Implanted Battery-Free Direct-Current Micro-Power Supply from in Vivo Breath Energy Harvesting

Advancements in flexible biomechanical energy harvesting for smart health applications

Advancing flexible electronics enables timely smart health management and diagnostic interventions. However, current health electronics typically rely on replaceable batteries or external power sources, requiring direct contact with the human skin or organs. This setup often results in rigid and bulky devices, reducing user comfort during long-term use. Flexible biomechanical energy harvesting technology, based on triboelectric or piezoelectric strategies, offers a promising approach for continuous and comfortable smart health applications, providing a sustainable power supply and self-powered sensing. This review systematically examines biomechanical energy sources around the human body, explores various energy harvesting mechanisms and their applications in smart health, and concludes with insights and future perspectives in this field.

Biocompatible triboelectric energy generators (BT-TENGs) for energy harvesting and healthcare applications

Electronic waste (e-waste) has become a significant environmental and societal challenge, necessitating the development of sustainable alternatives. Biocompatible and biodegradable electronic devices offer a promising solution to mitigate e-waste and provide viable alternatives for various applications, including triboelectric nanogenerators (TENGs). This review provides a comprehensive overview of recent advancements in biocompatible, biodegradable, and implantable TENGs, emphasizing their potential as energy scavengers for healthcare devices. The review delves into the fabrication processes of self-powered TENGs using natural biopolymers, highlighting their biodegradability and compatibility with biological tissues. It further explores the biomedical applications of ultrasound-based TENGs, including their roles in wound healing and energy generation. Notably, the review presents the novel application of TENGs for vagus nerve stimulation, demonstrating their potential in neurotherapeutic interventions. Key findings include the identification of optimal biopolymer materials for TENG fabrication, the effectiveness of TENGs in energy harvesting from physiological movements, and the potential of these devices in regenerative medicine. Finally, the review discusses the challenges in scaling up the production of implantable TENGs from biomaterials, addressing issues such as mechanical stability, long-term biocompatibility, and integration with existing medical devices, outlining future research opportunities to enhance their performance and broaden their applications in the biomedical field.

Self-Powered Hybrid Motion and Health Sensing System Based on Triboelectric Nanogenerators

Triboelectric nanogenerator (TENG) represents an effective approach for the conversion of mechanical energy into electrical energy and has been explored to combine multiple technologies in past years. Self-powered sensors are not only free from the constraints of mechanical energy in the environment but also capable of efficiently harvesting ambient energy to sustain continuous operation. In this review, the remarkable development of TENG-based human body sensing achieved in recent years is presented, with a specific focus on human health sensing solutions, such as body motion and physiological signal detection. The movements originating from different parts of the body, such as body, touch, sound, and eyes, are systematically classified, and a thorough review of sensor structures and materials is conducted. Physiological signal sensors are categorized into non-implantable and implantable biomedical sensors for discussion. Suggestions for future applications of TENG-based biomedical sensors are also indicated, highlighting the associated challenges.

Flexible self-powered bioelectronics enables personalized health management from diagnosis to therapy

Flexible self-powered bioelectronics (FSPBs), incorporating flexible electronic features in biomedical applications, have revolutionized the human-machine interface since they hold the potential to offer natural and seamless human interactions while overcoming the limitations of battery-dependent power sources. Furthermore, as biosensors or actuators, FSPBs can dynamically monitor physiological signals to reveal real-time health abnormalities and provide timely and precise treatments. Therefore, FSPBs are increasingly shaping the landscape of health monitoring and disease treatment, weaving a sophisticated and personalized bond between humans and health management. Here, we examine the recent advanced progress of FSPBs in developing working mechanisms, design strategies, and structural configurations toward personalized health management, emphasizing its role in clinical medical scenarios from biophysical/biochemical sensors for sensing diagnosis to robust/biodegradable actuators for intervention therapy. Future perspectives on the challenges and opportunities in emerging multifunctional FSPBs for the next-generation health management systems are also forecasted.

