Sang-Hoon Rhee

Synthesis of hydroxyapatite via mechanochemical treatment.

Hydroxyapatite powder was synthesized with calcium pyrophosphate (Ca2P2O7) and calcium carbonate (CaCO3) through solid-state reaction. The two powders were mixed in acetone and water, respectively, and the single phase of hydroxyapatite was observed to occur only in the powder milled in water, without the additional supply of water vapor during heat-treatment at 1100 degrees C for 1 h. The results were explained in terms of the mechanochemical reaction that could supply enough amount of hydroxyl group to the starting powders to form a single phase of hydroxyapatite. Practical implication of the results is that the powder of high crystalline hydroxyapatite can be obtained by the simple milling in water and subsequent heat-treatment.

Effect of citric acid on the nucleation of hydroxyapatite in a simulated body fluid.

The role of citric acid in a simulated body fluid (SBF) was examined with the main focus on its induction ability of hydroxyapatite (HAp) nucleation on a bioinert collagen membrane. Collagen membranes were soaked in the SBF with citric acid concentrations in the range of 0-4 mM; then, carbonate-containing HAp crystals grew within a limited range, i.e., 0.3-2 mM. The results were explained in terms of chemical interaction among calcium ion, citric acid and collagen membrane, especially strong chelation ability of citric acid with the calcium ion.

Preparation of a bioactive and degradable poly(ε-caprolactone)/silica hybrid through a sol–gel method

A bioactive and degradable poly(epsilon -caprolactone)/silica hybrid was synthesized for the application as a bone substitute. Triethoxysilane end capped polyepsilon -caprolactone) was prepared by the reaction with alpha,omega-hydroxyl poly(epsilon -caprolactone) and 3-isocyanatopropyl triethoxysilane using 1,4-diazabicyclo[2,2,2,]octane as a catalyst. It was then co-condensed with tetraethyl orthosilicate and calcium nitrate tetrahydrate via a sol-gel method. The bioactivity of the poly(epsilon -caprolactone)/silica hybrid was assessed using simulated body fluid and low crystalline apatite was successfully formed on its surface after soaking for 1 week at 36.5 degrees C. Its biodegradability was evaluated in the phosphate buffered saline and the degradability was mostly come from the poly(epsilon -caprolactone) phase in the hybrid. It means that this hybrid is likely to be applicable to a bioactive and degradable bone substitute.

Biomimetic configurational arrays of hydroxyapatite nanocrystals on bio-organics

Biomimetic configurational arrays of hydroxyapatite (HAp) nanocrystals on several bio-organics, collagen (Col), chondroitin sulfate (ChS), and their mixture, were comparatively studied. The nanocomposites of HAp/Col, HAp/ChS, and HAp/Col/ChS were synthesized through a precipitation method with calcium hydroxide suspension and phosphoric acid solution containing Col, ChS, and their mixture, respectively. The (0 0 2) diffraction of the synthesized HAp crystals on a Col fiber showed an around 60 arching angle, while that on a ChS fiber showed just around 10 degrees. The same configurational arrays of HAp crystals could also be obtained on the mixture of Col and ChS fibers. The different electron diffraction patterns of the HAp crystals on the Col and ChS fibers were explained by the different macromolecular configurations of the Col and ChS fibrils which compose their fibers. The results may be applicable to develop a bone substitute which mimics the peculiar configurational arrays of HAp crystals found in bone and their detailed organic composition.

Hydroxyapatite formation on cellulose cloth induced by citric acid.

Hydroxyapatite (HAp) formation on cellulose cloth with the aid of citric acid was investigated. The cellulose cloths were soaked in simulated body fluid (SBF) solutions (1.5 SBF) with ion concentrations 1.5 times that of SBF (1.0 SBF) with and without citric acid and carbonate containing HAp crystals were found to form only in the 1.5 SBF solution that contained citric acid. The results were explained in terms of hydrogen bonding of citric acid to the cellulose cloth and its chelating ability of calcium ions. Practical application may involve the inclusion of citric acid in the 1.5 SBF solution to promote formation of HAp on previously bioinert cellulose cloth.

Effect of molecular weight of poly(ε-caprolactone) on interpenetrating network structure, apatite-forming ability, and degradability of poly(ε-caprolactone)/silica nano-hybrid materials

Abstract The effect of molecular weight of poly(e-caprolactone) (PCL) on the bioactivity of a PCL/silica nano-hybrid containing calcium salt was investigated. Two hybrids were prepared with low and high molecular weight PCLs, respectively, through a sol–gel method. Their bioactivities were evaluated using a simulated body fluid (SBF), which had almost the same ion concentrations with human blood plasma. Fast and uniform nucleation and growth of the apatite crystals were observed to occur all through the hybrid surface when low molecular weight PCL was used, while slow and random nucleation and growth of the apatite crystals were observed to occur when high molecular weight PCL was used, after soaking for 3 days in the SBF. This phenomenon was explained in terms of the distribution and dispersion of silica phase in the hybrid and the ionic activity product of the apatite in the SBF, which were dependent on the free volume and degradation rate of non-bioactive PCL phase, respectively.

