Recent Progress on Flexible Self-Powered Tactile Sensing Platforms for Health Monitoring and Robotics.

Over the past decades, tactile sensing technology has made significant advances in the fields of health monitoring and robotics. Compared to conventional sensors, self-powered tactile sensors do not require an external power source to drive, which makes the entire system more flexible and lightweight. Therefore, they are excellent candidates for mimicking the tactile perception functions for wearable health monitoring and ideal electronic skin (e-skin) for intelligent robots. Herein, the working principles, materials, and device fabrication strategies of various self-powered tactile sensing platforms are introduced first. Then their applications in health monitoring and robotics are presented. Finally, the future prospects of self-powered tactile sensing systems are discussed.

Highly Stretchable, Knittable, Wearable Fiberform Hydrovoltaic Generators Driven by Water Transpiration for Portable Self-Power Supply and Self-Powered Strain Sensor.

The development of excellently stretchable, highly mobile, and sustainable power supplies is of great importance for self-power wearable electronics. Transpiration-driven hydrovoltaic power generator (HPG) has been demonstrated to be a promising energy harvesting strategy with the advantages of negative heat and zero-carbon emissions. Herein, this work demonstrates a fiber-based stretchable HPG with the advantages of high output, portability, knittability, and sustainable power generation. Based on the functionalized micro-nano water diffusion channels constructed by the discarded mask straps (MSs) and oxidation-treated carbon nanomaterials, the applied water can continuously produce electricity during the spontaneous flow and diffusion. Experimentally, when a tiny 0.1 mL of water encounters one end of the proposed HPG, the centimeter-length device can yield a peak voltage of 0.43 V, peak current of 29.5 µA, and energy density of 5.833 mW h cm-3. By efficiently integrating multiple power generation units, sufficient output power can be provided to drive commercial electronic devices even in the stretched state. Furthermore, due to the reversibility of the electrical output during dynamic stretching-releasing, it can passively convert physiological activities and motion behaviors into quantifiable and processable current signals, opening up HPG's application in the field of self-powered wearable sensing.

Multi-Attribute Triboelectric Materials and Innovative Applications Via TENGs.

Triboelectric nanogenerators (TENGs) as an avant-garde technology that transforms mechanical energy into electrical energy, offering a new direction for green energy and sustainable development. By means of high-efficiency TENGs, conventional materials as new triboelectric materials have exhibited multi-attribute characteristics, achieving innovative applications in the field of micro-nano energy harvesting and self-powered sensing. The progress of TENGs technology with the triboelectric materials is complementary and mutually promoting. On the one hand, one of the cruxes of TENGs lies in the triboelectric materials, which have a decisive impact on their performance. On the other hand, as the research and application of TENGs continue to deepen, higher demands are placed on triboelectric materials, which in turn promotes the advancement of the entire material system as well as the fields of materials science and physics. This work aims to delve into the characteristics, types, preferred choices, and modification treatments of triboelectric materials on the performances of TENGs, hoping to provide guidance and insights for future research and applications.

Comprehensive Insights on MXene-Based TENGs: from Structures, Functions to Applications.

The rapid advancement of triboelectric nanogenerators (TENGs) has introduced a transformative approach to energy harvesting and self-powered sensing in recent years. Nonetheless, the untapped potential of TENGs in practical scenarios necessitates multiple strategies like material selections and structure designs to enhance their output performance. Given the various superior properties, MXenes, a kind of novel 2D materials, have demonstrated great promise in enhancing TENG functionality. Here, this review comprehensively delineates the advantages of incorporating MXenes into TENGs, majoring in six pivotal aspects. First, an overview of TENGs is provided, stating their theoretical foundations, working modes, material considerations, and prevailing challenges. Additionally, the structural characteristics, fabrication methodologies, and family of MXenes, charting their developmental trajectory are highlighted. The selection of MXenes as various functional layers (negative and positive triboelectric layer, electrode layer) while designing TENGs is briefed. Furthermore, the distinctive advantages of MXene-based TENGs and their applications are emphasized. Last, the existing challenges are highlighted, and the future developing directions of MXene-based TENGs are forecasted.

Efficiently Fabricated Core-Sheath Piezoelectric Sensor Based on PVDF Microfibrillar Bundle.

