Enhanced Conductivity in Highly Stretchable Silver and Polymer Nanocomposite Conductors.

In stretchable conductors, there is a trade-off relationship between the stretchability and conductivity which makes it difficult to increase both properties simultaneously. From a practical point of view, however, high conductivity is a more important parameter for real-world applications of wearable and mobile electronics. To obtain a highly conductive stretchable conductor, we developed a stretchable conductor composed of silver (Ag) flat-type microparticles, Ag nanoparticles and a polyester binder. The printed stretchable conductor was then sintered using the intense pulse light sintering technique. The effects of different mixing ratios of Ag flat-type particles and nanoparticles on dispersibility, printability, surface properties, conductivity, and stretchability were examined. Increasing the content of Ag-flat type particles in the composite improved dispersibility, printability, and conductivity. The stretchable conductor exhibited the outstanding conductivity of 5.5×106 S/m. Increasing the Ag nanoparticles content increased the stretchability of the conductor. As the nanoparticle content increased to 30%, the stretchable conductor showed the excellent stretchability of 210%, and withstood 2,600 repeated stretching cycles at a fixed tensile strain of 50%. The conductors also exhibited superb foldability during 10,000 repeated folding tests, up to a radius of 1 mm, without any failures.

Printed Electrode for High-Performance Bow-Tie Antenna by Photonic Sintering Process.

Recently, flexible electronic device technology has evolved beyond curved devices with the development of flexible/stretchable devices that can be crumpled or stretched. Both elasticity and durability are essential for these devices, which should have high-conductivity for antennas and repeatability for sensors. In addition, electronic-skins, which can have a direct impact on the human-body, should be harmless to the human-body and should not be deformed by contact with sweat or organic matter. In this study, PDMS substrates were used to satisfy the above conditions. PDMS is used to fabricate human-friendly, flexible/stretchable substrates, and it has excellent repeat durability characteristics. To improve the adhesion of these PDMS films and electrodes, conductive paste was produced based on PDMS resins of the same properties. In addition, two types of Ag particles were selected as conductive fillers because the electrode characteristics of the antenna application requires excellent conductivity, and conductive paste were produced using flake Ag, which could affect conductivity, and Ag nanoparticles that affect stretchability and repeatability. The paste was applied using a high-efficiency printing technique. The printed electrodes were cured in a thermal oven. For higher conductivity, photonic-sintering was carried out during post-processing. As a result, 1.1117×106 (S/m) had excellent conductivity, performed well in repeated tensile-durability experiments of 30% to 100 times, and produced a bow-tie antenna for the above electrodes. As a result of tensing up to 35% through a Network-Analyzer, there was no performance change in the resonance-frequency or return-loss values, and excellent electrodes were developed that would achieve excellent performance even if they are applied in the sub-frequency area of 5G-antennas in the future.

Large-Scale Rapid Laser Sintering of Highly Stretchable Electrodes Using a Homogenized Rectangular Laser Beam.

This study explored the feasibility of a fast and uniform large-scale laser sintering method for sintering stretchable electrodes. A homogenized rectangular infrared (IR) laser with a wavelength of 980 nm was used in the sintering process. A highly stretchable composite electrode was fabricated using silver (Ag) microparticles and Ag flakes as the fillers and polyester resin as the binder on the polyurethane substrate. This laser-sintering method showed a sintering time of 1 sec and a very uniform temperature across the surface, resulting in enhancing the conductivity and stretchability of the electrodes. The effects of the laser power on the electrical and electromechanical properties of the electrodes were investigated. Using stretching, bending, and twisting tests, the feasibility of the laser-sintered stretchable electrodes was comprehensively examined. The electrode that was sintered at a laser power of 50 W exhibited superior stretchability at a strain of 210%, high mechanical endurance of 1,000 repeated cycles, and excellent adhesion. The stretchable electrodes showed excellent bendability and twistability in which the electrodes can be bent up to 1 mm and twisted up to 90° without any damage; thus, they are highly applicable as stretchable electrodes for wearable electronics. Additionally, the Ag composites were explored for use in a radio-frequency (RF) stretchable antenna to confirm the application of the laser-sintering method for stretchable and wearable electronic devices. The stretchable dipole antenna showed an excellent radiation efficiency of 95% and a highly stable operation, even when stretched to 90% strain.

