. High-frequency, repeated ion impacts result in a microannealing effect that leads to a quasicrystalline oxide beneath the amorphized layer. The crystalline layer slows down oxide growth. Growth rate is fitted to the temperature gradient due to ion-induced thermal agitations, to obtain an apparent activation energy of 1.0 eV. A strategy of lowering the substrate temperature and increasing plasma power is proposed as being favorable for more self-limited oxidation.

Effect of different surface treatments on the bonding potential and physical and mechanical properties of ultratranslucent zirconia

Statement of problemStudies to determine a suitable surface treatment that improves bonding without compromising the strength or translucency of ultratranslucent zirconia are scarce. PurposeThe purpose of this in vitro study was to evaluate the effect of different surface treatments on translucency, surface topography, phase transformation, biaxial flexural strength, bond strength, and durability. Material and methodsA total of 169 ultratranslucent zirconia disks were randomly divided into 4 groups according to the surface treatment applied: airborne-particle abrasion (APA) (n=46), tribochemical silica airborne-particle abrasion (TS) (n=46), nonthermal oxygen plasma (NTP) (n=46), and no treatment, control (C) (n=31). The translucency parameter (ΔTP00) was evaluated with a spectrophotometer (n=15), phase transformation was assessed with an X-ray diffractometer (n=5), surface topography was evaluated with a scanning electron microscope (SEM) (n=3), and biaxial flexural strength (BFS) was tested with a universal testing machine (n=15). For the microshear bond strength (μSBS) test, 40 composite resin specimens were attached to 8 disks and tested with a universal testing machine; 20 specimens were tested after 24 hours, and 20 specimens after hydrothermal aging in a thermocycler (TC). The data were analyzed with ANOVA followed by the Tukey post hoc test (α=.05). Weibull analysis was performed for the flexural strength and μSBS results. ResultsSignificant ΔTP00 differences were found among all groups and were highest for the APA group (7.33) and lowest for the NTP group (4.79). The NTP group had a significantly higher monoclinic weight fraction value (4.54%) than other groups. The NTP group had significantly higher BFS (581.31) than other groups, while the APA group showed significantly lower values than other groups (340.43). The APA group had significantly higher μSBS values after 24 hours (13.51 MPa) and after TC (13.68 MPa) than the other groups (P<.05). ConclusionsAlthough APA and TS are effective techniques for improving resin-zirconia bonding, they result in significantly higher deterioration of translucency and strength. NTP significantly improved the BFS of zirconia; however, it showed lower bond strength values than other methods.

Osseointegration of Zirconia Implants after UV-Light or Cold Atmospheric Plasma Surface Treatment In Vivo.

The influence of UV light and non-thermal plasma on the osseointegration of yttria-stabilized zirconia implants (Y-TZP) comparing the two methods is unclear. The aim of this study was to show the influence of these methods on the osseointegration of dental zirconia implants in an animal model. A total of 54 implants were either untreated, treated with UV light (UV), or non-thermal oxygen plasma for 12 min and inserted into the parietal bones of six domestic pigs. The animals were sacrificed after a healing interval of two, four, and nine weeks. The degree of osseointegration was determined using histomorphometric determination of bone-to-implant contact values (BIC) and the bone-to-implant contact values within the retentive parts of the implants (BAFO). BIC values decreased in all groups after four weeks of healing and re-increased after nine weeks in all groups. BAFO increased significantly over time in all groups. However, there were no statistically significant differences in BIC and BAFO values between the control group and the test groups and over time. Clinical studies may follow to confirm the influence of cold plasma and UV light on the healing and survival of zirconia implants.

