Jin Hoon Cho

An experimental burn wound-healing study of non-thermal atmospheric pressure microplasma jet arrays.

In contrast with a thermal plasma surgical instrument based on coagulative and ablative properties, low‐temperature (non‐thermal) non‐equilibrium plasmas are known for novel medicinal effects on exposed tissue while minimizing undesirable tissue damage. In this study we demonstrated that arrays of non‐thermal microplasma jet devices fabricated from a transparent polymer can efficiently inactivate fungi (Candida albicans) as well as bacteria (Escherichia coli), both in vitro and in vivo, and that this leads to a significant wound‐healing effect. Microplasma jet arrays offer several advantages over conventional single‐jet devices, including superior packing density, inherent scalability for larger treatment areas, unprecedented material flexibility in a plasma jet device, and the selective generation of medically relevant reactive species at higher plasma densities. The therapeutic effects of our multi‐jet device were verified on second‐degree burns in animal rat models. Reduction of the wound area and the histology of the wound after treatment have been investigated, and expression of interleukin (IL)‐1α, ‐6 and ‐10 was verified to evaluate the healing effects. The consistent effectiveness of non‐thermal plasma treatment has been observed especially in decreasing wound size and promoting re‐epithelialization through collagen arrangement and the regulation of expression of inflammatory genes. Copyright

Modular microplasma ozone generators for water treatment system

Compact and scalable ozone generator modules comprising multiple arrays of microchannel plasmas have been developed for commercial laundry and other water disinfection applications. Arrays consist of 24 channels each having a length and width of 1 ~ 5 cm and 250 ~ 500 μm, respectively. Modules consisting of 4 - 5 such arrays mounted into a plastic frame, produced ozone at a rate of 10 g-hr-1 and a concentration of 60 g-m-3 when O2 served as the feedstock gas and its pressure and flow rate in the modular reactor were 1 atm. and ~4 liters/min. The overall dimensions of one module are ~5 cm × ~7 cm × ~10 cm (W×L×H). Ozone output is observed to scale linearly with the number of microchannel plasma devices and the applied gas flow rate. Heat due to ozone production in the module system was efficiently controlled by air fan cooling and a tandem flow design. Finally, ozone is efficiently produced up to commercial levels for laundry applications in a module system with ~90 v/v% oxygen provided by a portable oxygen concentrator. Reduction of an order of magnitude in weight and volume of modular ozone generator, relative to conventional dielectric barrier discharge systems, is offered by microplasma technology.

Comparison of spatial and temporal characteristics between microplasma jet arrays and a single macroplasma jet

When low temperature plasma is generated in a flowing gas system, interactions with a material surface provide a versatile candidate for biochemical processing. By controlling the surrounding medium or tailoring the input gas, specific radicals and excited species can be produced within the plasma, which greatly benefit its applications in medical therapeutics and materials processing. The propagation of plasma jets into atmospheric pressure air is accompanied by spatially and temporally-resolved emission profiles that have been compared between microplasma jet arrays and a single macroplasma jet having the same cross-sectional area. The plasma-background gas interaction surface area, over which where plasma chemistry reactions occur has been significantly increased with a microplasma array. Multiple ionization bullets, with velocities of 0.3 -0.5 km/s, have been produced from a microchannel with a diameter of 355 μm. An order of magnitude increase in the velocity of the plasma jets has been observed by inserting a ground electrode and a dielectric barrier downstream to the jet aperture. The shape and velocity of propagation can be strongly influenced by the design of the jet aperture and the external ground. Spatial emission profiles confirm the advantage of large area treatment of tissue or a material surface with the microplasma array. The details will be discussed.

Plasma packet propagation in microchannels

Summary form only given. The temporal and spatial evolution of low temperature plasma packets has been examined in microchannels fabricated in nanoporous alumina (Al2O3). Patterned by conventional photolithographic techniques, microchannels having width of 200 ~ 250 μm and depth of 110 ~ 120 μm were etched and various channel arrangements (such as spirals, intersecting sinusoids, and “switchyard” geometries) have been tested successfully. Plasma propagation is monitored by a gated, intensified CCD detector that views the channels through a planar ITO electrode. Experiments with Ne at 500 Torr reveal plasma packets that propagate within the channels at velocities as large as several tens of km-s-1. The fundamental processes responsible for this behavior, as well as potential applications of specific microchannel array geometries, will be discussed.

