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

Abstract

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.

Bio‐Derived Natural Materials Based Triboelectric Devices for Self‐Powered Ubiquitous Wearable and Implantable Intelligent Devices

“…[25,27,45,46] The triboelectrification phenomena can occur in almost all types of materials, e.g., polymers, ceramics, and metals, and at different interfaces, e.g., solid-solid, solidliquid, and liquid-liquid. [47][48][49][50][51] The structure of TENG consists of conducting electrodes, [34,[52][53][54] (e.g., metals, conductive gel etc.) and two triboelectric layers that have different electronegativities.…”

“…Recently, natural materials derived hydrogels have also gained increased interest in being used in multifunctional wearable TENG devices. [53,54,66,229] For instance, Guan et al [66] developed a highly deformable selfhealing soft TENG made from poly(vinyl alcohol)/agarose hydrogel. The incorporation of multiwalled carbon nanotubes and photothermally active polydopamine particles enables the self-healing capability of this TENG when being exposed to near-infrared light for a short period (e.g., 1 min).…”

“…[8,59,78,79] Real-time monitoring of human body activities and vital signs are of great significance for health diagnostics and treatment. [32,54,57,89,106,297,317,318] He et al presented a selfpowered breathing monitoring system using a cellulose fiberbased triboelectric nanogenerator (cf-TENG), [89] which was realized by developing CNFs on cellulose microfibers (CMFs) skeleton to fabricate a 2D hierarchical nanostructure hybridized with silver nanofibers membranes (Figure 5a). The human's breathing can be monitored in real-time by this cf-TENG.…”

“…Fish gelatin-based devices can be used as a self-powered sensor for monitoring physiological signals, such as respiration, joint movement, and finger touch (Figure 5d). He et al reported a wearable and biocompatible strain/pressure sensor based on silk fibroin hydrogels [54] (Figure 5e). The strain/pressure sensor has a wide sensing range (pressure: 0.5−119.4 kPa; strain: 2−600%), which can be used for monitoring human physical signals, e.g., breathing, pulse, facial gesture etc.…”

“…Reproduced with permission. [54] Copyright 2020, American Chemical Society. f) Silk based strain sensors.…”