A soft implantable energy supply system that integrates wireless charging and biodegradable Zn-ion hybrid supercapacitors

A Supercapacitor Diode with High Rectification Ratio Induced by Carbon and Oxygen Vacancies

Supercapacitor-based ionic diode (CAPode) integrates ion-electron dual charge carriers in one device, thus possessing great potential in bioabiotic systems such as intelligent implantable devices and human-computer interfaces. Herein, we present a high-performance CAPode that takes carbon-modified anatase titania (C@TiO2-x) nanowires with abundant oxygen vacancies as the negative electrode. The modification of the thin carbon layer improves the conductivity and cycling stability of TiO2 nanowires, and more attractively, introduces a large amount of oxygen vacancies in them, enhancing the electrochemical kinetics and rectification capability of the C@TiO2-x nanowires. Consequently, the C@TiO2-x electrode exhibits a high rectification ratio I (RRI) of 204.6 and a rectification ratio II (RRII) of 98.3% at 1 mV s-1. Also, the assembled CAPode exhibits an RRI of 99.1 at 8 mV s-1 and a wide operating window of -1.0 to 1.4 V. Therefore, the assembled CAPodes successfully demonstrate the functionality of both "AND" and "OR" gates, revealing the potential to process information. The above results show that the rectification capability of CAPodes can be comparable to that of conventional ionic diodes and highlight the importance of modulating the electrochemical ion storage behavior to improve the rectification performance of CAPodes.

Edible batteries for biomedical innovation: advances, challenges, and future perspectives

In biomedical applications, the demand for advanced electronic devices that enable precise monitoring, targeted therapies, and non-invasive diagnostic tools is steadily increasing to enhance patient outcomes. Edible batteries seamlessly combine biocompatibility, energy efficiency, and safe ingestion, offering a reliable power source for in vivo devices and opening up new possibilities for innovative healthcare solutions. Beyond supporting precise monitoring and advanced therapeutic interventions, edible batteries overcome the inherent limitations of traditional batteries, such as rigidity, toxicity, and environmental concerns. Their unique properties make them essential for advancing precision medicine and promoting sustainable biomedical technologies. This transformative approach marks a significant leap in the evolution of battery technology for biomedical engineering applications. This review systematically categorizes edible batteries into various types, including lithium-based, sodium-based, magnesium-based, zinc-based, and other emerging systems. It further highlights key distinctions in material selection, structural design, and fabrication techniques, examining their influence on electrochemical performance and suitability for biomedical applications. Additionally, the review identifies existing challenges and outlines prospective research directions, paving the way for further advancements in this innovative field.

A Body Conformal Ultrasound Receiver for Efficient and Stable Wireless Power Transfer in Deep Percutaneous Charging

Wireless powering of rechargeable-implantable medical devices presents a challenge in developing reliable wireless energy transfer systems that meet medical safety and standards. Ultrasound-driven triboelectric nanogenerators (US-TENG) are investigated for various medical applications, including noninvasive percutaneous wireless battery powering to reduce the need for multiple surgeries for battery replacement. However, these devices often suffer from inefficiency due to limited output performance and rigidity. To address this issue, a dielectric-ferroelectric boosted US-TENG (US-TENGDF-B) capable of producing a high output charge with low-intensity ultrasound and a long probe distance is developed, comparatively. The feasibility and output stability of this deformable and augmented device is confirmed under various bending conditions, making it suitable for use in the body's curved positions or with electronic implants. The device achieved an output of ≈26 V and ≈6.7 mW output for remote charging of a rechargeable battery at a 35 mm distance. These results demonstrate the effectiveness of the output-augmented US-TENG for deep short-term wireless charging of implantable electronics with flexing conditions in curved devices such as future total artificial hearts.

A review on electrode materials of supercapacitors used in wearable bioelectronics and implantable biomedical applications

Supercapacitors, a class of electrochemical energy storage devices, offer a promising solution for powering wearable bioelectronics and implantable biomedical devices. Their high-power density, rapid charge-discharge capabilities, and long cycle life make them ideal for applications requiring quick bursts of energy and extended operation. To address the challenges of energy density, self-discharge, miniaturization, integration, and power consumption, researchers are exploring various strategies, including developing novel electrode materials, optimizing device architectures, and integrating advanced fabrication techniques. Metal oxides, carbon-based materials, MXenes, and their composites have emerged as promising electrode materials due to their high specific surface area, excellent conductivity, and biocompatibility. For wearable bioelectronics, supercapacitors can power a wide range of devices, including wearable sensors, smart textiles, and other devices that require intermittent or pulsed energy. In implantable biomedical devices, supercapacitors offer a reliable and safe power source for applications such as pacemakers, neural implants, and drug delivery systems. By addressing the challenges and capitalizing on emerging technologies, supercapacitors have the potential to revolutionize the field of bioelectronics and biomedical engineering, enabling the development of innovative devices that improve healthcare and quality of life.

