Suk Young Kim

Cytotoxicity and Antimicrobial Effect of Ag Doped Hydroxyapatite

In the synthesis of antimicrobial hydroxyapatite doped with silver, the amount of silver is the critical element affecting its properties. And also depending on the synthesis route, not only the amount of silver but also the release behavior was found to be altered. The cytotoxicity, antimicrobial effects and stability of effects were observed with Ag doped hydroxyapatite fabricated through various routes. The results suggested that the optimal antimicrobial property with none or mild cytotoxicity may be produced by modulating not only the doped silver amount but also their shape and synthesis route.

Hydroxyapatite Coated Porous Alumina as a New Orbital Implant

Abstract. A synthetic hydroxyapatite coated porous alumina ocular orbital impla nt w s developed by polymeric sponge method in order to overcome shortcoming of current corall ine HA implant and to obtain secure attachment of extraocular muscles and fibrovascular i n-growth. It allows porous alumina skeletal to be a load bearing member and synthetic HA coat ing l yer to provide biocompatibility and long-term stability in an eye. It was found that slower heating rate of < 1°C/min at 280°C400°Cwas effective to achieve a dense porous alumina skeletal, and defects on as-sintered alumina skeletal was considerably decreased by the second coating of alumina slurry and sintering. The thickness of coated HA layer was about 20 μm with relatively good bonding to alumina skeletal. From in-vivo study, fibrovascularization was noted at periphery of the implant 2 we eks after implantation in all of the three groups, and to the center of the impla nt 4 and 12 weeks after implantation. This fibrovascularization was most predominant in 500 μm por e-sized group compared to the rest two groups. It is believed that HA coated porous alumina w ill be a good candidate for an artificial orbital implant with improved biocompatibility and long-term stabil ity.

Mechano-Chemical Synthesis of Biphasic Calcium Phosphates with the Various Ratio of HA and β-TCP

Biphasic calcium phosphate powders (BCP) of hydroxyapatite (HA) and tricalcium phosphate (β-TCP) with the various ratio of HA to β-TCP were prepared by utilizing mechanochemical synthesis. Calcium hydrogen-phosphate dihydrate (brushite, CaHPO4⋅2H2O) and calcium carbonate (calcite, CaCO3) powders have been chosen as the starting materials. The original Ca/P ratio of CaHPO4⋅2H2O - CaCO3 batch was set to be 1.67. A mixture of starting materials was milled using a planetary mill (ZrO2 jar and balls) with water for 3, 4, 5, 6 and 7 hrs. The XRD study of calcined powders was conducted for phase identification and for HA/β-TCP ratio as well. The phases of the calcined powders were HA and β-TCP, and the HA/β-TCP ratio varied with the milling time. The mass fraction of HA and β-TCP phases was calculated from the XRD intensities of HA and β-TCP. The ratio of the mixture milled for 4 hrs and calcined at 900°C was 85(HA):15(β-TCP) (BCP 85/15) and the content of β-TCP increased with the milling time. It is believed defective HA powder formed at relatively short period of milling time (less than 3 hrs The research revealed that nanocrystalline BCP powders could be synthesized by an employment of a medium-high energy mechanical activation at room temperatures (~25°C) without any preliminary chemical processing.

Comparative Study of the Degradation Behavior of Mechanically Mixed and Chemically Precipitated Biphasic Calcium Phosphates

Surface morphology and degradation behavior of mechanically mixed and chemically precipitated biphasic calcium phosphate (M-BCP and P-BCP) were compared. For the M-BCP powder, commercial HA and TCP powders were used. In order to prepare P-BCP powder, precipitation method was used. The particle size of P-BCP was smaller than that of M-BCP. The disk-type specimens of each powder were prepared for the morphology comparison and degradation test. The surface morphology of sintered samples was porous in M-BCP and dense in P-BCP. The degradation test was conducted in the revised simulated body fluid (R-SBF) for 1, 7, and 21 days. Surface morphology and degradation rate of two samples were different. The weight gain in both samples increased linearly with immersion period due to apatite-like layer formation. However, the weight gain in M-BCP was much higher than that in P-BCP. The weight gain was related to the surface morphology and degradation with immersion period.

Tissue engineered bone formation with polymer/ ceramic composites by press-and-baking method

A novel process was developed to fabricate polymer/ceramic composites for bone tissue engineering. The mixture of polylactic acid (PLA), calcium metaphosphate (CMP), and NaCl were compressed and subsequently heated. After dissolving the NaCl salts, porous biodegradable polymer/ceramic composite scaffolds were formed. The characteristics of the scaffolds were compared to those of scaffolds fabricated using a conventional solvent casting method, in terms of pore structure, pore size distribution, and mechanical properties. The scaffolds were seeded by osteoblasts and cultured in vitro or implanted into nude mice subcutaneously for up to 5 weeks. Cells were better grown to form tissue-like structures on CMP/PLA composites fabricated by the Press-and-Baking method. In addition, the alkaline phosphatase activity of and calcium deposition in the scaffolds explanted from mice were enhanced significantly for the scaffolds by Press-and-Baking compared to them by solvent casting. Taken together, these results suggest that CMP promote cell differentiation and proliferation via direct interaction with cells in the CMP/PLA composites. This novel PLA/CMP composite will be applicable for bone tissue engineering to support and cell differentiation and growth.

