Papers by Author: Sang Hoon Rhee

Abstract: The low crystalline hydroxyl carbonate apatite forming capacity of a poly (70lactic-co-30glycolic acid)/15CaO-85SiO₂ composite, which had a dual pore structure, was newly examined in simulated body fluid. The bioactive 15CaO-85SiO₂ particles were synthesized by a sol-gel method using tetraethyl orthosilicate (TEOS) and calcium nitrate tetrahydrate under acidic condition followed by the heat treatment at 600°C for 3h. The poly (70lactic-co-30glycolic acid)/15CaO-85SiO₂ composite was then prepared by a solvent casting using dimethylformide as a solvent. The composite was loaded into a high pressure chamber and then carbon dioxide gas was introduced achieving a final pressure of 20 MPa. After 3 days, carbon dioxide gas was released quickly and resultantly the dual pore structure was obtained. The samples were observed by FE-SEM and its bioactivity was tested in simulated body fluid.

Abstract: The size of hydroxyapatite particles during spray pyrolysis was successfully controlled by varying the concentrations of the starting calcium phosphate (CaP) solutions. Three different concentrations of CaP solutions were prepared by dissolving Ca (NO₃)_2·4H₂O and (NH₄)₂HPO₄ into deionized water and then they were sprayed at 900°C with the carrier gas flowing rate of 10 L/min. The size of the resultant hydroxyapatite particles decreased as lowering the concentration of the starting CaP solution. The smaller the particle size, the higher the relative density of the hydroxyapatite disks after sintering at 1100°C for 1 hour. The practical implication of the results is that highly sinterable hydroxyapatite particles can be synthesized during spray pyrolysis by controlling the starting concentration of CaP solution.

Abstract: Dense and submicron-sized hydroxyapatite powders were synthesized through spray pyrolysis of calcium phosphate solution with polyethylene glycol (PEG). Irregular shaped and fragile hydroxyapatite aggregates, and spherical and hollow hydroxyapatite particles were obtained after spray pyrolysis at 1100 °C when using calcium phosphate solution with and without PEG, respectively. After dewaxing at 650 °C for 3 hours, the hydroxyapatite aggregates were broken into submicron-sized particles whereas micron-sized spherical hollow particles were almost intact. The relative densities of hydroxyapatite disks made by submicron and micron sized hydroxyapatite particles were about 90% and 81%, respectively, after sintering at 1110 °C for 3 hours. The results were explained in terms of the disintegrating function of carbon which was previously formed among the hydroxyapatite aggregates by the decomposition of PEG during spray pyrolysis.

Abstract: Effect of oxide layer formed on commercially pure titanium by heat-treatment on adhesion of serum proteins and differentiation activity of osteoblasts. Commercially pure titanium disks were polished and then heat-treated at 700°C for 30 minutes. Titanium oxide layer (rutile phase) was observed to form on the titanium disk surface after heat-treatment. The contact angle of a water droplet on the heat-treated titanium disk was about 14^o while that of non-heat treated one was about 68^o. The amount of adsorbed total serum protein on heat-treated titanium disk was four times higher than that on non-heat treated one. ALP activity of primary cultured mouse calvarial osteoblasts on heat-treated titanium disk was also higher than that on non-heat treated one with statistical significance of p < 0.05. It implies that the serum proteins preferentially adsorbed on titanium oxide layer formed on commercially pure titanium and it is likely to enhance the differentiation activity of primary cultured mouse cultured osteoblasts.

