Micro and Nano Systems Letters最新文献

Microelectronic retinal implants can restore a useful level of artificial vision in photoreceptor-damaged retina. Previously commercialized retinal prostheses require transocular connection lines to an external power supply and/or for data transmission, which are unwieldy and may cause unwanted side effects, such as infections. A recently reported wireless device used a rigid silicon substrate. However, it had the potential for a long-term mechanical mismatch with soft retinal tissue. In this work, we used organic photovoltaic materials which can be fabricated on flexible substrates as well as be operated without any physical connection to the external world. The present study employed PCE10 as an active layer for retinal prosthetic application for the first time. Compared to previously studied organic photovoltaic materials used in retinal prosthesis research (such as P3HT), our PCE10 devices showed higher efficiency, providing a huge advantage in this field. When the PCE10 was blended with other non-fullerene acceptors achieving a ternary organic photovoltaic layer (PCE10:ITIC:Y6 blend), it showed lower reduction of photocurrent under same irradiation frequency condition. The fabrication method for our organic photovoltaic device was simple and easy to control its thickness. The fabricated devices showed adequate photocurrent to stimulate the retinal neurons with a smaller reduction in generated photocurrent during repeating stimuli compared to P3HT or PCE10 alone.Author names: Please confirm if the author names are presented accurately and in the correct sequence (given name, middle name/initial, family name). Author: Given name [Jae Young] Last name [Kim]. Author: Given name [Byung Chul] Last name [Lee].Yes, they are correct.

Laser-induced graphene (LIG) has attracted significant interest in the field of pressure sensors owing to the high sensitivity associated with its inherent three-dimensional porous structure. However, the brittleness of fabricated LIG poses a critical challenge in terms of durability. To address this issue, current research on LIG-based pressure sensors has focused on the utilization of Si-elastomer encapsulation layers. Despite the importance of the mechanical properties of Si elastomers for the performance of physical sensors, few studies have been conducted on the characterization of pressure sensors based on the encapsulation layer. In this study, we investigated the electromechanical characteristics of LIG-based pressure sensors encapsulated in various Si-based elastomers. For an unbiased evaluation, we first introduce a simple and reliable fabrication process for LIG-based pressure sensors with different Si-elastomer encapsulation layers. Subsequently, the electromechanical responses of the sensors were characterized using an automated pressure machine, demonstrating that sensors with encapsulation layers with a lower Young’s modulus exhibited increased resistance changes and extended response times. Finally, an in-depth exploration of the environmental stability of the pressure sensors was conducted for various encapsulation materials, ultimately confirming negligible performance variations based on the encapsulation materials.

Two-photon lithography has emerged as a highly effective method for fabricating intricate three-dimensional (3D) microstructures. It enables the rapid fabrication of 3D microstructures, unlike conventional two-dimensional nanopatterning. Researchers have extensively investigated two-photon polymerization (TPP) for the fabrication of diverse 3D micro/nanodevices with high resolution. TPP can be applied in cell cultures, metamaterials, optical materials, electrical devices, and fluidic devices, to name a few. In this study, we investigate the applications and innovative research pertaining to TPP, which is an effective fabrication technique with significant advancement in various fields. In particular, we attempt to determine the reasons that cause the detachment or delamination of 3D microstructures during the development process and propose some solutions. A step-by-step fabrication process for a glass substrate, from photoresist deposition to laser scanning and the dissolution of the uncured photoresist, is presented. Defects such as pattern delamination are discussed, with emphasis on the cell scaffold structure and microlens array. Understanding and addressing these defects are vital to the success of 3D microstructure fabrication via TPP.

Human-machine interface has been considered as a prominent technology for numerous smart applications due to their direct communication between humans and machines. In particular, wearable electronic skins with a free form factor have received a lot of attention due to their excellent adherence to rough and wrinkled surfaces such as human skin and internal organs. However, most of the e-skins reported to date have some disadvantages in terms of mechanical instability and accumulation of by-products at the interface between the human skin and the device. Here, we report a mechanically stable e-skin via a newly designed pattern named the “eyes.” The ingeniously designed pattern of the eyes allowed mechanical stress and strain to be dissipated more effectively than other previously reported patterns. E-skin permeability of by-product was experimentally confirmed through sweat removal tests, showing superior sweat permeability compared to conventional e-skins. Finally, the real-time monitoring of the body temperature was carried out using our resistive-type thermometer in the e-skin.

This paper presents the development of a flexible temperature sensor array using multi-layer ceramic capacitors. By integrating the capacitors into a 5 × 5 array on a polydimethylsiloxane (PDMS) substrate, we exploit the principle of changing dielectric constant with temperature, which results in a change in capacitance. Our sensor array demonstrates a consistent decrease in capacitance with increasing temperature, with a sensitivity ranging from 1.42 to 1.62 pF/°C. This sensitivity range is maintained even when measurements are taken using a capacitance-to-voltage conversion circuit, with a sensitivity of 1.1 to 1.5 mV/°C. The repeatability and hysteresis of the sensors were also investigated, with the latter revealing a maximum error of 12.7%. Our findings provide valuable insights for the development of efficient, flexible, and reliable temperature sensor arrays using ceramic capacitors.

