Moon Kyu Lee

Rigid stepped plate for internal fixation for high tibial osteotomy.

High tibial osteotomy is regarded as an effective treatment for unicompartmental arthrosis of the knee, but the optimal fixation method has not yet been devised. The purpose of this study was to confirm the superior strength of a rigid stepped plate as compared to a 4-hole L-plate device. Lateral closing-wedge high tibial osteotomy was performed on 30 ten-month-old porcine tibiae. Fifteen tibiae were fixed using a rigid stepped plate and 15 were fixed with a 4-hole L-plate. Three types of deforming force-compression, valgus bending, and varus bending-were each applied to 5 pair of tibiae fitted with either the rigid stepped plate or the L-plate using a mechanical testing apparatus. Values of load, displacement, and stiffness were analyzed to compare the fixation powers. Mean stiffness in the rigid stepped plate and L-plate groups were 977.8 (SD 230.3) and 836.2 (SD 248.4) N/mm for compression testing (P=.465), 38.7 (SD 12.9) and 21.6 (SD 9.6) N/mm for valgus bending (P=.047), and 62.3 (SD 18.1) and 29.8 (SD 9.7) N/mm for varus bending (P=.009), respectively. The rigid stepped plate has greater fixation strength than the conventional 4-hole L-plate. Given this improved level of fixation with the rigid stepped plate, immobilization duration after high tibial osteotomy could be shortened and complications reduced.

Real-time bladder volume monitoring by the application of a new implantable bladder volume sensor for a small animal model

Although real‐time monitoring of bladder volume together with intravesical pressure can provide more information for understanding the functional changes of the urinary bladder, it still entails difficulties in the accurate prediction of real‐time bladder volume in urodynamic studies with small animal models. We studied a new implantable bladder volume monitoring device with eight rats. During cystometry, microelectrodes prepared by the microelectromechanical systems process were placed symmetrically on both lateral walls of the bladder, and the expanded bladder volume was calculated. Immunohistological study was done after 1 week and after 4 weeks to evaluate the biocompatibility of the microelectrode. From the point that infused saline volume into the bladder was higher than 0.6 mL, estimated bladder volume was statistically correlated with the volume of saline injected (p < 0.01). Additionally, the microelectromechanical system microelectrodes used in this study showed reliable biocompatibility. Therefore, the device can be used to evaluate changes in bladder volume in studies with small animals, and it may help to provide more information about functional changes in the bladder in laboratory studies. Furthermore, owing to its biocompatibility, the device could be chronically implanted in conscious ambulating animals, thus allowing a novel longitudinal study to be performed for a specific purpose.

The effect of vertebral material description during vertebroplasty

Abstract Vertebroplasty has attracted much attention as a medical treatment for the collapse of the spine by strengthening the vertebral body, correcting deformities, and relieving pain in patients through the injection of bone cement. The finite element method has become popular for analysing vertebroplasty. The numerical modelling of vertebrae under loading, as in many other cases of representing a composite bone with anatomically scattered properties through a simplified material model, entails difficulties in material assignment for analysis. The aim of this study is to compare and contrast material-assignment methods in the course of modelling through a tetrahedral meshing algorithm. In particular, the study seeks to contrast the element-wise material model with a uniform material assignment for trabecular bone and the bone—poly(methyl methacrylate) (PMMA) composite. The geometries of the vertebral body are constructed from computed tomography image data, which are obtained through scanning at intervals of 1 mm. The finite element models are constructed through a tetrahedral meshing algorithm. Various types of material assignment, which encompass the case of normal persons as well as the case of patients following vertebroplastic surgery, are analysed. The results clearly show that the oversimplification of the trabecular bone and the bone—PMMA composite body may lead to significant deviations in the assessment of the effectiveness of vertebroplastic surgery.

Simulation of Ceramic Powder Injection Moulding Based on the Behavior of Flow Stress Depended on the Thermal Viscosity Flowage Property and the Volume Fraction

The prediction of flow pattern and volume fraction distribution in ceramic powder injection moulding (CIM) is very important because their characteristics affect the mechanical stiffness and the sintering shrinkage. The definition of feedstock behavior in the simulation of CIM depends on the various parameters such as temperature, strain rate and volume fraction. The aim of this study is to generate the governing equation based on non-newtonian flow model and predict the distribution of volume fraction from the result of CIM simulation using the subroutine of finite element package. Material parameters of governing equation are obtained from the compressive test of feedstock. Initial volume fraction is defined as the value of 0.5 referred to experimental data. In the boundary condition, the velocity of injection is 3 mm/s and the frictional coefficient between the feedstock material and the die is assumed as the value of 0.7 which means the value in the condition of cold moulding. The flow pattern of feedstock is very consistent with the experimental result. The result indicates that the range of volume fraction is from 0.42 to 0.58 depended on the pressure distribution. This result aids to predict the material stiffness according to the location of product from the relationship of the volume fraction and stiffness via Micro-hardness test.

