Microplasma Treatment Research Articles

Development of a cold atmospheric pressure microplasma jet for freeform cell printing

An atmospheric pressure non-thermal microplasma jet (Ø 50 μm) was developed for localized functionalization of various substrates, including polymers, to allow maskless freeform cell printing. The applied microplasma jet power ranged from 0.1 to 0.2 W without causing any damage to the polyethylene substrate. The surface characterization results demonstrate that the microplasma treatment locally changes the surface roughness and the concentration of oxygen-containing functional groups on the polyethylene surface. The biological characterization confirms that the osteoblast cells attach and survive on the plasma activated line while untreated surfaces show almost no attachment and viability.

Surface patterning of bonded microfluidic channels.

Microfluidic channels in which multiple chemical and biological processes can be integrated into a single chip have provided a suitable platform for high throughput screening, chemical synthesis, detection, and alike. These microchips generally exhibit a homogeneous surface chemistry, which limits their functionality. Localized surface modification of microchannels can be challenging due to the nonplanar geometries involved. However, chip bonding remains the main hurdle, with many methods involving thermal or plasma treatment that, in most cases, neutralizes the desired chemical functionality. Postbonding modification of microchannels is subject to many limitations, some of which have been recently overcome. Novel techniques include solution-based modification using laminar or capillary flow, while conventional techniques such as photolithography remain popular. Nonetheless, new methods, including localized microplasma treatment, are emerging as effective postbonding alternatives. This Review focuses on postbonding methods for surface patterning of microchannels.

Basic Study of Bacteria Inactivation at Low Discharge Voltage by Using Microplasmas

Inactivation of microorganisms, such as <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> , by exposure to a microplasma is experimentally investigated. A microplasma is an atmospheric-pressure nonthermal plasma. Microplasmas, which generate high-intensity electric fields, can be formed using relatively low discharge voltages (0.7-1.1 kV) across small discharge gaps (0-100 ?m). The key benefits of the practical application of exposure to a microplasma are as follows: 1) the low discharge voltage and 2) the simple apparatus because a vacuum enclosure is not required. Hence, the apparatus for generating a microplasma could be relatively small and inexpensive and could be integrated into a portable device. The ozone generated by a microplasma at a low power level was measured, although the specific power density of the microplasma was larger than that of large-scale conventional plasmas. The emission spectra of the microplasma discharge in N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> was measured: 1) to confirm the UV light emission and 2) to identify the active chemical species generated by the microplasma discharge. The emission spectra was also measured with the presence of water droplets. The UV light from the microplasma discharge showed excited nitrogen molecules and OH radicals. In this paper, two cultures of bacteria, i.e., gram-negative <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> HB101 and gram-positive <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bacillus subtilis</i> JCB 20036 were the target microorganisms to be inactivated. In the experiments reported here, the number of bacteria decreased after microplasma treatment. The inactivation rate increases as the discharge voltage increases. <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Escherichia coli</i> is completely inactivated when air is used as carrier gas at a plasma discharge voltage of 1.05 kV. Using nitrogen as carrier gas, the highest inactivation rate is 77% at a discharge voltage of 1.15 kV. In addition, <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Bacillus subtilis</i> is inactivated with a rate of 97% at 1.07 kV with air as carrier gas. Using nitrogen as carrier gas and a discharge voltage of 1 kV results in an inactivation rate of 70% of bacteria. The inactivation of microorganisms by microplasma may be due to several factors either individually or in combination of the following: 1) the excited molecules and ions; 2) ozone; 3) high electrical fields; and 4) UV light. The effect of active species such as OH radicals may also be important since all the bacteria were carried within a small water droplet in between the electrodes.

Degradation of adhesion molecules of G361 melanoma cells by a non-thermal atmospheric pressure microplasma

Increased expression of integrins and focal adhesion kinase (FAK) is important for the survival, growth and metastasis of melanoma cells. Based on this well-established observation in oncology, we propose to use degradation of integrin and FAK proteins as a potential strategy for melanoma cancer therapy. A low-temperature radio-frequency atmospheric microplasma jet is used to study their effects on the adhesion molecules of G361 melanoma cells. Microplasma treatment is shown to (1) cause significant cell detachment from the bottom of microtiter plates coated with collagen, (2) induce the death of human melanoma cells, (3) inhibit the expression of integrin α2, integrin α4 and FAK on the cell surface and finally (4) change well-stretched actin filaments to a diffuse pattern. These results suggest that cold atmospheric pressure plasmas can strongly inhibit the adhesion of melanoma cells by reducing the activities of adhesion proteins such as integrins and FAK, key biomolecules that are known to be important in malignant transformation and acquisition of metastatic phenotypes.

