• The Journal of Korean Academy of Prosthodontics
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• v.49 no.3
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• pp.245-253
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• 2011

Purpose: The aim of this in vitro study was to estimate surface characteristic after peptide coating and investigate biological response of human mesenchymal stem cell to anodized titanium discs coated with RGD peptide by physical adhesion and chemical fixation. Materials and methods: Fluorescence isothiocyanate (FITC) modified RGD-peptide was coated on the anodized titanium discs (diameter 12 mm, height 3 mm) using two methods. One was physical adhesion method and the other was chemical fixation method. Physical adhesion was performed by dip and dry procedure, chemical fixation was performed by covalent bond via silanization. In this study, human mesenchymal stem cell was used for experiments. The experiments consisted of surface characteristic evaluation after peptide coating, analysis about cell adhesion, proliferation, differentiation, and mineralization. Obtained data are statistically treated using Kruskal-Wallis test and Bonferroni test was performed as post hoc test (P=.05). Results: The evaluation of FE-SEM images revealed no diffenrence at micro-surfaces between each groups. Total coating dose was higher at physical adhesion experimental group than at chemical fixation experimental group. In cell adhesion and proliferation, RGD peptide coating did not show a statistical significance compared with control group (P>.05). In cell differentiation and mineralization, physical adhesion method displayed significantly increased levels compared with control group and chemical fixation method (P<.05). Conclusion: RGD peptide coating seems to enhance osseointegration by effects on the response of human mesenchymal stem cell. Especially physical adhesion method showed more effective than chemical fixation method on response of human mesenchymal stem cell.

• Journal of Periodontal and Implant Science
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• v.33 no.1
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• pp.27-35
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• 2003

