Papers by Author: Hong Chae Park

Abstract: The sedimentation bulk density and rheology of tertiary-butyl alcohol (TBA)-based hydroxyapatite/calcium phosphate glass ceramic suspension system have been examined in terms of oxide solid loading (10, 15 vol.%), and types of additives (dispersant, dispersant/gelator, dispersant/gelator/surfactant), and calcium phosphate glass ceramic content. Sedimentation density of hydroxyapatite decreased by adding calcium phosphate glass ceramic mainly due to the coarse and hence low surface area of calcium phosphate glass ceramic powder; the decrease effect was nearly offset when the dispersant was added. The suspension viscosity generally behaved in an opposite manner to the sedimentation density. A shear thinning rheology was shown in applied shear rate, regardless of processing variables.

Abstract: Sedimentation bulk density and rheology of TBA-based hydroxyapatite suspensions have been investigated in terms of solid loading and types of additives (gelators, gelators/dispersant, gelators/dispersant/surfactant).

Abstract: For enhanced mechanical properties of ceramics for structural application, a great deal of attention has concentrated on preparation of layered composites. In this study, numerical simulation technique, which is applicable for the evaluation of mechanical performance for layered composite material, was developed. A generalized material constitutive equation coupled with material damage model based on the continuum damage mechanics approach was proposed and has been implemented to an in-house type finite element analysis code. The material behaviors for each component of layered composites can be simulated by the pre-defined material model on the simulation. A series of finite element analyses was carried out in order to elucidate the effect of fabrication related residual stress on the structural capacity of the layered composites.

Abstract: Particulate composites prepared by sintering compacts of Al2O3 and TZP powders, in air at 1500 and 1600 oC have been characterized in terms of microstructure and mechanical properties. The mechanical properties of the composites appear to be controlled by three main factors: the grain size of major phase, type of intergranular TZP, and presence of residual stress.

Abstract: Mullite whiskers have been manufactured by firing compacts of kaolin, Al2(SO4)3 and (NH4)2SO4 powders, with a small addition of Na2SO4, in air at 1400o C for 15 h. From the batch composition of Al2O3/SiO2 = 0.7, molar ratio, alumina-deficient (Al2O3/SiO2 = 1.02, molar ratio), orthorhombic mullite whiskers with an aspect ratio of >30 (0.2-0.4 μm in diameter) were obtained. With increasing Al2O3/SiO2 molar ratio, the size and aspect ratio of the mullite whiskers decreased.

Abstract: Porous HAp/chitosan-alginate composite scaffolds were successfully synthesized by insitu co-precipitation method. During the preparation of HAp/chitosan-alginate composite scaffolds, the interaction between chitosan-alginate molecules would be reduced with increasing HAp content, with the resulting that the chitosan-alginate molecules were homogeneously dispersed in the composite scaffolds. The chitosan-alginate content was found to be almost consistent as initially added during the preparation. These results imply that chitosan-alginate was almost perfectly incorporated into the composites. It was found that the pore structure of the composite scaffolds with low HAp content was similar to chitosan-alginate scaffolds, and the morphology of uniform microstructure was unaffected by the presence of HAp. However, the pore diameter decreased with increasing the HAp content up to HAp content of 30 wt%, eventually the pore structure was collapsed and the composites scaffolds appeared to be agglomerated at higher HAp content.

Abstract: The β-tricalcium phosphate (β-TCP)/ poly(lactide-co-glycolide) (PLGA) composites for biodegradable scaffolds in bone tissue engineering were synthesized by in situ polymerization with microwave energy. The degradation behavior of β-TCP/PLGA composite was investigated by soaking in simulated body fluid (SBF) for 4 weeks. The molecular weight of the β-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 β-TCP, indicating that the β-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 β-TCP/PLGA composites was influenced by the β-TCP content in the composite and the degradation rate of the composite could be controlled by the initial molecular weight of PLGA in the composite.

Abstract: The organic-inorganic hybrid nanocomposites were successfully obtained by the sol-gel process with tetraethylorthosilicate (TEOS) as an inorganic networking precursor and 2-hydroxyethylmethacrylate (HEMA) as the nonsurfactant template in the presence of benzil initiator. The characteristics of the obtained hybrid were examined by means of TGA, FTIR, SEM, and TEM. The synthesized HEMA/SiO2 hybrid was nearly transparent, monolithic, and monodispersed with the average size of 25 nm. It was found that the hybrid structure could be defined by intertwining organic and inorganic polymeric networks.

Abstract: Freeze casting is a useful forming technique to produce complex-shaped ceramic parts. In order to optimize freeze casting slurries, several processing additives are usually employed. Therefore, the relationships between additives and suspension characteristic should be understood. The effects of incorporating processing additives on dispersion and viscosity functions of aqueous alumina/zirconia and mullite/zirconia suspensions have been investigated.

Abstract: Various polymer-based scaffolds reinforced by the hydroxyapatite (HAp) for bone tissue engineering were successfully synthesized by in-situ co-precipitation method. The influence of HAp in composite scaffolds on the pore morphology, microstructure, and mechanical properties was investigated. The polymer-based scaffolds appeared to be macroporous and an interconnected open pore microstructure with pore size around 200 μm. The pore structure of the composite scaffolds was not much changed by the presence of HAp but the pore size of the composite scaffolds decreased with adding the HAp. The compressive modulus and yield strength of the polymer-based scaffolds improved by the presence of HAp.