Shape Memory Polymers for Body Motion Energy Harvesting and Self‐Powered Mechanosensing

Growing demand in portable electronics raises a requirement to electronic devices being stretchable, deformable, and durable, for which functional polymers are ideal choices of materials. Here, the first transformable smart energy harvester and self‐powered mechanosensation sensor using shape memory polymers is demonstrated. The device is based on the mechanism of a flexible triboelectric nanogenerator using the thermally triggered shape transformation of organic materials for effectively harvesting mechanical energy. This work paves a new direction for functional polymers, especially in the field of mechanosensation for potential applications in areas such as soft robotics, biomedical devices, and wearable electronics.     

Self‐Powered Pulse Sensor for Antidiastole of Cardiovascular Disease

Cardiovascular diseases are the leading cause of death globally; fortunately, 90% of cardiovascular diseases are preventable by long‐term monitoring of physiological signals. Stable, ultralow power consumption, and high‐sensitivity sensors are significant for miniaturized wearable physiological signal monitoring systems. Here, this study proposes a flexible self‐powered ultrasensitive pulse sensor (SUPS) based on triboelectric active sensor with excellent output performance (1.52 V), high peak signal‐noise ratio (45 dB), long‐term performance (10⁷ cycles), and low cost price. Attributed to the crucial features of acquiring easy‐processed pulse waveform, which is consistent with second derivative of signal from conventional pulse sensor, SUPS can be integrated with a bluetooth chip to provide accurate, wireless, and real‐time monitoring of pulse signals of cardiovascular system on a smart phone/PC. Antidiastole of coronary heart disease, atrial septal defect, and atrial fibrillation are made, and the arrhythmia (atrial fibrillation) is indicative diagnosed from health, by characteristic exponent analysis of pulse signals accessed from volunteer patients. This SUPS is expected to be applied in self‐powered, wearable intelligent mobile diagnosis of cardiovascular disease in the future.     

3D Orthogonal Woven Triboelectric Nanogenerator for Effective Biomechanical Energy Harvesting and as Self‐Powered Active Motion Sensors

The development of wearable and large‐area energy‐harvesting textiles has received intensive attention due to their promising applications in next‐generation wearable functional electronics. However, the limited power outputs of conventional textiles have largely hindered their development. Here, in combination with the stainless steel/polyester fiber blended yarn, the polydimethylsiloxane‐coated energy‐harvesting yarn, and nonconductive binding yarn, a high‐power‐output textile triboelectric nanogenerator (TENG) with 3D orthogonal woven structure is developed for effective biomechanical energy harvesting and active motion signal tracking. Based on the advanced 3D structural design, the maximum peak power density of 3D textile can reach 263.36 mW m^?2 under the tapping frequency of 3 Hz, which is several times more than that of conventional 2D textile TENGs. Besides, its collected power is capable of lighting up a warning indicator, sustainably charging a commercial capacitor, and powering a smart watch. The 3D textile TENG can also be used as a self‐powered active motion sensor to constantly monitor the movement signals of human body. Furthermore, a smart dancing blanket is designed to simultaneously convert biomechanical energy and perceive body movement. This work provides a new direction for multifunctional self‐powered textiles with potential applications in wearable electronics, home security, and personalized healthcare.     

Actively Perceiving and Responsive Soft Robots Enabled by Self‐Powered,Highly Extensible,and Highly Sensitive Triboelectric Proximity‐ and Pressure‐Sensing Skins