Application of Microplasma for $\hbox{NO}_{\rm x}$ Removal

In this paper, microplasma is investigated, which occurs between the narrow gap of the electrodes covered with dielectric materials. The discharge gap is set on the order of micrometers by changing a spacer from 0 to 100 mum. In this paper, the characteristics of microplasma, such as discharge voltages, discharge currents, and discharge power that is obtained with the help of Lissajous figures, and the relationships between these electric characteristics are presented. The characteristics of ozone generation by a microplasma electrode are investigated. Treatment by microplasma for the simulated exhaust gas, which contains NOx and C3H8 as a role of HC and CO, is estimated experimentally. In the absence of O2, the exhaust gas is decomposed by nitrogen atomic species in particular. In the presence of O2, it is decomposed by nitrogen atomic species and oxidized by ozone. By-product analysis of treated gases is carried out by Fourier transform infrared spectroscopy and gas chromatography-mass spectrometry. When HC, NOx, and N2 are included in the simulated exhaust gas, HCN, N2O, and CH4 are confirmed as by-products of the microplasma treatment.

Effects of gas bubbling on water-solubilization of carbon nanotube using microplasma generated in water

In this study, influences of gas bubbling on water-solubility of single-walled carbon nanotubes (SWCNTs) based on microplasma treatment in water were investigated. Oxygen (O2), argon (Ar), nitrogen (N2) and carbon dioxide (CO2) were used as the bubbling gases. Bubbling of O2, Ar and N2 enhanced the O⁎ and H⁎ radicals produced by the microplasma in water and the solubility of SWCNT was increased more than two times compared to that without gas bubbling. On the other hand, the solubility was very poor in case of CO2. The negative effect of CO2 on the solubility might be due to the decrease of radicals, which were scavenged by carbonate ion generated by dissociation of CO2 in water, and caused by the reaction of radicals with CO2 or CO rather than those with SWCNT.

A new method of formation of a durable microrelief on the surface of samples made of cobalt-chromium alloy

Experimental studies of strong local interaction between microplasma discharges and samples made of cobalt—chromium alloy were performed. It was established that, in the near-surface layer of samples treated with microplasma discharges, a remelted area with greatly changed physicochemical properties is formed. After microplasma treatment, the surface of samples becomes considerably rougher, which improves surface cohesion (adhesion) with various materials (ceramics, plastics, etc.) when durable composite structures are formed.

The effect of microplasma treatment on the properties of a near-surface layer in specimens of a Ni-Cr alloy

A strongly localized interaction of microplasma discharges with samples of a nickel-chrome (Ni-Cr) alloy is experimentally studied. In a near-surface layer of the specimens, a remelted area is created, which is characterized by strongly modified physicochemical properties of the material. This modification of the near-surface layer of Ni-Cr samples significantly improves their adhesion with different materials (ceramics, plastics, etc.) when durable composite structures are created.

Enhancement of microplasma-based water-solubilization of single-walled carbon nanotubesusing gas bubbling in water

The authors have previously proposed a novel technique for the preparation ofwater-soluble carbon nanotubes (CNTs) using microplasma generated by a pulsed streamerdischarge in water. This paper describes an improvement in the method of themicroplasma-based CNT solubilization process by the use of gas bubbling in water.Oxygen, argon and nitrogen were used as bubbling gas in order to clarify the effectsof the gas species on the single-walled CNT (SWCNT) solubilization efficiency.Ultraviolet–visible absorption spectra of the SWCNT suspensions revealed that theSWCNT solubility was increased by more than two times by using gas bubbling togetherwith microplasma treatment. No significant difference was observed among thethree gas species tested. Fourier transform infrared (FTIR)spectroscopy and x-rayphotoelectron spectroscopy (XPS) analysis showed that the number of –OH groups,introduced on the SWCNT surface by the microplasma treatment, was increasedby gas bubbling. Optical emission measurements also showed that the numberof highly oxidative oxygen and hydrogen radicals, which were generated by themicroplasma, was also increased by gas bubbling. These results indicate that gasbubbling has positive effects on microplasma-based SWCNT solubilization as aresult of enhanced radical formation and functionalization of the SWCNT surface.