Human osteoblast and fibroblast response to oral implant biomaterials functionalized with non-thermal oxygen plasma

Plasma-treatment of oral implant biomaterials prior to clinical insertion is envisaged as a potential surface modification method for enhanced implant healing. To investigate a putative effect of plasma-functionalized implant biomaterials on oral tissue cells, this investigation examined the response of alveolar bone osteoblasts and gingival fibroblasts to clinically established zirconia- and titanium-based implant surfaces for bone and soft tissue integration. The biomaterials were either functionalized with oxygen-plasma in a plasma-cleaner or left untreated as controls, and were characterized in terms of topography and wettability. For the biological evaluation, the cell adhesion, morphogenesis, metabolic activity and proliferation were examined, since these parameters are closely interconnected during cell-biomaterial interaction. The results revealed that plasma-functionalization increased implant surface wettability. The magnitude of this effect thereby depended on surface topography parameters and initial wettability of the biomaterials. Concerning the cell response, plasma-functionalization of smooth surfaces affected initial fibroblast morphogenesis, whereas osteoblast morphology on rough surfaces was mainly influenced by topography. The plasma- and topography-induced differential cell morphologies were however not strong enough to trigger a change in proliferation behaviour. Hence, the results indicate that oxygen plasma-functionalization represents a possible cytocompatible implant surface modification method which can be applied for tailoring implant surface wettability.

Time Dependency of Non-Thermal Oxygen Plasma and Ultraviolet Irradiation on Cellular Attachment and mRNA Expression of Growth Factors in Osteoblasts on Titanium and Zirconia Surfaces.

Ultraviolet (UV) light and non-thermal plasma (NTP) are promising chair-side surface treatment methods to overcome the time-dependent aging of dental implant surfaces. After showing the efficiency of UV light and NTP treatment in restoring the biological activity of titanium and zirconia surfaces in vitro, the objective of this study was to define appropriate processing times for clinical use. Titanium and zirconia disks were treated by UV light and non-thermal oxygen plasma with increasing duration. Non-treated disks were set as controls. Murine osteoblast-like cells (MC3T3-E1) were seeded onto the treated or non-treated disks. After 2 and 24 h of incubation, the viability of cells on surfaces was assessed using an MTS assay. mRNA expression of vascular endothelial growth factor (VEGF) and hepatocyte growth factor (HGF) were assessed using real-time reverse transcription polymerase chain reaction analysis. Cellular morphology and attachment were observed using confocal microscopy. The viability of MC3T3-E1 was significantly increased in 12 min UV-light treated and 1 min oxygen NTP treated groups. VEGF relative expression reached the highest levels on 12 min UV-light and 1 min NTP treated surfaces of both disks. The highest levels of HGF relative expression were reached on 12 min UV light treated zirconia surfaces. However, cells on 12 and 16 min UV-light and NTP treated surfaces of both materials had a more widely spread cytoskeleton compared to control groups. Twelve min UV-light and one min non-thermal oxygen plasma treatment on titanium and zirconia may be the favored times in terms of increasing the viability, mRNA expression of growth factors and cellular attachment in MC3T3-E1 cells.

Oxygen Plasma Improved Shear Strength of Bonding between Zirconia and Composite Resin

Improving the strength of the bonding of zirconia to composite resins remains a challenge in dental restorations. The purpose of this study was to evaluate the shear strength of the bonding of zirconia to composite resins, thereby verifying the hypothesis that as the power of the non-thermal oxygen plasma increases, the bonding strength of the plasma-treated zirconia is increased. The effects of the oxygen plasma power (100, 200, and 400 W) on the surface structure, chemical composition, and hydrophilicity of the zirconia and the strength of the bonding between zirconia and composite resin were investigated. As a result, after different plasma power treatments, the surface structure and phase composition of zirconia were not different from those of zirconia without treatment. However, the oxygen plasma treatment not only reduced carbon adsorption but also greatly increased the hydrophilicity of the zirconia surface. More importantly, the strength of the bonding between the plasma-treated zirconia and composite resin was significantly higher than that in the corresponding control group without plasma treatment. Regardless of whether the zirconia was pristine or sandblasted, the higher the plasma power, the greater the bond strength obtained. The conclusion is that the oxygen plasma treatment of zirconia can effectively improve the strength of the bonding between the zirconia and composite resin without damaging the microstructure and phase composition of the zirconia.

Plasma-Induced Crystallization of TiO₂ Nanotubes.

