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On‐skin electronics can be conformably deployed on body for health monitoring, assisted living, and human/computer interfaces. However, developing corresponding energy devices is a critical challenge. Herein, a permeable and stretchable multifunctional liquid‐metal electronic skin that can generate electricity by recovering ambient electromagnetic pollution (from surrounding electrical appliances) and biomechanical energy (from body movements) is presented for epidermal energy and self‐powered sensing applications. To the best of the authors' knowledge, this is the first demonstration that a breathable on‐skin device can convert ambient electromagnetic pollution into useful electricity. The device is constructed using two stretchable microfibrous films sandwiching self‐organized mesh‐like and wrinkled liquid‐metal that affords electricity via induced electrification (±9.3 V, ±1.7 µA; 60 Hz) and triboelectricity (205.6 V, ±2.3 µA; 4 Hz). Its applicability in powering electronic devices is demonstrated. Moreover, it can serve as an epidermal self‐powered sensor for continuously monitoring whole‐body physiological signals and motions of the eyelids, face, throat, chest, and limbs, thus demonstrating its potential to remotely collect clinical and biomechanical information. Finally, it is used as an interface in diverse system‐level applications. These results shed light on new directions in on‐skin energy and sensing, enabling to usher electronics toward untethered and diversified applications. [ABSTRACT FROM AUTHOR]

Electronic skin (e‐skin) is facing new challenges owing to the development of artificial intelligence. Among the existing working modes, triboelectric‐based e‐skin (TES) can convert mechanical energy into electrical energy and can be used as a sensor to directly output an electrical signal without additional power supply. Therefore, with the advantages of self‐powering, low cost, and wide application of materials, TES provides a new concept for developing e‐skin and has been extensively studied. Starting from TES, this review describes the working principle and application of triboelectric nanogenerators (TENGs) in e‐skin. Existing materials for TES can be mainly divided into fiber textiles, gels, liquid‐based materials, and degradable materials. Therefore, the material section is divided into four chapters to describe the properties of each material. As for the structure of TES, the transition from single‐channel to multi‐channel for the multifunctionalization of TES is described, and the various links required for a TES‐based closed‐loop system are introduced. Based on these advanced units, the recent progress as well as the current challenges and future development prospects of TES are reviewed. [ABSTRACT FROM AUTHOR]

The simultaneous achievement of multiple functional attributes, such as flexibility, stretchability, transparency, comfortability, biodegradability, and self‐powered ability into electronic skins (e‐skins) is vital to their long‐term practical applications. Due to the internal contradiction between functional material combination and simple structural design, this kind of multifunctional e‐skin has rarely been fabricated or even reported. To this end, chitosan (CS), a natural material with remarkable biocompatibility, biodegradability, and electron‐donating ability, is integrated with a single‐mode triboelectric nanogenerator (TENG) to develop a multifunctional e‐skin, which includes sweat permeability, controllable biodegradability, high transparency, and self‐powered sensing ability. In addition, a facile, efficient, and large‐scale fabrication strategy is proposed to construct stretchable, ultrathin, transparent, and shape‐adaptable gold nanofibers (Au NFs) electrodes. Furthermore, the e‐skin can achieve a voltage response pressure sensitivity of 0.012 kPa−1 in the pressure range of 0–70 kPa and a fast response time of 70 ms. Finally, it shows controllable and excellent degradability in various solutions. It is believed that the proposed e‐skin based on the design and integration of CS and Au NFs will provide a paradigm shift for the next‐generation self‐powered transient electronics. [ABSTRACT FROM AUTHOR]

Energy‐harvesting electronic skin (E‐skin) is highly promising for sustainable and self‐powered interactive systems, wearable human health monitors, and intelligent robotics. Flexible/stretchable electrodes and robust energy‐harvesting components are critical in constructing soft, wearable, and energy‐autonomous E‐skin systems. A stretchable energy‐harvesting tactile interactive interface is demonstrated using liquid metal nanoparticles (LM‐NPs)‐based electrodes. This stretchable energy‐harvesting tactile interface relies on triboelectric nanogenerator composed of a galinstan LM‐NP‐based stretchable electrode and patterned elastic polymer friction and encapsulation layer. It provides stable and high open‐circuit voltage (268 V), short‐circuit current (12.06 µA), and transferred charges (103.59 nC), which are sufficient to drive commercial portable electronics. As a self‐powered tactile sensor, it presents satisfactory and repeatable sensitivity of 2.52 V·kPa−1 and is capable of working as a touch interactive keyboard. The demonstrated stretchable and robust energy‐harvesting E‐skin using LM‐NP‐based electrodes is of great significance in sustainable human–machine interactive system, intelligent robotic skin, security tactile switches, etc. [ABSTRACT FROM AUTHOR]

Self-powered flexible sensors play an increasingly important role in wearable and even implantable electronic devices. Silk protein is an ideal material for flexible sensors because of its terrific biocompatibility and controllable degradation rate. Here, we overcome the problem of mechanical flexibility and poor electrical conductivity of proteins, and develop a highly transparent, biocompatible, full-degradable and flexible triboelectric nanogenerator (Bio-TENG) for energy harvesting and wireless sensing. First, the mechanical flexibility of the silk protein film is greatly enhanced by the mesoscopic functionalization of regenerated silk fibroin (RSF) via adding glycerol and polyurethane (PU). Second, hollow silver nanofibers are constructed on the silk film to form an air-permeable, stretchable, biocompatible and degradable thin layer and utilized as friction electrode. The obtained Bio-TENG demonstrates high transparency (83% by one Ag gird layer), stretchability (Ɛ = 520%) and an instantaneous peak power density of 0.8 W m−2 that can drive wearable electronics. Besides, the Bio-TENG can work as artificial electronic skin for touch/pressure perception, and also for wirelessly controlling Internet of Things as a switch. • Conductive and ultrastretchable (520%) silk protein film was prepared. • Hollow silver nanofibers were constructed on silk film to enhance conductivity. • Bio-TENG was air permeable, biocompatible, stretchable and degradable. • Bio-TENG was applied for energy harvesting and wirelessly controlling Internet of Things. [ABSTRACT FROM AUTHOR]