With the rapid development of information technology (e.g., Internet of Things (IoT) and artificial intelligence (AI)), piezoelectric sensor (i.e., piezoelectric nanogenerator, PENG) receives an increasing number attention in the field of self-powered wearable devices. Taking piezoelectric fiber as an example, it shows promising application for wearable devices owing to its light weight and high flexibility compared with block electronic devices. However, it still remains a challenge to fabricate low-cost and high-performance piezoelectric fiber via a large-scale but efficient method. In this study, via extrusion molding and leaching, a core-sheath piezoelectric sensor is facilely fabricated, whose core and sheath layer are respectively slender steel wire (i.e., electrode) and PVDF microfibrillar bundle (PMB) (i.e., piezoelectric layer). Such piezoelectric sensor shows decent output performance in both pressing (12.3 V) and bending (0.32 V) mode. Meanwhile, it possesses sensitive stress responsiveness when serving for self-powered sensing. Furthermore, such piezoelectric sensors can realize wearable signal transmission and human motion monitoring, showing promising potential for wearable devices in the future. This work proposes a large-scale but efficient method for fabricating high-performance PVDF microfibril based piezoelectric fiber, opening a new pathway to develop self-powered sensors following the concept of polymer "structuring" processing.

From Body Monitoring to Biomolecular Sensing: Current Progress and Future Perspectives of Triboelectric Nanogenerators in Point-of-Care Diagnostics.

In the constantly evolving field of medical diagnostics, triboelectric nanogenerators (TENGs) stand out as a groundbreaking innovation for simultaneously harnessing mechanical energy from micromovements and sensing stimuli from both the human body and the ambient environment. This advancement diminishes the dependence of biosensors on external power sources and paves the way for the application of TENGs in self-powered medical devices, especially in the realm of point-of-care diagnostics. In this review, we delve into the functionality of TENGs in point-of-care diagnostics. First, from the basic principle of how TENGs effectively transform subtle physical movements into electrical energy, thereby promoting the development of self-powered biosensors and medical devices that are particularly advantageous for real-time biological monitoring. Then, the adaptable design of TENGs that facilitate customization to meet individual patient needs is introduced, with a focus on their biocompatibility and safety in medical applications. Our in-depth analysis also covers TENG-based biosensor designs moving toward exceptional sensitivity and specificity in biomarker detection, for accurate and efficient diagnoses. Challenges and future prospects such as the integration of TENGs into wearable and implantable devices are also discussed. We aim for this review to illuminate the burgeoning field of TENG-based intelligent devices for continuous, real-time health monitoring; and to inspire further innovation in this captivating area of research that is in line with patient-centered healthcare.

Versatile Electronic Textile Enabled by a Mixed-Dimensional Assembly Strategy.

Electronic textiles (e-textiles) hold great promise for serving as next-generation wearable electronics owing to their inherent flexible, air-permeable, and lightweight characteristics. However, these e-textiles are of limited performance mainly because of lacking powerful materials combination. Herein, a versatile e-textile through a simple, high-efficiency mixed-dimensional assembly of 2D MXene nanosheets and 1D silver nanowires (AgNWs) are presented. The effective complementary actions of MXene and AgNWs endow the e-textiles with superior integrated performances including self-powered pressure sensing, ultrafast joule heating, and highly efficient electromagnetic interference (EMI) shielding. The textile-based self-powered smart sensor systems obtained through the screen-printed assembly of MXene-based supercapacitor and pressure sensor are flexible and lightweight, showing ultrahigh specific capacitance (2390 mF cm-2 ), robust areal energy density (119.5 µWh cm-2 ), excellent sensitivity (474.8 kPa-1 ), and low detection limit (1 Pa). Furthermore, the interconnected conductive MXene/AgNWs network enables the e-textile with ultrafast temperature response (10.4 °C s-1 ) and outstanding EMI shielding effectiveness of ≈66.4 dB. Therefore, the proposed mixed-dimensional assembly design creates a multifunctional e-textile that offers a practical paradigm for next-generation smart flexible electronics.

Surface Wettability for Skin-Interfaced Sensors and Devices.

The practical applications of skin-interfaced sensors and devices in daily life hinge on the rational design of surface wettability to maintain device integrity and achieve improved sensing performance under complex hydrated conditions. Various bio-inspired strategies have been implemented to engineer desired surface wettability for varying hydrated conditions. Although the bodily fluids can negatively affect the device performance, they also provide a rich reservoir of health-relevant information and sustained energy for next-generation stretchable self-powered devices. As a result, the design and manipulation of the surface wettability are critical to effectively control the liquid behavior on the device surface for enhanced performance. The sensors and devices with engineered surface wettability can collect and analyze health biomarkers while being minimally affected by bodily fluids or ambient humid environments. The energy harvesters also benefit from surface wettability design to achieve enhanced performance for powering on-body electronics. In this review, we first summarize the commonly used approaches to tune the surface wettability for target applications toward stretchable self-powered devices. By considering the existing challenges, we also discuss the opportunities as a small fraction of potential future developments, which can lead to a new class of skin-interfaced devices for use in digital health and personalized medicine.

