Il Song Park

Titania Nanotubes Supported Gelatin Stabilized Gold Nanoparticles for Medical Implants

TiO2 nanotube (TN) arrays produced by electrochemical anodization have been studied extensively in recent years as a new biomaterial for implants, drug delivery systems, immuno-isolation, biosensors, cell growth, bioartifical organs and tissue engineering. A bare TiO2 nanotube implant has many weaknesses when placed in contact with biological systems and surface modification is a possible solution for this problem. The aim of this study is to develop a very simple method for surface modification of TiO2 nanotubes to tailor new interfacial properties important in many biomedical applications. TiO2 nanotubes were fabricated by electrochemical anodization of titanium plate using 70 wt% glycerol in deionized water with 1 wt% NH4F as an electrolyte. The lyophilization method has been applied to impregnate gelatin stabilized gold nanoparticles into the TiO2 nanotubes followed by vacuum drying. This approach for tailoring different surface chemistry of TiO2 nanotubes develops a new platform for biomedical applications.

Tailoring the composition of fluoride conversion coatings to achieve better corrosion protection of magnesium for biomedical applications

The methodology of deposition of fluoride conversion coatings is modified with the use of galvanic coupling, agitation of the electrolyte solution, and addition of K2CO3, which helps to provide a better understanding of the mechanism and new avenues to tailor the composition of the coating. A very good correlation exists between the F/O ratio of the coatings prepared under varying experimental conditions and their icorr, |Z| and phase angle maximum; the higher the F/O ratio, the better the corrosion protective ability of the coatings in Hanks balanced salt solution. The corrosion behaviour of the coatings of the present study suggests that fluoride conversion coatings show much promise for their use for biomedical applications, as long as their uniformity is improved and the composition is tailored to enrich the MgF2 phase, encompassing a higher F/O ratio.

Formation of bioceramic coatings containing hydroxyapatite on the titanium substrate by micro-arc oxidation coupled with electrophoretic deposition

Bioactive ceramic coatings on titanium substrates were prepared successfully by micro-arc oxidation coupled with electrophoretic deposition (MAO and EPD) in NaOH electrolyte solution containing hydroxyapatite (HA) particles. The HA suspensions with various NaOH concentrations were prepared by ultrasonic dispersion. The microstructure, as well as the elemental and phase composition of the coatings was examined by scanning electron microscopy, energy dispersive spectrometry, and X-ray diffraction. X-ray diffraction showed that the coatings were composed mainly of rutile, Na(2)Ti(6)O(13), and HA phases. The composition and surface morphologies are strongly dependent on the NaOH electrolyte concentration. The corrosion behavior of the coating layers in simulated body fluids was evaluated using a potentiodynamic polarization test. The corrosion resistance of the coated sample was increased compared with the untreated titanium sample. The in vitro bioactivity assessment showed that the MAO and EPD-treated titanium substrate possesses higher apatite-forming ability than the only MAO-treated titanium substrate. In addition, the cell behavior was also examined using cell proliferation assay, cell morphology, and alkaline phosphatase activity. They obtained an agreement with the result of apatite-forming ability. The results clearly show that combining the MAO and EPD techniques provides an optimal surface for cell differentiation and osseointegration.

Effect of AOT-assisted multi-walled carbon nanotubes on antibacterial activity

The dispersing power of surfactant-modified multiwalled carbon nanotubes (MWCNTs) and their effect on the antibacterial activity were examined. The MWCNTs were modified using a dioctyl sodium sulfosuccinate (AOT) surfactant. UV-vis spectroscopy and transmission electron microscopy (TEM) were used to characterize the dispersion of MWCNTs in the aqueous phase. Fourier transform infrared spectroscopy confirmed the results of UV-vis spectroscopy and TEM, indicating that the AOT molecules had been adsorbed successfully onto the MWCNT surface. The highly dispersed AOT-modified MWCNTs showed strong antibacterial activity to Streptococcus mutans. The fluorescence images showed that the AOT-modified MWCNTs were capable of capturing bacteria and forming cell aggregates as well as killing them. The optical density growth curves and colony-forming units assays confirmed that the antibacterial activity of the AOT-modified MWCNTs was concentration-dependent and treatment time-dependent. This finding might be useful for applications of AOT-modified MWCNTs as an antibacterial agent to eliminate pathogens from a biocontaminated water phase.

Synthesis and Morphology of TiO2 Nanotubes by Anodic Oxidation Using Surfactant Based Fluorinated Electrolyte

This study examined the effects of the anodization parameters (both surfactant in electrolyte and applied voltage) on the geometrical dimensions of nanotubes. The nanotube topography, diameter, length and wall thickness were affected by the addition of a surfactant to the electrolyte and applied voltage. As a consequence, TiO2 nanotube arrays with mean tube diameters and wall thicknesses ranging from 65 to 120 nm and 20 to 28 nm, respectively, were obtained. The mean tube diameter was decreased by adding a surfactant to the electrolyte, whereas the length of the tube was increased. The nanotube diameter and length increased linearly with increasing applied potential. At 30 V, the tube to tube spacing was increased by adding a surfactant to the electrolyte. At 40 V, the tubular surface morphology collapsed completely when the electrolyte contained the surfactant but the tube length was not affected in the electrolyte without the surfactant. The TiO2 structure was dependent on the heating conditions; an amorphous and anatase phase was observed at room temperature and 500 � C, respectively. The mean roughness (Ra) of the nanotube surface fabricated in the electrolyte with the surfactant was lower than that without the surfactant.

