• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2015년도 춘계학술대회 논문집
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• pp.24-24
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• 2015

최근 생체재료의 개발이 눈부시게 발전되고 생체적합성이 우수한 표면을 요구함에 따라 생체재료의 표면처리에 대한 연구가 활발히 진행되고 있다. Laser Deposition법은 항공기 부품제조 분야에 주로 사용되고 있으며 최근에 오하이오 주립대 타이타늄합금연구센터를 중심으로 표면처리에 관한 연구가 주로 이루어졌다. 특히 이를 이용하여 치과재료의 표면처리에 응용을 시도하였다. 치과에서 응용될 수 있는 경우는 주로 임플란트는 부분 또는 완전 무치악 환자의 보철수복에 사용되는 보철물의 제작등에 사용될 수 있으며 이중에서도 특히 생체용 임플란트의 표면처리응용으로 임플란트와 조직간의 접합성을 개선하는 표면처리법으로 연구되었다. 임플란트의 성공과 실패는 물성적인 측면에서 임플란트의 형태, 표면거칠기 및 표면처리방법, 초기하중 등에 의하여 좌우되며 임플란트 재료에 작용하는 응력차폐는 생체적합성을 좌우하는 큰 요인이 되고 있다. 이를 위하여 저 탄성계수합금을 설계하지만 하중을 버티는 강도가 낮아지는 단점이 있어 레이저증착법을 이용하여 임플란트재료인 Ti6Al4V합금에 탄성계수가 낮은 Ta, Nb등을 코팅하는 방법을 통하여 이를 해결하고자하는 시도가 이루어지고 있다. 이 방법은 최근의 3D 프린팅의 원리가 되고 있다. 따라서 발표에서는 Laser Deposition방법을 이용하여 치의학분야에서 응용되고 있는 예를 강연하고 응용 가능 분야에 대하여 토론 하고자한다. 또한 펨토레이저를 이용하여 생체합금의 표면처리는 생체활성화를 더욱 증진시키며 이를 위하여 많은 연구 수행되고 있다. 본 발표에서는 매식용 합금 표면에 펨토레이저를 이용하여 텍스춰링하여 세포가 잘 성장 할 수 있는 크기의 조절함으로써 기존의 표면처리와는 다른 효과를 얻을 수 있는 장점을 알아본다. 펨토레이저를 이용하면 여러 가지 형태의 텍스춰링이 가능하며 원형, 사각형등등 자유자제로 형태의 묘사가 가능하고 깊이 또한 쉽게 조절할 수 있는 장점이 있다. 지금까지는 표면 개질에 사용되는 레이저는 주로 Nd:YAG 레이저의 파장을 반으로 줄인 녹색레이저 (${\lambda}=532nm$)를 사용하거나, 자외선파장영역의 레이저를 사용하는 경우가 일반적으로 가장 보편화되었다. 이를 이용하여 제조된 Ti합금에 펨토 초(10-15 second) 펄스폭 대역을 갖는 레이저를 이용하여 나노크기의 미세 요철을 표면에 형성한 후, 나노튜브를 형성하여 그 표면특성의 변화를 알아보고 펨토레이저가 의료분야에 적용되고 있는 예를 살펴보고자 한다.

• Communications for Statistical Applications and Methods
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• 제15권3호
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• pp.465-481
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• 2008

문항반응이론(Item response theory: IRT)에서는 문항이 가지고 있는 특성을 기초로 피험자의 능력을 추정하고 동시에 각 문항별 문항특성곡선(Item characteristics curve: ICC)을 이용하여 문항모수를 추정하게 된다. 그러나 모수추정에 있어서 최대 우도추정의 경우는 초기값과 다른 여러 문제들이 발생할 수 있다. 본 연구에서는 추정 문제 해결방법의 대안으로 점근적 근사화 방법(Asymptotic approximation method: AAM)을 제안한다. 이는 자료의 수가 적거나 국소 변동이 있는 경우에 효과적인 추정방법이라고 할 수 있다. 이에 개발된 'Any Assess' 시스템을 모의실험을 통하여 신뢰성을 검정하였다.