Facile crystallization of titanium oxide (TiO2) nanotubes (NTs), synthesized by electrochemical anodization, with low pressure non-thermal oxygen plasma is reported. The influence of plasma processing conditions on TiO2 NTs crystal structure and morphology was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). For the first time we report the transition of amorphous TiO2 NTs to anatase and rutile crystal structures upon treatment with highly reactive oxygen plasma. This crystallization process has a strong advantage over the conventional heat treatments as it enables rapid crystallization of the surface. Thus the crystalline structure of NTs is obtained in a few seconds of treatment and it does not disrupt the NTs’ morphology. Such a crystallization approach is especially suitable for medical applications in which stable crystallized nanotubular morphology is desired. The last part of the study thus deals with in vitro biological response of whole blood to the TiO2 NTs. The results indicate that application of such surfaces for blood connecting devices is prospective, as practically no platelet adhesion or activation on crystallized TiO2 NTs surfaces was observed.

Non-thermal plasma increase bond strength of zirconia to a resin cement

Objective: This study investigated the influence of different surface treatments on zirconia surface energy, roughness and microshear bond strength. Material and Methods: Forty eight slices of Yttria-stabilized tetragonal zirconia polycrystal (Y-TZP- VITA In-Ceram® YZ for inLab®) (6.4 x 3.2 x 1.6 mm) were divided into 3 groups according to the surface treatment (n = 16): YTZP_control -untreated; YTZP_plasma -surface treatment with non-thermal oxygen plasma; YTZP_primer - coating with ceramic primer. Surface energy (n = 6) was measured with a goniometer; and surface roughness (n = 10) was analyzed with a 3D profilometer were performed over zirconia surface. On the same specimens of surface roughness, on the treated zirconia's surface, resin cement (PANAVIA V5 - Kuraray Noritake Dental) was built up by inserting the resin cement into Tygon tubes (1 mm of internal diameter X 1 mm length). After 24 h storage, microshear test was assessed. Data were analyzed by one-way ANOVA and Tukey post-hoc test (p &lt; 0.05). Results: Non-thermal oxygen plasma treated specimens exhibited higher statistically significant surface energy (p = 0.00) and bond strength (p = 0.00) when compared to control and primer groups. Roughness test (p = 0.897) could not detect statistical difference among the tested groups. Conclusion: Non-thermal oxygen plasma should be a suitable alternative for zirconia surface treatment prior to luting hence it improved microshear bond strength and provided higher surface energy without affecting surface roughness. Keywords Adhesion; Non-thermal plasma; Surface treatment.

Nano-graphene oxide incorporated into PMMA resin to prevent microbial adhesion

ObjectiveAlthough polymethyl methacrylate (PMMA) is widely used as a dental material, a major challenge of using this substance is its poor antimicrobial (anti-adhesion) effects, which increase oral infections. Here, graphene-oxide nanosheets (nGO) were incorporated into PMMA to introduce sustained antimicrobial-adhesive effects by increasing the hydrophilicity of PMMA. MethodsAfter characterizing nGO and nGO-incorporated PMMA (up to 2wt%) in terms of morphology and surface characteristics, 3-point flexural strength and hardness were evaluated. The anti-adhesive effects were determined for 4 different microbial species with experimental specimens and the underlying anti-adhesive mechanism was investigated by a non-thermal oxygen plasma treatment. Sustained antimicrobial-adhesive effects were characterized with incubation in artificial saliva for up to 28 days. ResultsThe typical nanosheet morphology was observed for nGO. Incorporating nGO into PMMA roughened its surface and increased its hydrophilicity without compromising flexural strength or surface hardness. An anti-adhesive effect after 1h of exposure to microbial species in artificial saliva was observed in nGO-incorporated specimens, which accelerated with increasing levels of nGO without significant cytotoxicity to oral keratinocytes. Plasma treatment of native PMMA demonstrated that the antimicrobial-adhesive effects of nGO incorporation were at least partially due to increased hydrophilicity, not changes in the surface roughness. A sustained antimicrobial-adhesive property against Candida albicans was observed in 2% nGO for up to 28 days. SignificanceThe presence of sustained anti-adhesion properties in nGO-incorporated PMMA without loading any antimicrobial drugs suggests the potential usefulness of this compound as a promising antimicrobial dental material for dentures, orthodontic devices and provisional restorative materials.

