Papers by Author: Kyo Han Kim

Abstract: Mg substituted hydroxyapatite (Mg-HA) has been reported to promote activity of osteoblast and inhibit function of osteoclast in vitro. Mg-HA was synthesized by ion implantation of Ca²⁺, P²⁺ and Mg²⁺ beams by using an electrostatic medium energy accelerator. Oxygen injection had a major role in the formation of HA on Ti substrate. The osteoblast cells spread and formed lamellae on the coating surfaces. But Mg²⁺ ion implanted HA had shown higher osteoblast cell count and higher protein activity. The presence of Mg in the coating had better osteoblast activity and differentiation. Implantation of Ca and P ions into Ti substrate to successfully form HA and subsequent Mg ion incorporation in this layer shows that medium energy ions are very helpful in increasing the tensile strengths drastically.

Abstract: Electrochemical surface treatments of micro-arc oxidation (MAO) and following cathodic polarization were performed on zirconium (Zr) disks in this study to enhance the bioactivity of Zr. The surface oxide layers formed with electrochemical treatments on Zr disks were characterized using surface analyses; the calcium phosphate formation on the specimens after immersion in Hanks’ solution was evaluated. As a result, thick calcium phosphate layers formed on only Zr specimens that underwent both MAO treatment with a mixture of calcium glycerophosphate and magnesium acetate and subsequent cathodic polarization treatment with sodium sulfate solution, while no precipitate was observed without treatment. Thus, this technique was confirmed to be a promising method to improve the bioactivity of Zr.

Abstract: Cathodic deposition of nanocrystalline hydroxyapatite coatings on titanium surface was carried out under different magnetic field conditions. The electrolyte was prepared to maintain physiological pH and was agitated using a magnetic stirrer throughout the time of electrolysis. Silver was incorporated in the current coating because of its antibactericidal and cytotoxic nature. It was found that the silver concentration in HA coated titanium without magnetic field was higher than the coating formed under magnetic fields. This may be attributed to the diamagnetic nature of silver in different magnetic field conditions.

Abstract: Hydroxyapatite powder is produced using combustion synthesis method. The powder was produced using a low-temperature processing method involving time as short as 15 minutes. As silver is known to have anti-bacterial properties, silver-doped hydroxyapatite was also produced by the same method. Both the powders were fully crystalline. XRD indicated the presence of an additional phase of CaO in both the samples. FT-IR indicated the presence of hydroxide, phosphate and carbonate groups. Silver addition tends to control the reactions of powder with a test Tris buffer environment and maintain a stable pH for a longer period of 500-hour duration.

Abstract: The objective of the present study was to define the optimal conditions and characterizations of hydroxyapatite (HA) coatings on titanium by electrophoretic deposition (EPD). The EPD processing parameters, such as deposition time, HA concentration level in the suspension, and applied voltage are experimentally determined. A good packing, crack-free and uniform HA coating on titanium was prepared. Then the coatings were sintered at 800 °C for 2 h. The sintered coatings presented a very homogeneous polycrystalline structure free of cracks. The results show that the application of EPD is an effective method in obtaining HA coatings with good properties.

Abstract: The effect of anodic oxide films produced by β-glycerophosphate (β-GP) and calcium acetate (CA) anodizing on osteoblast-like cell attachment and spreading were evaluated in this study. Anodic oxide films were produced in different conditions: Group 1, 0.02 M β-GP and 0.2 M CA; Group 2, 0.03 M β-GP and 0.2 M CA; Group 3, 0.03 M β-GP and 0.2 M CA. Anodic oxide surface was significantly rougher in comparison to the control untreated titanium surfaces, and the surface roughness and composition of phosphate and oxide increased as the concentration of β-GP was increased. There was no significant difference in the cell viability when cells were cultured on the control or anodized surface using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Scanning electron micrographs revealed more spread cells on the anodized surface than on the smooth control surface. In conclusion, we suggested that the positive effects of anodized surfaces produced by β-GP and CA on spreading of osteoblast-like cells may be the result of the difference of surface roughness and amount of Ca and P in the oxide layer.

Abstract: Commercial hydroxyapatite powders were electrophoretically deposited on titanium substrates. In this study, the effect of deposition durations and applied voltages on deposition yield was investigated. Green and sintered coatings were studied by SEM and XRD. It was observed that by applying low voltages and presedimentation, uniform and smooth hydroxyapatite coating can be prepared. In order to obtain roughened hydroxyapatite coatings, high voltages have to be applied. It was concluded that experimental conditions of powder concentration, applied potential, and presedimentation have a significant effect on the deposited coating morphology.

Abstract: Grit blasting using bioactive HA and biodegradable CMP followed by acid etching has been done. HNO3 and H3PO4 were used for the etching solution by controlling the concentration and etching time to know the effect on the surface chemistry and morphology of the Ti implant. Characterization of samples was done by using SEM, EDX and surface profilometer. The contents of residues on Ti surface decreased with increasing acid concentration and etching time. It was observed that the acidic etching rate of HA grits on Ti surface was faster than that of CMP grits. And HNO3 etched more rapidly the HA and CMP grits on Ti surface, compared to H3PO4. Therefore, the surface roughness of dental implants can be controlled by having appropriate combination of acid concentration and etching time.

Abstract: Five kinds of gypsums, (1) CaSO4•2H2O (caldium sulfate dihydrate; CSD), (2) CaSO4•1/2H2O (calcium sulfate hemihydrate; CSH), (3) CaSO4 (calcium sulfate anhydrite; CSA), (4) CSH200 (CSH heat-treated at 200°C after self-hardening), and (5) CSH600 (CSH heat-treated at 600°C after self-hardening) were used as candidates for coating materials on calcium metaphosphate (CMP) scaffod to control degradation rate of CMP and to extend degradation limit. The disks of CSD, CSH, CSA, CSH 200, and CSH600 were prepared by self-hardening after mixing with water, where CSH200 and CSH600 were heat-treated at 200°C and 600°C, respectively. In order to control fast resorption rate of gypsum, CMP-CSA composites were prepared with different CSA contents such as 0, 5, 10, 20, 30, 50, and 70 vol% and heat-treated at 900°C for 4 hours. The degradation rates of various gypsums were evaluated in revised simulated body fluid (r-SBF) for 1, 3, 7, and 21 days, respectively. Degradation rate of each specimen was measured in terms of weight loss change with time and degraded surface morphology was examined by SEM. All kinds of gypsums were transformd into CSD after self-hardening with water. Most of gypsums were degraded by 35~60 wt% at 7 days and by 70~99 wt% at 21 days of soaking in SBF. In the group of CMP-CSA composites, the degree of degradation of them was considerably retarded compared to that of five pure gypsums. The surface morphology showed elongated needle-like crystals during the degradation with time.

Abstract: Degradation characteristics of calcium metaphosphate (CMP) ceramics substituted by 5, 10, 15, 20 mol% of NaPO3 and KPO3, respectively, was evaluated in revised simulated body fluid (R-SBF) by measuring the weight change, flexural strength, crystalline phases, and surface morphology with immersion period. The weight loss of CMP substituted by KPO3 was significantly higher than that of CMP substituted by NaPO3. The weight loss in the KCa(PO3)3–CMP samples was due to the dissolution of KCa(PO3)3 phase. The flexural strength of NaCa(PO3)3–CMP samples increased, however, that of KCa(PO3)3–CMP samples decreased significantly due to the dissolution of KCa(PO3) phase with immersion period. The dissolution of KCa(PO3)3 phase formed a pore structure in KCa(PO3)3–CMP samples.