Ji Yong Bae

Biomechanical analysis of the effects of medial meniscectomy on degenerative osteoarthritis

To investigate the effects of meniscectomy on degenerative osteoarthritis, a three-dimensional (3D) finite element (FE) model of the human lower limb is constructed from a combination of magnetic resonance (MR) images and computed tomographic (CT) images that can provide anatomically suitable boundary conditions for a knee joint. Four cases, i.e., the intact meniscus, and the partial, sub-total, and total meniscectomy of the medial meniscus are modeled and simulated. We consider that the cartilage-to-cartilage contact area and the peak contact pressure in the meniscus may be significant parameters in evaluating degenerative osteoarthritis. Partial meniscectomy can be regarded as a better treatment than sub-total/total meniscectomy, and a high possibility of degenerative osteoarthritis is anticipated after total meniscectomy. Moreover, medial meniscectomy has the potential to bring about degenerative osteoarthritis in both the medial compartment and the lateral compartment of a knee joint.

Finite element analysis of the multiple drilling technique for early osteonecrosis of the femoral head.

We used finite element (FE) method to investigate the effect of the drilling number and entry location of holes used in the multiple drilling technique on the stress and strain state in femur. Different three-dimensional FE models of a human hip joint with or without multiple drilling were fabricated using computed tomographic images obtained from the hip joint of a cadaver. The analysis technique was evaluated in a compression test using the cadaver specimen and FE analysis for the test using an FE model of the specimen. Von Mises stresses, principal stresses, and principal strains in the cancellous and cortical bone were calculated by using the different models, and changes in these values in relation to drilling number and entry hole locations were evaluated. Calculated peak values were much smaller than the yield strength, tensile strength, and yield strain of the cancellous and cortical bone for all cases of multiple drilling. Our results support that the multiple drilling technique for osteonecrosis of the femoral head is a stable operation technique.

Evaluation of pre-stresses in the menisci of human knee joint using microindentation.

To evaluate the pre-stress in the menisci of a human knee joint, the technique of microindentation was adopted. Five specimens each for lateral and medial menisci attached to the tibia were prepared from the knee joints of Korean cadavers to represent the pre-stress state of the meniscus. To create test specimens for the stress-free state of the meniscus, each meniscus was resected from the tibia and cut into three parts, which were subsequently attached to a metal plate. Indentations were carried out in each meniscus in both the pre-stress state and the stress-free state. The pre-stresses in the menisci were evaluated using the load-versus-depth curves. Compressive pre-stresses were found in the menisci. For each indentation region, the pre-stresses in the medial meniscus were higher than in the lateral meniscus. The highest pre-stress in both the lateral and medial meniscus was found in the posterior regions, while the anterior regions experienced the lowest pre-stress. The obtained pre-stresses can be used for the accurate numerical analysis, the fabrication of artificial menisci, and the diagnosis of meniscal disease progression for human knee joints.

High speed parallel spectral-domain OCT using spectrally encoded line-field illumination

We report parallel spectral-domain optical coherence tomography (OCT) at 500 000 A-scan/s. This is the highest-speed spectral-domain (SD) OCT system using a single line camera. Spectrally encoded line-field scanning is proposed to increase the imaging speed in SD-OCT effectively, and the tradeoff between speed, depth range, and sensitivity is demonstrated. We show that three imaging modes of 125k, 250k, and 500k A-scan/s can be simply switched according to the sample to be imaged considering the depth range and sensitivity. To demonstrate the biological imaging performance of the high-speed imaging modes of the spectrally encoded line-field OCT system, human skin and a whole leaf were imaged at the speed of 250k and 500k A-scan/s, respectively. In addition, there is no sensitivity dependence in the B-scan direction, which is implicit in line-field parallel OCT using line focusing of a Gaussian beam with a cylindrical lens.

Study on Nonlinear Heat Transfer Effect in the Lock-in Thermography for Defects Characterization on a Three-Dimensional Integrated Circuit

The use of the lock-in thermography (LIT) as a non-destructive evaluation technique is becoming increasingly attractive for detecting and characterizing the defects such as the shorts and resistive opens in a 3D package or stacked IC [1,2]. According to this trend, the study for improving the performance of the LIT system is required such as synchronous undersampling method [3]. One of the performance degradation factors of the LIT system is nonlinear distortion effects. Although the heat action is applied periodically, the resulting surface temperature is not synchronized with the periodic heating due to nonlinear heat transfer. A new approach to overcome unsynchronized result is proposed in one-dimensional systems [4]. In this study, we developed the 3D FE model of TSV structure with silicon chip integration and experimentally validated our FE model using measured current–voltage (I–V) and lock-in thermography (LIT) measurements in order to analysis nonlinear heat transfer. From the finite element analysis, the thermal distributions including nonlinear heat transfer in the TSV model and phase angle for the lock-in frequency are calculated and compared with experimental results of a TSV-based 3D IC sample.

Characterization of Heat Generation of Gold Nanorods Radiated by a NIR Laser for Clinical Cancer Therapy

Photothermal therapy provides a strong potential in treatment of tumors through the ability of gold nanoparticles to target destructive heat preferentially to tumor regions. And yet, Clinical application of the thermal therapies has not accomplished due to insufficient processes of the heating methods and temperature measuring techniques leading to low reproducibility of such treatment. In this study, we demonstrate various three-dimensional artificial tissue platforms to characterize the heating method and to control the generated heat in the tissue used for a superficial cancer model using gold nanorods (GNRs) and near-infrared (NIR, 808 nm) laser. GNRs have been shown to be the large absorption cross sections generating localized photothermal effects and hyperthermic effects on destructive consequences in the cell dynamics and survival rates. In particular, the GNRs were coated with polystyrenesulfonate (PSS, CTAB-free) to increase their stability and biocompatibility, and to enable the effectiveness for cancer therapy. The 3D tissue platforms had a 2 mm wide half dome considered as where cancers cells are thought to be, covered with 20 μm thick polymer film to confine the GNRs in the room. Various biomaterials were tested to mimic mechanical and optical properties of the soft tissue those found in vivo. To investigate the photothermal effect of GNRs in the tissue, three variables (the depth of the tissue, the amount of GNRs, and light density) were controlled to characterize the heat generation and distribution of GNRs created in the tissue.

Numerical analysis for characterization of the gold nanorod mediated-plasmonic heating with temporary NIR laser radiation for superficial breast cancer therapy

Over the last decade, plasmonic photothermal therapy (PPTT) has received significant attention as the new therapeutic strategy for the cancer therapy due to unique characteristics of the gold-nanoparticles. The characterization of the spatiotemporal heating potential for the gold nanorods (GNR) through mimicking PPTT process on the various conditions can help more quantitative approaches to treatment planning. The purpose of this study was to clearly understand the optical-thermal interactions between the laser, GNRs, and bio-tissues, and provide the information in clinical applications to implement the concept of heterogeneity, which can enable the optimization of treatment parameters for superficial breast cancer treatment.