Robots that can move, feel, and respond like organisms will bring revolutionary impact to today's technologies. Soft robots with organism‐like adaptive bodies have shown great potential in vast robot–human and robot–environment applications. Developing skin‐like sensory devices allows them to naturally sense and interact with environment. Also, it would be better if the capabilities to feel can be active, like real skin. However, challenges in the complicated structures, incompatible moduli, poor stretchability and sensitivity, large driving voltage, and power dissipation hinder applicability of conventional technologies. Here, various actively perceivable and responsive soft robots are enabled by self‐powered active triboelectric robotic skins (tribo‐skins) that simultaneously possess excellent stretchability and excellent sensitivity in the low‐pressure regime. The tribo‐skins can actively sense proximity, contact, and pressure to external stimuli via self‐generating electricity. The driving energy comes from a natural triboelectrification effect involving the cooperation of contact electrification and electrostatic induction. The perfect integration of the tribo‐skins and soft actuators enables soft robots to perform various actively sensing and interactive tasks including actively perceiving their muscle motions, working states, textile's dampness, and even subtle human physiological signals. Moreover, the self‐generating signals can drive optoelectronic devices for visual communication and be processed for diverse sophisticated uses.     

High‐Performance Al/PDMS TENG with Novel Complex Morphology of Two‐Height Microneedles Array for High‐Sensitivity Force‐Sensor and Self‐Powered Application

Triboelectric nanogenerators (TENGs) are widely applied to self‐powered devices and force sensors. TENGs consist of the electrode‐layer frequently made of high‐cost conductors (Ag, Au, ITO) and the tribo‐layer of rigid negative‐triboelectricity fluoropolymers (PTFE, FEP). The surface morpholoy is studied for enhancing performance. Here, a high‐performance Al/PDMS‐TENG is proposed with a complex morphology of overlapped deep two‐height microneedles (OL‐DTH‐MN) fabricated by the integrated process of low‐cost CO₂ laser ablation and PDMS casting for self‐powered devices and high‐sensitivity force/pressure sensors. The high open‐circuit voltage and short‐circuit current of the OL‐DTH‐MN‐TENG are 167 V and 129.3 µA. Also, the sensitivity of the force/pressure sensor of the OL‐DTH‐MN‐TENG is very high, 1.03 V N^?1 and about 3.11 V kPa^?1, at an area of 30 cm² that is much higher than the sensitivity of about 0.18–0.414 V N^?1 and 0.013–0.29 V kPa^?1 of conventional TENG sensors. Meanwhile, the high‐performance OL‐DTH‐MN‐TENG not only exhibits the energy storage capability of charging a 0.1 µF capacitor to 2.75 V at 1.19 s, to maximum 3.22 V, but also activates various self‐powered devices including lighting colorful 226 LEDs connected in series, the “2020‐ME‐NCKU” advertising board, a calculator and a temperature sensor. Numerical simulation is also performed to support the experiments.     

Vitrimer Elastomer‐Based Jigsaw Puzzle‐Like Healable Triboelectric Nanogenerator for Self‐Powered Wearable Electronics

Functional polymers possess outstanding uniqueness in fabricating intelligent devices such as sensors and actuators, but they are rarely used for converting mechanical energy into electric power. Here, a vitrimer based triboelectric nanogenerator (VTENG) is developed by embedding a layer of silver nanowire percolation network in a dynamic disulfide bond‐based vitrimer elastomer. In virtue of covalent dynamic disulfide bonds in the elastomer matrix, a thermal stimulus enables in situ healing if broken, on demand reconfiguration of shape, and assembly of more sophisticated structures of VTENG devices. On rupture or external damage, the structural integrity and conductivity of VTENG are restored under rapid thermal stimulus. The flexible and stretchable VTENG can be scaled up akin to jigsaw puzzles and transformed from 2D to 3D structures. It is demonstrated that this self‐healable and shape‐adaptive VTENG can be utilized for mechanical energy harvesters and self‐powered tactile/pressure sensors with extended lifetime and excellent design flexibility. These results show that the incorporation of organic materials into electronic devices can not only bestow functional properties but also provide new routes for flexible device fabrication.     