Effects of anodizing voltage on the anodized and hydrothermally treated titanium surface

Anodic oxidation is the process of creating a titanium oxide layer with various defects more dense and stable. In this study, a dense, stable and porous oxide layer was formed using anodic spark oxidation on pure titanium surface and hydroxyapatite crystals were formed on its surface via a hydrothermal treatment. A mixture of 0.02M−GP (Glycerolphosphate disodium salt) and 0.2M-CA (Calcium acetate) was used as an electrolyte. By increasing the anodizing voltage to 220, 260, 300, and 360 V, the effects of the anodizing voltage were examined by evaluating the film properties after anodization and a hydrothermal treatment. Breakdown occurred around 230 V. As the voltage increased after breakdown, the pore size increased. After the hydrothermal treatment, the amount of HA crystal precipitation was also increased as the voltage increased. The mean surface roughness (Ra) of the anodizing surface was also increased as the voltage increased. The Ra value was larger in the hydrothermally treated group compared with the group treated with anodization as a result of the HA crystals present on the surface after the hydrothermal treatment. Corrosion resistance of the surface modified by anodization was significantly increased in a saline solution compared to that for the non-treated group; this increased further after the hydrothermal treatment. These increases were most likely due to a thick stable oxide layer formed through anodization. Thus, it is believed that titanium with its surface modified through anodic spark oxidation would be a suitable biomaterial due to its corrosion resistance and biocompatibility.

Influence of heat treatment on morphological changes of nano-structured titanium oxide formed by anodic oxidation of titanium in acidic fluoride solution

TiO(2) nanotube array (TN) on titanium plate was fabricated by using an electrochemical method. The crystal structure and surface morphology of TN array was examined by X-ray diffraction (XRD) and Field Emission Scanning Electronic Microscopy (FE-SEM), respectively. The stability of the nanotube structure and crystal phase transition was studied at different temperatures in dry oxygen ambient. The as-deposited films were found to be amorphous. The tubes crystallized in the anatase phase at a temperature of 450 degrees C. Anatase crystallites formed inside the tubes walls was transformed completely to rutile at 500 degrees C in dry environment. With the heating temperature increased the intensity of rutile peak increased with decrease in reflection from titanium. Intense rutile peak was observed at 600 degrees C. The average pore diameter as calculated from FE-SEM images was 50-100 nm. At higher temperature tubular structure completely collapsed leaving dense rutile crystallites. A model was proposed to explain the formation mechanism of TN fabricated on titanium plate in HF/H(2)SO(4) electrolyte.

Biodegradation and cytotoxic properties of pulse anodized Mg alloys

Magnesium has the potential to be used as an implant material owing to its non-toxicity. On the other hand, magnesium alloys corrode rapidly in subcutaneous gas bubbles. Consequently, the approach of using magnesium alloys as a biodegradable biomaterial is not well established. Therefore, the aim of this study was to provide corrosion protection by anodizing to surface for a biodegradable material. Micro-arc oxidation by pulsed DC was applied to AZ91D and AZ31B, and the cell bioactivity was defined. The anodic film was characterized by XRD and SEM. The specific mass loss variation from immersion test and potentiodynamic electrochemical test was performed for the quantification of corrosion resistance. Although the AZ91D had better corrosion resistance properties but the result of the in vitro tests showed low cell viability compared with the AZ31B. The results of the cell staining and agar overlay test revealed the AZ31B group had good biocompatibility and a low corrosion rate. In this study, the surfaces of AZ91D and AZ31B showed the formation of a uniform film by pulse power anodization improving corrosion resistance. Also, the cytotoxicity of the materials was examined by the aluminum content change of compound metal.

The effect of APH treatment on surface bonding and osseointegration of Ti-6Al-7Nb implants: An in vitro and in vivo study

This study investigated the effects of anodization-cyclic precalcification-heat (APH) treatment on the bonding ability of Ca-P coating to the parent metal and osseointegration of Ti-6Al-7Nb implants. Eighteen Ti-6Al-7Nb discs, 9 untreated and 9 APH-treated, were cultured with osteoblast cells in vitro, and the cellular differentiation ability was assayed at 1, 2, and 3 weeks. For in vivo testing, 28 Ti-6Al-7Nb implants (14 implants of each group) were inserted to rat tibias, and after each 4 and 6 weeks of implantation, bone bonding, and osseointegration were evaluated through removal torque and histological analysis. Osteoblast-culturing showed twice as much of the alkaline phosphatase activity on the treated surface at 3 weeks than on the untreated surface (p < 0.05). The treated implants exhibited higher removal torque values than the untreated ones (15.5 vs. 1.8 Ncm at 4 weeks and 19.7 vs. 2.6 Ncm at 6 weeks, p < 0.05). Moreover, the excellent bonding quality of coats was confirmed by the existence of cohesive fractures on the surface of removed APH implants (field emission scanning electron microscopy and histological observation). Within the limits of this study, it can be concluded that the APH treatment significantly enhanced osseointegration of the Ti-6Al-7Nb implant, with the stable bonding between the coating and the implant surface.

Surface Characteristics of Magnesium Alloys Treated by Anodic Oxidation Using Pulse Power

Magnesium has been proposed as an implant metal due to its low weight and inherent biocompatibility. However, it use as a biomaterial is seriously limited by its poor corrosion n resistance. Die-cast AZ91D and rolled AZ31B alloys, which are commercial magnesium alloys, were used in this study. After plasma anodization, SEM showed that the surface had a relatively high porosity with some micro-cracks. EDX revealed Mg, Al and Zn on the surface of the samples before anodization. After anodization , there was an increase in the oxygen EDX peak intensity with a concomitant decrease in the magnesium intensity . Anodized AZ91D had the best corrosion resistance according to the potentiodynamic polarization curves. After immersion in Hanks solution for 10 days, the untreated AZ31B sample had the highest pH value due to formation of OH- on the film surface.