ICMCTF2014 Session DP: Symposium D Poster Session

Authors have been concerned with research and development of high density oxygen plasma generators. Owing to high electron density and ionized oxygen flux, carbon-base films on the substrate can be removed with fast ashing rate. In the present study, this system is applied to pasteurization to solve the above issues related to plasma sterilizing. As a bio-indicator, the geobacillus stearothermophilus sample with the sporophyte content of 104 and 105 is employed as a target for sterilizing experiment. This gram-positive bacteria is shielded by peptidoglycan; without direct oxidation and bombardment against this shield layer, this bacteria could be alive to germinate during long-term cultivation culture. In the sterilizing experiment, this bacteria sporophyte is enclosed by the glassine paper to make a test-piece. Plasma parameters are varied to find that no bacteria is cultured from the sporophyte at 323 K after cultivation time of 604.8 ks or one week when 3000 kw is applied to this test-piece. This assures that generated oxygen atoms and ions should penetrate the glassine paper and sporophyte membrane and to make direct interaction with bacteria for pasteurization.

Yttria-Tetragonal Zirconia Polycrystal(Y-TZP) is a preference material used as biomaterials due to its good mechanical properties. In order to improve the biocompatibility of zirconia, RGD-peptide derived from extracellular matrix proteins was employed to modify the surface of YTZP to promote cell adhesion.

In this study, the surfaces of YTZP were modified using hydrothermal method at different periods. The topographies of modified YTZP were analyzed by contact angle, XRD, FTIR, AFM and FE-SEM, as well as the mechanical properties were evaluated by Vickers hardness, fracture toughness and three point bending. The RGD-peptide was immobilized on the surface of YTZP by chemical treatment. This RGD-peptide immobilized YTZP were characterized by FTIR, AFM and FE-SEM, and then were cocultured with MG-63 osteoblast cells for the biocompatibility assay. The cell morphology and proliferation were evaluated by SEM, WST-1 and ALP activity assay.

The XRD results indicated that the phase transformation, from tetragonal phase to monoclinic phase, was increased with increasing the incubation time of hydrothermal treatment. However, there are no significant differences in mechanical strengths after RGD-peptide was successfully grafted onto the YTZP surface. The SEM images showed that the MG-63 cells appeared polygonal, spindle-shaped, and attached on the RGD-peptide modified YTZP. The proliferation and cellular activities of MG-63 cells on the RGD-peptide modified YTZP were better than that on the YTZP.

Due to the increasing cardiovascular diseases, it has a significant impact on human’s life and thereby raises the demand of blood-contacting biomaterials. In this study, the film composed of plasma-polymerized hexamethyldisiloxane (HMDSO) containing silica nano-particles as the main layer and a very thin plasma-polymerized fluorocarbon layer over the top was developed to exhibit super-hydrophobic property. The polyurethrane (PU), a broadly used biomaterial for medical applications such as vascular grafts, catheters and prostheses was used as substrate. A pulsed-dc plasma polymerization process was employed by adjusting the precursor flow rate and the power input. The deposited films were examined their microstructure, water contact angle, cytotoxicity and in vitro platelet adhesion tests.

Experimental results show that the deposited films are amorphous with randomly dispersed silica nanoparticles exposed to the surface of the deposited films. Water contact angle of the obtained film, after optimizing deposition parameters, was measured at 153.4^o, namely super-hydrophobicity, which shall attribute to the synergistic effect of both nano-structural surface morphology (resulting from the inserted silica nano-particles) and low surface energy (resulting from surface flourocarbon groups). Results of in vitro cytotoxicity and platelet adhesion tests showed satisfactory fibroblasts cell proliferation and decreased platelet adhesion on the coated specimens. These quantitative indications as revealed above imply that such films may have the potential to avoid thrombosis and possibly provide an alternative for surface modification of blood-contacting biomaterials.

Keywords : super-hydrophobic; plasma-polymerization; polyurethrane (PU); blood-contacting biomaterials.