Self‐Powered Wearable Electronics Based on Moisture Enabled Electricity Generation

Most state‐of‐the‐art electronic wearable sensors are powered by batteries that require regular charging and eventual replacement, which would cause environmental issues and complex management problems. Here, a device concept is reported that can break this paradigm in ambient moisture monitoring—a new class of simple sensors themselves can generate moisture‐dependent voltage that can be used to determine the ambient humidity level directly. It is demonstrated that a moisture‐driven electrical generator, based on the diffusive flow of water in titanium dioxide (TiO₂) nanowire networks, can yield an output power density of up to 4 µW cm^?2 when exposed to a highly moist environment. This performance is two orders of magnitude better than that reported for carbon‐black generators. The output voltage is strongly dependent on humidity of ambient environment. As a big breakthrough, this new type of device is successfully used as self‐powered wearable human‐breathing monitors and touch pads, which is not achievable by any existing moisture‐induced‐electricity technology. The availability of high‐output self‐powered electrical generators will facilitate the design and application of a wide range of new innovative flexible electronic devices.     

Toward Wearable Self‐Charging Power Systems: The Integration of Energy‐Harvesting and Storage Devices

One major challenge for wearable electronics is that the state‐of‐the‐art batteries are inadequate to provide sufficient energy for long‐term operations, leading to inconvenient battery replacement or frequent recharging. Other than the pursuit of high energy density of secondary batteries, an alternative approach recently drawing intensive attention from the research community, is to integrate energy‐generation and energy‐storage devices into self‐charging power systems (SCPSs), so that the scavenged energy can be simultaneously stored for sustainable power supply. This paper reviews recent developments in SCPSs with the integration of various energy‐harvesting devices (including piezoelectric nanogenerators, triboelectric nanogenerators, solar cells, and thermoelectric nanogenerators) and energy‐storage devices, such as batteries and supercapacitors. SCPSs with multiple energy‐harvesting devices are also included. Emphasis is placed on integrated flexible or wearable SCPSs. Remaining challenges and perspectives are also examined to suggest how to bring the appealing SCPSs into practical applications in the near future.     

Self‐Powered Intracellular Drug Delivery by a Biomechanical Energy‐Driven Triboelectric Nanogenerator

Nondestructive, high‐efficiency, and on‐demand intracellular drug/biomacromolecule delivery for therapeutic purposes remains a great challenge. Herein, a biomechanical‐energy‐powered triboelectric nanogenerator (TENG)‐driven electroporation system is developed for intracellular drug delivery with high efficiency and minimal cell damage in vitro and in vivo. In the integrated system, a self‐powered TENG as a stable voltage pulse source triggers the increase of plasma membrane potential and membrane permeability. Cooperatively, the silicon nanoneedle‐array electrode minimizes cellular damage during electroporation via enhancing the localized electrical field at the nanoneedle–cell interface and also decreases plasma membrane fluidity for the enhancement of molecular influx. The integrated system achieves efficient delivery of exogenous materials (small molecules, macromolecules, and siRNA) into different types of cells, including hard‐to‐transfect primary cells, with delivery efficiency up to 90% and cell viability over 94%. Through simple finger friction or hand slapping of the wearable TENGs, it successfully realizes a transdermal biomolecule delivery with an over threefold depth enhancement in mice. This integrated and self‐powered system for active electroporation drug delivery shows great prospect for self‐tuning drug delivery and wearable medicine.     

Conjuncted Pyro‐Piezoelectric Effect for Self‐Powered Simultaneous Temperature and Pressure Sensing

Ferroelectric materials use both the pyroelectric effect and piezoelectric effect for energy conversion. A ferroelectric BaTiO₃‐based pyro‐piezoelectric sensor system is demonstrated to detect temperature and pressure simultaneously. The voltage signal of the device is found to enhance with increasing temperature difference with a sensitivity of about 0.048 V °C^?1 and with applied pressure with a sensitivity of about 0.044 V kPa^?1. Moreover, no interference appears in the output voltage signals when piezoelectricity and pyroelectricity are conjuncted in the device. A novel 4 × 4 array sensor system is developed to sense real‐time temperature and pressure variations induced by a finger. This system has potential applications in machine intelligence and man–machine interaction.     