Advances in Wireless, Batteryless, Implantable Electronics for Real-Time, Continuous Physiological Monitoring

This review summarizes recent progress in developing wireless, batteryless, fully implantable biomedical devices for real-time continuous physiological signal monitoring, focusing on advancing human health care. Design considerations, such as biological constraints, energy sourcing, and wireless communication, are discussed in achieving the desired performance of the devices and enhanced interface with human tissues. In addition, we review the recent achievements in materials used for developing implantable systems, emphasizing their importance in achieving multi-functionalities, biocompatibility, and hemocompatibility. The wireless, batteryless devices offer minimally invasive device insertion to the body, enabling portable health monitoring and advanced disease diagnosis. Lastly, we summarize the most recent practical applications of advanced implantable devices for human health care, highlighting their potential for immediate commercialization and clinical uses.

Advanced Self-Powered Biofuel Cells with Capacitor and Nanogenerator for Biomarker Sensing

Self-powered biofuel cells (BFCs) have evolved for highly sensitive detection of biomarkers such as noncodon micro ribonucleic acids (miRNAs) in the presence of interfering substrates. Self-charging supercapacitive BFCs for in vivo and in vitro cellular microenvironments represent the most prevalent sensing mechanism for diagnosis. Therefore, self-powered biosensing (SPB) with a capacitor and contact separation with a triboelectric nanogenerator (TENG) offers electrochemical and colorimetric dual-mode detection via improved electrical signal intensity. In this review, we discuss three major components: stretchable self-powered BFC design, miRNA sensing, and impedance spectroscopy. A specific focus is given to 1) assembling of sensors for biomarkers, 2) electrical output signal intensification, and 3) role of supercapacitors and nanogenerators in SPBs. We outline the key features of stretchable SPBs and the sequence of miRNA sensing by SPBs. We have emphasized the need of a supercapacitor and nanogenerator for SPBs in the context of advanced assembly of the sensing unit. Finally, we outline the role of impedance spectroscopy in the detection and estimation of biomarkers. We highlight key challenges in SPBs for biomarker sensing, which needs improved sensing accuracy, integration strategies of electrochemical biosensing for in vitro and in vivo microenvironments, and the impact of miRNA sensing on cancer diagnostics. This article attempts a specific focus on the accuracy and limitations of sensing unit for miRNA biomarkers and associated tool for boosting electrical signal intensity for a potential big step further.

Biodegradable Piezoelectric Polymers: Recent Advancements in Materials and Applications

Recent materials, microfabrication, and biotechnology improvements have introduced numerous exciting bioelectronic devices based on piezoelectric materials. There is an intriguing evolution from conventional unrecyclable materials to biodegradable, green, and biocompatible functional materials. As a fundamental electromechanical coupling material in numerous applications, novel piezoelectric materials with a feature of degradability and desired electrical and mechanical properties are being developed for future wearable and implantable bioelectronics. These bioelectronics can be easily integrated with biological systems for applications, including sensing physiological signals, diagnosing medical problems, opening the blood-brain barrier, and stimulating healing or tissue growth. Therefore, the generation of piezoelectricity from natural and synthetic bioresorbable polymers has drawn great attention in the research field. Herein, the significant and recent advancements in biodegradable piezoelectric materials, including natural and synthetic polymers, their principles, advanced applications, and challenges for medical uses, are reviewed thoroughly. The degradation methods of these piezoelectric materials through in vitro and in vivo studies are also investigated. These improvements in biodegradable piezoelectric materials and microsystems could enable new applications in the biomedical field. In the end, potential research opportunities regarding the practical applications are pointed out that might be significant for new materials research.

Recent Advances in Triboelectric Nanogenerators: From Technological Progress to Commercial Applications

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.