1. 목적 생체재료의 생체친화성을 증진시키고 치유를 촉진하기 위한 목적으로 생체재료의 생화학적 표면개질에 관한 연구가 널리 진행되고 있다. 이와 같은 목적으로 이용되어 온 부착분자에는 아미노산, 펩타이드, 단백질, 효소 및 성장인자들을 들 수 있으며, 이들 분자들을 금속, 골대체물질 및 폴리머와 같은 생체재료의 표면개질에 이용하여 왔다. 이 연구의 목적은 생체적합성이 우수하고 생분해성을 지닌 키토산으로 얇은 막을 제작한 후, 세포외 기질의 구성성분 중 세포부착에 관여하는 RGD 펩타이드를 부착시킨, 표면개질 키토산막의 생물학적 영향을 MG-63 조골양세포를 이용하여 관찰하는 것이다. 2. 방법 2% acetic acid에 키토산 가루를 녹여 만든 2% 키토산 용액으로 24-well 배양접시의 표면을 도포 후 24시간 동안 건조시켜 키토산막을 제작하였다. GRGDS 펩타이드를 cross-linker(EDC, NHS) (Sigma, MO, USA) 용액과 반응시켜서 펩타이드의 카르복실기를 활성화시켰다. 이들을 PBS 완충용액으로 수화시킨 키토산막과 결합시켜 펩타이드의 활성화된 카르복실기와 키토산의 아민기 간에 안정적인 아미드 결합(amide bond)이 형성되도록 하였다. 하루 동안 반응을 일으킨 후 PBS 완충용액과 증류수로 씻어내고 냉동 건조시킴으로써 GRGDS가 결합된 키토산막을 제작하였다. 재료 표면의 화학 성분을 알아보는데 사용되는 방법의 일종인 X-ray photoelectron spectroscopy(XPS) 분석을 통하여 부착분자가 키토산막에 결합된 여부를 확인하였다. GRGDS 펩타이드에 요오드를 결합시킨 후, 이것을 키토산막에 공유 결합시키고 XPS를 통해 요오드가 재료 표면에서 검출되는지를 검사하였다. 요오드가 검출된다면 이것은 키토산막 표면에 실제로 GRGDS 펩타이드가 존재하는 것을 의미하게 된다. 표면개질된 키토산막에 사람조골양세포인 MG-63을 접종하여 이를 실험군으로 하였고, 표면이 개질 되지 않은 키토산막을 대조군으로 하였다. 세포부착의 최적화 농도를 확인하기 위하여 GRGDS를 0.01, 0.05, 0.1, 0.25, 0.5, 1.0mg/ml의 농도로 준비하였다. 배양 후 1일, 7일째에 각 well에서 trypsin EDTA를 이용하여 세포를 분리한 후, 이를 원심 분리하여 세포수측정기를 이용하여 부착 세포의 수를 측정하여 세포의 부착 정도를 비교하였다. 배양 2시간, 24시간 후 주사전자현미경을 이용하여 키토산막에 부착된 세포의 양상을 관찰하였다. 3. 결과 XPS를 통한 표면의 화학 성분 분석 결과 GRGDS 펩타이드를 결합시킨 키토산막에서 요오드가 검출되었으며 펩타이드를 부착하지 않은 대조군에서는 검출되지 않았다. 따라서 cross-linker를 이용한 펩타이드와 키토산막의 공유결합을 확인할 수 있었다. 세포 배양 후 1일째 부착된 세포 수를 측정한 결과 0.1mg/ml 이상의 GRGDS 펩타이드 농도로 공유 결합시킨 키토산막에서 부착 세포 수가 다른 농도에 비해 유의성 있게 많이 관찰되었다. 이 농도 이하에서는 대조군과 실험군간에 세포부착의 유의한 차이가 없었다. 따라서 주사전자현미경을 이용한 부착 세포의 양상에 관한 관찰은 0.1mg/ml 농도의 펩타이드를 이용하였다. 세포 배양 7일째, 부착된 세포 수 측정 결과 GRGDS의 농도에 따른 유의성 있는 차이가 없었으며, 실험군과 대조군간에도 유의성 있는 차이가 없었다. 주사전자현미경 관찰결과 2시간 및 24시간 배양된 실험군 모두에서 별모양의 세포들이 키토산막 표면에 편평하게 잘 부착되어 있으며 많은 위족이 발달된 소견을 보인 반면, 대조군에서는 원형 또는 다각형 모양의 세포들이 실험군에 비해 부착이 덜 되어있는 양상을 보였다. 이 연구를 통하여 기능성 펩타이드를 생체재료의 표면에 공유결합 시키는 방법을 확립할 수 있었으며, RGD 펩타이드의 공유결합으로 표면개질된 키토산막이 조골세포의 부착능을 증진시킬 수 있음을 확인하였다. 표면개질된 생체재료를 소, 중동물에 적용시켜 생체 내에서의 생물학적 영향을 평가할 필요가 있으며, 이 실험의 결과는 향후 다양한 기능성 부착분자를 선발, 고안하여 임플란트용 생체재료의 표면개질에 이용하는 이른바 모방생체재료분야에 널리 활용될 수 있을 것으로 생각된다.

• Applied Chemistry for Engineering
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• v.10 no.4
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• pp.557-562
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• 1999

The reaction properties of Pd. Pd-Ce and Pd-La catalysts supported on ${\gamma}-Al_2O_3$ were investigated in the oxidation reaction of methane($CH_4$) exhausted from the compressed natural gas vehicle in a U-tube flow reactor with gas hourly space velocity of $72,000h^{-1}$. The catalysts were characterized by X-ray diffraction(XRD), X-ray photoelectron spectroscopy(XPS), BET surface area and hydrogen chemisorption. Pd catalyst prepared by $Pd(NO_3)_2$ as a palladium precursor and calcined at $600^{\circ}C$ showed the highest activity for a methane oxidation. Catalytic activity of calcined $Pd/{\gamma}-Al_2O_3$ in which most of palladium was converted into palladium oxide species was higher than that of reduced $Pd/{\gamma}-Al_2O_3$ in which most of palladium existed in palladium metal by XRD. As increasing the number of reaction cycles in the wide range of redox, the catalytic activity of $Pd/{\gamma}-Al_2O_3$ was decreased and the highly active window became narrower. Lanthanum oxide promoted Pd catalyst, $Pd/La/{\gamma}-Al_2O_3$ showed enhanced thermal stability compared with $Pd/{\gamma}-Al_2O_3$ even after aging at $1000^{\circ}C$, which was ascribed to the role of La as a promoter to suppress the sintering of palladium metal and ${\gamma}-Al_2O_3$ support. Almost all of methane was removed by the reaction with NO at the redox ratio of 1.2 in case of oxygen excluded steam, but that activity was significantly decreased in the steam containing oxygen.

