Papers by Author: Kui Won Choi

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Authors: Moon Kyu Lee, Jae Bong Choi, Kui Won Choi, H.N. Lim
Abstract: In the area of biomaterials, the structures with negative Poisson’s ratio are able to be applied to the polymer component of prosthesis, artificial blood-vessel and catheter. To induce its characteristic, previous studies postulated many structural shapes such as non-convex shape with reentrant corners and re-entrant honeycomb. In this study, we proposed the rotational particle structures and investigated the Poisson’s ratio and the ratio (Ee/E) of the elastic modulus of these structures based on structural design variables using finite element method. The auto-meshing preprocessor was coded using MATLAB in order to construct numerical models as design variables and perform finite element analysis (FEA) effectively. Three selected design variables were the ratio of fibril’s length to particle’s diameter (0.2~2.0), the ratio of fibril’s length to its width (0.02~0.2) and the angle of fibril about horizontal axis (0 degree ~ tangential angle). Finite element model has 2D plain stress quadratic element and composed of 515 particles and 6-linked fibrils per each particle. For all of 213 cases, one side of each model is applied a tension, 0.1% strain and analyze Poisson’s ratio and the ratio (Ee/E) of the elastic modulus. As the ratio of fibril’s length to particle’s diameter increased and the ratio of fibril’s diameter to fibril’s length decreased fixing the fibril’s angle with 45 degree, the negative Poisson effect of rotational particle structures increased. The ratio of elastic modulus of these structures decreased with Poisson’s ratio. The results show the reasonable values as compared with the previous analytical results.
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Authors: Moon Kyu Lee, Kui Won Choi, Tae Soo Lee, H.N. Lim
Abstract: The indentation test has been in the spotlight due to easy and non-destructive testing characteristics. However, there are little studies for the indentation test of porous materials in the evaluation aspect of methodology. The goal of this study was to evaluate a spherical indentation test in the aspect of indenter-size and indentation depth by measuring elastic modulus of porous materials such as a cancellous bone using a FEM. We developed a microstructure-based FE model of cancellous bone with apparent density 0.2~0.8 g/cm3 in order to simulate uniaxial compression test and indentation test in the light of anatomical observation with a scanning electron microscope (SEM). We obtained a load-displacement curve through the indentation simulation and calculated the Young’s modulus of cancellous structure based on Pharr's hypothesis. The result indicated that indenter diameter has to be more than five times of pore size and indentation depth should be about 8% of indenter diameter at least to obtain the appropriate result of the indentation test. It is expected that this result may guide to the design and the simulation of indentation test for porous materials
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Authors: Tae Soo Bae, Tae Soo Lee, Kui Won Choi
Abstract: The elastic modulus and the apparent density of the trabecular bone were evaluated from spherical indentation tests and Computed Tomography and their relationship was quantified. After the femurs were prepared and embedded with respect to their anatomical orientation, the transverse planes of the trabecular bone specimens were scanned at 1mm intervals using a CT scanner. The metaphyseal regions were sectioned with a diamond-blade saw, producing 8mm cubes. Using a custom-made spherical indentation tester, the cubes were mechanically tested in the anteriorposterior (AP), medial-lateral (ML), and inferior-superior (IS) directions. After determination of modulus from the mechanical testing, the apparent densities of the specimens were measured. The results showed that the IS modulus was significantly greater than both the AP and ML moduli with the AP modulus greater than the ML modulus. This demonstrated that orthogonality was a structural characteristic of the trabecular bone. The power relationship between the modulus and the apparent density was also found to be statistically significant.
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Authors: Sung Won Kim, Yun Sik Nam, Yeon Jin Min, Jong Ho Kim, Kwang Meyong Kim, Kui Won Choi, In Sup Noh, Ik Chan Kwon
Abstract: Stability and disintegration of natural polyelectrolyte complex microspheres for protein drugs delivery have been extensively investigated because of their great influence on the drug release patterns. In this study, we tested stability of microspheres with alginate (Alg) core layered by either chitosan (Chi) or glycol chitosan (GChi) by examining release profiles of fluorophorelabeled bovine serum albumin (BSA) and lysozyme (Lys) from the microspheres. While GChi shell was disintegrated quickly, Chi-shell microspheres showed good stability in PBS. Disintegration of the coated layer induced the core material instable. The results indicated that while the charges of the shell material provided additional diffusion barrier against the protein release, the key factor to hold the proteins inside the microspheres was the integrity of the outer coating layer.
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Authors: Moon Kyu Lee, Chang Yang Lee, Dong Ryul Kim, Ik Chan Kwon, Kui Won Choi
Abstract: The purpose of the present study was to develop a polymer film loaded with drug to effectively prevent pin tract infection. It was found that the polymer, poly ethylene-co-vinyl acetate blended with tetrahydrofuran, showed better flexibility and deformability than the other polymers: poly caprolactone18 and poly caprolactone44. Polymer films, poly ethylene-co-vinyl acetate, were divided into five testing groups dependent on the loading concentration of rifampici (5, 10, 15, and 20 wt %). The surface morphology of polymer films was examined by a scanning electron microscopy. It was found that the concentration of drug was a main factor to determine the roughness of the film. Considering the roughness of polymer films, 5 wt % of rifampicin might be the maximum concentration for further applications. Hence, the antibiotic drug-loaded polymer films were manufactured by mixing poly(ethylene-co-vinylacetate) and tetrahydrofuran with rifampicin(antibiotic drug). The film cast was designed as a shape of disk (inner Ø5mm and outer Ø20mm) to be suitable for pins for external fixation in orhtopaedics. The drug-loaded polymer solvent, the amount of 0.6cc, was molded into the disk-shaped film and dried into a airtight box at 15°C for 24 hrs. The drug release characteristics(1, 2, 3, 4 and 5 wt%) were examined as a function of soaking time in phosphate buffered saline (PBS, 10 ml) using an enzyme-linked immunosorbent assay. Rifampicin was linearly released for first 100 hrs(~4 days) for all antibiotic drug-loaded polymer films. Afterward, the drug was released at a slower pace as a function of square root of time until 1000 hrs (~40 days). This slow drug release can be explained by their hydrophobic characteristics of poly ethylene-co-vinyl acetate and rifampicin. The antibiotic drug-loaded polymer film can be intrinsically able to prevent the bacteria adhesion by wrapping the pin track area, and perform active and effective infection-resistant by a sustained antibiotic-release.
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