Kui Won Choi

Self-Assembled Nanoparticles of Bile Acid-Modified Glycol Chitosans and Their Applications for Cancer Therapy

This review explores recent works involving the use of the self-assembled nanoparticles of bile acid-modified glycol chitosans (BGCs) as a new drug carrier for cancer therapy. BGC nanoparticles were produced by chemically grafting different bile acids through the use of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide (EDC). The precise control of the size, structure, and hydrophobicity of the various BGC nanoparticles could be achieved by grafting different amounts of bile acids. The BGC nanoparticles so produced formed nanoparticles ranging in size from 210 to 850 nm in phosphate-buffered saline (PBS, pH=7.4), which exhibited substantially lower critical aggregation concentrations (0.038-0.260 mg/mL) than those of other low-molecular-weight surfactants, indicating that they possess high thermodynamic stability. The BGC nanoparticles could encapsulate small molecular peptides and hydrophobic anticancer drugs with a high loading efficiency and release them in a sustained manner. This review also highlights the biodistribution of the BGC nanoparticles, in order to demonstrate their accumulation in the tumor tissue, by utilizing the enhanced permeability and retention (EPR) effect. The different approaches used to optimize the delivery of drugs to treat cancer are also described in the last section.

Level walking and stair climbing gait in above-knee amputees.

To evaluate quantitatively the contribution of each muscle to amputee gait during level walking and stair climbing in transfemoral amputees and healthy individuals, gait analysis and electromyography with transfemoral amputees (n = 8) and healthy adults (n = 10) were performed to evaluate muscle balance during each ambulatory task. Time – distance and kinematic parameters by gait analysis were calculated, and the rms EMG of major muscles and hamstring and tibialis anterior coactivity were measured by electromyography. Most kinematic parameters showed no statistical difference between each task, excluding pelvic tilt, pelvic obliquity and hip abduction. Major muscle activities and coactivities of hamstring and tibialis anterior showed that the stair ascent task needed excessive muscle activity compared with the stair descent task and level walking, and that muscle activity and coactivity of amputees were greater than those of healthy individuals, excluding hamstring coactivity during stair ascent (p < 0.05).

Mechanical properties of ultra-high molecular weight polyethylene irradiated with gamma rays

With the goal of enhancing the creep resistance of ultra-high molecular weight polyethylene (UHMWPE), we performed gamma irradiation and post-irradiation annealing at a low temperature, and investigated the crystalline structures and mechanical properties of the samples. Electron spin resonance spectra reveal that most of the residual radicals are stabilized by annealing at 100 °C for 72 h under vacuum. Both the melting temperature and crystallinity increase after increasing the dose and by post-irradiation annealing. When irradiated with the same dose, the quenched sample having a higher amorphous fraction exhibits a lower swell ratio than does the slow-cooled sample. The measured tensile properties correlate well to the crystalline structure of the irradiated and annealed samples. For enhancing creep resistance, high crystallinity appears to be more critical than a high degree of crosslinking.

Dynamic mechanical behavior of ultra-high molecular weight polyethylene irradiated with gamma rays

We have investigated the dynamic mechanical behavior of ultra-high molecular weight polyethylene (UHMWPE) irradiated with varying doses of gamma rays. A relaxation peak in the loss factor curve, which has not been reported previously in the literature, is observed at a temperature above the crystal melting temperature. The peak is unique to UHMWPE and appears to be related to the high degree of entanglement. Because the temperature and intensity of the peak are reduced by irradiation-induced chain scission and crosslinking, respectively, we believe that the peak is associated with disentanglement relaxation. The behavior of the storage modulus in the melt state agrees with the classical theory of rubber elasticity.

Three-dimensional reconstruction of human femur using consecutive computer tomography images and simulated implantation system

This study is concerned with the construction of a simulated implantation system (SIS) for a human femur using various algorithms of image processing and computer graphics. The SIS is the software which performs 3D visualization as well as various numeric analyses between the patients femur and the artificial hip joint through certain stages of processing on consecutive CT images and projected images. We present the concrete methods that were to be implemented into the suggested prototype of SIS and the corresponding experimental results will also be shown.

Release Profile of a Model Protein Drug Depending on the Stability of Microspheres Based on Polyelectrolyte Complex

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.