Biodegradable polymeric materials for flexible and degradable electronics

Biodegradable electronics have great potential to reduce the environmental footprint of electronic devices and to avoid secondary removal of implantable health monitors and therapeutic electronics. Benefiting from the intensive innovation on biodegradable nanomaterials, current transient electronics can realize full components’ degradability. However, design of materials with tissue-comparable flexibility, desired dielectric properties, suitable biocompatibility and programmable biodegradability will always be a challenge to explore the subtle trade-offs between these parameters. In this review, we firstly discuss the general chemical structure and degradation behavior of polymeric biodegradable materials that have been widely studied for various applications. Then, specific properties of different degradable polymer materials such as biocompatibility, biodegradability, and flexibility were compared and evaluated for real-life applications. Complex biodegradable electronics and related strategies with enhanced functionality aimed for different components including substrates, insulators, conductors and semiconductors in complex biodegradable electronics are further researched and discussed. Finally, typical applications of biodegradable electronics in sensing, therapeutic drug delivery, energy storage and integrated electronic systems are highlighted. This paper critically reviews the significant progress made in the field and highlights the future prospects.

Emerging Development of Auto-Charging Sensors for Respiration Monitoring

In recent years, the development of biomedical monitoring systems, including respiration monitoring systems, has been accelerated. Wearable and implantable medical devices are becoming increasingly important in the diagnosis and management of disease and illness. Respiration can be monitored using a variety of biosensors and systems. Auto-charged sensors have a number of advantages, including low cost, ease of preparation, design flexibility, and a wide range of applications. It is possible to use the auto-charged sensors to directly convert mechanical energy from the airflow into electricity. The ability to monitor and diagnose one's own health is a major goal of auto-charged sensors and systems. Respiratory disease model output signals have not been thoroughly investigated and clearly understood. As a result, figuring out their exact interrelationship is a difficult and important research question. This review summarized recent developments in auto-charged respiratory sensors and systems in terms of their device principle, output property, detecting index, and so on. Researchers with an interest in auto-charged sensors can use the information presented here to better understand the difficulties and opportunities that lie ahead.

From Triboelectric Nanogenerator to Polymer-Based Biosensor: A Review

Nowadays, self-powered wearable biosensors that are based on triboelectric nanogenerators (TENGs) are playing an important role in the continuous efforts towards the miniaturization, energy saving, and intelligence of healthcare devices and Internets of Things (IoTs). In this review, we cover the remarkable developments in TENG−based biosensors developed from various polymer materials and their functionalities, with a focus on wearable and implantable self-powered sensors for health monitoring and therapeutic devices. The functions of TENGs as power sources for third-party biosensors are also discussed, and their applications in a number of related fields are concisely illustrated. Finally, we conclude the review with a discussion of the challenges and problems of leveraging TENG−based intelligent biosensors.

Stretchable Encapsulation Materials with High Dynamic Water Resistivity and Tissue-Matching Elasticity

Flexible implantable medical devices (IMDs) are an emerging technology that may substantially improve the disease treatment efficacy and quality of life of patients. While many advancements have been achieved in IMDs, the constantly straining application conditions impose extra requirements for the packaging material, which needs to retain both high stretchability and high water resistivity under dynamic strains in a physiological environment. This work reports a polyisobutylene (PIB) blend-based elastomer that simultaneously offers a tissue-like elastic modulus and excellent water resistivity under dynamic strains. The PIB blend is a homogeneous mixture of two types of PIB molecules with distinct molecular weights. The blend achieved an optimal Young's modulus of 62 kPa, matching those of soft biological tissues. The PIB blend film also exhibited an extremely low water permittivity of 1.6-2.9 g m^-2 day^-1, from unstrained to 50% strain states. The combination of high flexibility and dynamic water resistivity was tested using triboelectric nanogenerators (TENGs). The PIB blend-packaged TENG was able to stably operate in water for 2 weeks, substantially surpassing the protection offered by Ecoflex. This work offered a promising material solution for packaging flexible IMDs to achieve stable performance in a strained physiological environment.

