• 대한치주과학회:학술대회논문집
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• 2005.11a
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• pp.201-202
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• 2005

• 한국생물공학회:학술대회논문집
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• 2003.04a
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• pp.98-100
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• 2003

Synthetic polymers such as PET and ePTFE have widely been used for artificial vascular patches. However, these materials cannot function for a long term as blood vessel due to thrombotic occlusion and calcification. To overcome this limitation, a biocompatible vascular patch was developed using stem cell and tissue engineering approach. Autologous bone marrow mesenchymal stem cells were differentiated into vascular endothelial cells and smooth muscle cells. These cells were seeded onto collagen patch matrices. The matrices were anastomosed to abdominal arteries in canine models. Prior to implantation, histological and scanning electron microscopical examination revealed stem cell adhesion and growth on the matrices. At 3 weeks, the implanted vascular patches were patent. Histological examination showed the regeneration of endothelium, media and adventitia in the grafts. Cell tracing analysis using fluorescent reagent showed that labeled stem cells were present in the implanted grafts and contributed to the regeneration of vascular tissues. This study may help us develop a tissue-engineered vascular patch appropriate for clinical applications.

• Journal of Radiation Protection and Research
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• v.15 no.2
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• pp.87-100
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• 1990

For the quantitative evaluation and assessment of radiation exposure from terrestrial component of natural environmental radiation, successive thermoluminescence dosimetry and periodical in-situ gamma ray spectrometry were carried out for a period of 24 months. LiF PTFE dise TLDs and $3&{\phi}{\times}3'$cylindrical NaI(Tl)scintill ation detector in association of portable multichannel analyzer (4096 ch) were used in this study. The doses measured were evaluated and assessed in terms of effective dose equivalent. As a concomitant output, the dose equivalent due to ionizing component of cosmic ray was able to be evaluated. According to the results obtained in terms of variance weighted mean, the annual effective dose equivalents of terrestrial gamma ray and cosmic ray ionizing component in Taejeon area came out to be $564{\pm}4\;{\mu}Sv(64.8{\pm}0.5nSv{\cdot}h^{-1}$ and $300{\pm}2\;{\mu}Sv(34.3{\pm}0.2nSv{\cdot}h^{-1}$, respectively, which are reasonable comparably with that appeared in UNSCEAR Report[28]as per caput annual effective dose equivalent in 'areas of normal background radiation'.

• Journal of Chest Surgery
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• v.57 no.4
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• pp.413-417
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• 2024

A 70-year-old man with dilated cardiomyopathy underwent left ventricular assist device (LVAD) implantation, using a HeartWare ventricular assist device, as a bridge to candidacy. After 26 months, computed tomography (CT) angiography indicated stenosis in the LVAD outflow graft; however, the patient was asymptomatic, prompting a decision to manage his condition with close monitoring. Ten months later, the patient presented with dizziness and low-flow alerts. Subsequent CT angiography revealed a critical obstruction involving the entire LVAD outflow graft. The patient underwent emergency surgery, during which an organized seroma causing the graft obstruction was found between a wrapped expanded polytetrafluoroethylene (ePTFE) graft and a Dacron outflow graft. The covering of the outflow graft was removed, along with the organized seroma. Following removal of the ePTFE wrap and decompression of the outflow graft, normal LVAD flow was reestablished. The practice of wrapping the outflow graft with synthetic material, commonly done to facilitate later redo sternotomy, may pose a risk for outflow graft obstruction.

• Membrane and Water Treatment
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• v.4 no.4
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• pp.277-291
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• 2013

The transport and recovery of Levafix brilliant red E-4BA and Levafix brilliant red E-6BA were investigated using polytetrafluoroethylene (PTFE) fiber based supported liquid membrane containing tetra butyl ammonium bromide (TBAB) in coconut oil as a carrier. The influencing parameters studied are: pH of the feed solution, concentration of dye in the feed solution, extractant concentration, and various kind of stripping agent, rate of stirring, time of transport, reusability of membrane and stability of membrane. Increase in TBAB concentration inside the membrane enhances the flux with its maximum value at $1.553{\times}10^{-4}$ M TBAB. Further increase in the concentration of TBAB leads to decreased rate of transport due to increase in viscosity of membrane liquid. The optimum conditions for dye transport are: pH of feed ($7{\pm}0.1$), $1.553{\times}10^{-4}$ M extractant concentration, 350 rpm for stirring, $4.9{\times}10^{-1}$ M potassium hydrogen phthalate as a stripping solution, the time of transport 6 h. It was noticed that flux values were increased with increasing dye concentration in the feed phase. Applying this study to textile wastewater, dyes were transported up to 98% in 6 h. This recovery technique is rewarding to environment and economic.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.20 no.2
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• pp.112-126
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• 1998