Highly Porous Silica Nanoaerogels for Ultrafast Nonlinear Optical Applications

Highly porous silica nanoaerogels with low apparent density of ~0.1 g/cm3 and ~0.07 g/cm3 were synthesized through two-step sol-gel processing and low temperature supercritical fluid drying. The nonlinear refraction (γ) of silica nanoaerogels was estimated to be ~ -3.4 x 10-16 m2/W for ~0.1 g/cm3 and ~0.07 g/cm3 apparent densities with a signal-beam femtosecond z-scan spectroscopy. The third-order nonlinear refraction coefficient of nanostructure silica nanoaerogels was almost four orders larger than that of bulk silica materials. The large nonlinearrefraction with high nonlinear figure of merit (γ/βλ, β~2×10-10 m/W for 0.07 g/cm3 apparent density, β~6×10-10 m/W for 0.1 g/cm3 apparent density, λ~0.775 µm) is an ideal optical property for nonlinear applications of homeland security, battlefield enhancement, and industrial uses.

Tissue Response of Calcium Polyphosphate in Beagle Dog Part II: 12 Month Result

CPP is chemically similar to natural bone and has higher stiffness. As one of our previ ous studies has shown, CPP had osteoconductivity and biocompatibility. The pur pose of this study was to compare the new bone formation in CPP granules between 3 and 12 mo nths and to evaluate CPP as bone substituting materials.

Evaluation of 5% Na2O-Incorporated Calcium Metaphosphate as a Scaffold for Tissue-Engineered Bone Regeneration

As a part of the effort to develop a suitable scaffold for tissue-engineered bone regeneration, we modified calcium metaphosphate (CMP) ceramic with Na20 and evaluated its efficiency as a scaffold. We incorporate 5% Na20 into pure CMP and prepare for an average pore size of 250 or 450 µm average pore sizes. The incorporation of 5% Na2O caused reduced compressive strength and there was no change in biodegradability. The in vitro cellular attachment and proliferation rate, however, were slightly improved. The 5% Na2O-incorporated macroporous CMP ceramic-cell constructs treated with Emdogain induced ectopic bone formation more effectively than those without Emdogain treatment. These results suggest that the incorporation of 5% Na2O into pure CMP is not effective for improving the physical characteristics of pure CMP but it is positive for improving the cellular reaction and osteogenic effect with the addition of Emdogain.

Development of Hydroxyapatite Thin Film on Titanium Substrate by Electrophoretic Deposition

Electrophoretic deposition was used for HA coating on dental implants with different coating thickness. The HA coating thickness was examined in terms of applied voltage and time, and powder concentration in suspension. Nano-size HA and SiO2-CaO-P2O5-B2O3 bioglass powders were synthesized by sol-gel method. Polyvinyl alcohol (3 wt%) as a binder was resolved in ethyl alcohol, then, nano HA powder was dispersed ultrasonically in the mixture for 15 min and pH was adjusted with HNO3 for positive charging on particle. Titanium substrate was held on cathode and counter electrode was platinum. HA with 0.5 % and 0.03 % of powder concentration was deposited electrophoretically at 10~20 V for 1~20 minutes. The thickness of as-deposited HA layer decreased from nearly 80 µm (0.5 %, 20 V, 10 min) to 4~5 µm (0.03%, 10V, 1 min) as powder concentration, applied voltage and time decreased, respectively. The surface of HA coating layer deposited in lower powder concentration showed much more homogeneous and relatively dense morphology, in contrast, the surface in thick suspension became rough or porous and was easily spalled. In a co-deposition of HA and bioglass, co-deposited glass played an important role in increasing bonding strength between coating layer and substrate. It is believed that electrophoretic deposition method can be one of alternatives for relatively thin and easy HA coating.

Effectiveness of biphasic calcium phosphate block bone substitutes processed using a modified extrusion method in rabbit calvarial defects

Purpose This study evaluated the mechanical and structural properties of biphasic calcium phosphate (BCP) blocks processed using a modified extrusion method, and assessed their in vivo effectiveness using a rabbit calvarial defect model. Methods BCP blocks with three distinct ratios of hydroxyapatite (HA):tricalcium phosphate (TCP) were produced using a modified extrusion method:HA8 (8%:92%), HA48 (48%:52%), and HA80 (80%:20%). The blocks were examined using scanning electron microscopy, X-ray diffractometry, and a universal test machine. Four circular defects 8 mm in diameter were made in 12 rabbits. One defect in each animal served as a control, and the other three defects received the BCP blocks. The rabbits were sacrificed at either two weeks (n=6) or eight weeks (n=6) postoperatively. Results The pore size, porosity, and compressive strength of the three types of bone block were 140-170 µm, >70%, and 4-9 MPa, respectively. Histologic and histomorphometric observations revealed that the augmented space was well maintained, but limited bone formation was observed around the defect base and defect margins. No significant differences were found in the amount of new bone formation, graft material resorption, or bone infiltration among the three types of BCP block at either of the postoperative healing points. Conclusions Block bone substitutes with three distinct compositions (i.e., HA:TCP ratios) processed by a modified extrusion method exhibited limited osteoconductive potency, but excellent space-maintaining capability. Further investigations are required to improve the processing method. Graphical Abstract