Spheres Multiple Physical Network-Based Triboelectric Materials for Self-Powered Contactless Sensing.

Non-contact mode triboelectric nanogenerators effectively avoid physical contact between two triboelectric materials and achieve long-term reliable operation, providing broad application prospects in the field of self-powered sensing. However, the low surface charge density of triboelectric materials restricts application of contactless sensing. Herein, by controlling Rayleigh Instability deformation of the spinning jet and vapor-induced phase separation during electrostatic spinning, a polyvinylidene fluoride@Mxene (Ti3 C2 Tx ) composite film with spheres multiple physical network structures is prepared and utilized as the triboelectric material of a self-powered contactless sensor. The structure of the composite film and high conductivity of Ti3 C2 Tx provide triboelectric materials with high output performance (charge output and power output up to 128 µC m-2 and 200 µW cm-2 at 2 Hz) and high output stability. The self-powered contactless sensor shows excellent speed sensitivity (1.175 Vs m-1 ). Additionally, it could accurately identify the motion states such as running (55 mV), jumping (105 mV), and walking (40 mV) within the range of 70 cm, and present the signals in different pop forms. This work lays a solid foundation for the development and application of high-performance triboelectric materials, and has guiding significance for the research of self-powered contactless sensing.

Toward a New Era of Sustainable Energy: Advanced Triboelectric Nanogenerator for Harvesting High Entropy Energy.

Widely distributed across the environment, irregular micro-nano mechanical high entropy energy (HEE) is a new promising recoverable energy, in which the development of matched harvesting technology is imperative to fit in with the requirements of booming sustainable energy in the new era. The triboelectric nanogenerator (TENG) is a very efficient technology for harvesting micro-nano HEE, especially when converting irregular, low-frequency, weak mechanical energy into electricity. Here, the latest advancements are comprehensively reviewed in using TENGs for sustainable energy, sensing, and other applications. The fundamental theory and overwhelming superiority of TENG is systematically analyzed as a sustainable energy with four representative domains: micro-nano distributed power sources, self-powered sensing systems, direct high-voltage power sources, and large-scale blue energy. The review is concluded with a discussion of the challenges of leveraging TENGs for sustainable energy engineering. The striving directions of TENG technologies are proposed with a concentration on basic research and commercialization for the new ear of 5G and Internet of Things.

Ambient Humidity-Induced Phase Separation for Fiber Morphology Engineering toward Piezoelectric Self-Powered Sensing.

Electrospun polymeric piezoelectric fibers have a considerable potential for shape-adaptive mechanical energy harvesting and self-powered sensing in biomedical, wearable, and industrial applications. However, their unsatisfactory piezoelectric performance remains an issue to be overcome. While strategies for increasing the crystallinity of electroactive ß phases have thus far been the major focus in realizing enhanced piezoelectric performance, tailoring the fiber morphology can also be a promising alternative. Herein, a design strategy that combines the nonsolvent-induced phase separation of a polymer/solvent/water ternary system and electrospinning for fabricating piezoelectric poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE) fibers with surface porosity under ambient humidity is presented. Notably, electrospun P(VDF-TrFE) fibers with higher surface porosity outperform their smooth-surfaced counterparts with a higher ß phase content in terms of output voltage and power generation. Theoretical and numerical studies also underpin the contribution of the structural porosity to the harvesting performance, which is attributable to local stress concentration and reduced dielectric constant due to the air in the pores. This porous fiber design can broaden the application prospects of shape-adaptive energy harvesting and self-powered sensing based on piezoelectric polymer fibers with enhanced voltage and power performance, as successfully demonstrated in this work by developing a communication system based on self-powered motion sensing.

Classification and utilization of waste electronic components based on triboelectric nanogenerator.