Ambient Species Density and Gas Temperature Radial Profiles Derived from a Schlieren Technique in a Low-Frequency Non-thermal Oxygen Plasma Jet

A quantitative interpretation of the schlieren technique applied to a non-thermal atmospheric-pressure oxygen plasma jet driven at low-frequency (50 Hz) is reported. The jet was operated in the turbulent regime with a hole-diameter based Reynolds number of 13,800. The technique coupled to a simplified kinetic model of the jet effluent region allowed deriving the temporally-averaged values of the gas temperature of the jet by processing the gray-level contrast values of digital schlieren images. The penetration of the ambient air into the jet due to turbulent diffusion was taken into account. The calibration of the optical system was obtained by fitting the sensitivity parameter so that the oxygen fraction at the nozzle exit was unity. The radial profiles of the contrast in the discharge off case were quite symmetric on the whole outflow, but with the discharge on, relatively strong departures from the symmetry were evident in the near field. The time-averaged gas temperature of the jet was relatively high, with a maximum departure of about 55 K from the room temperature; as can be expected owing to the operating molecular gas. The uncertainty in the temperature measurements was within 6 K, primarily derived from errors associated to the Abel inversion procedure. The results showed an increase in the gas temperature of about 8 K close to the nozzle exit; thus suggesting that some fast-gas heating (with a heating rate ~0.3 K/μs) still occurs in the near field of the outflow.

PANi/PAN copolymer as scaffolds for the muscle cell-like differentiation of mesenchymal stem cells

Nowadays, regeneration medicine or skeletal muscle tissue engineering can be a useful solution for the replacement of damaged or lost tissue. This study was carried out to evaluate the human bone marrow-derived mesenchymal stem cells differentiated into muscle-like cells on polyaniline (PANi)/polyacrylonitrile (PAN) copolymer conductive. After electrospinning of biocompatible PANi/PAN copolymers, they were modified by non-thermal oxygen plasma. The scaffold was characterized by scanning electron microscope (SEM), contact angle, and attenuated total reflectance-Fourier transform infrared spectroscopy. Cytocompatibility and viability of mouse fibroblast cells and mesenchymal stem cells were conducted by 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide assay. 4,6-Diamidino 2-phenylindole and SEM tests were performed to determine the cell survival on scaffolds. Reverse transcription polymerase chain reaction and immunocytochemistry assay performed to ensure that mesenchymal stem cells differentiated into muscle-like cells. SEM images of PANi/PAN nanofibers, contact angle, and attenuated total reflectance-Fourier transform infrared spectroscopy showed that oxygen-treated plasma scaffolds have more favorable hydrophilic structure. The test results of cell culture, 3-[4,5-dimethylthiazol-2yl]-2,5-diphenyl tetrazolium bromide assay, SEM, and 4,6-diamidino 2-phenylindole showed that the cells have proliferated well on the scaffolds and have good adhesion, so nanofiber could support the cellular growth. After 21 days of induction of muscle differentiation, expressions of α-ACTININ, MYOSIN, and MYOGENIN genes were confirmed by reverse transcription polymerase chain reaction and expressions of M-cadherin and troponin were approved by immunocytochemistry test. According to our data, PANi/PAN scaffolds promoted and supported mesenchymal cells to muscle-like cells. Therefore, the scaffolds were able to perform as substrates for soft tissue engineering. Copyright © 2017 John Wiley & Sons, Ltd.

Functionalisation of viscose fabric with chitosan particles using non-thermal oxygen plasma

In this study, the spandex mixed viscose fabric was modified by applying a hydrophilic surface finishing agent that contains cellulose. To impart superior hydrophilicity, cellulose fabric was further cationic charge modified through chitosan polymer. The surface finish was coated on the fabric using a plasma modification process. The modified fabric was characterised in terms of crystalline and wettability. The results from the X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and thermogravimetric analyses confirmed the polymer coated surface finish of the sample. Furthermore, the textile surface finish was capable of withstanding multiple washing cycles.