Effects of Binder and Substrate Materials on the Performance and Reliability of Stretchable Nanocomposite Strain Sensors.

In stretchable strain sensors, highly elastic elastomers such as polydimethylsiloxane (PDMS), Ecoflex, and polyurethane are commonly used for binder materials of the nanocomposite and substrates. However, the viscoelastic nature of the elastomers and the interfacial action between nanofillers and binders influence the critical sensor performances, such as repeatability, response, and hysteresis behavior. In this study, we developed a stretchable nanocomposite strain sensor composed of multiwalled carbon nanotubes and a silicone elastomer binder. The effects of binder and substrate materials on the repeatability, response, hysteresis behavior, and long-term endurance of the strain sensors were systematically investigated using stretching, bending, and repeated cyclic bending tests. Three different binder and substrate materials including PDMS, Ecoflex, and a mixture of PDMS/Ecoflex were tested. The stretchable strain sensors showed an excellent linearity and stretchability of more than 130%. Therefore, the long-term endurance of the strain sensors fabricated with Ecoflex binder should be improved. The strain sensors fabricated with Ecoflex binder showed a relatively large variation in electrical resistance during 10,000-cycle bending tests and repeatability errors at large bending angles. The strain sensors fabricated with PDMS binder showed repeatability errors at small bending angles and a slight response delay of 1 second. On the contrary, the strain sensors fabricated with a mixture of PDMS/Ecoflex binder showed excellent repeatability and response characteristics. The PDMS material showed hysteresis behavior; therefore, the strain sensors fabricated with PDMS binder on PDMS substrate exhibited a large hysteresis behavior in the first stretch-release cycle. It was found that the hysteresis behavior of the strain sensors was mainly dependent on substrate materials than on binder materials. The stretchable strain sensors made of the mixture of PDMS/Ecoflex exhibited excellent repeatability, response, hysteresis behavior, and excellent capability in detecting finger and wrist bending.

Highly Stretchable and Durable Nanocomposite Bow-Tie Antenna for Wearable Application.

We present a highly stretchable and compact bow-tie antenna which operates at 5 GHz for wearable applications. The dimensions of the bow-tie antenna were 7.9 mm×17.8 mm. The stretchable antenna was fabricated with a composite mixture of silver flake and polymer binder. The composite paste was printed on polyurethane and textile using the screen printing technique. The RF performances, stretchability, bendability, and durability of the antennas were evaluated, which are critical requirements in wearable electronics. The stretchable bow-tie antennas showed excellent RF performances and stretchability up to a stretching strain of 40%. The antennas could be bent up to a bending radius of 20 mm without degrading RF performance. The stretchable antennas also exhibited outstanding mechanical endurance after 10,000 cyclic stretching tests. The antennas were not affected by the presence of the body and showed very stable RF performances, exhibiting promising results for mobile and wearable applications.

Validation of the Oxford Classification of IgA Nephropathy: A Single-Center Study in Korean Adults

BACKGROUND/AIMS: The recently published Oxford classification of IgA nephropathy (IgAN) proposed a split system for histological grading, based on prognostic pathological features. This new classification system must be validated in a variety of cohorts. We investigated whether these pathological features were applicable to an adult Korean population. METHODS: In total, 69 adult Korean patients with IgAN were analyzed using the Oxford classification system at Soonchunhyang University Hospital, Seoul, Korea. All cases were categorized according to Lee's classification. Renal biopsies from all patients were scored by a pathologist who was blinded to the clinical data for pathological variables. Inclusion criteria were age greater than 18 years and at least 36 months of follow-up. We excluded cases with secondary IgAN, diabetic nephropathy combined other glomerulopathies, less than 36 months of follow-up, and those that progressed rapidly. RESULTS: The median age of the patients was 34 years (range, 27 to 45). Mean arterial blood pressure was 97 +/- 10 mmHg at the time of biopsy. The median follow-up period was 85 months (range, 60 to 114). Kaplan-Meier analysis showed significant prognostic predictions for M, E, and T lesions. A Cox proportional hazard regression analysis also revealed prognostic predictions for E and T lesions. CONCLUSIONS: Using the Oxford classification in IgAN, E, and T lesions predicted renal outcome in Korean adults after taking clinical variables into account.