The rapid development of the internet of things is accompanied by a large number of equipment deployment. When the equipment fails or reaches its service life, tons of e-waste will be generated. Therefore, there is an urgent need to find environmentally friendly and effective ways to recycle and treat e-waste. In this paper, a method of classification detection and resource utilization of waste electronic components based on the triboelectric nanogenerator (TENG) is proposed, which provides a novel idea for electronic waste treatment. We studied the output voltage characteristics of different kinds of TENG based on waste electronic components subject to different environmental loadings. The output characteristics of TENG are explored, reflecting the e-waste categories and processing environment. TENG is also connected with hundreds of light-emitting diodes (LEDs) through rectifier bridge circuit, and the output performance of TENG is characterized by the number and intensity of LEDs.

A Tubular Flexible Triboelectric Nanogenerator with a Superhydrophobic Surface for Human Motion Detecting.

The triboelectric nanogenerator (TENG) is a newly arisen technology for mechanical energy harvesting from the environment, such as raindrops, wind, tides, and so on. It has attracted widespread attention in flexible electronics to serve as self-powered sensors and energy-harvesting devices because of its flexibility, durability, adaptability, and multi-functionalities. In this work, we fabricated a tubular flexible triboelectric nanogenerator (TF-TENG) with energy harvesting and human motion monitoring capabilities by employing polydimethylsiloxane (PDMS) as construction material, and fluorinated ethylene propylene (FEP) films coated with Cu as the triboelectric layer and electrode, serving in a free-standing mode. The tube structure has excellent stretchability that can be stretched up to 400%. Modifying the FEP films to obtain a superhydrophobic surface, the output performance of TF-TENG was increased by at least 100% compared to an untreated one. Finally, as the output of TF-TENG is sensitive to swing angle and frequency, demonstration of real-time monitoring of human motion state was realized when a TF-TENG was worn on the wrist.

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.

Zero-Biased Bionic Fingertip E-Skin with Multimodal Tactile Perception and Artificial Intelligence for Augmented Touch Awareness.

Electronic skins (E-Skins) are crucial for future robotics and wearable devices to interact with and perceive the real world. Prior research faces challenges in achieving comprehensive tactile perception and versatile functionality while keeping system simplicity for lack of multimodal sensing capability in a single sensor. Two kinds of tactile sensors, transient voltage artificial neuron (TVAN) and sustained potential artificial neuron (SPAN), featuring self-generated zero-biased signals are developed to realize synergistic sensing of multimodal information (vibration, material, texture, pressure, and temperature) in a single device instead of complex sensor arrays. Simultaneously, machine learning with feature fusion is applied to fully decode their output information and compensate for the inevitable instability of applied force, speed, etc, in real applications. Integrating TVAN and SPAN, the formed E-Skin achieves holistic touch awareness in only a single unit. It can thoroughly perceive an object through a simple touch without strictly controlled testing conditions, realize the capability to discern surface roughness from 0.8 to 1600 µm, hardness from 6HA to 85HD, and correctly distinguish 16 objects with temperature variance from 0 to 80 °C. The E-skin also features a simple and scalable fabrication process, which can be integrated into various devices for broad applications.

Advanced Dielectric Materials for Triboelectric Nanogenerators: Principles, Methods, and Applications.

Triboelectric nanogenerator (TENG) manifests distinct advantages such as multiple structural selectivity, diverse selection of materials, environmental adaptability, low cost, and remarkable conversion efficiency, which becomes a promising technology for micro-nano energy harvesting and self-powered sensing. Tribo-dielectric materials are the fundamental and core components for high-performance TENGs. In particular, the charge generation, dissipation, storage, migration of the dielectrics, and dynamic equilibrium behaviors determine the overall performance. Herein, a comprehensive summary is presented to elucidate the dielectric charge transport mechanism and tribo-dielectric material modification principle toward high-performance TENGs. The contact electrification and charge transport mechanism of dielectric materials is started first, followed by introducing the basic principle and dielectric materials of TENGs. Subsequently, modification mechanisms and strategies for high-performance tribo-dielectric materials are highlighted regarding physical/chemical, surface/bulk, dielectric coupling, and structure optimization. Furthermore, representative applications of dielectric materials based TENGs as power sources, self-powered sensors are demonstrated. The existing challenges and promising potential opportunities for advanced tribo-dielectric materials are outlined, guiding the design, fabrication, and applications of tribo-dielectric materials.

Triboelectric Nanogenerator-Enabled Digital Twins in Civil Engineering Infrastructure 4.0: A Comprehensive Review.

