• Journal of the Korean Crystal Growth and Crystal Technology
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• v.22 no.6
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• pp.279-285
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• 2012

The co-precipitation technique has been applied to synthesize Biphasic Calcium Phosphate (BCP), Mg-BCP and Si-BCP. X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy were used to characterize the structure of synthesized BCP, Mg-BCP and Si-BCP powders. The results have shown that BCP and substitution of magnesium and silicon in the calcium deficient apatites revealed the formation of biphasic mixtures of Hydroxyapatite (HAp)/${\beta}$-Tricalcium phosphate (${\beta}$-TCP) ratios after heating at $1000^{\circ}C$. Ionic substituted BCP is able to develop a new apatite phase on the surface in contact with physiological fluids faster than BCP does. An MTT assay indicated that BCP, Mg-BCP, and Si-BCP powders had no cytotoxic effects on MG-63 cells, and that they have good biocompatibility.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.5
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• pp.243-248
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• 2010

Si-substituted biphasic calcium phosphates (Si-BCP) were prepared by co-precipitation method. X-ray diffraction and fourier transform infrared spectroscopy were used to characterize the structure of Si-BCP powders. The Si-BCP powders with various Ca/(P+Si) molar ratio were carried out on structural change of hydroxyapatite (HAp) and ${\beta}$-tricalcium phosphate ($\ss$-TCP). The in-vitro bioactivity of the Si-BCP powders was determined by immersing the powders in SBF solution, after that observing the chemical composition and morphology change by X-ray diffraction, scanning electron microscope and energy dispersive spectroscopy.

• Korean Journal of Materials Research
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• v.21 no.6
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• pp.347-351
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• 2011

Hydroxyapatite (HAp) powders with different crystallinities were synthesized at various calcination temperatures through the co-precipitation of $Ca(OH)_2$ and $H_3PO_4$. The degradation behavior of these HAp powders with different crystallinities was assessed in a simulated body fluid solution (SBF) for 8 weeks. Below $800^{\circ}C$, the powders were nonstochiometric HAp, and the single HAp phase was successfully synthesized at $800^{\circ}C$. The degree of crystallinity of the HAp powders increased with an increasing calcination temperature and varied in a range from 39.6% to 92.5%. In the low crystallinity HAp powders, the Ca and P ion concentrations of the SBF solution increased with an increasing soaking time, which indicated that the low crystallinity HAp degraded in the SBF solution. The mass of the HAp powders linearly decreased with respect to the soaking time, and the mass loss was higher at lower crystallinities. The mass loss ranged from 0.8% to 13.2% after 8 weeks. The crystallinity of the HAp powders increased with an increasing soaking time up to 4 weeks and then decreased because of HAp degradation. The pH of the SBF solution did not change much throughout the course of these experiments. These results suggested that the crystallinity of HAp can be used to control the degradation.

• Journal of the Korean Ceramic Society
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• v.40 no.9
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• pp.897-901
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• 2003

The sulfating reaction of coal fly ash with ammonium sulfate and the microwave extraction of aluminum ions from the resultant materials using sulfuric acid have been investigated. The (NH$_4$)$_3$Al(SO$_4$)$_3$ formed by the reaction of coal fly ash and ammonium sulfate decomposed to NH$_4$Al(SO$_4$)$_2$ at $\geq$ 350$^{\circ}C$. The maximum efficiency of aluminum ions extracted from the sulfating reaction product (400$^{\circ}C$, 120 min) by microwave heating (90$^{\circ}C$, 240 min) using 1 M H$_2$SO$_4$ was 84％ (based on Al content in coal fly ash) but 77％ by conventional heating at same condition.

• Journal of the Korean Ceramic Society
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• v.50 no.4
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• pp.263-268
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• 2013

Porous biphasic calcium phosphate scaffolds were fabricated by a freeze-gel casting technique using a tertiary-butyl alcohol (TBA)-based slurry. After sintering, unidirectional macropore channels of scaffolds aligned regularly along the TBA ice growth direction were tailored simultaneously with micropores formed in the outer wall of the pore channels. The crystallinity, micro structure, pore configuration, bulk density, and compressive strength for the scaffolds were investigated with X-ray diffractometery, scanning electron microscopy analysis, a water immersion method, and a universal test machine. The results revealed that the sintered porosity and pore size generally resulted in a high solid loading which resulted in low porosity and small pore size, which relatively increased the higher compressive strength. After being sintered at $1100-1300^{\circ}C$, the scaffolds showed an average porosity and compressive strength in the range 35.1-74.9% and 65.1-3.0 MPa, respectively, according to the processing conditions.

• Korean Journal of Materials Research
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• v.16 no.11
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• pp.676-680
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• 2006

The biodegradable $\beta$-tricalcium phosphate ($\beta$-TCP)/poly(lactide-co-glycolide) (PLGA) composites were synthesized by in situ polymerization with microwave energy. The degradation behavior of $\beta$-TCP/PLGA composite was investigated by soaking in simulated body fluid (SBF) for 4 weeks. The molecular weight of the $\beta$-TCP/PLGA composites decreased with soaking time until week 2, whereas the loss rate of molecular weight reduced after week 2. The incubation time was needed for the degradation of the $\beta$-TCP, indicating that the $\beta$-TCP should be detached from the PLGA matrix and then degraded into SBF solution. The studies of mass loss of the composites with the soaking time revealed that the degradation behavior of PLGA would be processed with the transformation from the polymer to the oligomer followed by the degradation. Morphological changes, whisker-like, due to transformation and degradation of polymer in the composites were observed after week 2. On the basis of the results, it found that the degradation behavior of $\beta$-TCP/PLGA composites was influenced by the $\beta$-TCP content in the composites and the degradation rate of the composites could be controlled by the initial molecular weight of PLGA in the composites.

