Ag flake/silicone rubber composite with high stability and stretching speed insensitive resistance via conductive bridge formation.

High stability, stretchable speed insensitive properties, high stretchability, and electrical conductivity are key characteristics for the realisation of wearable devices. However, conventional research is mainly focused on achieving only high stretchability and electrical conductivity. Studies on the stability and stretching speed insensitive properties generally require complex fabrication processes, which are in need of further improvement. In this study, we propose a facile formation of a conductive bridge in composites by using surface damage and the viscoelastic property of the polymer. Surface cracks due to repeated stretching cycles formed conductive bridges via stress relaxation of the viscoelastic polymer matrix. The conductive bridge resulted in the conductor having highly stable resistance values at target strains and stretching speed insensitive resistance, even at stretching speeds that were 20 times faster than the minimum.

Extraction of Light Using Random Nanocone on Poly(vinyl-butyral) for Flexible OLEDs.

In this study, we designed a smooth, highly flexible, mechanically robust poly(vinyl-butyral) (PVB)/silver nanowire (AgNW) composite transparent conducting electrode (TCE) integrated with a random nanocone (RNC) to enhance the light extraction of flexible organic light-emitting diodes (OLEDs). The RNC was fabricated by reactive-ion etching (RIE) on AgNW embedded in PVB. As the etching time increased, the size of the RNC became larger. The sheet resistance and transmittance of PVB/AgNW with the RNC was 21.7 Ω/sq and ~87%, respectively. For the PVB/AgNW, the change in sheet resistance was only 2.6% when a 2,000-bend test was performed. The maximum external quantum efficiency was 28.3% when RNC 700 s was used as a green phosphorescent OLED. In addition, for current efficiency and power efficiency, RNC 700 s increased 1.4 times over RNC 0 s. RNC is free of viewing-angle-dependent color and brightness distortion. PVB/AgNW and RNC are practical ways to overcome the brittleness of conventional indium tin oxide and improve the efficiency of flexible OLEDs. Finally, this product is expected to be applied to various flexible optical devices.

Ultrastretchable Conductor Fabricated on Skin-Like Hydrogel-Elastomer Hybrid Substrates for Skin Electronics.

Printing technology can be used for manufacturing stretchable electrodes, which represent essential parts of wearable devices requiring relatively high degrees of stretchability and conductivity. In this work, a strategy for fabricating printable and highly stretchable conductors are proposed by transferring printed Ag ink onto stretchable substrates comprising Ecoflex elastomer and tough hydrogel layers using a water-soluble tape. The elastic modulus of the produced hybrid film is close to that of the hydrogel layer, since the thickness of Ecoflex elastomer film coated on hydrogel is very thin (30 µm). Moreover, the fabricated conductor on hybrid film is stretched up to 1780% strain. The described transfer method is simpler than other techniques utilizing elastomer stamps or sacrificial layers and enables application of printable electronics to the substrates with low elastic moduli (such as hydrogels). The integration of printed electronics with skin-like low-modulus substrates can be applied to make wearable devices more comfortable for human skin.

Flash-induced nanowelding of silver nanowire networks for transparent stretchable electrochromic devices.

Electrochromic devices (ECDs) are emerging as a novel technology for various applications like commercialized smart window glasses, and auto-dimming rear-view mirrors. Recently, the development of low-power, lightweight, flexible, and stretchable devices has been accelerated to meet the growing demand in the new wearable devices market. Silver nanowires (AgNWs) can become new primary transparent conducting electrode (TCE) materials to replace indium tin oxide (ITO) for ECDs. However, issues such as substrate adhesion, delamination, and higher resistance still exist with AgNWs. Herein, we report a high-performance stretchable flash-induced AgNW-network-based TCE on surface-treated polydimethylsiloxane (PDMS) substrates. A Xe flash light method was used to create nanowelded networks of AgNWs. Surface silane treatments increased the adhesion and durability of the films as well. Finally, ECDs were fabricated under the optimal conditions and examined under strained conditions to demonstrate the resistance and mechanical behaviours of the devices. Results showed a flexible and durable film maintaining a high level of conductivity and reversible resistance behaviour, beyond those currently achievable with standard ITO/PET flexible TCEs.

Masking nanoparticle surfaces for sensitive and selective colorimetric detection of proteins.

We have developed a convenient and efficient colorimetric detection system for protein targets using aptamer-gold nanoparticle conjugates. We take advantage of the correlation between the catalytic properties and the exposed surface area of the nanoparticles, which is inversely proportional to the amount of the aptamer-bound protein targets. As the concentration of the protein target increases, the nanoparticle surface area becomes more masked, thus increasing the reduction time of 4-nitrophenol for the color change. We also reduce the detection time by either redesigning the aptamer sequences or regulating their density. This detection system is highly selective, discriminating the target protein even at a concentration 1000 times higher than the limit of detection (LOD). Importantly, to the best of our knowledge, the LOD with the unaided eye in this work is the lowest for a colorimetric detection system using lysozyme as a model protein (16 nM). Lysozyme in chicken egg whites is directly analyzed using our detection system, whose results are in excellent agreement with the enzyme-linked immunosorbent assay (ELISA) analysis.

Electroconvulsive shock increases SIRT1 immunoreactivity in the mouse hippocampus and hypothalamus.

OBJECTIVES: Recent study shows that silent mating-type information regulation 2 homolog 1 (SIRT1) regulation may be involved with depression. Electroconvulsive shock (ECS) has been used for the treatment of depression, but little is known about the effect of ECS on the changes in SIRT1 levels in the brain. The present study was designed to observe whether ECS dynamically regulates SIRT1 levels in the hippocampus and hypothalamus; both of these regions have been implicated in the pathophysiology of depression. METHODS: Male imprinting control region mice were given a single ECS via ear clip electrodes, and then killed 0.5, 2, 8, 24, or 48 hours after ECS. Changes in SIRT1 were observed by Immunohistochemistry, and obtained results were compared with sham controls that did not receive ECS. RESULTS: Silent mating-type information regulation 2 homolog 1 immunoreactivity levels in the CA1 and CA3 subfields of the hippocampus peaked 2 hours after ECS and then returned to control levels by 24 hours after ECS. Silent mating-type information regulation 2 homolog 1 immunoreactivity levels in the dentate gyrus of hippocampus, hypothalamic paraventricular, dorsomedial, arcuate, and suprachiasmatic nuclei peaked 8 hours after ECS but had not completely returned to baseline levels 48 hours after ECS, except for the dentate gyrus. Electroconvulsive shock resulted in a gradual increase of SIRT1 immunoreactivity in the hypothalamic ventromedial nucleus and lateral hypothalamic area, which appeared to be still rising or peaking at the 48-hour post-ECS time point. CONCLUSIONS: The present results demonstrate that a single ECS increases SIRT1 in the mouse hippocampus and hypothalamus differentially in a region-specific time-dependent manner.