Crack-Based Sensor with Microstructures for Strain and Pressure Sensing.

Recent extensive research on flexible electronics has led to the development of various flexible sensors. In particular, sensors inspired by the slit organs of a spider, which utilize cracks in a metal film to measure strain, have garnered considerable interest. This method exhibited significantly high sensitivity, repeatability, and durability in measuring strain. In this study, a thin-film crack sensor was developed using a microstructure. The results exhibited its ability to simultaneously measure the tensile force and pressure in a thin film, further expanding its applications. Furthermore, the strain and pressure characteristics of the sensor were measured and analyzed using an FEM simulation. The proposed method is expected to contribute to the future development of wearable sensors and artificial electronic skin research.

Reversible Wrinkling Surfaces for Enhanced Grip on Wet/Dry Conditions.

Friction is important in material design for robotic systems that need to perform tasks regardless of environmental changes. Generally, robotic systems lose their friction in wet environments and fail to accomplish their tasks. Despite the significance of maintaining friction in dry and wet environments, it is still challenging. Here, we report a smart switching surface, which helps to complete missions in both wet and dry environments. Inspired by the reversible wrinkling mechanism of a human finger, the surface reversibly generates and removes wrinkles to adapt to both environments using volume-changing characteristics of the Nafion film. The switchable surfaces with manipulated wrinkle morphologies via patterns of diverse densities, sizes, and shapes induce a relationship between the wrinkle morphologies and friction: wrinkles on denser and smaller hexagonal patterns generate six times more friction than non-switching flat surfaces in wet environments and a similar amount of friction to the flat surfaces in dry environments. In addition, the wrinkle morphologies according to the patterns are predicted through numerical simulation, which is in good agreement with experimental results. This work presents potential applications in robotic systems that are required to perform in and out of water and paves the way for further understanding of wrinkling dynamics, manipulation, and evolutionary function in skin.

Highly durable crack sensor integrated with silicone rubber cantilever for measuring cardiac contractility.

To date, numerous biosensing platforms have been developed for assessing drug-induced cardiac toxicity by measuring the change in contractile force of cardiomyocytes. However, these low sensitivity, low-throughput, and time-consuming processes are severely limited in their real-time applications. Here, we propose a cantilever device integrated with a polydimethylsiloxane (PDMS)-encapsulated crack sensor to measure cardiac contractility. The crack sensor is chemically bonded to a PDMS thin layer that allows it to be operated very stably in culture media. The reliability of the proposed crack sensor has been improved dramatically compared to no encapsulation layer. The highly sensitive crack sensor continuously measures the cardiac contractility without changing its gauge factor for up to 26 days (>5 million heartbeats), while changes in contractile force induced by drugs are monitored using the crack sensor-integrated cantilever. Finally, experimental results are compared with those obtained via conventional optical methods to verify the feasibility of building a contraction-based drug-toxicity testing system.

Ultra-sensitive Pressure sensor based on guided straight mechanical cracks.

Recently, a mechanical crack-based strain sensor with high sensitivity was proposed by producing free cracks via bending metal coated film with a known curvature. To further enhance sensitivity and controllability, a guided crack formation is needed. Herein, we demonstrate such a ultra-sensitive sensor based on the guided formation of straight mechanical cracks. The sensor has patterned holes on the surface of the device, which concentrate the stress near patterned holes leading to generate uniform cracks connecting the holes throughout the surface. We found that such a guided straight crack formation resulted in an exponential dependence of the resistance against the strain, overriding known linear or power law dependences. Consequently, the sensors are highly sensitive to pressure (with a sensitivity of over 1 × 105 at pressures of 8-9.5 kPa range) as well as strain (with a gauge factor of over 2 × 106 at strains of 0-10% range). A new theoretical model for the guided crack system has been suggested to be in a good agreement with experiments. Durability and reproducibility have been also confirmed.

Facile Multiscale Patterning by Creep-Assisted Sequential Imprinting and Fuel Cell Application.

The capability of fabricating multiscale structures with desired morphology and incorporating them into engineering applications is key to realizing technological breakthroughs by employing the benefits from both microscale and nanoscale morphology simultaneously. Here, we developed a facile patterning method to fabricate multiscale hierarchical structures by a novel approach called creep-assisted sequential imprinting. In this work, nanopatterning was first carried out by thermal imprint lithography above the glass transition temperature (Tg) of a polymer film, and then followed by creep-assisted imprinting with micropatterns based on the mechanical deformation of the polymer film under the relatively long-term exposure to mechanical stress at temperatures below the Tg of the polymer. The fabricated multiscale arrays exhibited excellent pattern uniformity over large areas. To demonstrate the usage of multiscale architectures, we incorporated the multiscale Nafion films into polymer electrolyte membrane fuel cell, and this device showed more than 10% higher performance than the conventional one. The enhancement was attributed to the decrease in mass transport resistance because of unique cone-shape morphology by creep-recovery effects and the increase in interfacial surface area between Nafion film and electrocatalyst layer.

Robust microzip fastener: repeatable interlocking using polymeric rectangular parallelepiped arrays.