• Korean Journal of Materials Research
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• v.10 no.10
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• pp.677-683
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• 2000

Three- and five-layer 3Y-YZP/12Ce- TZP composites prepared by a slip casting method have been char­acterized in terms of mechanical properties. The fracture strength of mutilayer c$\alpha$nposites determined in a diametral compression test was 327~534 MPa. Although the indentation strength of the materials was generally reduced with i increasing Vickers indentation load up to 300 N, the damage resistance of multilayer composites was superior com­pared to monolithic layer TZP material. The four-point bend strength of the layered material remained at the values of 620~674 MPa after indentation with a load of 49 N, while that of the monolithic TZP material was 129~339 MPa. The microindentation toughness of the multilayer material was $7.7~13.1\;MPa{\cdot}m^{1/2}$.

• Journal of Bio-Environment Control
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• v.14 no.4
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• pp.289-297
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• 2005

This study was conducted to develop the suitable nutrient solutions for variable Cruciferae leafy vegetables. l/2, 1 and 3/2 strength of nutrient solution recommended by National Horticultural Research Institute were supplied to plants in deep flow technique systems during 25 days. The growth of pak-choi and leaf mustard 'Asia curled' was highest in the 3/2 strength, and kaie 'TBC' in the 1 strength. Mean cation ratio of nutrient solution for pak-choi, leaf mustard and kale was K $49.5\%$, Ca $35.8\%$ and Mg $14.7\%$, which was obtained by calculating the uptake rates of water and nutrients. Suitable composition of the nutrient solution for Cruciferae leafy vegetables was N 14, P 3, K 6.8, Ca 4.8, $Mg 2m{\cdot}L^{-1}$. To examine the suitability of nutrient solution developed for Cruciferae vegetables (NSC), plants were grown 4 times from Sep. 2003 to Oct. 2004. When plants were grown in NSC, relative growth rate increased 1.1 to 2.5 times and vitamin C content 1.06 to 1.52 times. The proper plants to apply NSC for functional leaf vegetable production were leaf mustard 'Asia recurled', 'Redcurled' and 'Pamagreen', kale 'TBC', 'Portugal' and 'Hanchu collard', leaf broccoli 'New green', pak-choi, baby cabbage 'Red king' and 'Green king', flowering red chinese cabbage and Korean cabbage.

• Journal of The Korean Ophthalmological Society
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• v.59 no.11
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• pp.1049-1055
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• 2018

Purpose: To investigate the factors associated with glaucoma in patients with pseudoexfoliation syndrome by comparing features of the anterior segments and ocular biometry according to the presence or absence of open-angle glaucoma in pseudoexfoliation syndrome. Methods: We analyzed 96 patients (115 eyes) diagnosed as having pseudoexfoliation syndrome in this study. The patients were divided into two groups of simple pseudoexfoliation syndrome (64 patients, 76 eyes) and pseudoexfoliation glaucoma (32 patients, 39 eyes). We compared the age, sex, underlying disease, location of pseudoexfoliative material, iris change, degree of nuclear cataract, pupil dilatation, corneal endothelial cell counts, central corneal thickness, anterior chamber depth, axial length, corneal curvature, and intraocular pressure (IOP). Results: There were no significant differences between the two groups in terms of age (p = 0.694), sex (p = 0.161), diabetes (p = 0.440), hypertension (p = 0.238), pseudoexfoliative material observed in anterior capsule (p = 0.700), pupillary margin (p = 0.210), iris depigmentation (p = 0.526), pupillary ruff loss (p = 0.708), degree of nuclear cataract (p = 0.617), pupil dilatation (p = 0.526), central corneal thickness (p = 0.097), anterior chamber depth (p = 0.283), axial length (p = 0.095), or horizontal and vertical corneal curvature (p = 0.066 and 0.306, respectively). In pseudoexfoliation glaucoma, significantly higher IOP (p = 0.026), a high frequency of membrane formation (p = 0.047), and decreased corneal endothelial cell counts (p = 0.048) were observed. Conclusions: Pseudoexfoliation syndrome with open-angle glaucoma was shown to be associated with high IOP, decreased corneal endothelial cell counts, and a high frequency of membrane formation. Therefore, when such changes are observed in pseudoexfoliation syndrome patients, a higher risk of open-angle glaucoma should be recognized, and careful attentionis required accordingly.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.20 no.2
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• pp.93-100
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• 2010

The calcium to phosphate ratio (Ca/P) in biphasic calcium phosphates powders using X-ray diffraction analysis (XRD) was characterized. The BCP powders with various stoichiometric Ca/P molar ratio were synthesized with coprecipitation process and calcination. Compositions of the powders with Ca/P molar ratio between 1.5 and 1.67 were subjected to starting Ca/P molar ratio, pH = 10, and thermal treatment up to $900^{\circ}C$. The structural, morphological and chemical characterizations for BCP powders with stoichiometric Ca/P ratio were carried out with scanning electron microscope (SEM) and inductively coupled plasma atomic emission spectroscopy (ICP-AES) and a phase quantification was investigated by XRD. The solubility of HAp, $\beta$-TCP, and BCP powders was tested in the phosphate buffer solution (PBS) at $36.5^{\circ}C$ and pH = 7.4.