Self-assembly phenomenon of hydroxyapatite nanocrystals on chondroitin sulfate.

Self-assembly phenomenon of hydroxyapatite (HAp) nanocrystals on chondroitin sulfate (ChS) templates was investigated. A HAp/ChS hybrid was synthesized through a precipitation method with a calcium hydroxide suspension and phosphoric acid solution containing the ChS. The preferential alignment of the crystallographic c-axis of the HAp crystals parallel to the long axis direction of the ChS templates was observed to occur with the chemical interactions between the HAp crystals and the functional groups of the ChS. This phenomenon was interpreted by the crystallochemical specific nucleation and growth of the HAp crystals regulated by the pre-organized functional groups of the ChS template. Practical implication may involve a biomimetic artificial bone or cartilage can be made through a precipitation method with suitable bio-organics.

Effect of initial particle size on microstructure of liquid-phase sintered α-silicon carbide

Abstract Three α-SiC powders of different particle sizes (∼0.42, ∼0.50 and ∼0.71 μm), containing 7.2 wt% Y 3 Al 5 O 12 (YAG) and 4.8 wt% SiO 2 as sintering aids, were hot-pressed at 1850°C and subsequently annealed at 1950°C to initiate grain growth. All the hot-pressed specimens consisted of equiaxed grains and showed unimodal grain size distribution. The smaller the starting powder the finer the microstructure was developed. After annealing, the fine (∼0.7 μm) and the medium (∼1.1 μm) grain-sized specimens showed self-reinforced microstructures whereas the large (∼1.5 μm) grain-sized specimen maintained an unimodal grain size distribution. These results suggest that the abnormal grain growth of α-SiC grains during annealing is critically dependent on the average grain size of sintered materials, which in turn depends on initial particle size. The fracture toughnesses (5.6 and 6.1 MPa m 1 2 ) of the annealed specimens with self-reinforced microstructures were higher than for the specimen with an unimodal grain size distribution (5.0 MPa m 1 2 ).

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO2-CaO nanocomposite

The mechanical properties and bioactivity of poly(methyl methacrylate)/SiO(2)-CaO nanocomposite were investigated using dimethyldiethoxysilane (DMDES) and tetraethoxysilane (TEOS), which could produce two and four siloxane linkages, respectively, after a sol-gel reaction. Methyl methacrylate was co-polymerized with 3-(trimethoxysilyl)propyl methacrylate and then co-condensed with DMDES (specimen D) and TEOS (specimen T), respectively, with calcium nitrate tetrahydrate under acidic conditions. The fracture toughness of specimen D was much improved compared to that of specimen T, whereas its fracture strength, hardness, and apatite-forming ability in simulated body fluid (SBF) were slightly decreased. The improved fracture toughness of specimen D without losing apatite-forming ability was explained by the decrease of siloxane linkage numbers and the introduction of alkyl groups in silica structure because covalently bonded siloxane linkages produce hard and brittle fracture behavior in the nanocomposite while the alkyl groups help to make the silica as linear chain structure. The practical implication of these results is that this new nanocomposite can be applied to the filler materials for bone cement and dental composite resin because of its good bioactivity and improved mechanical properties.

Evaluations of osteogenic and osteoconductive properties of a non-woven silica gel fabric made by the electrospinning method

Evaluations of the osteoblast-like cell responses and osteoconductivity of a non-woven silica gel fabric were carried out to determine its potential for application as a scaffold material for use in bone tissue engineering. The silica gel solution was prepared by condensation following hydrolysis of tetraethyl orthosilicate under acidic conditions. The solution was spun under a 2kVcm(-1) electric field. The diameters of the as-spun silica gel fibers were in the range of approximately 0.7-6microm. The fabric was then heat-treated at 300 degrees C for 3h. The proliferation of pre-osteoblastic MC3T3-E1 cells evaluated by the MTS assay was lower than on the tissue culture plate (TCP) as many cells leaked through the large voids formed by the randomly placed long, narrow silica gel fibers, which further retarded cell growth. However, the expressions of extracellular signal-regulated kinase and transcriptional factor from the cells were higher when cultured on the non-woven silica gel fabrics than on TCP. The alkaline phosphatase (ALP) activity and differentiation marker expressions assessed by amplication via the reverse transcription-polymerase chain reaction, such as type I collagen, ALP and osteocalcin, were higher for cells cultured on non-woven silica gel fabrics than on TCP. The non-woven silica gel fabric showed good osteoconductivity in the calvarial defect New Zealand white rabbit model. To this end, the non-woven silica gel fabric has good potential as a scaffold material for bone tissue engineering due to its good biological properties.