We report a highly repeatable and robust microzip fastener based on the van der Waals force-assisted interlocking between rectangular parallelepiped arrays. To investigate zipperlike interlocking behaviors, various line arrays were fabricated with three different spacing ratios (1, 3, and 5 of 800 nm in width) and width of parallelepipeds (400 nm, 800 nm, and 5 µm with the spacing ratio of 1). In addition, the different rigidity of line arrays was inspected for a repeatable microzip fastener. The normal and shear locking forces were measured with variation of the material rigidity as well as geometry of the array, in good agreement with a proposed theory based on the contact area and force balance. The maximum adhesion forces as high as ∼8.5 N cm(-2) in the normal direction and ∼29.6 N cm(-2) in the shear direction were obtained with high stability up to 1000 cycles. High stability of our fastening system was confirmed for preventing critical failures such as buckling and fracture in practical applications.

Ultrasensitive mechanical crack-based sensor inspired by the spider sensory system.

Recently developed flexible mechanosensors based on inorganic silicon, organic semiconductors, carbon nanotubes, graphene platelets, pressure-sensitive rubber and self-powered devices are highly sensitive and can be applied to human skin. However, the development of a multifunctional sensor satisfying the requirements of ultrahigh mechanosensitivity, flexibility and durability remains a challenge. In nature, spiders sense extremely small variations in mechanical stress using crack-shaped slit organs near their leg joints. Here we demonstrate that sensors based on nanoscale crack junctions and inspired by the geometry of a spider's slit organ can attain ultrahigh sensitivity and serve multiple purposes. The sensors are sensitive to strain (with a gauge factor of over 2,000 in the 0-2 per cent strain range) and vibration (with the ability to detect amplitudes of approximately 10 nanometres). The device is reversible, reproducible, durable and mechanically flexible, and can thus be easily mounted on human skin as an electronic multipixel array. The ultrahigh mechanosensitivity is attributed to the disconnection-reconnection process undergone by the zip-like nanoscale crack junctions under strain or vibration. The proposed theoretical model is consistent with experimental data that we report here. We also demonstrate that sensors based on nanoscale crack junctions are applicable to highly selective speech pattern recognition and the detection of physiological signals. The nanoscale crack junction-based sensory system could be useful in diverse applications requiring ultrahigh displacement sensitivity.

Repetitive cleavage of elastomeric membrane via controlled interfacial fracture.

Here, we report a method of fabricating thin layer of polydimethylsiloxane (PDMS), with a thickness in the range of 60-80 nm, which can be repeatedly generated (more than 10 times) from the same block of PDMS via controlled interfacial fracture. The thin layers can be transferred to various substrates by peeling off from the bulk PDMS. The cleavage is attributed to the built-in stress at the fracture interface due to plasma treatment, resulting in the repetitive formation of the thin membranes, with no residue from processing, and with a surface roughness of ∼5 nm. We were able to demonstrate transferred patterns with controlled thickness by varying the oxygen plasma treatment conditions and the composition of bulk PDMS stamp. Using the method, we achieved residual-free patterns with submicrometer resolution for applications in biomolecule array templates.

Hybrid microfabrication of nanofiber-based sheets and rods for tissue engineering applications.

Electrospun nanofibers have been developed into a variety of forms for tissue engineering scaffolds to regulate the cellular functions guided by nanotopographical cues. Here, we have successfully fabricated nanofiber-based scaffold complexes of rod and sheet type by combining the three microfabrication techniques of electrospinning, spin coating, and polymer melt deposition. It was demonstrated that this hybrid fabrication could produce uniaxially aligned nanofiber scaffolds supported by a thin film, allowing for a mechanically enforced substrate for cell culture as well as facile scaffold manipulation. The results of cell analysis indicated that nanofibers on spin-coated films could provide contact guidance effects on cells and retain them even after manipulation. As an application of the cell-laden nanofiber film, we built a rod-type structure by rolling up the film around a mechanically supporting core microfiber, which was incorporated by polymer melt deposition. A biocompatible and biodegradable polymer, polycaprolactone, was used throughout the processes and thus could be used as a directly implantable substitute in tissue regeneration.

Shape-controllable microlens arrays via direct transfer of photocurable polymer droplets.

A simple method is presented to form an array of shape-controllable microlenses by partial photocuring of an UV-curable polymer and direct transfer. Using the transferred lens array, nanoscale metal patterns as small as 130-nm gaps are detected under an optical microscope with a distinguishable resolution.

[A case of cholestatic hepatitis induced by epstein-barr virus infection].

Acute viral hepatitis in human can be caused by a large number of viruses with a wide range of clinical manifestations and laboratory findings. EBV is a rare causative agent of an acute hepatitis, during the course of infectious mononucleosis. Hepatic manifestations of EBV are usually mild and resolve without serious complications. EBV is rather uncommonly confirmed as an etiologic agent in acute viral hepatitis of adults and it rarely causes cholestatic hepatitis. We report a case of EBV hepatitis with cholestatic feature that was verified through serum viral marker and liver biopsy.