The emergence of digital twins has ushered in a new era in civil engineering with a focus on achieving sustainable energy supply, real-time sensing, and rapid warning systems. These key development goals mean the arrival of Civil Engineering 4.0.The advent of triboelectric nanogenerators (TENGs) demonstrates the feasibility of energy harvesting and self-powered sensing. This review aims to provide a comprehensive analysis of the fundamental elements comprising civil infrastructure, encompassing various structures such as buildings, pavements, rail tracks, bridges, tunnels, and ports. First, an elaboration is provided on smart engineering structures with digital twins. Following that, the paper examines the impact of using TENG-enabled strategies on smart civil infrastructure through the integration of materials and structures. The various infrastructures provided by TENGs have been analyzed to identify the key research interest. These areas encompass a wide range of civil infrastructure characteristics, including safety, efficiency, energy conservation, and other related themes. The challenges and future perspectives of TENG-enabled smart civil infrastructure are briefly discussed in the final section. In conclusion, it is conceivable that in the near future, there will be a proliferation of smart civil infrastructure accompanied by sustainable and comprehensive smart services.

Multi-Objective Bayesian Optimization for Laminate-Inspired Mechanically Reinforced Piezoelectric Self-Powered Sensing Yarns.

Piezoelectric fiber yarns produced by electrospinning offer a versatile platform for intelligent devices, demonstrating mechanical durability and the ability to convert mechanical strain into electric signals. While conventional methods involve twisting a single poly(vinylidene fluoride-co-trifluoroethylene)(P(VDF-TrFE)) fiber mat to create yarns, by limiting control over the mechanical properties, an approach inspired by composite laminate design principles is proposed for strengthening. By stacking multiple electrospun mats in various sequences and twisting them into yarns, the mechanical properties of P(VDF-TrFE) yarn structures are efficiently optimized. By leveraging a multi-objective Bayesian optimization-based machine learning algorithm without imposing specific stacking restrictions, an optimal stacking sequence is determined that simultaneously enhances the ultimate tensile strength (UTS) and failure strain by considering the orientation angles of each aligned fiber mat as discrete design variables. The conditions on the Pareto front that achieve a balanced improvement in both the UTS and failure strain are identified. Additionally, applying corona poling induces extra dipole polarization in the yarn state, successfully fabricating mechanically robust and high-performance piezoelectric P(VDF-TrFE) yarns. Ultimately, the mechanically strengthened piezoelectric yarns demonstrate superior capabilities in self-powered sensing applications, particularly in challenging environments and sports scenarios, substantiating their potential for real-time signal detection.

Magnetic Material in Triboelectric Nanogenerators: A Review.

Nowadays, magnetic materials are also drawing considerable attention in the development of innovative energy converters such as triboelectric nanogenerators (TENGs), where the introduction of magnetic materials at the triboelectric interface not only significantly enhances the energy harvesting efficiency but also promotes TENG entry into the era of intelligence and multifunction. In this review, we begin from the basic operating principle of TENGs and then summarize the recent progress in applications of magnetic materials in the design of TENG magnetic materials by categorizing them into soft ferrites and amorphous and nanocrystalline alloys. While highlighting key role of magnetic materials in and future opportunities for improving their performance in energy conversion, we also discuss the most promising choices available today and describe emerging approaches to create even better magnetic TENGs and TENG-based sensors as far as intelligence and multifunctionality are concerned. In addition, the paper also discusses the integration of magnetic TENGs as a power source for third-party sensors and briefly explains the self-powered applications in a wide range of related fields. Finally, the paper discusses the challenges and prospects of magnetic TENGs.

Chemical Cross-Linking Cellulose Aerogel-Based Triboelectric Nanogenerators for Energy Harvesting and Sensing Human Activities.

Zinc oxide (ZnO) is a widely employed material for enhancing the performance of cellulose-based triboelectric nanogenerators (C-TENGs). Our study provides a novel chemical interpretation for the improved output efficiency of ZnO in C-TENGs. C-TENGs exhibit excellent flexibility and integration, achieving a maximum open-circuit voltage (Voc) of 210 V. The peak power density is 54.4 µW/cm2 with a load resistance of 107 Ω, enabling the direct powering of 191 light-emitting diodes with the generated electrical output. Moreover, when deployed as self-powered sensors, C-TENGs exhibit prolonged operational viability and responsiveness, adeptly discerning bending and motion induced by human interaction. The device's sensitivity, flexibility, and stability position it as a promising candidate for a diverse array of energy-harvesting applications and advanced healthcare endeavors. Specifically, envisaging sensitized wearable sensors for human activities underscores the multifaceted potential of C-TENGs in enhancing both energy-harvesting technologies and healthcare practices.