Recent Progress in Flexible Microstructural Pressure Sensors toward Human-Machine Interaction and Healthcare Applications.

With the rapid growth of artificial intelligence, wearable electronic devices have caught intensive research interest recently. Flexible sensors, as the significant part of them, have become the focus of research. Particularly, flexible microstructural pressure sensors (FMPSs) have attracted extensive attention because of their controllable shape, small size, and high sensitivity. Microstructures are of great significance to improve the sensitivity and response time of FMPSs. The FMPSs present great application prospects in medical health, human-machine interaction, electronic products, and so on. In this review, a series of microstructures (e.g., wave, pillar, and pyramid shapes) which have been elaborately designed to effectively enhance the sensing performance of FMPSs are introduced in detail. Various fabrication strategies of these FMPSs are comprehensively summarized, including template (e.g., silica, anodic aluminum oxide, and bionic patterns), pre-stressing, and magnetic field regulation methods. In addition, the materials (e.g., carbon, polymer, and piezoelectric materials) used to prepare FMPSs are also discussed. Moreover, the potential applications of FMPSs in human-machine interaction and healthcare fields are emphasized as well. Finally, the advantages and latest development of FMPSs are further highlighted, and the challenges and potential prospects of high-performance FMPSs are outlined.

Stretchable, Biocompatible, and Multifunctional Silk Fibroin-Based Hydrogels toward Wearable Strain/Pressure Sensors and Triboelectric Nanogenerators.

Nowadays, great effort has been devoted to establishing wearable electronics with excellent stretchability, high sensitivity, good mechanical strength, and multifunctional characteristics. Herein, a soft conductive hydrogel is rationally designed by proportionally mixing silk fibroin, polyacrylamide, graphene oxide, and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate). The resultant hydrogel has considerable stretchability and compressibility, which enables it to be assembled into a strain/pressure sensor with a wide sensing range (strain, 2%-600%; pressure, 0.5-119.4 kPa) and reliable stability. Then, the corresponding sensor is capable of monitoring a series of physical signals of the human body (e.g., joint movement, facial gesture, pulse, breathing, etc.). In particular, the hydrogel-based sensor is biocompatible, with no anaphylactic reaction on human skin. More interestingly, this conductive hydrogel exhibits a positive response when it works in a triboelectric nanogenerator; consequently, it lights up 20 commericial green light-emitting diodes. Thus, this silk fibroin-based hydrogel is a kind of multifunctional material toward wearable electronics with versatile applications in health and exercise monitors, soft robots, and power sources.

Hierarchical Cu2S nanorods with different crystal phases for asymmetrical supercapacitors and visible-light photocatalysis.

Nanomaterials with hierarchical structures have attracted much attention recently due to their impressive behavior in many fields. Herein, hierarchical Cu2S nanorods with monoclinic and hexagonal phases are first in situ grown on copper sheets by simple hydrothermal methods. The solvent largely influences the feature of Cu2S nanorods during the growth process and the proposed mechanism is elaborately elucidated for these different Cu2S nanorods. Owing to their wheat-like architecture and higher electrical conductivity, the hexagonal Cu2S nanorods exhibit superior electrochemical performance with a specific capacitance of 346 mF cm-2 at 5 mA cm-2 and more than 90% capacitance after 2000 cycles. The solid-state asymmetrical supercapacitors based on the hexagonal Cu2S electrodes have a specific capacitance of 172 mF cm-2 at 5 mA cm-2 and excellent electrochemical stability with ∼90% capacitance after 2000 cycling tests. Moreover, the hierarchical Cu2S nanorods show great photocatalytic ability in the degradation of methylene blue (MB) and rhodamine B (RhB) dyes with the assistance of H2O2 under visible light. This work provides a way to fabricate copper sulfides with hierarchical structures and multi-functions.