Advanced Implantable Biomedical Devices Enabled by Triboelectric Nanogenerators

Implantable biomedical devices (IMDs) play essential roles in healthcare. Subject to the limited battery life, IMDs cannot achieve long-term in situ monitoring, diagnosis, and treatment. The proposal and rapid development of triboelectric nanogenerators free IMDs from the shackles of batteries and spawn a self-powered healthcare system. This review aims to overview the development of IMDs based on triboelectric nanogenerators, divided into self-powered biosensors, in vivo energy harvesting devices, and direct electrical stimulation therapy devices. Meanwhile, future challenges and opportunities are discussed according to the development requirements of current-level self-powered IMDs to enhance output performance, develop advanced triboelectric nanogenerators with multifunctional materials, and self-driven close-looped diagnosis and treatment systems.

Recent progress of self-powered respiration monitoring systems

Wearable and implantable medical devices are playing more and more key roles in disease diagnosis and health management. Various biosensors and systems have been used for respiration monitoring. Among them, self-powered sensors have some special characteristics such as low-cost, easy preparation, highly designable, and diversified. The respiratory airflow can drive the self-powered sensors directly to convert mechanical energy of the airflow into electricity. One of the major goals of the self-powered sensors and systems is realizing health monitoring and diagnosis. The relationship between the output signals and the models of respiratory diseases has not been studied deeply and clearly. Therefore, how to find an accurate relationship between them is a challenging and significant research topic. This review summarized the recent progress of the self-powered respiratory sensors and systems from aspects of device principle, output property, detecting index and so on. The challenges and perspectives have also been discussed for reference to the researchers who are interested in the field of self-powered sensors.

Long-term in vivo operation of implanted cardiac nanogenerators in swine

Implantable nanogenerators (i-NG) provide power to cardiovascular implantable electronic devices (CIEDs) by harvesting biomechanical energy locally eliminating the need for batteries. However, its long-term operation and biological influences on the heart have not been tested. Here, we evaluate a soft and flexible i-NG system engineered for long-term in vivo cardiac implantation. It consisted of i-NG, leads, and receivers, and was implanted on the epicardium of swine hearts for 2 months. The i-NG system generated electric current throughout the testing period. Biocompatibility and biosafety were established based on normal blood and serum test results and no tissue reactions. Heart function was unchanged over the testing period as validated by normal electrocardiogram (ECG), transthoracic ultrasound, and invasive cardiac functional measures. This research demonstrates the safety, long term operation and therefore the feasibility of using i-NGs to power the next generation CIEDs.

Materials Perspectives for Self-Powered Cardiac Implantable Electronic Devices toward Clinical Translation

Represented by pacemakers, implantable electronic devices (CIEDs) are playing a vital life-saving role in modern society. Although the current CIEDs are evolving quickly in terms of performance, safety, and miniaturization, the bulky and rigid battery creates the largest hurdle toward further development of a soft system that can be attached and conform to tissues without causing undesirable physiologic changes. Over 50% of patients with pacemakers require additional surgery procedures to replace a drained battery. Abrupt battery malfunction and failure contributes up to 2.4% of implanted leadless pacemakers. The battery also has risks of lethal interference with diagnostic magnetic resonance imaging (MRI). Applying the implantable nanogenerators (i-NGs) technology to CIEDs is regarded as a promising solution to the battery challenge and enables self-powering capability. I-NGs based on the principle of either triboelectricity (TENG) or piezoelectricity (PENG) can convert biomechanical energy into electricity effectively. Meanwhile, a complete heartbeat cycle provides a biomechanical energy of ~0.7 J or an average power of 0.93 W, which is sufficient for the operation of CIEDs considering the power consumption of 5-10 μW for a pacemaker and 10-100 μW for a cardiac defibrillator. It is therefore practical to leverage the effective, soft, flexible, lightweight, and biocompatible i-NGs to eliminate the bulky battery component in CIEDs and achieve self-sustainable operation. In this rapidly evolving interdisciplinary field, materials innovation acts as a cornerstone that frames the technology development. Here we bring a few critical perspectives regarding materials design and engineering, which are essential in leading the NG-powered CIEDs toward clinical translations. This Account starts with a brief introduction of the cardiac electrophysiology, as well as its short history to interface the state-of-the-art cardiac NG technologies. Three key components of NG-powered CIEDs are discussed in detail, including the NG device itself, the packaging material, and the stimulation electrodes. Cardiac NG is the essential component that converts heartbeat energy into electricity. It demands high-performance electromechanical coupling materials with long-term dynamic stability. The packaging material is critical to ensure a long-term stable operation of the device on a beating heart. Given the unique operation environment, a few criteria need to be considered in its development, including flexibility, biocompatibility, antifouling, hemocompatibility, and bioadhesion. The stimulation electrodes are the only material interfacing the heart tissue electrically. They should provide capacitive charge injection and mimic the soft and wet intrinsic tissues for the sake of stable biointerfaces. Driven by the rapid materials and device advancement, we envision that the evolution of NG-based CIEDs will quickly move from epicardiac to intracardiac, from single-function to multifunction, and with a minimal-invasive implantation procedure. This trend of development will open many research opportunities in emerging materials science and engineering, which will eventually lead the NG technology to a prevailing strategy for powering future CIEDs.