• Journal of the Korean Chemical Society
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• v.47 no.6
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• pp.614-618
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• 2003

$Sr_2Ru_{1-x}Cu_xO_{4-y}(0.0{\le}x{\le}0.5)$ compounds were prepared using a conventional solid state reaction. Based on the Rietveld refinements of X-ray diffraction results, it is revealed that $Sr_2Ru_{1-x}Cu_xO_{4-y}$ compounds are the single phases with K2NiF4 type tetragonal system in the range of 0=x=0.3, while the mixed phases of$Sr_2RuO_4$ and $Sr_2CuO_3$ in the range of $0.4{\le}x{\le}0.5$. By means of X-ray photoelectron spectroscopy, the valence states of Ru and Cu in $Sr_2Ru_{1-x}Cu_xO_{4-y}$, have been confirmed to 4+ and 2+, respectively. The bond length difference between $Ru-O_1 ({\times}4)\;and\;Ru-O_2 ({\times}2)\;in\;RuO_6$ octahedron is gradually decreased with increasing Cu content in $Sr_2Ru_{1-x}Cu_xO_{4-y}$, which results in the lower c/a ratio. So, it might be assured that the variation of local symmetry of $RuO_6$ octahedron is very closely related to the transporting property of $Sr_2Ru_{1-x}Cu_xO_{4-y}$ compounds. The behavior of resistivity discloses that the metallic property in $Sr_2RuO_4$ changes into the semiconducting one in proportion to the Cu content in $Sr_2Ru_{1-x}Cu_xO_{4-y}$.

• Korean Journal of Materials Research
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• v.8 no.12
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• pp.1158-1164
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• 1998

Aluminium sulfate solution was prepared by sulfuric acid treatment from gibbsite. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was precipitated from aluminium sulfate solution by adding it into ethylalcohol. From XRD analysis as-prepared $Al_2(SO_4)_3$ · $nH_2O$ was confirmed to have mixed-crystalization water(n=18, 16, 12, 6). The average water of crystalization calculated from thermogravimetry(TG) was 14.7. Aluminium sulfate hydrate [$Al_2(SO_4)_3$ · $nH_2O$] was thermally decomposed and converted to $Al_2(SO_4)_3$ at $800^{\circ}C$, $\gamma-Al_2O_3$ at $900-1000^{\circ}C$, and $\alpha-Al_2O_3$ at $1200^{\circ}C$. Ni-doped $\gamma-Al_2O_3$, was synthesized from the slurry of as-prepared $\gamma-Al_2O_3$, with the ratio of [Ni]/[Al]=0.5. The reaction conditions of synthesis were determined as initial pH 9.0 and temperature $80^{\circ}C$ The basicity(pH) of slurry was controlled by using urea and $NH_4OH$ solution. Urea was also used for deposition-precipitation. For determining termination of reaction, the data acquisition was performed by oxidation reduction potential(ORP), conductivity and pH value in the process of reaction. Termination of the reaction was decided by observing the reaction steps and rapid decrease in conductivity. On the other hand, BET(Brunauer, Emmett and Teller) and thermal diffusity of Ni- doped $\gamma-Al_2O_3$, with various content of Ni were measured and compared. Thermal stability of Ni- doped $\gamma-Al_2O_3$ at $1250^{\circ}C$ was confirmed from BET and XRD analysis. The surface state of Ni-doped $\gamma-Al_2O_3$ was investigated by X-ray photoelectron spectroscopy(XPS). The binding energy at $Ni2P_{3/2}$ increased with increasing the formation of $NiAl_2O_4$ phase.

