ICMCTF2015 Session TS6: Atmospheric Plasma Applications

The ultimate aim in medicine, besides prevention, is the healing of diseases and repairing damage after injuries. In reconstructive surgery, the task of engineers, material scientists and physicists is to provide an optimal system for each application. One particular application is the replacement of joints such as knee, shoulder and hip prosthesis in which ultra-high molecular weight polyethylene (UHMWPE) polymer is used. Since the interaction between the biological environment and biomaterial takes place on the material surface, the success of an implant is determined to a large extent by its surface properties. However, UHMWPE is non-polar and thus not optimal for cell adhesion and proliferation; its hydrophobic nature also limits its lubrication by synovial fluid in the joint increasing its friction and wear leading to a decreased longevity. Plasma technology (plasma polymerization and plasma surface treatment) is widely used to alter the surface properties of polymers by incorporation of functional groups on their surfaces without affecting their bulk properties. Among others, nitrogen functional groups are known to increase surface wettability and promote cell adhesion and proliferation.

In this research, plasma polymerization (continuous and pulsed plasma), and plasma post-irradiation grafting were used in order to deposit allylamine polymer thin films onto the surface of UHMWPE. Different process parameters such as power, monomer concentration, pressure and treatment time were varied for optimization. After treatment, surfaces were characterized via different physical and chemical characterization techniques such as: water contact angle measurements (WCA), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM) and optical reflectance spectroscopy (OPS). Moreover, films stability and ageing behaviors were investigated by soaking the substrates in a phosphate buffer solution at 37°C while agitating and by storing the substrates at ambient temperature respectively for 7 days. Cell culture tests were also done on the treated surfaces in order to evaluate their biocompatibility. Eventually, a comparison between the different methods and different process parameters on the film properties and biocompatibility has been made.

The main objective of this research is to improve the electrochemical performances of TiO₂ Li-ion anode material by introducing plasma treatment of TiO₂ powder. A specially designed atmospheric dielectric barrier discharge (DBD) plasma generator that are feasible to treat powders is proposed. TiO₂ powder underwent N₂ and H₂ mixed argon plasma treatment for 5, 10, 20, and 40 min. The rate capability of 20 min plasma treated TiO₂ anode had the best performance. As-treated TiO₂ reached a maximum nitrogen doping content 1.0% which was analyzed from x-ray photoelectron spectroscopy (XPS) peak analysis. In addition, Ti (IV) was partially reduced to Ti (III). The effectiveness of plasma treatment was evaluated by diagnosing plasma using optical emission spectroscopy (OES). Significant amount of excited argon was presented. Excitation of nitrogen second positive system, and presence of hydrogen excited spectrum were also identified. Although results of scanning and transmission electron spectroscopy (SEM, and TEM) did not show noticeable surface morphology and microstructure change, it is still believed that hydrogen contributed TiO₂ reduction causing oxygen vacancy. These oxygen vacancy further provides the chance to let excited nitrogen doped onto surface of TiO₂ particle. Electrochemical properties of TiO₂ is raised due to the production of oxygen vacancy and nitrogen doping. These findings enhance the understanding of the atmospheric plasma treatment on the potential application of TiO₂ anode material in Li-ion battery.

In the past decade cold atmospheric pressure plasma jets (APPJs) have attracted much attention due to their simple construction, versatility, easy scalability, low production costs and most importantly because they can produce very reactive chemistry at room temperature. A very interesting feature of APPJs is their ability to penetrate inside small holes and propagate along flexible dielectric tubes. This property makes the plasma jets very attractive tools for biomedical applications such as generation and propagation of plasma through catheters, endoscopic tubes, tooth channels etc. However, for each specific medical application usually a different kind of plasma source is needed. Therefore, it is very important to continuously developed new plasma jet prototypes that can be tested for different applications.

In this work we address three major issues for the design and development of APPJs. First of them is the precise power determination of a plasma jet, which is essential for biomedical applications. Most commonly used techniques are the direct integration of current - voltage waveforms and the Lissajous figure method. We compare these approaches, discuss their advantages and drawbacks and also determine the range of their applicability.

An important concern in plasma medicine, where clinical treatments are performed by APPJs, is the precise control of the device power. A manner for fine power adjustment of plasma jets is the use of burst mode operation of a conventional AC power supply. As we will show in this way very stable and cold plasma jets can be generated. Finally we describe a novel method for generation of cold atmospheric pressure plasma jet at the downstream end of a long flexible plastic tube without igniting plasma inside it. The device consists of a closed chamber where dielectric barrier discharge (DBD) is ignited. The discharge is driven by a conventional AC low frequency power supply. The exit of DBD reactor is connected to a long (up to 4 meters) commercial flexible plastic tube with a thin floating Cu wire passing through it. The gas flow is guided by the plastic tube while the metal wire, when there is plasma inside the DBD reactor, acquires the plasma potential. There is no discharge inside the plastic tube however under certain conditions a small plasma jet can be extracted from the downstream tube end. The jet obtained by this method is cold enough to be put in direct contact with human skin without electric shock. Therefore, by using this approach a cold plasma jet is generated far from the discharge generation region and the produced active species can be used for medical treatment and decontamination.