Observation of temporal behavior in an array of microplasma jet devices with different electrode driving conditions

Summary form only given. Temporally resolved behavior of microplasma jet arrays fabricated in a moldable, and optically transparent polymer have been investigated by shaping the electrical field within the microplasma channel at atmospheric pressure. Attributed to a series of micropatterning process for a moldable plastic, array of microchannels having a diameter less than 355 μm are precisely prepared and stable plasma jet with a He flow at ~800 Torr was obtained by a ac waveform of 800 VRMS at 20 kHz. Optical emission spectra were obtained from the He microplasma jet in air and the gas temperature of the microplasma has been calculated from the emission intensity profile of N2+ first negative system in the spectrum. The temporal propagation of the microjets is significantly dependent on the electrode configuration, geometries and driving waveform. In particular, the spatiotemporal behavior of microplasma jet indicates that a controlled sequence of multiple electrode driving can modulate either plasma propagation and glow mode of the microplasma jet. The ability to modulate plasma performance in the microchannel array promises various potential applications in the future. The characteristics and control of microplasma propagation inside the microcavity with various structural and operational parameters will be discussed.

Propagation-decay characteristics of locally ionized microplasma packets in arrays of microchannels

Summary form only given. Plasma propagation and its decay properties in an array of microscale channels has been investigated at atmospheric pressure in He and Ar. Microplasmas in channels having a width of 200-300 μm, a length to width aspect ratio of up to ~ 103: 1, and a volume of 1-50 mm3 have been generated by micromachining and wet chemical processes, these channels are situated in a dielectric barrier structure fabricated in 125-250 μm thick Al foil. Spatiotemporally-resolved optical emission profiles, recorded with a gated CCD camera and a telescope, reveal a plasma optical interaction with neighboring channels and propagation speed (and direction of excited emission along the microchannel) which varies with gas mixture. In Ar 760 Torr, propelled by the accumulation of charge on the microchannel wall, packets of low temperature, nonequilibrium plasma propagate at a uniform velocity of ~20 km-s-1. The dominant mechanism for volumetric electron loss to be dissociative recombination.

Spatially confined air microplasmas in an array of microcavity devices with asymmetric air flow geometry

Summary form only given. Arrays of microcavity devices designed for the operation in a forced flow of laboratory air. Microcavities having a diameter of 100 ~300 μm and are encapsulated and protected with a Al2O3 ring-shaped dielectric for the protection from plasma sputtering. With a micropatterning process by simple lithography and a microfabrication technique for microcavity formation, precise control of microcavity and its array geometry was obtained with an accuracy of less than 5 %. In particular, to control the plasma properties and flow dynamics of air inside the microcavities of device, the shape of microcavity has been modified to be asymmetric between electrodes. The device was stably operated in air with flow rate of 180-6000 cfm which are equivalent to the velocity of 2.5-7 m/s. Confinement of air plasma inside the microcavity was measured by optical microscopy and ozone generation from the array was measured quantitatively by calibrated UV absorption spectroscopy. Detailed performance and spatial distribution of microdischarges in different air flow rates will discussed in this presentation.

Plasma propagation and standing waves in spiral microplasma channels

Summary form only given. Plasma propagation in a microplasma channel having the form of a spiral has been studied in the rare gases and gas mixtures. Microchannels having widths of 200–300 µm, and a length-to - width aspect ratio of ∼103∶1, have been fabricated in nanoporous Al 2 O 3 by a sequence of wet chemical and micropowder machining processes, Produced from 125–250 µm thick aluminum foil, these channels are situated in a dielectric barrier structure having Al electrodes straddling the Al 2 O 3 channel. For the experiments reported here, the channels are formed (by photolithographic patterning) into a spiral having an overall diameter of 3 cm.

Influence of multiple electrode configurations on atmospheric pressure microplasma jet arrays in flexible polymer

Summary form only given. Novel microcavity plasma jet devices operating at atmospheric gas pressure have been fabricated in a flexible, robust and optically transparent polymer. By a micromolding process, large scale arrays of microcavities, each having a diameter of hundreds of microns and embedded electrodes, have been fabricated with various form factors that can be precisely controlled.

Dual sided Al/Al 2 O 3 microchannel plasma ozone reactor

Summary form only given. Arrays of low temperature microchannel plasmas have been demonstrated to be an efficient generator of ozone in an atmospheric pressure environment.1 An on-chip chemical reactor was fabricated from Al foil by a sequence of electrochemical processes and micropowder abrasion techniques. Having a thickness of ∼ 1 mm, arrays of parallel microchannels can be stacked to yield increasing throughput. The Al/Al 2 O 3 structure chosen for the reactor renders it well-suited for demanding operating conditions and for use with attaching and corrosive gases and vapors, in particular.