Amorphous titanium carbide (a-TiC_x) was deposited on Ti6Al4V substrates as an interlayer of functional diamond-like carbon (DLC) to improve the corrosive drawback of the silicon interlayer by radio frequency plasma enhanced chemical vapor deposition (rf PECVD) technique. The a-TiC_x thin films were obtained by using a mixture of titanium tetrachloride (TiCl₄) and methane (CH₄) gases. Fluorinated amorphous DLC (F-DLC) was then coated on the samples by the same CVD system from the precursors of tetrafluoromethane (CF₄) and CH₄. The structure and surface properties of a-TiC_x interlayers, prepared by various TiCl₄ flow ratios, were investigated by using X-ray diffraction spectroscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. The mechanical properties were evaluated by nano-indentation and the adhesion, by micro-scratch. The corrosion behavior was studied in a physiological solution. An F-DLC coating with a 100 nm Si interlayer prepared by physical vapor deposition process was also implemented as a benchmark. The results showed that the anti-corrosion capability and the adhesive strength of the F-DLC coatings with an a-TiC_x interlayer is much better than that with an a-Si one.

The Plasma Electrolytic Oxidation (PEO) is a traditional technique that promotes the transformation of the titanium substrate into a high hardness ceramic layer by the interaction of anodic oxide growth and plasma channel shock caused by the dielectric break down at high voltages, taking place in an aqueous electrolyte. There are two principal methods used in anodic oxidation, the potentiostatic mode, which the voltage is maintained constant and the galvanostatic mode, which the current density is maintained constant. However, the differences between these two methods are unclear. The aim of this work is to evaluate the influence of the PEO method and time on the surface and corrosion properties. Titanium samples were submitted to potentiostatic PEO at 250, 300, 350 and 400V and galvanostatic PEO at 200, 400, 600 and 800 mA/cm² for 1 and 3 min. The surface properties were evaluated by scanning electron microscopy (SEM), X-Ray Diffraction (XRD), roughness and surface wettability measurements. The corrosion properties were evaluated by open circuit potential, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. The oxide layer is significantly altered with the applied voltage, while there is no change for different applied current densities. Pore size, contact angle, and the amount of rutile phase increased with applied voltage in the potentiostatic PEO. In the galvanostatic PEO, the oxide surface properties remain practically the same. Corrosion resistance is improved with applied voltage, and with anodization time for current densities.

The usage of biomedical implant has been gradually increased for couple of decades due to replace for injuries and old aged diseases. The metallurgical implant materials is one of the most frequently used to restore for damaged hard tissue such as dental and orthopedic field, which should be have non-toxic and high biocompatibility. The surface modification and alloy development of implant materials have been encouraged to have more successful and higher biocompatibility between replacement materials and human tissue. Regarding these reasons, Hydroxyapatite [Ca₁₀(PO₄)₆(OH)₂, HA] is used as a bio-ceramic coating on metal implant surface due to their bioactivity and osseoconductive properties in vivo. To be more effective HA coating layer, the silicon substitution of HA (Si-HA) coatings are greater than single HA coating for bone on-growth. As a coating substrate of implant materials, β phased Ti-Nb-Zr alloy system has significant low elastic modulus and has non-toxic elements than that of conventional alloys such as pure titanium or Ti-6Al-4V alloy, Ti-35Nb-10Zr alloy has appropriate properties with reasonable mechanical and chemical properties to be used as a Si-HA coating substrate. The objective of this study was to investigate the silicon-substituted hydroxyapatite coating on biomedical Ti-Nb-Zr alloy using cyclic electrochemical deposition method.

The Ti-Nb-Zr alloy was manufactured with 35 wt.% of Nb and 10 wt.% of Zr by arc melting furnace to be a β phase. Electrochemical deposition of Si substituted Ca/P was performed by pulsing the potential with a method of cyclic voltammetry, and changed cyclic time between 10 and 150. The electrolyte was prepared by dissolving the reagent-grade chemicals: Ca(NO₃)₂, NH₄H₂PO₄, and Na₂SiO₃․9H₂O to be 1.67 of Ca/P ratio and Si contents were controlled to be 1 - 2.5 wt.% in the total portion. The surface characteristics were observed by field-emission scanning electron microscopy, X-ray diffractometer, Fourier transform infrared spectroscopy, electrochemical corrosion test (potentiodynamic and AC impedance test). Analysis of variance (ANOVA) was performed to compare the variation of corrosion parameters and significance was p<0.05. As results, more cyclic time of coatings layer could be have increased corrosion potential and decreased current density, also has more plate like structure than that of less cyclic time. (NRF: R13-2008-010-00000-0; hcchoe@chosun.ac.kr [mailto:hcchoe@chosun.ac.kr] )