Biopolymers are often subjected to surface modification in order to improve their surface characteristics. The goal of this study is to show the use of atmospheric pressure plasma technology to enhance the adhesion of polyethylene (PE) shoulder prostheses. Two different plasma techniques (atmospheric pressure plasma activation and atmospheric pressure plasma polymerization) are performed on PE to increase the adhesion between the polymer and osteoblast cells or between the polymer and a PMMA bone cement. Both techniques are performed using a dielectric barrier discharge (DBD). A previous paper showed that atmospheric pressure plasma activation of PE results in the incorporation of oxygen-containing hydrophilic functional groups, which leads to an increased surface wettability. Atmospheric pressure plasma polymerization of methyl methacrylate (MMA) on PE results in a PMMA-like coating, which could be deposited with a high degree of control of chemical composition and layer thickness. The thin film also proved to be relatively stable upon incubation in a phosphate buffer solution (PBS).

This paper will discuss the next stage of the study, which includes testing the adhesion of the plasma-treated and plasma-coated samples to bone cement through a pull-out test and testing the cell adhesion and proliferation on the samples. In order to perform the pull-out tests, all samples were cut to standard dimensions and fixed in bone cement in a reproducible way with a sample holder specially designed for this purpose. The cell adhesion and proliferation were tested by means of an MTS assay after culturing MC3T3 osteoblast cells on disc-shaped samples for 7 days. The results show that both atmospheric plasma activation and atmospheric plasma polymerization significantly improve the adhesion to bone cement and enhance cell adhesion and proliferation. In conclusion, it can be stated that the use of atmospheric pressure plasma technology can lead to an implant with improved quality and a subsequent longer lifespan.

Functionalization of carbon nanotubes (CNTs) for the fuel cell application has been paid much attention recently as it has been realized that mechanical and electrical properties of CNTs can be altered by adding species to the side walls. Generally, such functionalization is accomplished by immersing the CNTs in diverse chemical solutions or exposing them to vapors at high temperatures. Plasma discharge in solution, so-called solution plasma process (SPP) was a one-step method to synthesize nitrogen-functionalized CNTs (N-CNTs) using simple equipment system. The superior properties of SPP not only include no requirements of heat and/or pressure owing to the high active species generated during discharge in solution, but also enable to control the morphology of CNTs through the change of electronic properties of discharge.

In this study, the CNTs and N-CNTs were synthesized by arc discharge in pure water and ammonia solution. The effect of N-functional group on the microstructure, morphology, and electrocatalytic activities of the CNTs was examined using the transmission electron microscopy (TEM), X-ray diffraction (XRD) and fourier transformed-infrared (FT-IR) in terms of nitrogen-functionalization. Electrochemical properties of the nitrogen-functionalized CNTs supported Pt catalysts were analyzed by electrochemical impedance spectroscopy (EIS).

From the results of FT-IR, the spectrum of CNTs and N-CNTs displays bands characteristic of N-H stretching (3430 cm^-1), C=N stretching (1630 cm^-1), N-O stretching (1380 cm^-1). The results of EIS indicated that the charge transfer resistance (Rct) of CNTs and N-CNTs with Pt was separately 1.46ⅹ10⁴ Ω and 4.47ⅹ10³ Ω . Compared to CNTs and N-CNTs, the peak intensity of FT-IR was increased with increasing the nitrogen concentration due to the formation of functional groups and the N-CNTs showed much improved electrochemical performances. The detailed results will be presented.

Acknowledgement : This study was supported by the National Research Foundation of Korea (NRF) funded by the Korea government (MSIP, Grant No. 2013R1A1A2060918)

Si/SiC composites were extracted from the wastes of solar cell industries after cutting ingots. Electrodes were fabricated with recycled waste, Super P (SP) and sodium alginate (SA) on copper foil, and the as-prepared electrodes were treated with oxygen plasma by atmospheric pressure plasma jet (APPJ). According to the electrochemical measurement, the sample with APPJ technique shows outstanding performance, which exhibits lesser resistance of solid electrode interface (R_SEI) and resistance of charge transfer (R_ct) through the fitting of equivalent circuit. Moreover, the broad peak of SEI formation at first cycle had vanished and the difference between oxidation and reduction peaks had reduced after APPJ treatment by cyclic voltammetry test. The mechanisms of APPJ could be interpreted via analyzing electrode by X-ray photoelectron spectroscopy (XPS) after cycling, which had shown the smootherorganic bonding. Conclusively, APPJ has the function to purify the surface of electrode to suppress the intrinsic formation of SEI to enhance the performance of silicon lithium ion battery.

In this study, a plasma electrolytic oxidation (PEO) process is used to form ceramic coating on AJ series magnesium. The present work is mainly to study the protective effects of coating on magnesium and galvanic coupling containing AJ series magesium and Aluminized steel. A potentiodynamic polarization corrosion test has been employed to investigate the corrosion resistance of the coating on magnesium in 3.5% NaCl solution.The galvanic corrosion rates of uncoated and coated Mg alloy respectively coupling with steel, aluminized steel, oxide-coated aluminized steels are studied by the zero resistance ammeter (ZRA) test. The scan electron microscopy (SEM) is used to investigate the coating microstructure and the coating/substrate interface. It is found that the plasma discharge behavior and treatment time significantly influence the microstructure of oxide coatings, corrosion resistances and galvanic corrosion extent.