Stretchable multifunctional sensor based on porous silver nanowire/silicone rubber conductive film

As one of the promising human–machine interfaces,wearable sensors play an important role in modern society,which advances the development of wearable fields,especially in the promising applications of electronic skin(e-skin),robotics,prosthetics,healthcare.In the last decades,wearable sensors tend to be capable of attractive capabilities such as miniaturization,multifunction,smart integration,wearable properties such as lightweight,flexibility,stretchability,conformability for wider applications.In this work,we developed a stretchable multifunctional sensor based on porous silver nanowire/silicone rubber conductive film(P-AgNW/SR).Its unique structural configuration,i.e.,an assembly of the P-AgNW/SR with good conductivity,stability,resistance response,the insulated silicone rubber layer,provided the feasibility for realizing multiple sensing capabilities.Specifically,porous microstructures of the P-AgNW/SR made the device to be used for pressure sensing,exhibiting outstanding dynamic and static resistive responsive behaviors and having a maximum sensitivity of 9.062%∙N^(−1) in a continuous compressive force range of~16 N.With the merit of the good piezoresistive property of AgNW/SR networks embedded into the surface of micropores of the P-AgNW/SR,the device was verified to be a temperature sensor for detecting temperature changes in the human body and environment.The temperature sensor had good sensitivity of 0.844%∙℃^(−1),high linearity of 0.999 in the range of 25–125℃,remarkable dynamic stability.Besides,the developed sensor was demonstrated to be a single electrode-triboelectric sensor for active sensing,owing to the unique assembly of the conductive PAgNW/SR electrode and the silicone rubber friction layer.Based on the coupling effect of the triboelectrification and electrostatic induction,the generated electrical signals could be used to sense the human motions,according to the quantitative correlation between the human motions and the features in amplitude and waveform of the output signals.Thus,the developed stretchable sensor successfully achieved the integration of two types of passive sensing capabilities,i.e.,pressure and temperature sensing,and one type of active sensing capability,i.e.,triboelectric sensing,demonstrating the feasibility of monitoring multiple variables of the human body and environment.

Recent progress in silk fibroin-based flexible electronics

With the rapid development of the Internet of Things(loT)and the emergence of 5G,traditional silicon-based electronics no Ion ger fully meet market dema nds such as nonplanar application scenarios due to mechanical mismatch.This provides unprecedented opportunities for flexible electronics that bypass the physical rigidity through the introduction of flexible materials.In recent decades,biological materials with outstanding biocompatibility and biodegradability,which are considered some of the most promising candidates for next-generation flexible electronics,have received increasing attention,e.g.,silk fibroin,cellulose,pectin,chitosan,and melanin.Among them,silk fibroin presents greater superiorities in biocompatibility and biodegradability,and moreover,it also possesses a variety of attractive properties,such as adjustable water solubility,remarkable optical transmittance,high mechanical robustness,light weight,and ease of processing,which are partially or even completely lacking in other biological materials.Therefore,silk fibroin has been widely used as fundamental components for the construction of biocompatible flexible electronics,particularly for wearable and implantable devices.Furthermore,in recent years,more attention has been paid to the investigation of the functional characteristics of silk fibroin;such as the dielectric properties,piezoelectric properties,strong ability to lose electrons,and sensitivity to environmental variables.Here,this paper not only reviews the preparation technologies for various forms of silk fibroin and the recent progress in the use of silk fibroin as a fundamental material but also focuses on the recent advaneed works in which silk fibroin serves as functional components.Additi on ally,the challenges and future development of silk fibroin-based flexible electronics are summarized.