Self-powered technology based on nanogenerators for biomedical applications

Biomedical electronic devices have enormous benefits for healthcare and quality of life. Still, the long-term working of those devices remains a great challenge due to the short life and large volume of conventional batteries. Since the nanogenerators (NGs) invention, they have been widely used to convert various ambient mechanical energy sources into electrical energy. The self-powered technology based on NGs is dedicated to harvesting ambient energy to supply electronic devices, which is an effective pathway to conquer the energy insufficiency of biomedical electronic devices. With the aid of this technology, it is expected to develop self-powered biomedical electronic devices with advanced features and distinctive functions. The goal of this review is to summarize the existing self-powered technologies based on NGs and then review the applications based on self-powered technologies in the biomedical field during their rapid development in recent years, including two main directions. The first is the NGs as independent sensors to converts biomechanical energy and heat energy into electrical signals to reflect health information. The second direction is to use the electrical energy produced by NGs to stimulate biological tissues or powering biomedical devices for achieving the purpose of medical application. Eventually, we have analyzed and discussed the remaining challenges and perspectives of the field. We believe that the self-powered technology based on NGs would advance the development of modern biomedical electronic devices.

Self-rechargeable cardiac pacemaker system with triboelectric nanogenerators

Self-powered implantable devices have the potential to extend device operation time inside the body and reduce the necessity for high-risk repeated surgery. Without the technological innovation of in vivo energy harvesters driven by biomechanical energy, energy harvesters are insufficient and inconvenient to power titanium-packaged implantable medical devices. Here, we report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator (I-TENG) based on body motion and gravity. We demonstrate that the enclosed five-stacked I-TENG converts mechanical energy into electricity at 4.9 μW/cm³ (root-mean-square output). In a preclinical test, we show that the device successfully harvests energy using real-time output voltage data monitored via Bluetooth and demonstrate the ability to charge a lithium-ion battery. Furthermore, we successfully integrate a cardiac pacemaker with the I-TENG, and confirm the ventricle pacing and sensing operation mode of the self-rechargeable cardiac pacemaker system. This proof-of-concept device may lead to the development of new self-rechargeable implantable medical devices.

Self-powered implantable devices have the potential to extend device operation, though current energy harvesters are both insufficient and inconvenient. Here the authors report on a commercial coin battery-sized high-performance inertia-driven triboelectric nanogenerator based on body motion and gravity that can be used to charge a lithium-ion battery and integrated into a cardiac pacemaker.