• Macromolecular Research
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• 제16권2호
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• pp.139-148
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• 2008

Biodegradable and elastic poly(L-lactide-co-$\varepsilon$-caprolactone) (PLCL) was electrospun to prepare nanofibers, and N-isopropylacrylamide (NIPAAm) was then grafted onto their surfaces under aqueous conditions using $^{60}Co-{\gamma}$ irradiation. The graft yield increased with increasing irradiation dose from 5 to 10 kGy and the nanofibers showed a greater graft yield compared with the firms. SEM confirmed that the PLCL nanofibers maintained an interconnected pore structure after grafting with NIPAAm. However, overdoses of irradiation led to the excessive formation of homopolymer gels on the surface of thc PLCL nanofibers. The equilibrium swelling and deswelling ratio of the PNIPAAm-g-PLCL nanofibers (prepared with 10 kGy) was the highest among the samples, which was consistent with the graft yield results. The phase-separation characteristics of PNIPAAm in aqueous conditions conferred a unique temperature-responsive swelling behavior of PNIPAAm-g-PLCL nanofibers, showing the ability to absorb a large amount of water at < $32^{\circ}C$, and abrupt collapse when the temperature was increased to $40^{\circ}C$. In accordance with the temperature-dependent changes in swelling behavior, the release rate of indomethacin and FITC-BSA loaded in PNIPAAm-g-PLCL nanofibers by a diffusion-mediated process was regulated by the change in temperature. Both model drugs demonstrated greater release rate at $40^{\circ}C$ relative to that at $25^{\circ}C$. This approach of the temperature-controlled release of drugs from PNIPAAm-g-PLCL nanofibers using gamma-ray irradiation may be used to design drugs and protein delivery carriers in various biomedical applications.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2009년도 제38회 동계학술대회 초록집
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• pp.98-98
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• 2010

Ion beam irradiation has been extensively used for surface modification of polymers, glassy metals and amorphous and crystalline materials at micron and submicron scales. The surface structures created by exposure to an ion beam range from dots, steps and one-dimensional straight wrinkles to highly complex hierarchical undulations and ripples. In general, the morphology of these nanoscale features can be selected by controlling the ion beam parameters (e.g. fluence and acceleration voltage), making ion beam irradiation a promising method for the surface engineering of materials. In the work, we presented that ion beam irradiation results in creation of a peculiar nanoscale dimple-like structure on the surface of polyimide - a common polymer in electronics, large scale structures, automobile industry, and biomedical applications. The role of broad Ar ion beam on the morphology of the structural features was investigated and insights into the mechanisms of formation of these nanoscale features were provided. Moreover, a systematic experimental study was performed to quantify the role of ion beam treatment time, and thus the morphology, on the coefficient of friction of polyimide surfaces covered by nanostructure using a tribo-experiment. Nano-indentation experiment were performed on the ion beam treated surfaces which shows that the hardness as well as the elastic modulus of the polyimide surface increased with increase of Ar ion beam treatment time. The increased of hardness of polyimide have been explained in terms of surface structure as well as morphology changes induced by Ar ion beam treatment.

• 대한핵의학회지
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• 제37권1호
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• pp.43-52
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• 2003

