Papers by Author: Han Sung Kim

Abstract: New medicines for treatment of osteoporotic bones have developed. In the previous studies, there were lots of pre-clinical experiments on animals to analyze the virtue of new medicine. However, the previous methods sacrificed a number of animals. They induced lots of expenses and ethical problems. In the present study, to investigate the effect of a medicine for osteoporosis by using in-vivo micro computed tomography (In-vivo Micro-CT, skyscan 1076, skyscan, Belgium) and micro finite element (*FE) analysis, morphological and mechanical characteristic changes of rat bone were detected and tracked. The 8 female Sprague-Dawley rats, used in the experiment, were randomized into 3 groups (Control, Sham and Risedronate group). The Risedronate (actonel, 0.58mg/Kg and 5days/week) for 8 weeks was administered in RIS group. The 4th lumbar vertebrae of rats were scanned by In-vivo Micro-CT with 35*m at week 0 (just before dose) and week 8 (after dose). Three-dimensional (3D) structural parameters were calculated. Simulated compression tests of 3D FE models were carried out to investigate the mechanical characteristics in the whole vertebral bone model of the 4th lumbar vertebra. The change rate of quantity and structure in Risedronate (RIS) group was smaller than that of control (CON) group. The change rate of structural modulus in RIS group was also smaller than that of CON group. This result shows the virtue of risedronate quantitatively as well as qualitatively. The study introduced the improved noninvasive biomechanical evaluation method, combined with In-vivo Micro-CT and *FE analysis, which was more effective and useful than the previous pre-clinical experiments.

Abstract: Several researchers investigated the mechanical characteristics of human trabecular bone using finite element analysis (FEA) based on micro computed tomography (μ-CT). There were few investigations on morphological and mechanical characteristics of vertebral trabecular bones. This study analyzed the relationship between morphological and mechanical characteristics in the regional vertebral trabecular bones using μ-CT and μ-FEA. Two specimens were obtained from the 12th thoracic vertebral bodies of cadavers (85 years female and 48 years male). In each vertebral body, fifteen regions were selected from two-dimensional (2D) images acquired from μ-CT. Voxelbased three-dimensional (3D) finite element models, with 4
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4 cubic block, were generated from each region for simulated compression test. The relationship between morphological characteristics, such as bone volume fraction, trabecular thickness, trabecular separation, trabecular number and structure model index, and mechanical characteristics, such as structural modulus (E†), was analyzed by bivariate correlation coefficient. As a result, the region of center column and inferior layer had the highest density. However, structural moduli in center column and middle layer were the biggest. The results indicated that there was a regional difference between morphological and mechanical characteristics of vertebral trabecular bone. In addition, for more exact evaluation of osteoporosis, it was recommended to analyze not only the mechanical characteristics but also the morphology characteristics.

Abstract: Considerable researchers analyzed the effects of hormone treatment on osteoporotic vertebral bones. Hormone treatment of age-related osteoporotic bone has a potential to decrease an incidence of osteoporosis. In the present paper, experimental and simulated tests for the mechanical characteristics of osteoporotic models and their hormone-treated models were investigated. Three dimensional (3D) geometries of the models (rapid prototyped and finite element models) were generated from high resolution micro-computed tomography ($-CT, Skyscan 1076, Skyscan, Belgium) scan data for the central parts of the second lumbar vertebrae. From these 3D geometries, cubic specimens with side length 6.5mm were formed and analyzed. Rapid prototyped (RP) models, instead of the real bone specimen, of vertebral trabecular bones were created in the fused deposition modeling (FDM) machine. In the present study, experimental compressions test for RP models were carried out by the INSTRON testing machine (8874 series, Instron, UK). The mechanical characteristics of finite element (FE) models for simulated compression tests were compared with physical predictions from RP models for experimental compression test. As a result, it is found that the hormone therapy is likely to be less effective than reported by previous researchers. A remarkable agreement was achieved between the results obtained from the experimental tests for RP models and simulated tests for FE models.

Abstract: In the present study, changes of morphologies and mechanical characteristics in the lumbar vertebrae of the ovariectomised (OVX) rats were investigated and analyzed by Finite Element (FE) and Rapid-Prototyped (RP) models based on micro-computed tomography (micro-CT). In previous researches, there were many studies about morphology such as bone mineral density and trabecular microstructure. However, detecting and tracking local changes were few in the trabecular and cortical bone of the lumbar vertebrae for the OVX rats. Experimental and simulated studies were used to investigate mechanical characteristics of the lumbar vertebral bones for the OVX rats. Three dimensional (3D) geometries of the models (RP and FE models), generated from in-vivo micro-CT scan data, were obtained from the 4th lumbar of the OVX rats. Three specimens (whole vertebral, trabecular and cortical bone models) were generated and analyzed in the simulated compression tests. For further verification, the experimental compression test for RP models ‘instead of real bone specimens’ was performed to indirectly validate the results of the simulated compression test for the FE models. The results were similar to those of the compression test simulated by micro-FE analysis. The present study showed the efficiency of the combined method (FE and RP techniques based on in-vivo micro-CT) as a nondestructive evaluation.

Abstract: This study investigated effects on foot/ankle roll-over characteristics according to heel heights during walking. Fifteen female volunteers who have neither musculoskeletal nor foot problems participated in gait analyses, wearing totally four pairs of shoes with different heel heights. To obtain roll-over shape of foot/ankle complex, we used trajectories of ankle, knee and the center of pressure (COP) between initial contact(IC) and opposite initial contact(OIC) to represent as circular arc using the least-square method. We found that the entire roll-over shape moved distally as the heel height increased but roll-over characteristics did not change significantly with different heel heights. In addition, we found that nondisabled persons automatically adapt their foot/ankle complex to changes in heel height shoes up to 6cm, by moving the origin of roll-over shape distally to keep the roll-over characteristics uniform. Roll-over characteristics in human walking would provide a new understanding of human walking, and furthermore can be applied to the design of prosthetics and orthotics of the lower extremity.

Abstract: Pressure distributions on the buttocks and thighs by the functional electrical stimulation on the gluteus maximus, sartorius and hamstring in the seating posture were analyzed for ten healthy young volunteers in order to determine which muscle can be stimulated for pressure ulcer prevention. Muscles were stimulated every 5 seconds over 30 seconds by the MP150 stimulator. Pressure distribution and ground reaction forces on the stimulated buttocks and thighs increased when the gluteus maximus was stimulated. Pressure on the stimulated thigh slightly decreased when stimulating sartorius and hamstring individually. With a simultaneous stimulation of the gluteus maximus and sartorius, pressures on the stimulated buttocks and thighs increased significantly, but pressure on the opposite buttock decreased significantly. With a simultaneous stimulation of the sartorius and hamstring, both pressure on the stimulated thigh and the ground reaction force significantly decreased.