High-Performance Polyimide-Based Water-Solid Triboelectric Nanogenerator for Hydropower Harvesting

Water-solid triboelectric nanogenerators (TENGs) are insensitive to ambient humidity, providing a wide range of possibilities for designing stable water-energy-based harvesters and self-powered sensors. However, the wide application of most water-solid TENGs has been limited by low triboelectrification performance. To boost the output performance of water-solid TENGs, a newly structured TENG has been developed by adding a polyimide (PI) as a charge storage intermediate layer between the friction layer and the conducting layer, significantly improving the output performance (1.260 mW), with a 5-fold increase compared to the water-solid TENG without the PI intermediate layer (0.234 mW). This analysis shows that adding an intermediate layer with a high density of electron capture sites to the TENG results in more triboelectric charge being retained, thereby improving the electrical performance of TENG. The electrical performance of TENG is related to the thickness of the PI layer, but this is not a positive correlation. Contact angles and falling heights between the droplet and the device also affect the output performance. Finally, the water-solid PI-TENG we have developed has promise in hydropower harvesting capabilities and can be used to power warning signals on a dark and rainy night to ensure the safety of people.

Progress on Self-Powered Wearable and Implantable Systems Driven by Nanogenerators

With the rapid development of the internet of things (IoT), sustainable self-powered wireless sensory systems and diverse wearable and implantable electronic devices have surged recently. Under such an opportunity, nanogenerators, which can convert continuous mechanical energy into usable electricity, have been regarded as one of the critical technologies for self-powered systems, based on the high sensitivity, flexibility, and biocompatibility of piezoelectric nanogenerators (PENGs) and triboelectric nanogenerators (TENGs). In this review, we have thoroughly analyzed the materials and structures of wearable and implantable PENGs and TENGs, aiming to make clear how to tailor a self-power system into specific applications. The advantages in TENG and PENG are taken to effectuate wearable and implantable human-oriented applications, such as self-charging power packages, physiological and kinematic monitoring, in vivo and in vitro healing, and electrical stimulation. This review comprehensively elucidates the recent advances and future outlook regarding the human body's self-powered systems.

Wearable and Implantable Electroceuticals for Therapeutic Electrostimulations

Wearable and implantable electroceuticals (WIEs) for therapeutic electrostimulation (ES) have become indispensable medical devices in modern healthcare. In addition to functionality, device miniaturization, conformability, biocompatibility, and/or biodegradability are the main engineering targets for the development and clinical translation of WIEs. Recent innovations are mainly focused on wearable/implantable power sources, advanced conformable electrodes, and efficient ES on targeted organs and tissues. Herein, nanogenerators as a hotspot wearable/implantable energy-harvesting technique suitable for powering WIEs are reviewed. Then, electrodes for comfortable attachment and efficient delivery of electrical signals to targeted tissue/organ are introduced and compared. A few promising application directions of ES are discussed, including heart stimulation, nerve modulation, skin regeneration, muscle activation, and assistance to other therapeutic modalities.

Energy Harvesting Floor from Commercial Cellulosic Materials for a Self-Powered Wireless Transmission Sensor System

Cellulose-based materials have gained increasing attention for the development of low-cost, eco-friendly technologies, and more recently, as functional materials in triboelectric nanogenerators (TENGs). However, the low output performance of cellulose-based TENGs severely restricts their versatility and employment in emerging smart building and smart city applications. Here, we report a high output performance of a commercial cellulosic material-based energy harvesting floor (CEHF). Benefiting from the significant difference in the triboelectric properties between weighing and nitrocellulose papers, high surface roughness achieved by a newly developed mechanical exfoliation method, and large overall contact area via a multilayered device structure, the CEHF (25 cm × 15 cm × 1.2 cm) exhibits excellent output performance with a maximum output voltage, current, and power peak values of 360 V, 250 μA, and 5 mW, respectively. It can be directly installed or integrated with regular flooring products to effectively convert human body movements into electricity and shows good durability and stability. Moreover, a wireless transmission sensing system that can produce a 1:1 footstep-to-signal (transmitted and received) ratio is instantaneously powered by a TENG based entirely on cellulosic materials for the first time. This work provides a feasible and effective way to utilize commercial cellulosic materials to construct self-powered wireless transmission systems for real-time sensing applications.

