Micro and Nano Systems Letters最新文献

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.

In this study, we present a method to quantitatively analyze the thrombus formation process through image analysis in an in vitro thrombus model with a circular cross section. The thrombus model used was designed based on the mechanism between the physical principle of wall shear rate (WSR) and thrombus formation. Image analysis was used to help visualize the thrombus formation process and calculate the thrombus area. Through this method, the thrombus formation and growth from the channel wall was demonstrated without the use of fluorescence. In addition, by dividing the image into sub-sections, the accuracy of the thrombus growth pattern was improved. The departing blood clots which are called embolus, were observed being separated from the thrombus.

Unique self-assembled germanium structures known as Germanium-on-Nothing (GON), which are fabricated via annealing, have buried multiscale cavities with different morphologies. Due to their unique sub-surface morphologies, GON structures are utilized in various applications including optoelectronics, micro-/nanoelectronics, and precision sensors. Each application requires different cavity shapes, and a simulation tool is able to determine the required annealing duration for a given shape. However, a theoretical simulation inevitably requires simplifications which limit its accuracy. Herein, to resolve such dependence on simplification, we introduce a deep learning-based method for simulating the transformation of sub-surface morhpology of GON over annealing. Namely, a deep learning model is trained to predict GON’s morphological transformation from 4 cross-sectional images acquired at different annealing times. Compared to conventional simulation schemes, our proposed deep learning-based simulation method is not only computationally efficient ((sim 10) min) but also physically accurate with its use of empirical data.

Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEMS) for the formation of freestanding (e.g., cantilevers) and fixed (e.g., cavities) microstructures. Wet anisotropic etching is a popular technique to perform silicon micromachining as it is low-cost, scalable, and suitable for large scale batch processing, which are the major factors considered in the industry to reduce the cost of the product. In this work, we report the wet anisotropic etching characteristics of Si{111} in sodium hydroxide (NaOH) without and with addition of hydroxylamine (NH₂OH). 10M NaOH and 12% NH₂OH are used for this study. The effect of NH₂OH is investigated on the etch rate, etched surface roughness and morphology, and the undercutting at mask edges aligned along < 112 > direction. These are the major etching characteristics, which should be studied in a wet anisotropic etchant. A 3D laser scanning microscope is utilized to measure the surface roughness, etch depth, and undercutting length, while the etched surface morphology is examined using a scanning electron microscope (SEM). The incorporation of NH₂OH in NaOH significantly enhances the etch rate and the undercutting at the mask edges that do not consist of {111} planes. To fabricate freestanding structure (e.g., microcantilever) on Si{111} wafer, high undercutting at < 112 > mask edges is desirable to reduce the release time. Moreover, the effect of etchant age on the abovementioned etching characteristics are investigated. The etch rate and undercutting reduce significantly with the age of the modified NaOH. The present paper reports very interesting results for the applications in wet bulk micromachining of Si{111}.

The separation of biological cells or microorganisms in a liquid based on their size by deterministic lateral displacement is widely used in laboratories. The analytical equation for the critical diameter is derived under the assumption that flow between two posts is better described by flow in a rectangular tube than between parallel plates. The height position of the particle is an additional parameter that affects the critical diameter. Preliminary experiments were carried out on the separation of particles in deep and shallow microchannels. This study shows that the critical diameter is not a constant value for a given design but is different on each plane parallel to the top and bottom of the channel. The theoretical model was used to analyze experimental data on the separation of particles larger than 4.2 µm from particles ranging in size from 2.5 to 7.9 µm.

Neural interfaces are fundamental tools for transmitting information from the nervous system. Research on the immune response of an invasive neural interface is a field that requires continuous effort. Various efforts have been made to overcome or minimize limitations through modifying the designs and materials of neural interfaces, modifying surface characteristics, and adding functions to them. In this study, we demonstrate microfluidic channels with crater-shaped structures fabricated using parylene-C membranes for fluid delivery from the perspective of theory, design, and simulation. The simulation results indicated that the fluid flow depended on the size of the outlet and the alignment of microstructures inside the fluidic channel. All the results can be used to support the design of microfluidic channels made by membranes for drug delivery.