• Korean Chemical Engineering Research
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• v.51 no.5
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• pp.609-614
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• 2013

This study investigated the spontaneous combustion behavior of solvent-treated low rank coals. Indonesian lignite (a KBB and SM coal) and sub-bituminous (a Roto coal) were mixed with non-polar 1-methyl naphthalene (1MN) either by mechanical agitation or ultrasonication. The property change associated with 1MN treatment was then analyzed using proximate analysis, calorific value analysis, Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy and moisture re-adsorption test. Susceptibility to spontaneous combustion was evaluated using crossingpoint temperature (CPT) measurement along with gas analysis by GC. A FT-IR profile showed that oxygen functional groups and C-H bonding became weaker when treated by 1 MN. XPS results also indicated a decrease of the oxygen groups (C-O-, C=O and COO-). Increased hydrophobicity was found in the 1MN treated coals during moisture readsorption test. A CPT of the treated coals was ${\sim}20^{\circ}C$ higher than that of the corresponding raw coals and the ultrasonication was more effective way to enhance the stability against spontaneous combustion than the agitation. In the gas analysis less CO and $CO_2$ were emitted from 1MN treated coals, also indicating inhibition of pyrophoric behavior. The surface functional groups participating in the oxidation reaction seemed to be removed by the ultrasonication more effectively than by the simple mechanical agitation.

• Proceedings of the Korean Institute of Surface Engineering Conference
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• 2000.11a
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• pp.3-4
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• 2000

Many researchers are interested in the synthesis and characterization of carbon nitride and diamond-like carbon (DLq because they show excellent mechanical properties such as low friction and high wear resistance and excellent electrical properties such as controllable electical resistivity and good field electron emission. We have deposited amorphous carbon nitride (a-C:N) thin films and DLC thin films by shielded arc ion plating (SAIP) and evaluated the structural and tribological properties. The application of appropriate negative bias on substrates is effective to increase the film hardness and wear resistance. This paper reports on the deposition and tribological OLC films in relation to the substrate bias voltage (Vs). films are compared with those of the OLC films. A high purity sintered graphite target was mounted on a cathode as a carbon source. Nitrogen or argon was introduced into a deposition chamber through each mass flow controller. After the initiation of an arc plasma at 60 A and 1 Pa, the target surface was heated and evaporated by the plasma. Carbon atoms and clusters evaporated from the target were ionized partially and reacted with activated nitrogen species, and a carbon nitride film was deposited onto a Si (100) substrate when we used nitrogen as a reactant gas. The surface of the growing film also reacted with activated nitrogen species. Carbon macropartic1es (0.1 -100 maicro-m) evaporated from the target at the same time were not ionized and did not react fully with nitrogen species. These macroparticles interfered with the formation of the carbon nitride film. Therefore we set a shielding plate made of stainless steel between the target and the substrate to trap the macropartic1es. This shielding method is very effective to prepare smooth a-CN films. We, therefore, call this method "shielded arc ion plating (SAIP)". For the deposition of DLC films we used argon instead of nitrogen. Films of about 150 nm in thickness were deposited onto Si substrates. Their structures, chemical compositions and chemical bonding states were analyzed by using X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and infrared spectroscopy. Hardness of the films was measured with a nanointender interfaced with an atomic force microscope (AFM). A Berkovich-type diamond tip whose radius was less than 100 nm was used for the measurement. A force-displacement curve of each film was measured at a peak load force of 250 maicro-N. Load, hold and unload times for each indentation were 2.5, 0 and 2.5 s, respectively. Hardness of each film was determined from five force-displacement curves. Wear resistance of the films was analyzed as follows. First, each film surface was scanned with the diamond tip at a constant load force of 20 maicro-N. The tip scanning was repeated 30 times in a 1 urn-square region with 512 lines at a scanning rate of 2 um/ s. After this tip-scanning, the film surface was observed in the AFM mode at a constant force of 5 maicro-N with the same Berkovich-type tip. The hardness of a-CN films was less dependent on Vs. The hardness of the film deposited at Vs=O V in a nitrogen plasma was about 10 GPa and almost similar to that of Si. It slightly increased to 12 - 15 GPa when a bias voltage of -100 - -500 V was applied to the substrate with showing its maximum at Vs=-300 V. The film deposited at Vs=O V was least wear resistant which was consistent with its lowest hardness. The biased films became more wear resistant. Particularly the film deposited at Vs=-300 V showed remarkable wear resistance. Its wear depth was too shallow to be measured with AFM. On the other hand, the DLC film, deposited at Vs=-l00 V in an argon plasma, whose hardness was 35 GPa was obviously worn under the same wear test conditions. The a-C:N films show higher wear resistance than DLC films and are useful for wear resistant coatings on various mechanical and electronic parts.nic parts.