Advances in triboelectric nanogenerators for biomedical sensing

Biomedical sensors have been essential in improving healthcare outcomes over the past 30 years, though limited power source access and user wearability restraints have prevented them from taking a constant and active biomedical sensing role in our daily lives. Triboelectric nanogenerators (TENGs) have demonstrated exceptional capabilities and versatility in delivering self-powered and wear-optimized biomedical sensors, and are paving the way for a novel platform technology able to fully integrate into the developing 5G/Internet-of-Things ecosystem. This novel paradigm of TENG-based biomedical sensors aspires to provide ubiquitous and omnipresent real-time biomedical sensing for us all. In this review, we cover the remarkable developments in TENG-based biomedical sensing which have arisen in the last octennium, focusing on both in-body and on-body biomedical sensing solutions. We begin by covering TENG as biomedical sensors in the most relevant, mortality-associated clinical fields of pneumology and cardiology, as well as other organ-related biomedical sensing abilities including ambulation. We also include an overview of ambient biomedical sensing as a field of growing interest in occupational health monitoring. Finally, we explore TENGs as power sources for third party biomedical sensors in a number of fields, and conclude our review by focusing on the future perspectives of TENG biomedical sensors, highlighting key areas of attention to fully translate TENG-based biomedical sensors into clinically and commercially viable digital and wireless consumer and health products.

A Review and Perspective for the Development of Triboelectric Nanogenerator (TENG)-Based Self-Powered Neuroprosthetics

Neuroprosthetics have become a powerful toolkit for clinical interventions of various diseases that affect the central nervous or peripheral nervous systems, such as deep brain stimulation (DBS), functional electrical stimulation (FES), and vagus nerve stimulation (VNS), by electrically stimulating different neuronal structures. To prolong the lifetime of implanted devices, researchers have developed power sources with different approaches. Among them, the triboelectric nanogenerator (TENG) is the only one to achieve direct nerve stimulations, showing great potential in the realization of a self-powered neuroprosthetic system in the future. In this review, the current development and progress of the TENG-based stimulation of various kinds of nervous systems are systematically summarized. Then, based on the requirements of the neuroprosthetic system in a real application and the development of current techniques, a perspective of a more sophisticated neuroprosthetic system is proposed, which includes components of a thin-film TENG device with a biocompatible package, an amplification circuit to enhance the output, and a self-powered high-frequency switch to generate high-frequency current pulses for nerve stimulations. Then, we review and evaluate the recent development and progress of each part.

Respiration-driven triboelectric nanogenerators for biomedical applications

As a fundamental and ubiquitous body motion, respiration offers a large amount of biomechanical energy with an average power up to the Watt level through movements of multiple muscles. The energy from respiration featured with excellent stability, accessibility and continuality inspires the design and engineering of biomechanical energy harvesting devices, such as triboelectric nanogenerators (TENGs), to realize human-powered electronics. This review article is thus dedicated to the emerging respiration-driven TENG technology, covering fundamentals, applications, and perspectives. Specifically, the human breathing mechanics are first introduced serving as the base for the developments of TENG devices with different configurations. Biomedical applications including electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering implantable medical devices are then analyzed focusing on the design-application relationships. At last, current developments are summarized and critical challenges for driving these intriguing developments toward practical applications are discussed together with promising solutions.

Respiration-driven triboelectric nanogenerators for biomedical applications

As a fundamental and ubiquitous body motion, respiration offers a large amount of biomechanical energy with an average power up to the Watt level through movements of multiple muscles. The energy from respiration featured with excellent stability, accessibility and continuality inspires the design and engineering of biomechanical energy harvesting devices, such as triboelectric nanogenerators (TENGs), to realize human-powered electronics. This review article is thus dedicated to the emerging respiration-driven TENG technology, covering fundamentals, applications, and perspectives. Specifically, the human breathing mechanics are first introduced serving as the base for the developments of TENG devices with different configurations. Biomedical applications including electrical energy generation, healthcare monitoring, air filtration, gas sensing, electrostimulation, and powering implantable medical devices are then analyzed focusing on the design-application relationships. At last, current developments are summarized and critical challenges for driving these intriguing developments toward practical applications are discussed together with promising solutions.

