• 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.

• BMB Reports
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• v.43 no.11
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• pp.726-731
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• 2010

We report the tissue-specific distribution of chitinolytic activity in Korean ginseng root and characterize two 31-kDa chitinolytic enzymes. These two enzymes (SBF1 and SBF2) were purified 70- and 81-fold with yields of 0.75 and 1.25%, respectively, and exhibited optimal pH and temperature ranges of 5.0-5.5 and 40-$50^{\circ}C$. With [$^3H$]-chitin as a substrate, $K_m$ and $V_{max}$ values of SBF1 were 4.6 mM and 220 mmol/mg-protein/h, respectively, while those of SBF2 were 7.14 mM and 287 mmol/mg-protein/h. The purified enzymes showed markedly less activity with p-nitrophenyl-N-acetylglucosaminide and fluorescent 4-methylumbelliferyl glycosides of D-N-acetylglucosamine oligomers than with [$^3H$]-chitin. End-product inhibition of both enzymes demonstrated that both are endochitinases with different N-acetylglucosaminidase activity. Furthermore, the $NH_2$-terminal sequence of SBF1 showed a high degree of homology with other plant chitinases whereas the $NH_2$-terminal amino acid of SBF2 was blocked.

• Korean Journal of Dental Materials
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• v.44 no.3
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• pp.263-272
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• 2017

In this study, antibacterial chlorhexidine (CHX)-containing hydroxyapatite (HAp) was coated on titanium and investigated its characteristics. Ti-mSBF-CHX group was prepared by soaking titanium disks in the modified simulated body fluid (mSBF) mixed with CHX. Ti-mSBF group was coated using mSBF without CHX. Ti-mSBF-adCHX group was prepared by soaking Ti-mSBF specimen in CHX-containing solution. The crystallines clusters composed with nano-shaped crystallites were coated on the surface of the Ti-mSBF specimen. The ribbon-shaped crystallites were observed with the crystalline clusters on the Ti-mSBF-CHX specimen. The content of CHX chemical compositions was high in ribbon-shaped crystallites. HAp crystalline structure was dominant for all prepared specimens, and ${\beta}-TCP$ (tricalcium phosphate) and OCP (octacalcium phosphate) crystalline structures were observed in the Ti-mSBF-CHX specimen. FT-IR spectra showed the strong peaks of CHX in Ti-mSBF-adCHX and Ti-mSBF-CHX groups. However, after immersing in a phosphate buffered saline (PBS), CHX was rapidly released in Ti-mSBF-adCHX group, while it was slowly released in Ti-mSBF-CHX. We expect that the coating method of Ti-mSBF-CHX group could be used for protecting inflammation of titanium implant by incorporating antibacterial agent CHX into HAp layer.

• Korean Journal of Materials Research
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• v.15 no.10
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• pp.671-677
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• 2005

Ti and Ti alloys are known to have excellent corrosion properties, which is an important aspect for biocompability of these implants in human body. In our study, four types of samples (Cp-Ti, Ti-6Al-4V, $0.5wt.\%$ Fe-Ti and ECAP Ti) were tested for their apatite forming ability and corrosion properties. The micropolished samples were treated with 5M NaOH solution at $60^{\circ}C$ for 24 hours. Each samples was gently washed with distilled water and heat-treated at 600"C for 1 hour. The heat-treated samples were soaked in Simulated Body Fluid (SBF) solution at $36.5^{\circ}C$ in an incubator for different period of time. The test revealed that $0.5 wt.\%$ Fe-Ti showing faster apatite growth on the surface (7th day) compared to other samples. Polarization curve test (PCT) was also carried out to determine the corrosion resistance of each samples in SBF solution. ECAP-Ti showed highest corrosion resistance compared to any other samples. $0.5wt.\%Fe-Ti$ showed higher corrosion potential and corrosion current compared to other samples.

• Korean Journal of Materials Research
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• v.17 no.11
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• pp.622-627
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• 2007

Porous poly(e-caprolactone) (PCL) scaffolds were fabricated by salt leaching method. The PCL scaffolds were treated with aqueous NaOH for 0h, 2h, 4h, 8h, and 12h at $40^{\circ}C$. The NaOH-treated PCL scaffolds were dipped in $CaCl_2$ and $K_2HPO_4{\cdot}_3H_2O$ solution alternately three times to induce apatite nuclei onto the surface of the scaffolds. The NaOH-treated PCL scaffolds were immersed into SBF solution for 1day to grow the apatite. The apatite formation were investigated as a fuction of NaOH treatment time. The hydrophilicty and surface area of the PCL scaffolds were increased with NaOH-treatment time. The NaOH-treated PCL scaffolds were successfully formed a dense and uniform bone-like apatite layer after immersion for 1 day in SBF solution.