In dentistry, bony defects can be formed by cyst, tumor, inflammation, trauma and surgery in maxilla and mandible. If the overlying soft tissue invades and preoccupies the jaw bony defects, regenerated bony tissue same as adjacent bone can not replace whole space of the defects, thus preventing osteogenesis from occurring. Guided bone regeneration(GBR) is based on the prevention of overlying soft tissue from entering the bony defect during the initial healing periods. E-polytetrafluoroethylene(e-PTFE) is one of an effective and widely used barrier membrane for GBR, but it has the disadvantages such as surgical removal and high price. To overcome such disadvantages of e-PTFE, many investigators have proposed various absorbable barrier membranes. Inexpensive oxidized cellulose($Surgicel^{(R)}$) membrane was shown to have potential for use as an absorbable barrier membrane for regenerative procedure and it would not require surgical removal. The purpose of this study is to investigate the absorption periods of oxidized cellulose at the implant site and usefulness as a mechanical barrier, preventing the ingrowth of the overlying soft tissue into the bony defects. Two bony defects were made in each tibia of a dog using drill and one defect covered with oxidized cellulose and the other covered with periosteum directly as control. The experimental animals were sacrificed at 1st-7th, 10th, 14th, 21th, 28th day postoperatively, Inspection of the specimens was done to evaluate gross changes. Specimens were examined histopathologically by hematoxylin-eosin and Masson's trichrome staining under light microscope. The results were as follows : 1. There was no significant differences of inflammatory reaction between the experimental and the control group. 2. The resorption of oxidized cellulose was almost completed within 14th day. 3. Histologically, bone formation in the experimental group was somewhat more than that of the control group at 10th, 14th, 21th and 28th day postoperatively. The bone forming pattern of the experimental group was more regular than that of the control group. 4. There was no evidence of soft tissue invasion into the bony defect in the experimental group. In conclusion, oxidized cellulose membrane might be used as an alternative absorbable barrier membrane to prevent overlying soft tissue invasion into the bony defects.

• Membrane and Water Treatment
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• v.5 no.1
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• pp.41-56
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• 2014

A series of microporous PVDF membranes were prepared by isothermal immersionprecipitation of PVDF/TEP casting dopes in both soft and harsh coagulation baths. Morphologies of the membranes' top surfaces were found to depend strongly on the bath strength, which could be controlled by the TEP content in the bath. By changing the bath gradually from pure water to 70% TEP, the top surface evolved from a dense skin-like (asymmetric) to a totally open porous morphology (symmetric). The latter structure could similarly be obtained by precipitation of the same dope in an alcoholic bath, e.g., 1-butanol. Membrane distillation processes to desalt sodium chloride aqueous solutions were conducted using various prepared membranes and two commercial microporous membranes, PTFE (Toyo, Japan, code: J020A330R) and PVDF (GE, USA, code: YMJWSP3001). The permeation fluxes were compared and correlated with the morphologies of the tested membranes.

• Smart Structures and Systems
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• v.17 no.5
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• pp.709-724
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• 2016

This study investigates the optimum design parameters of a superelastic friction base isolator (S-FBI) system through a multi-objective genetic algorithm to improve the performance of isolated buildings against near-fault earthquakes. The S-FBI system consists of a flat steel-PTFE sliding bearing and superelastic NiTi shape memory alloy (SMA) cables. Sliding bearing limits the transfer of shear across the isolation interface and provides damping from sliding friction. SMA cables provide restoring force capability to the isolation system together with additional damping characteristics. A three-story building is modeled with S-FBI isolation system. Multiple-objective numerical optimization that simultaneously minimizes isolation-level displacements and superstructure response is carried out with a genetic algorithm in order to optimize S-FBI system. Nonlinear time history analyses of the building with optimal S-FBI system are performed. A set of 20 near-fault ground motion records are used in numerical simulations. Results show that S-FBI system successfully control response of the buildings against near-fault earthquakes without sacrificing in isolation efficacy and producing large isolation-level deformations.

• 대한치주과학회:학술대회논문집
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• 2007.11a
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• pp.112-112
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• 2007

• Journal of the Korean Electrochemical Society
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• v.2 no.3
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• pp.171-175
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• 1999

Novel process for high power catalyst electrode for PEM fuel cell has been developed. MEA having this catalyst electrode showed $0.5W/cm^2\;with\;0.2mg/cm^2$ of Pt loading at aunospheric humid hydrogen and oxygen condition. In this process, platinized carbon and plain carbon powders were coated with ionomer (Nafion) and hydrophobic polymer (PTFE), respectively and it could maximize two roles of catalyst electrode, l.e., reaction and gas supplying component. Those polarization characteristics proved the improved performance by reducing potential drop especially in the concentration polarization region.