Yong-Hoon Jeong

Surface characteristics of HA coated Ti-Hf binary alloys after nanotube formation

Abstract Ti-Hf binary alloys contained 10%, 20%, 30% and 40% (mass fraction)Hf were manufactured in the vacuum furnace system. And then, specimens were homogenized for 24 h at 1 000 °C in argon atmosphere. The formation of oxide nanotubes was conducted by anodic oxidation on the Ti-Hf alloy in 1 mol/L H 3 PO 4 electrolytes containing small amounts of NaF at room temperature. The hydroxyapatite (HA) coating made of tooth ash prepared by electron-beam physical vapor deposition (EB-PVD) method. The corrosion behaviors of the specimens were examined through potentiodynamic test in 0.9% NaCl solution by potentiostat. The microstructures of the alloys were examined by field emission scanning electron microscopy (FE-SEM) and x-ray diffractometer (XRD). It was observed that the lamellar structure translated to needle-like structure with Hf contents. Nanotube formed and HA coated Ti- x Hf alloys had a good corrosion resistance.

Corrosion characteristics of anodized Ti–(10–40wt%)Hf alloys for metallic biomaterials use

The effect of anodizing on corrosion resistance of Ti–xHf alloys has been investigated. Ti–xHf alloys were prepared and anodized at 120, 170 and 220xa0V in 1xa0M H3PO4 solution, and crystallized at 300 and 500°C. Corrosion experiments were carried out using a potentiostat in 0.15xa0M NaCl solution at 36.5xa0±xa01°C. The Ti–xHf alloys exhibited the α′ and anatase phases. The pore size on the anodized surface increases as the applied voltage is increased, whereas the pore size decreases as the Hf content is increased. The anodized Ti–xHf alloys exhibited better corrosion resistance than non-anodized Ti–xHf alloys.

Electrochemical behavior of dental implant system before and after clinical use

Abstract Electrochemical behavior of dental implant system before and after clinical use (in vivo and in vitro) was researched by using abutment and titanium fixture. To simulate an oral environment, the samples of clinically used and non-used implant systems as a working electrode were exposed to artificial saliva at (36.5±1) °C. Electrochemical tests were carried out using a potentiostat. After electrochemical test, the corrosion morphology of each sample was investigated by FE-SEM and EDS. The corrosion potential and pitting potential of clinically used implant system are lower than those of non-used implant system, and clinically used implant system exhibits a lower range of passivation, indicating a less degree of inherent resistance against chloride ion. The polarization resistance decreases in the case of clinically used implant system, whereas, R p for clinically non-used implant system increases compared with clinically used implant system.

Influence of Ketamine on Catecholamine Secretion in the Perfused Rat Adrenal Medulla

The aim of the present study was to examine the effects of ketamine, a dissociative anesthetics, on secretion of catecholamines (CA) secretion evoked by cholinergic stimulation from the perfused model of the isolated rat adrenal gland, and to establish its mechanism of action, and to compare ketamine effect with that of thiopental sodium, which is one of intravenous barbiturate anesthetics. Ketamine (30~300microM), perfused into an adrenal vein for 60 min, dose- and time-dependently inhibited the CA secretory responses evoked by ACh (5.32 mM), high K(+) (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic NN receptor agonist, 100microM) and McN-A-343 (a selective muscarinic M1 receptor agonist, 100microM). Also, in the presence of ketamine (100microM), the CA secretory responses evoked by veratridine (a voltage-dependent Na(+) channel activator, 100microM), Bay-K-8644 (an L-type dihydropyridine Ca(2+) channel activator, 10microM), and cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10microM) were significantly reduced, respectively. Interestingly, thiopental sodium (100microM) also caused the inhibitory effects on the CA secretory responses evoked by ACh, high K(+) , DMPP, McN-A-343, veratridine, Bay-K-8644, and cyclopiazonic acid. Collectively, these experimental results demonstrate that ketamine inhibits the CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors and the membrane depolarization from the isolated perfused rat adrenal gland. It seems likely that the inhibitory effect of ketamine is mediated by blocking the influx of both Ca(2+) and Na(+) through voltage-dependent Ca(2+) and Na(+) channels into the rat adrenal medullary chromaffin cells as well as by inhibiting Ca(2+) release from the cytoplasmic calcium store, which are relevant to the blockade of cholinergic receptors. It is also thought that, on the basis of concentrations, ketamine causes similar inhibitory effect with thiopental in the CA secretion from the perfused rat adrenal medulla.

Electrochemical Characteristics of TiN/ZrN Multilayers on the Ti–35Ta–xHf Alloy by Magnetron Sputtering

In this study, we investigated the electrochemical characteristics of TiN/ZrN multilayers on a Ti–35Ta–xHf alloy by radio frequency (RF) magnetron sputtering. The Ti–35Ta–xHf alloy had an α+ β phase structure. The Ti–35Ta–15Hf alloy had a higher intensity β phase peak than Ti–35Ta–3Hf and 7Hf alloy, which contained lower Hf content. The martensite traces disappeared with increasing Hf content and the Ti–35Ta–15Hf alloy showed an entirely equiaxed structure with a β phase. The multilayer film was developed by alternately depositing TiN and ZrN layers on Ti–35Ta–15Hf substrates using the RF magnetron sputtering system to improve the interface properties between the coating and substrate. The uncoated specimen showed a passive region between 60 and 1300 mV with a current density of 0.38 µA/cm2, whereas, the TiN/ZrN multilayered specimen had a passive region between 210 and 1500 mV with a current density of 0.09 µA/cm2. The experimental results suggest that the as-sputtered layer coated well on the substrate. The TiN/ZrN multilayered film on Ti–35Ta–15Hf substrate exhibited better electrochemical resistance than that of the uncoated Ti–35Ta–15Hf substrate.

Surface Characteristics of Dental Implant Fixture with Various Manufacturing Process

In this study, surface characteristics of dental implant fixture with various manufacturing process have been researched using electrochemical methods. The dental implant fixture was selected with 5 steps by cleaning, surface treatment and sterilization with same size and screw structure; the 1st step-machined surface, 2nd step-cleaned by thinner and prosol solution, 3th step-surface treated by RBM (resorbable blasting media) method, 4th step-cleaned and dried, 5th step-sterilized by gamma-ray. The electrochemical behavior of dental implant fixture has been evaluated by using potentiostat (EG&G Co, 2273A) in 0.9% NaCl solution at . The corrosion surface was observed using field-emission scanning electron microscopy (FE-SEM) and energy dispersive x-ray spectroscopy (EDS). The step 5 sample showed the cleaner and rougher surface than step 3 sample. The step 5 sample of implant fixture treated by RBM and gamma sterilization showed the low corrosion current density compared to others. Especially, the step 3 sample of implant fixture treated by RBM was presented the lowest value of corrosion resistance and the highest value of corrosion current density. The step 3 sample showed the low value of polarization resistance compared to other samples. In conclusion, the implant fixture treated with RBM and gamma sterilization has the higher corrosion resistance, and corrosion resistance depends on the step of manufacturing process.