Micro-plasma textured Ti-implant surfaces

The surface state of titanium implants modulates bone response and implant anchorage. This evidence brought implant manufacturers to switch from the standard surface refinements and implement new surface treatments for more bone apposition and enhanced interfacial strength measured by removal torque or push-out tests. Anodic plasma-chemical treatment of implant surfaces is a cost-effective process to modify surface topography and chemistry. This technique is used for structuring connected with a coating of implant surfaces. The aim of our investigations, here, is to texture the implant surface in the nanoscale without coating. Ti disks with different mechanical pre-treatment (grinded, glass blasted) were used as substrate. Micro-plasma texturing was carried out in an aqueous electrolyte. By applying a pulsed DC voltage to the specimen, micro-plasma discharge was generated in the thin steam film between immersed specimen and electrolyte. The electrical process parameter current density was varied. The micro-plasma textured Ti surfaces were characterised optically by SEM and electrochemically by CV- (for testing the corrosion parameters), CA- (to give the enlargement of the real surface) and EIS-measurement in range of 100 kHz–100 μHz. We found that the initial structure of the material surface has small or no influence on the results of the micro-plasma treatment. The properties of the thick oxide layer resulting from the plasma process are influenced by electrical process parameters. After removal of the thick oxide layer a fine, micro- and nanoscaled surface structure of the titanium remains.

Control of uniformity of plasma-surface modification inside of small-diameter polyethylene tubing using microplasma diagnostics

A hollow-cathode microplasma was used to modify the lumenal surface of small-diameter polyethylene (PE). We make use of two microplasma diagnostics to monitor the plasma properties during the treatment process. A microwave cavity was used to measure the density of the microplasma. Emitted light from the microplasma was fed into a monochromator at various positions along the PE tube to assess uniformity of the microplasma. Effectiveness of plasma treatments were evaluated using the capillary-rise method at various positions along the tubing. We show a correlation between the properties of the inner surface of the PE tubing and the light emitted from the plasma. A Poly(ethylene oxide) (PEO) surfactant was immobilized to the lumenal surface of the PE tubing using the microplasma discharge. An in vitro blood-circulation loop was constructed to test the hematocompatibility of the PE tubes. After blood exposure, scanning electron microscope images were taken to assess the density of adhering platelets along the length of the tubes. The plasma-treated tubing showed fewer blood adherents than the untreated tubing. By suitably controlling the pressure drop along the tube, the uniformity of the microplasma treatment along the tubing can be optimized.

Reduced adhesion of human blood platelets to polyethylene tubing by microplasma surface modification

A hollow-cathode microplasma modified the lumenal surface of small-diameter polyethylene (PE) tubing. A microwave cavity diagnostic was used to measure the density of the microplasma. Plasma light output was observed with a monochromator at various positions along the PE tube to assess uniformity. Treatment effectiveness was evaluated by measuring the variation in capillary rise at various positions along the tubing. A correlation between the properties of the inner surface of the PE tubing and the emitted light intensity was found. A poly(ethylene oxide) surfactant was immobilized to the lumenal surface of the PE tubing with an argon microplasma discharge. To test hematocompatibility, an in vitro blood-flow loop circulated heparinized human blood through both a plasma-treated and -untreated PE tubes, simultaneously. After blood exposure, the tubes were examined with a scanning electron microscope to assess the density of adhering platelets along the length of the tubes. By modifying the plasma parameters, the uniformity of the microplasma treatment along the tubing can be optimized.

Microplasma oxidation of metals and alloys

The new technology described here is a means of obtaining electrically insulating coatings resistant to wear, heat, and corrosion on aluminum, titanium, zirconium, and different steels. The coatings can be formed on parts of different shapes, including pistons, cylinder rings, pump elements, parts of drilling equipment, different types of linings, graphite molds, components of heat exchangers, turbine blades, vessels for storing and transporting liquids, and medical instruments. Application of the coatings increases service life and improves product performance. The technology is simple and does not require complicated equipment. The surface of the product is subjected to microplasma treatment in an electrolyte, resulting in the formation of an oxide coating 1-500/~m thick. The coating has excellent physico-chemical properties (microhardness up to 2000 kg/mm2). The temperature of the product remains low during the treatment (going no higher than 80~ The surface of the product does not require special preparation, and the technology can even be used to remove contaminants (oil, grease, etc.) from a surface. The electrolyte is simple to regenerate. Regeneration is necessary only once every several months. The dimensions of the bath are determined by the dimensions of the parts that are to be treated. Coating time ranges from 3-5 rain to 3-5 h, depending on the coating thickness required and the service characteristics that the coating must have. The coatings are uniform through their thickness and adhere well to the product. The color of the coatings is gray, white, or black. The color of the coatings can be changed by using a paint or polymer filler, which also improves the service characteristics of the product. The technology can be modified to suit the needs of the customer. An automatic line can also be built to apply the coatings.