Human Motion Driven Self-Powered Photodynamic System for Long-Term Autonomous Cancer Therapy

Long-term and low-dose photodynamic therapy for treating tumors requires a sustainable energy supply. The power source technology of batteries and wireless charging for driving a light-emitting diode (LED) may cause inconveniences during treatment. In addition, the development of telemedicine and Internet medicine put forward higher demands on treatment methods, such as better patient compliance and autonomous management. Here, we show a self-powered photodynamic therapy (s-PDT) system with two different irradiation modes that can be autonomously managed by patients. The as-fabricated s-PDT system based on a twinning structured piezoelectric nanogenerator is powered by energy harvested from body motion and realizes effective tumor tissue killing and inhibition. As demonstrated at the cellular level, the s-PDT system can significantly suppress tumor cell growth with the pulsed light stimulation mode. When the miniature LED was implanted subcutaneously in mice with transplanted tumors, the s-PDT system led to significant antitumor effects by irradiation with intermittent continuous light stimulation mode for 12 days, and an 87.46% tumor inhibition rate was obtained. This innovative s-PDT system combined with two treatment modes may provide a great opportunity to develop wearable/implantable and self-controllable devices for long-term photodynamic therapy, which would be a promising method for clinical cancer treatment.

Degradable Piezoelectric Biomaterials for Wearable and Implantable Bioelectronics

Current bioelectronics are facing a paradigm shift from old-fashioned unrecyclable materials to green and degradable functional materials with desired biocompatibility. As an essential electromechanical coupling component in many bioelectronics, new piezoelectric materials are being developed with biodegradability, as well as desired mechanical and electromechanical properties for the next generation implantable and wearable bioelectronics. In this review, we provide an overview of the major advancements in biodegradable piezoelectric materials. Different natural (such as peptide, amino acids, proteins, cellulose, chitin, silk, collagen, and M13 phage) and synthetic piezoelectric materials (such as polylactic acid) are discussed to reveal the underlying electromechanical coupling mechanism at the molecular level, together with typical approaches to the alignment of orientation and polarization to boost their electromechanical performance. Meanwhile, in vivo and in vitro degradation manners of those piezoelectric materials are summarized and compared. Representative developments of typical electronic prototypes leveraging these materials are also discussed. At last, challenges toward practical applications are pointed out together with potential research opportunities that might be critical in this new materials research area.

Untethered Disposable Health Monitoring Electronic Patches with an Integrated Ag2O-Zn Battery, a AgInGa Current Collector, and Hydrogel Electrodes

Stretchable electronics stickers that adhere to the human skin and collect biopotentials are becoming increasingly popular for biomonitoring applications. Such stickers include electrodes, stretchable interconnects, silicon chips for processing and communication, and batteries. Here, we demonstrate a material architecture and fabrication technique for a multilayer, stretchable, low-cost, rapidly deployable, and disposable sticker that integrates skin-interfacing hydrogel electrodes, stretchable interconnects, and a Ag₂O-Zn (silver oxide-zinc) battery. In addition, the application of a printed biphasic current collector (AgInGa) for the Ag₂O-Zn battery is reported for the first time. Surprisingly, and unlike previously reported batteries, the battery capacity increases after being subjected to strain cycles and reaches a record-breaking areal capacity of 6.88 mAh cm^-2 post stretch. As a proof of concept, an application of heart rate monitoring is presented. The disposable patch is interfaced with a miniature battery-free electronics circuit for data acquisition, processing, and wireless transmission. A version of the patch partially covering the patient's chest can supply enough energy for continuous operation for ∼6 days.