Microarray technology allows the simultaneous analysis of gene expression patterns of thousands of genes, in a systematic fashion, under a similar set of experimental conditions, thus making the data highly comparable. In some cases arrays are used simply as a primary screen loading to downstream molecular characterization of individual gene candidates. In other cases, the goal of expression profiling is to begin to identify complex regulatory networks underlying developmental processes and disease states. Microarrays were originally used with ceil lines or other simple model systems. More recently, microarrays have been used in the analysis of more complex biological tissues including neural systems and the brain. The application of cDNA arrays in neuropsychiatry has lagged behind other fields for a number of reasons. These include a requirement for a large amount of input probe RNA In fluorescent-glass based array systems and the cellular complexity introduced by multicellular brain and neural tissues. An additional factor that impacts the general use of microarrays in neuropsychiatry is the lack of availability of sequenced clone sets from model systems. While human cDNA clones have been widely available, high qualify rat, mouse, and drosophilae, among others are just becoming widely available. A final factor in the application of cDNA microarrays in neuropsychiatry is cost of commercial arrays. As academic microarray facilitates become more commonplace custom made arrays will become more widely available at a lower cost allowing more widespread applications. in summary, microarray technology is rapidly having an impact on many areas of biomedical research. Radioisotope-nylon based microarrays offer alternatives that may in some cases be more sensitive, flexible, inexpensive, and universal as compared to other array formats, such as fluorescent-glass arrays. In some situations of limited RNA or exotic species, radioactive membrane microarrays may be the most practical experimental approach in studying psychiatric and neurodegenerative disorders, and other complex questions in the brain.

• 비파괴검사학회지
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• 제32권5호
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• pp.585-596
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• 2012

PVDF와 P(VDF-TrFE)로 대별되는 압전고분자는 종래의 대표적인 압전재료인 PZT에 비해 전기음향변환효율이 떨어지며 내부손실이 큰 단점은 있으나, 음향임피던스가 물 또는 생체와 비슷하고 수신효율이 우수하며 광대역 특성을 나타내는 등의 장점을 가진 재료이다. 또한 다른 압전재료에 비해 얇은 막으로의 제작이 쉽고, 그 막은 유연하므로 복잡한 곡면을 갖는 고주파 초음파 트랜스듀서 재료로 유용하다. 그러한 특성은 생의학적 응용에 적합한바, 다양한 형태의 초음파 트랜스듀서가 연구 개발되어져 왔다. 본 논문에서는 먼저, 압전고분자막을 이용하여 초음파 트랜스듀서를 설계 제작하는데 있어서 고려해야할 몇 가지 주요사항을 기술하고, KLM 모델을 사용한 해석을 통하여 그 고려사항들이 트랜스듀서의 동작에 미치는 영향을 파악하였다. 다음으로, 의학적 또는 생물학적 응용을 목적으로 초음파 영상을 얻고 있는 몇몇 주요 응용분야에서 사용되는 압전고분자 트랜스듀서의 구조와 그것을 이용하여 얻은 영상의 특징에 대하여 간략히 해설하였다.

• 대한의용생체공학회:의공학회지
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• 제24권4호
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• pp.275-280
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• 2003

일반적으로 MR Angiography(MRI)는 사전 포화방법(presaturation)을 이용하여 동맥과 정맥의 분리된 영상을 획득한다. 하지만 이러한 일반적인 사전포화방법으로 동맥과 정맥영상을 획득하기 위해서는 두 번의 영상획득이 필요하다. 따라서 본 연구에서는 동맥과 정맥의 구분된 영상을 한번의 영상획득으로 얻을 수 있는 SAAV 기법을 0.3T MRI system에 적용하고, 획득한 동맥과 정맥의 두 MRA 영상을 Colot-Mapping으로 동$.$정맥을 한 영상에 구분하여 나타냄으로써 0.3T MRI system에서 MRI의 임상적 적용 및 활용 가능성을 높이고자 하였다. 마산 삼성병원의 0.3T MRI system (Magfinder, AILab. Korea)어서 SAAV sequence를 이용하여 정상적인 피험자로부터 목 부위의 동맥과 정맥 혈관영상 (volume : 256${\times}$256${\times}$64)을 동시에 얻었다. 그리고. 이들의 각 2D 영상들에서 위치정보를 획득한 후 MIP 기법과 Color Mapping으로 조합하여 3D Artery-Vein Color Mapping(AVCM) MRA 영상으로 재구성하였다.