A case of eosinophilic gastroenteritis with eosinophilic ascites / 대한내과학회지

Eosinophilic gastroenteritis is an uncommon disease of unknown cause characterized by eosinophilic infiltration in various areas of the gastrointestinal tract with gastrointestinal symptoms. It is generally classified according to the layer of the gastrointestinal tract involved. Eosinophilic infiltration of the serosa is the rarest form of presentation and may manifest eosinophilic ascites. We report a case of a 29-year-old woman who experienced rapidly progressing abdominal distension and pain. A diffuse erythematous change of the gastric mucosa was observed on gastroscopy. An abdominal computed tomography and colonoscopy showed diffuse wall thickening of the small bowel and colon with a large amount of ascites. Eosinophilic infiltration was confirmed by multiple biopsies of the gastrointestinal tract and peritoneal fluid analysis. The patient was treated with corticosteroid and responded dramatically.

A Case of Double Pylorus Accompanied by Duodenal Ulcer / 대한소화기내시경학회지

Double pylorus is a rare abnormality of the gastrointestinal tract and it presents as two openings between the gastric antrum and the duodenal bulb. The acquired type is more common than the congenital one and this acquired type arises secondary to peptic ulcer disease. A 68-year-old man visited the gastrointestinal clinic and he presented with chronic epigastric pain and dyspepsia. Upper endoscopy showed double pylorus with an accessory channel on the lesser curvature side of the prepyloric antrum and also an active duodenal ulcer. Upon review of the patient's past history and examination, the findings of the upper endoscopy that was done 7 years previously were within the normal limits. The patient was diagnosed as having a double pylorus secondary to duodenal ulcer and he treated conservatively with anti-ulcer therapy. We report here on a case of double pylorus along with the brief review of the literature.

A Case of Double Pylorus Accompanied by Duodenal Ulcer / 대한소화기내시경학회지

Double pylorus is a rare abnormality of the gastrointestinal tract and it presents as two openings between the gastric antrum and the duodenal bulb. The acquired type is more common than the congenital one and this acquired type arises secondary to peptic ulcer disease. A 68-year-old man visited the gastrointestinal clinic and he presented with chronic epigastric pain and dyspepsia. Upper endoscopy showed double pylorus with an accessory channel on the lesser curvature side of the prepyloric antrum and also an active duodenal ulcer. Upon review of the patient's past history and examination, the findings of the upper endoscopy that was done 7 years previously were within the normal limits. The patient was diagnosed as having a double pylorus secondary to duodenal ulcer and he treated conservatively with anti-ulcer therapy. We report here on a case of double pylorus along with the brief review of the literature.

A Case of Primary Upper Esophageal Small Cell Cancer with Cervical Lymph Node Metastasis / 대한소화기내시경학회지

Esophageal small cell carcinoma is a very rare disease. Primary extra-pulmonary small cell carcinoma was reported to account for 4% of primary small cell carcinoma and only 2% of all esophageal malignancy. Because the rate of early distant metastasis is very high, the prognosis is very poor. In Korea, 20 cases were reported. Seventeen cases were located at the mid or lower esophagus and 3 cases were located at the upper esophagus. We have experienced a case of primary upper esophageal small cell cancer, a 65-year-old female with cervical lymph node metastasis, which were diagnosed by endoscopy, open surgical lymph node biopsy and immunohistochemical analysis.