CP Ti and Ti-6Al-4V alloy has been widely used for implant materials such as dental and orthopedic implants due to a good mechanical property, corrosion resistance, and biocompatibility. Even though these advantages, many researchers have focused on the surface modification for improvement of biocompatibility on interface between implant and bone.

Especially, one of surface modification methods is nanotube formation on the alloy for improvement for biocompatibility. It is possible to form nanotubes on the surface of the implant alloy under the conditions of constant voltage in general. However, in this study, given the gradual change of the various applied potential, to nanotube formation, was studied how nanotubes form would change accordingly for drug dopping and bioactive materials coating.

In this study, nanotube shape and morphology control of Ti-6Al-4V alloy by various applied potentials for drug dopping and bioactive materials coating have been researched by using electrochemical methods in 1 M H₃PO₄ with small amounts of fluoride ions. The nanotube formation was carried out by DC power supply with applied voltage variation in range of 10~40V after washing three times with distillation water for 15 minutes. Nanotube shape and morphology was observed by FE-SEM, EDS, XRD, STEM, AFM, XPS. Nanotube shape can be controlled by applied potential for drug dopping and bioactive materials coating(hcchoe@chosun.ac.kr [mailto:hcchoe@chosun.ac.kr] ).

Keywords: Ti-6Al-4V alloys, Applied potential, Nanotube shape, Drug dopping, Coating

The tribocorrosion phenomenon is present in biomedical alloys that are used in artificial implants to replace natural joints. This damage limit the service life of such implants, the hard coatings can improve the resistance of wear and corrosion. The multilayers of TiAlPtN/TiAlPt were deposited on CoCrMo alloys by magnetron sputtering. In this work we study the wear mode of the samples coated and alone in a simulated body fluid with an ion concentration similar to that in the human blood. The structure of coatings was studied by means of XRD and the composition by RBS and EDS techniques. The tribocorrosion behavior of CoCrMo alloys alone and coated with TiAlPtN/TiAlPt multilayers was studied in simulated body fluid. The tribocorrosion was performed using a ball on plate reciprocating tribometer, the tests were conducted at 37 °C of temperature. The loads used were between 0.25 N to 2N, the oscillating frequencies was 1Hz. The corrosion and tribocorrosion were studied using open circuit potential (OCP) and potentiodynamic polarizations. The potentiodynamic polarization was used to estimate the change in the corrosion rate due to wear and the potensiostatic polarization in the passive region to measure the change in the wear rate due to corrosion. In order to study the wear mechanisms, the debris, the topography and composition of worn surfaces were analyzed by means of SEM and EDS. For the CoCrMo alloy the corrosion augmentation factor was greater than the wear augmentation factor. The coatings improve the corrosion and tribocorrosion resistance of CoCrMo alloys.

To improve the corrosion resistance and hemocompatibility of biomedical NiTi alloy, hydrophobic polymer coatings are deposited by plasma polymerization in the presence of a fluorine-containing precursor by an atmospheric-pressure plasma jet. This process takes place at a low temperature in air and can be used to deposit fuoropolymer films using organic compounds that cannot be achieved by conventional techniques. The composition and chemical states of the polymer coatings are characterized by Fourier transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS). The corrosion behavior of the coated and bare NiTi samples is assessed and compared using polarization tests and electrochemical impedance spectroscopy (EIS) in physiological solutions including simulated body fluids (SBF) and Dulbecco's Modification of Eagle's Medium (DMEM). The corrosion resistance of the coated NiTi alloy is evidently improved. Protein adsorption and platelet adhesion tests reveal that the adsorption ratio of albumin to fibrinogen is increased and the number of the adherent platelets is greatly reduced on the coating. The plasma polymerized coating produces better hemocompatibility and is promising as a protective and hemocompatible coating on cardiovascular implants.