• Current Optics and Photonics
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• 제4권4호
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• pp.286-292
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• 2020

Imaging through multicore fiber (MCF) is of great significance in the biomedical domain. Although several techniques have been developed to image an object from a signal passing through MCF, these methods are strongly dependent on the surroundings, such as vibration and the temperature fluctuation of the fiber's environment. In this paper, we apply a new, strong technique called deep learning to reconstruct the phase image through a MCF in which each core is multimode. To evaluate the network, we employ the binary cross-entropy as the loss function of a convolutional neural network (CNN) with improved U-net structure. The high-quality reconstruction of input objects upon spatial light modulation (SLM) can be realized from the speckle patterns of intensity that contain the information about the objects. Moreover, we study the effect of MCF length on image recovery. It is shown that the shorter the fiber, the better the imaging quality. Based on our findings, MCF may have applications in fields such as endoscopic imaging and optical communication.

• International Journal of Industrial Entomology and Biomaterials
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• 제37권2호
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• pp.36-42
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• 2018

Recently, silk sericin has attracted attention because of its unique properties as a biomaterial, including its UV resistance, moisturizing effect on skin, and wound-healing effect. Therefore, the preparation of sericin in various forms such as gel, film, fiber, and sponge is studied for cosmetic and biomedical applications, and the effect of the preparation conditions on the structure and properties of sericin forms is examined to maximize its performance. In this study, silk sericin films were prepared under different preparation conditions and heat-treated at high temperatures ($100-250^{\circ}C$) to examine the effect of heat treatment on the film structure. The order of the crystallinity index of the untreated sericin film is as follows: F25 (sericin film cast from formic acid) > WE25 (ethanol treated sericin film cast from water at $250^{\circ}C$) > W25 (sericin film cast from water at $250^{\circ}C$) > W100 (sericin film cast from water at $100^{\circ}C$). As the heat-treatment temperature was increased, the color of the sericin films changed gradually from colorless to yellow, brown, and black depending on the temperature. The crystallinity of the sericin film changed after the heat treatment, depending on the preparation condition. Whereas a sericin film cast from formic acid (F25) started to lose its crystallinity at $200^{\circ}C$, thus undergoing the highest loss of crystallinity among the sericin films studied, the rest (W25, WE25, and W100) showed a decrease in crystallinity at $250^{\circ}C$, owing to the disruption of the ${\beta}$-sheet crystallites due to heat.

• 대한의용생체공학회:의공학회지
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• 제40권1호
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• pp.1-6
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• 2019

Human mesenchymal stem cells (hMSC) are multipotent stromal cells that have great potential to differentiate into a variety of cell types such as osteocytes, chondrocytes, and myocytes. Although there have been many studies on their clinical availability, little is known about how intracellular signals can be modulated by topographic features of the extracellular matrix (ECM). In this study, we investigated whether and how microwavy-patterned extracellular matrix (ECM) could affect the signaling activity of focal adhesion kinase (FAK), a key cellular adhesion protein. The fluorescence resonance energy transfer (FRET)-based FAK biosensor-transfected cells are incubated on microwavy-patterned surfaces and then platelet derived growth factor (PDGF) are treated to trigger FAK signals, followed by monitoring through live-cell FRET imaging in real time. As a result, we report that PDGF-induced FAK was highly activated in cells cultured on microwavy-patterned surface with L or M type, while inhibited by H type-patterned surface. In further studies, PDGF-induced FAK signals are regulated by functional support of actin filaments, microtubules, myosin-related proteins, suggesting that PDGF-induced FAK signals in hMSC upon microwavy surfaces are dependent on cytoskeleton (CSK)-actomyosin networks. Thus, our findings not only provide new insight on molecular mechanisms on how FAK signals can be regulated by distinct topographical cues of the ECM, but also may offer advantages in potential applications for regenerative medicine and tissue engineering.