Bactericidal effects of nonthermal low-pressure oxygen plasma on S. typhimurium LT2 attached to fresh produce surfaces

This work investigates the feasibility of nonthermal low-pressure oxygen plasma on sanitization of spinach, lettuce, tomato and potato surfaces from Salmonella enterica subsp. enterica serovar Typhimurium str. LT2 (Salmonella typhimurium LT2). It was shown that the time of exposure and plasma power density were two critical parameters influencing the bactericidal efficiency. Surface roughness and hydrophobicity did not influence the sanitization of produce. Oxygen plasma was more effective than washing with 3% H2O2 on eliminating S. typhimurium LT2 on spinach. Plasma treatment chemically changed a very thin section of tomato wax cuticle layer by oxidation reaction and decomposition of carbon chains, which could readily and completely be removed by water. Overall, this study confirms that nonthermal oxygen plasma can be a new effective method of sanitization for fresh produce.

In vitro cell-biological performance and structural characterization of selective laser sintered and plasma surface functionalized polycaprolactone scaffolds for bone regeneration

In the present study a structural characterization and in vitro cell-biological evaluation was performed on polycaprolactone (PCL) scaffolds that were produced by the additive manufacturing technique selective laser sintering (SLS), followed by a plasma-based surface modification technique, either non-thermal oxygen plasma or double protein coating, to functionalize the PCL scaffold surfaces. In the first part of this study pore morphology by means of 2D optical microscopy, surface chemistry by means of hydrophilicity measurement and X-ray photoelectron spectroscopy, strut surface roughness by means of 3D micro-computed tomography (CT) imaging and scaffold mechanical properties by means of compression testing were evaluated before and after the surface modifications. The results showed that both surface modifications increased the PCL scaffold hydrophilicity without altering the morphological and mechanical properties. In the second part of this study the in vitro cell proliferation and differentiation of human osteoprogenitor cells, over 14days of culture in osteogenic and growth medium were investigated. The O2 plasma modification gave rise to a significant lower in vitro cell proliferation compared to the untreated and double protein coated scaffolds. Furthermore the double protein coating increased in vitro cell metabolic activity and cell differentiation compared to the untreated and O2 plasma PCL scaffolds when OM was used.

Principal Limitations in Homogeneous Gas Phase Chemistry in Non-Thermal Plasmas

This study highlights the oxidation of H2, CH4, and HCl present in the range of some volume percent in a homogeneous O2 or air phase in a flow through glass barrier discharge reactor. The oxidation of all three compounds is highly exothermic and exergonic at ambient temperature and proceeds at sufficiently high temperatures as radical chain reaction. The conversion of each compound was below 10% in a non-thermal oxygen plasma under various reaction conditions. Increasing concentrations of H2 and CH4 above the lower explosion limit did not lead to higher conversion degrees. It is assumed that only initial radical formation by electron impact dissociation and exothermic steps within the chain process run in a sufficiently fast manner at ambient temperature. For endothermic steps within the radical chain, the necessary activation energy is not available and the chain reaction aborts, most likely, after formation of peroxyl (hydro- or methyl-peroxyl) radicals.

Estimation of point of zero charge for activated carbon treated with atmospheric pressure non-thermal oxygen plasmas

Commercial activated carbon was treated with a non-thermal oxygen plasma under atmospheric pressure using three types of reactors: a dielectric barrier discharge (DBD) parallel-plate reactor; an atmospheric pressure glow discharge plasma jet reactor and a DBD coaxial type reactor. The samples treated with the plasma were characterized by the pH value at the point of zero charge. An estimation of the adsorption properties of samples for copper ions in aqueous solution was also carried out in order to explain the effect of pH value on the adsorption results.

Relaxation of partial particle concentrations in a non-thermal oxygen plasma

Using a kinetic oxygen plasma model the temporal change of the partial particle concentrations caused by a step-like variation of the electron energy is calculated. In the case of a decaying plasma at ≈1 Torr the results are compared with experimental data. The reaction kinetics are discussed.