Numerical Analysis of Touch Mode Capacitive Pressure Sensor Using Graphical User Interface

Design through numerical methods requires experimental verification of micro electrical mechanical system (MEMS) processes and numerous parametric analyses. In particular, to evaluate the performance of capacitive pressure sensor, electrical calculations are necessary along with structured numerical analysis. For this reason, pre- and post- processors are necessary that would create models and manage results through a dedicated graphic user interface for sensor analysis. Therefore, this study is designed to make efficient and convenient numerical methodology of touch mode capacitive pressure sensor (TMCPS) using graphical user interface (GUI), appropriate for measuring tire pressure, and analyze its capability and linearity responding to geometric design parameters. Design parameters are size of diaphragm, thickness of diaphragm and gap distance between diaphragm and insulator. All of the analysis process is controlled by GUI program. Analysis results show capacitive-pressure graph, regression curve and pressurecontact area graph using calculation and finite element analysis. This research shows negative association between the thickness and the gap for optimum diaphragm. Optimum diaphragm is 2.5mm by 2.5mm size, 25μm thickness, 4.5 μm gap within 20~40psi which means the range of tire pressure.

A study on the mechanical properties and deformation behavior of injection molded PMMA-TSP laminated composite

To evaluate the deformed features of a polymer and touch screen panel laminated material and to secure a reliability of the design method, it is crucial to predict a thermo-mechanical behavior of the polymers. The reliability problems of polymer-TSP laminated module subjected to temperature and humidity changes mainly occur due to features with time-dependent material properties as well as differences in the coefficients of thermal expansion between the polymer and TSP. Therefore, it is necessary to consider the viscous behavior which causes changes in material properties which include temperature-dependent properties along with the time-dependent properties. In this study, a tensile test is conducted to obtain fundamental material properties and a creep test is used to characterize viscous properties of the polymer. Material properties from the tensile and the creep test are verified by the tensile and creep simulations. Also, the finite element analysis is used to simulate the time-dependent behaviors during a high temperature conditions while predicting thermal deformations. Numerical results are compared with experimental results. The result shows that the shape deformations of the polymer-TSP laminated module calculated by the finite element analysis with visco-elastic-plastic material model are in a good agreement with the experiment. Based on analytical results, we predict the thermal deformation of the PMMA-TSP composite plate in consideration of the effect of viscous features and set up the organized numerical analysis procedure using FE analysis.

A Numerical Study on Dynamic Characteristics of Counter-Rotating Rigid/Deformable Rolls in Press Contact

It is important to analyze the dynamic behavior of counter-rotating rigid/deformable rolls in the roll-coating process, because the stability of the process is affected by the dynamic characteristics. In the present study, the effects of material property, angular velocity, and gap size on the contact pressure and contact shape of the deformable roll are numerically investigated. The behavior of two rolls with a negative gap was analyzed using the finite element method, and the material property of the deformable roll was applied with the Mooney-Rivlin coefficients of the hyper-elastic model. The contact shape is affected by the gap size, and the contact pressure mainly depends on the stiffness of the deformable roll and the gap size. To maintain a negative gap between two rolls, controls such as load and displacement controls must be used. The results indicate that displacement control can reduce the instability.

Effect of Bladder Wall Thickness Through Change of Bladder Volume and Material Properties on Detrusor activity Study

The structural and functional disorder of a detrusor induces a bladder hypertrophy and degenerates a bladder muscle gradually by preventing normal urination. Thus, the thickness of the bladder wall has been increased in proportion to the degree of bladder outlet obstruction. In this study, the mechanical characteristics of the detrusor is analyzed for the physical properties and the thickness changes of the bladder muscle using a mathematically analytic method. In order to obtain the mechanical property of the bladder muscle, the tensile test of porcine bladder tissue is performed because its property is similar to that of human. The result of tensile test is applied to the mathematically model as Mooney Rivlin coefficients which represent the hyperelastic material. The model of the bladder is defined as the spherical shape with the initial volume of 50ml. The principal stress and strain according to the thickness are analyzed. Also, computer simulations for three types of the material property for the model of the bladder are performed based on the fact that the stiffness of the bladder is weakened as the progress of the benign prostatic hyperplasia. As a result, the principal stress is 341kPa at the initial thickness of 2.2mm, and is 249kPa at 6.5mm. As the bladder wall thickness increases, the principal stress decreases. The principal stress and strain decrease as the stiffness of the bladder decreases under the same thinkness.