• Journal of the Korean institute of surface engineering
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• v.41 no.5
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• pp.226-231
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• 2008

Titanium and its alloy have been widely used in dental implant and orthopedic prostheses. Electrochemical characteristics of dental implant in the various simulated body fluids have been researched by using electrochemical methods. Ti-6Al-4V alloy implant was used for corrosion test in 0.9% NaCl, artificial saliva and simulated body fluids. The surface morphology was observed using scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDX). The electrochemical stability was investigated using potentiosat (EG&G Co, 263A). The corrosion surface was observed using scanning electron microscopy (SEM). From the results of potentiodynamic test in various solution, the current density of implant tested in SBF and AS solution was lower than that of implant tested in 0.9% NaCl solution. From the results of passive film stability test, the variation of current density at constant 250 mV showed the consistent with time in the case of implant tested in SBF and AS solution, whereas, the current density at constant 250mV in the case of implant tested in 0.9% NaCl solution showed higher compared to SBF and AS solution as time increased. From the results of cyclic potentiodynamic test, the pitting potential and |$E_{pit}\;-\;E_{corr}$| of implant tested in SBF and AS solution were higher than those of implant tested in 0.9% NaCl solution.

• Nuclear Engineering and Technology
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• v.51 no.2
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• pp.369-376
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• 2019

A complete solution for a soluble-boron-free (SBF) small modular reactor (SMR) is pursued with a new burnable absorber concept, namely centrally-shielded burnable absorber (CSBA). Neutronic flexibility of the CSBA design has been discussed with fuel assembly (FA) analyses. Major design parameters and goals of the SBF SMR are discussed in view of the reactor core design and three CSBA designs are introduced to achieve both a very low burnup reactivity swing (BRS) and minimal residual reactivity of the CSBA. It is demonstrated that the core achieves a long cycle length (~37 months) and high burnup (~30 GWd/tU), while the BRS is only about 1100 pcm and the radial power distribution is rather flat. This research also introduces a supplementary reactivity control mechanism using stainless steel as mechanical shim (MS) rod to obtain the criticality during normal operation. A further analysis is performed to investigate the local power peaking of the CSBA-loaded FA at MS-rodded condition. Moreover, a simple $B_4C$-based control rod arrangement is proposed to assure a sufficient shutdown margin even at the cold-zero-power condition. All calculations in this neutronic-thermal hydraulic coupled investigation of the 3D SBF SMR core are completed by a two-step Monte Carlo-diffusion hybrid methodology.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.31 no.5
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• pp.203-211
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• 2021

Octacalcium phosphate(OCP, Ca₈H₂(PO₄)₆·5H₂O) is one of biodegradable calcium phosphate materials with osteoconductivity and biocompatibility. It has the advantage of rapid bone formation and resorption due to the property of stimulating stromal cells to differentiate into osteoblasts. However, if OCP is inserted in body, it is immediately decomposed without maintaining of its shape as scaffolds due to their weak cohesive force between powder. On the other hand, hydroxyapatite (HA, Ca₁₀(PO₄)₆(OH)₂), which has a crystal structure similar to that of OCP, remains in the body without decomposition until the bone defect is restored. In this study, the degradation behavior of OCP/HA disc with different amount of HA in SBF (simulated body fluid) solution was characterized in terms of the weight loss, pH variation and microstructure change with immersion duration in SBF solution. As a result, the OCP/HA disc was not quickly decomposed and maintained its own shape for 2 weeks regardless of HA content. In particular, the surface of 40HA specimen was uniformly dissolved and then CDHA (calcium deficient hydroxyapatite) phase were formed onto the surface of disc after 7 days in SBF solution. It would be suggested that the 40HA specimen would be suitable candidate material as the scaffolds for the restoration of bone defect.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.32 no.5
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• pp.191-198
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• 2022

Zirconia and titanium alloys, which are mainly used for dental implant materials, have poor osseointegration and osteogenesis abilities due to their bioinertness with low bioactivity on surface. In order to improve their surface bioinertness, surface modification with a bioactive material is an easy and simple method. In this study, akermanite (Ca₂MgSi₂O₇), a silicate-based bioceramic material with excellent bone bonding ability, was synthesized by a solid-state reaction and investigated its bioactivity from the analysis of surface dissolution and precipitation of hydroxyapatite particles in SBF solution. Calcium carbonate (CaCO₃), magnesium carbonate (MgCO₃), and silicon dioxide (SiO₂) were used as starting materials. After homogeneous mixing of starting materials by ball milling and the drying of at oven, uniaxial pressing was performed to form a compacted disk, and then heat-treated at high temperature to induce the solid-state reaction to akermanite. Bioactivity of synthesized akermanite disk was evaluated with the reaction temperature from the immersion test in SBF solution. The higher the reaction temperature, the more pronounced the akermanite phase and the less the surface dissolution at particle surface. It resulted that synthesized akermanite particles had high bioactivity on particle surface, but it depended on reacted temperature and phase composition. Moderate dissolution occurred at particle surfaces and observed the new precipitated hydroxyapatite particles in synthetic akermanite with solid-state reaction at 1100℃.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.19 no.1
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• pp.19-24
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• 2009

The purpose of this study was to investigate the formation of apatite layer on two different titanium substrate treated with biomimetic method, Titanium plates were heat-treated at different temperatures of $400^{\circ}C$, $600^{\circ}C$, and $800^{\circ}C$ for 5 h in air atmosphere, And then, that plates were chemically treated with an alkali solution of 1 M sodium hydroxide (NaOH), The pre-treated titanium plates were soaked in the simulated body fluid (SBF) of Kokubo's recipe, After soaking for 7 days and 21 days in SBF, the coated layers formed on the titanium plates were characterized and compared with the morphology and chemical composition, The apatite formation was more activated on the titanium plates chemically treated with NaOH compared with the only heat-treated titanium plates.