[The clinical usefulness of balloon occluded retrograde transvenous obliteration in gastric variceal bleeding].

BACKGROUND/AIMS: Gastric variceal bleeding is difficult to treat endoscopically because the hemodynamics of the gastric varix are different from that of the esophageal varix. Transjugular intrahepatic portosystemic shunt (TIPS), which has been used widely, does not always result in the regression of gastric varix and it may aggravate the hepatic encephalopathy. Balloon occluded retrograde transvenous obliteration (BRTO) was introduced as a new procedure for gastric variceal bleeding with minimal invasiveness. The purpose of this study was to evaluate the therapeutic effects and complications on follow-up of BRTO as a new treatment option for gastric variceal bleeding. METHODS: Patients with gastric variceal bleeding, who were treated with BRTO form September, 2001 to April, 2003, were included in the study. After the definite confirmation of the shunts with abdominal CT, the sclerosing agent, 5% ethanolamine oleate, was injected into the gastric varix during occlusion through gastrorenal shunts. The procedure was deemed a technical success when the clotting of the sclerosing agent was observed without leakage, and a clinical success when bleeding stopped and the varix decreased in size or was eradicated during the follow-up period (6-23 months, mean: 17.7). RESULTS: Technical success was achieved in 12 of 13 patients (92%) with gastric variceal bleeding. There were no significant side effects. In the one case of failure, the bleeding was controlled with TIPS. Eleven of the 12 patients who had technical success were shown to be clinically successful. The follow-up endoscopic exam showed some aggravation of pre-existing esophageal varices in four patients and a new development of esophageal varices in two patients. Endoscopic variceal ligation was done on one patient in whom esophageal variceal bleeding was present during the follow-up period. CONCLUSIONS: BRTO was proven to be a feasible, safe and less invasive procedure than TIPS and found to be an effective treatment of a gastric variceal bleeding. Considering the possible aggravation of pre-existing esophageal varices or the new development of esophageal varices, regular endoscopic examinations might be needed during the follow-up period.

[Two cases of systemic amyloidosis presenting with abnormalities in liver function tests].

Systemic amyloidosis results from the deposition of insoluble, fibrous amyloid proteins. It occurs mainly in the extracellular spaces of multiple organs and tissues including the kidney, heart, and liver. Although amyloid deposition in the liver is common in patients with systemic amyloidosis, clinically apparent liver disease is relatively rare. Indeed, most patients with systemic amyloidosis manifest only minimal to moderate hepatomegaly and trivial abnormalities in liver function tests. Recently, we experienced two cases of patients who presented with abnormalities in liver function tests and hepatomegaly as manifestations of systemic amyloidosis. We report these cases with a review of the relevant literatures.

[The diagnostic value of serum hyaluronic acid, 7S domain of type IV collagen and AST/ALT ratio as markers of hepatic fibrosis in chronic hepatitis B and cirrhosis patients].

BACKGROUND/AIMS: The prognosis of chronic liver disease is closely related to the development of hepatic fibrosis. Liver biopsy is the gold standard method to assess inflammatory activity and fibrosis stage, but this is associated with morbidity and mortality. This study aimed to evaluate the diagnostic value of serum hyaluronic acid, 7S domain of type IV collagen and AST/ALT ratio as markers of hepatic fibrosis in chronic hepatitis B and cirrhosis. METHODS: This study included 100 patients with chronic hepatitis B and cirrhosis. Liver biopsy and histopathologic classification were done. Serum hyaluronic acid and 7S domain of type IV collagen were measured by one step sandwich binding protein assay and radioimmunoassay using polyclonal antibody to 7S domain of type IV collagen, respectively. RESULTS: The serum concentrations of hyaluronic acid, 7S domain of type IV collagen and AST/ALT ratio in the cirrhosis group (139 +/- 98.4 ng/mL, 6.9 +/- 3.5 ng/mL, 1.6 +/- 1.5) were significantly higher (p<0.01) than those in the normal and fatty liver group (20.2 +/- 12.5 ng/mL, 3.5 +/- 0.5 ng/mL, 0.7 +/- 0.3), mild hepatitis group (32.3 +/- 52.7 ng/mL, 3.9 +/- 1.4 ng/mL, 0.7 +/- 0.4), and moderate to severe hepatitis group (68.2 +/- 72.3 ng/mL, 5.3 +/- 2.4 ng/mL, 0.8 +/- 0.4). At the cutoff value of 77 ng/mL for hyaluronic acid and 6.3 ng/mL for 7S domain of type IV collagen and 0.62 for AST/ALT ratio, the sensitivities were 81.8%, 63.6%, 90.9% and specificities were 87.3%, 88.6%, 53.1% for discriminating cirrhosis (fibrosis score: 4) from the mild to severe fibrosis (fibrosis score: 0-3). CONCLUSIONS: Serum hyaluronic acid, 7S domain of type IV collagen and AST/ALT ratio measurement may be clinically useful as markers of hepatic fibrosis in chronic hepatitis B and cirrhosis.