Photovoltaic–Pyroelectric Coupled Effect Induced Electricity for Self‐Powered Photodetector System

Ferroelectric materials have demonstrated novel photovoltaic effect to scavenge solar energy. However, most of the ferroelectric materials with wide bandgaps (2.7–4 eV) suffer from low power conversion efficiency of less than 0.5% due to absorbing only 8–20% of solar spectrum. Instead of harvesting solar energy, these ferroelectric materials can be well suited for photodetector applications, especially for sensing near‐UV irradiations. Here, a ferroelectric BaTiO₃ film‐based photodetector is demonstrated that can be operated without using any external power source and a fast sensing of 405 nm light illumination is enabled. As compared with photovoltaic effect, both the responsivity and the specific detectivity of the photodetector can be dramatically enhanced by larger than 260% due to the light‐induced photovoltaic–pyroelectric coupled effect. A self‐powered photodetector array system can be utilized to achieve spatially resolved light intensity detection by recording the output voltage signals as a mapping figure.     

A Shape‐Adaptive Thin‐Film‐Based Approach for 50% High‐Efficiency Energy Generation Through Micro‐Grating Sliding Electrification

Effectively harvesting ambient mechanical energy is the key for realizing self‐powered and autonomous electronics, which addresses limitations of batteries and thus has tremendous applications in sensor networks, wireless devices, and wearable/implantable electronics, etc. Here, a thin‐film‐based micro‐grating triboelectric nanogenerator (MG‐TENG) is developed for high‐efficiency power generation through conversion of mechanical energy. The shape‐adaptive MG‐TENG relies on sliding electrification between complementary micro‐sized arrays of linear grating, which offers a unique and straightforward solution in harnessing energy from relative sliding motion between surfaces. Operating at a sliding velocity of 10 m/s, a MG‐TENG of 60 cm² in overall area, 0.2 cm³ in volume and 0.6 g in weight can deliver an average output power of 3 W (power density of 50 mW cm^?2 and 15 W cm^?3) at an overall conversion efficiency of ～50%, making it a sufficient power supply to regular electronics, such as light bulbs. The scalable and cost‐effective MG‐TENG is practically applicable in not only harvesting various mechanical motions but also possibly power generation at a large scale.     

High‐Performance Piezoelectric Nanogenerators with Imprinted P(VDF‐TrFE)/BaTiO3 Nanocomposite Micropillars for Self‐Powered Flexible Sensors

Piezoelectric nanogenerators with large output, high sensitivity, and good flexibility have attracted extensive interest in wearable electronics and personal healthcare. In this paper, the authors propose a high‐performance flexible piezoelectric nanogenerator based on piezoelectrically enhanced nanocomposite micropillar array of polyvinylidene fluoride‐trifluoroethylene (P(VDF‐TrFE))/barium titanate (BaTiO₃) for energy harvesting and highly sensitive self‐powered sensing. By a reliable and scalable nanoimprinting process, the piezoelectrically enhanced vertically aligned P(VDF‐TrFE)/BaTiO₃ nanocomposite micropillar arrays are fabricated. The piezoelectric device exhibits enhanced voltage of 13.2 V and a current density of 0.33 µA cm^?2, which an enhancement by a factor of 7.3 relatives to the pristine P(VDF‐TrFE) bulk film. The mechanisms of high performance are mainly attributed to the enhanced piezoelectricity of the P(VDF‐TrFE)/BaTiO₃ nanocomposite materials and the improved mechanical flexibility of the micropillar array. Under mechanical impact, stable electricity is stably generated from the nanogenerator and used to drive various electronic devices to work continuously, implying its significance in the field of consumer electronic devices. Furthermore, it can be applied as self‐powered flexible sensor work in a noncontact mode for detecting air pressure and wearable sensors for detecting some human vital signs including different modes of breath and heartbeat pulse, which shows its potential applications in flexible electronics and medical sciences.