The stable recovery of gas sensors is an important indicator for evaluating their performance. Hitherto, the use of external light sources and/or an increase in the operating temperature has been effective in improving the recovery rate of gas sensors. Herein, heterojunctions were formed between the two-dimensional transition metal dichalcogenide nanosheets and zero-dimensional ZnO nanoparticles to improve the recovery rate of a NO₂ sensor. Scanning electron microscopy and Raman spectroscopy suggested a successful deposition of ZnO nanoparticles onto the MoS₂ and WSe₂ nanosheets. The sensing response to 10 ppm NO₂ gas at 100 °C indicated that the heterojunction formed by ZnO and MoS₂ or WSe₂ successfully improved the recovery rate of the sensor by 11.87% and 19.44%, respectively, whereas the sensitivity remained constant. The proposed approach contributes to improving the performance of gas sensors.

Photopolymerization of hydrogels films has gained interest in many biomedical and industrial fields. Hydrogel micro-patterns fabricated directly on a device are used as filtering barriers, however, due to weak mechanical properties, these parts require a stable support but deposition of hydrogel in non-polymerized state brings a risk of sinking inside the structure. These limitations can be overcome by applying a hydrophobic surface. This paper presents a novel two-step method, in which a hydrophobic surface was designed and manufactured using mask-projection vat photopolymerization additive manufacturing (VPP). Afterwards, PEGDA-based hydrogel photopolymers were deposited on the surface and a micro-scale patterns were cured. The parts were subjected to water immersion and heating in order to evaluate the swelling and shrinking behaviour of hydrogel. The parts remained stable on the substrate and maintained the properties and the results revealed the shape retention over 97%. This work shows that VPP can be applied in the manufacturing of hydrophobic surfaces for hydrogel photopolymer deposition and curing without sacrificing critical properties.

Graphical Abstract

Perovskites are of significant interest in the field of photocatalysis. To date, many perovskite nanostructures have been developed, and their applications in photocatalysis have been studied. There has been considerable improvement in the research on metal doping in the perovskite structure to improve their optical and structural properties. This mini-review examines the recent progress in the synthesis of lead-free double perovskite nanoparticles and their application in visible-light photocatalysis. Lead-free perovskites are emerging as an eco-friendly solution in energy, electrochemistry, and sensing. Double perovskites are known for their flexible structural, optical, and morphological properties due to their lattice framework having a general form AAʹBBʹO₆. They are more useful for hydrogen evolution due to their higher conduction band potential than simple perovskites. Here, we summarize the current progress and provide insights for the future development of double perovskites toward efficient photodegradation.

Soft robotics enables various applications in certain environments where conventional rigid robotics cannot deliver the same performance due to their form factor and stiffness. Animals use their soft external organs to carry out activities in response to challenging natural environments efficiently. The objective of soft robots is to provide biologically inspired abilities and enable adaptable and flexible interactions with complex objects and surroundings. Recent advances in stimuli-responsive soft robot technology have heavily used polymer-based multifunctional materials. Soft robots with incredibly sophisticated multi-mechanical, electrical, or optical capabilities have demonstrated the ability to modify their shape intelligently in response to external stimuli, such as light, electricity, thermal gradient, and magnetic fields. This short review covers recent advances in scientific techniques for incorporating multifunctional polymeric materials into stimuli-responsive bioinspired soft robots and their applications. We also discuss how biological inspiration and environmental effects can provide a viable viewpoint for bioinspired design in the innovative field of soft robotics. Lastly, we highlight the future outlooks and prospects for soft, stimuli-responsive, bio-inspired robots.

Microneedle electrode (ME) is used to monitor bioelectrical signals by penetrating via the skin, and it compensates for a limitation of surface electrodes. However, existing fabrication of ME have limited in controlling the shape of microneedles, which is directly relevant to the performance and durability of microneedles as an electrode. In this study, a novel method using 3D printing is developed to control needle bevel angles. By controlling the angle of printing direction, needle bevel angles are changed. Various angles of printing direction (0–90°) are investigated to fabricate moldings, and those moldings are used for microneedle fabrications using biocompatible polyimide (PI). The height implementation rate and aspect ratio are also investigated to optimize PI microneedles. The penetration test of the fabricated microneedles is conducted in porcine skin. The PI microneedle of 1000 μm fabricated by the printing angle of 40° showed the bevel angle of 54.5°, which can penetrate the porcine skin. The result demonstrates that this suggested fabrication can be applied using various polymeric materials to optimize microneedle shape.