Abstract: Poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. Poly(lactic-co-glycolic)acid solution was prepared by dissolving it in the hexafluoroisopropanol. Then, they were transferred to two separate syringes which were connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica gel containing calcium and poly(lactic-co-glycolic)acid solution were spun together under the electric field of 2 ㎸/㎝. The FE-SEM observations showed that the silica gel and poly(lactic-co-glycolic)acid fibers were mixed together completely and its handling property was much improved compared to that of the non-woven silica gel fabric. After soaking in the SBF for 1 week, low crystalline apatite crystals were also observed to occur on the silica fiber surfaces first and then they were also observed to occur on the poly(lactic-co-glycolic)acid fiber surfaces. From the results, it can be concluded that the poly(lactic-co-glycolic)acid and silica gel fibers mixed non-woven fabric made by electro-spinning method has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Abstract: The poly(methyl methacrylate)/silica nano-composite made from trimethoxysilyl functionalized poly(methyl methacrylate) and dimethyl diethoxysilane was newly prepared and its apatite-forming ability and mechanical properties were evaluated comparing to poly(methyl methacrylate)/silica nano-composite made from trimethoxysilyl functionalized poly(methyl methacrylate) and tetraethyl orthosilicate. Its apatite-forming ability was similar to that of poly(methyl methacrylate)/silica nano-composite using tetraethyl orthosilicate but its fracture toughness was much improved. Its high fracture toughness might come from the less quantity of siloxane linkages in its structure because dimethyl diethoxysilane had only two ethoxysilane groups while tetraethyl orthosilicate had four ethoxysilane groups. From the results, it can be concluded that it has a possibility to be used as bioactive bone cement.

Abstract: Non-woven silica fabric was made by electro-spinning method for the potential application as a bone grafting material. The silica gel, the source material for electro-spinning, was prepared by the hydrolysis of tetraethyl orthosilicate in the presence of calcium salt, water, hydrochloric acid and ethanol. It was transferred to a syringe, which was connected to the high voltage supply generating a high electric field between the spinneret and the ground collecting drum. The silica fibers containing calcium were spun under the electric field of 2 KV/cm. Their diameters were in the range from about 0.3 μm to 8 μm. It was heat-treated at 300 oC for 3 hours. After soaking in the SBF for 1 week, low crystalline apatite crystals were observed to occur on their surfaces. From the results, it can be concluded that the non-woven silica fabric containing calcium made by electro-spinning method and then heat-treated has a bioactivity. It means it has a potential to be used as a bone grafting material because of its apatite-forming ability, high surface area to volume ratio and high porosity.

Abstract: Novel poly(ε-caprolactone)-organosiloxane hybrid containing amine group was synthesized through sol-gel method. Triethoxysilane end-capped poly(ε-caprolactone) was prepared by reaction with α,ω-hydroxyl poly(ε-caprolactone) and 3-isocyanatopropyl triethoxysilane. It was then hydrolyzed and co-condensed with aminopropyl triethoxysilane through sol-gel method. The success of hybridization was evaluated by FT-IR by new formation of siloxane group. Osteoblast-like cell responses were assessed on this new hybrid material for the potential application as a bone tissue engineering scaffold. The cell responses were compatible with those on pure poly(ε-caprolactone) used as a control.

Abstract: The method which gives a low crystalline hydroxyl carbonated apatite forming ability to originally non-bioactive high crystalline hydroxyapatite surface was newly developed. The granules of trabecular bovine bone, which had a size range from 212 to 1000 μm, were defatted, deproteinized, and then heat-treated at 1000 oC for 3 hours to remove organics completely. They were treated with the mixed solution of calcium chloride and calcium hydroxide in Soxhlet’s apparatus at 100 oC for 3 days and then dried completely. Low crystalline hydroxyl carbonated apatite was observed to occur on the surface of high crystalline hydroxyapatite granules after soaking them into the simulated body fluid (SBF) for 1 week. This method is likely to have a potential to be used as a new process to give a bioactivity to originally non-bioactive materials.

Abstract: Previous study showed that the novel poly(ε-caprolactone)–organosiloxane nano-hybrid material (SiOPCL) had bioactivity, biodegradability, and mechanical properties comparable to those of human cancellous bone. In this study, hydroxyl carbonate apatite layer (HCA) was preformed on the surface of SiOPCL, which mimicked the events likely to occur in vivo, and cellular behaviors of human bone marrow stromal cells (hBMSCs) were investigated during the osteogenic differentiation on its surface (SiOPCL/HCA). Initial attachment, proliferation, and ALP activities of hBMSCs were comparable to those on tissue culture plates (TCPs), while the calcium content in the cell layer showed significantly higher value. It means that this novel bioactive nano-hybrid material is likely to be a promising candidate for bone grafting materials because of good hBMSCs responses as well as apatite forming ability in the simulated body fluid.