Sargassum Nanocellulose-Based Fully Ingestible Supercapacitor

Small high-performance energy modules have significant practical value in the biomedical field, such as painless diagnosis, alleviation of gastrointestinal discomfort, and electrical stimulation therapy. However, due to performance limitations and safety concerns, it is a formidable challenge to design a small, emerging ingestible power supply. Here, a fully ingestible supercapacitor (FISC) constructed of sargassum cellulose nanofiber is presented. FISCs exhibit an electrode areal capacitance of 2.29 F cm-2 and a high energy density of 307 µWh cm-2. Furthermore, over 90% of the antibacterial activity against Escherichia coli is achieved during the self-discharge process. Therefore, following insertion into an enteric capsule, this device can enable a disposable power supply and electrostimulation for bacteriostasis in the intestine after being swallowed by a human, which offers new possibilities for scientific and simple therapy.

Synergistic integration of energy harvesters and supercapacitors for enhanced performance

In this paper, it is integrated a piezoelectric energy harvester and a supercapacitor storage device on a flexible substrate with a connection through an innovative alternative current (AC) to direct current (DC) boosting power management system for wearable biosensors' power supply. Flexible substrates can conform to irregular surfaces or shapes, enabling energy harvesting and storage devices to be integrated into a variety of form factors, including curved or bendable surfaces. Having an integrated energy harvester and storage system ensures a reliable and portable power source, providing power autonomy. The proposed element was layer-by-layer design including silver electrode, polyvinylidene fluoride-trifluoroethylene/multiwall carbon nanotubes, poly(3,4-ethylenedioxythiophene) polystyrene sulfonate: carbon nanotubes, aluminium oxide, graphene and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate: carbon nanotubes (Ag/PVDF-TrFE:MWCNT/PEDOT:PSS:CNT/Al2O3/Gr/PEDOT:PSS:CNT), prepared by spray coating. A voltage rectifier with a low-pass filter and a direct current to direct current (DC-DC) converter was used as a power management system and intermediate unit between the harvester and storage part of the element. The type of the electronic circuit is voltage-doubler rectifier. It was found that piezoelectric harvester can generates voltage with a magnitude of 2V at loading of 110 g/cm2@10 Hz and with the proposed electronic circuit can be determined the workability of the created element during repeated charging and discharging, without introducing interfering changes in the capacity. The behaviour of the supercapacitor part is dependent on the thickness of Al2O3 and demonstrates more favourable characteristics at the thicker film of 750 nm, where the charging time is short (6s), the voltage ripples are small (±0.50 mV), and the maximum output voltage after charging almost reached the input supply voltage (∼1.94 V output voltage at 2 V input voltage). In addition, it resists up to 15500 cycles and shows a stable retention capacitance of 1.63 mF. The devices retain their capacity at multiple bending (1000) to 93 % and 91 %, according to the aluminium oxide film thickness, which is suitable for wearable devices.

Advances in integrated power supplies for self-powered bioelectronic devices

Bioelectronic devices with medical functions have attracted widespread attention in recent years. Power supplies are crucial components in these devices, which ensure their stable operation. Biomedical devices that utilize external power supplies and extended electrical wires limit patient mobility and increase the risk of discomfort and infection. To address these issues, self-powered devices with integrated power supplies have emerged, including triboelectric nanogenerators, piezoelectric nanogenerators, thermoelectric generators, batteries, biofuel cells, solar cells, wireless power transfer, and hybrid energy systems. This mini-review highlights the recent advances in the power supplies utilized in these self-powered devices. A concluding section discusses the subsisting challenges and future perspectives in integrated power supply technologies and design and manufacturing of self-powered devices.

Advances in Symbiotic Bioabsorbable Devices

Symbiotic bioabsorbable devices are ideal for temporary treatment. This eliminates the boundaries between the device and organism and develops a symbiotic relationship by degrading nutrients that directly enter the cells, tissues, and body to avoid the hazards of device retention. Symbiotic bioresorbable electronics show great promise for sensing, diagnostics, therapy, and rehabilitation, as underpinned by innovations in materials, devices, and systems. This review focuses on recent advances in bioabsorbable devices. Innovation is focused on the material, device, and system levels. Significant advances in biomedical applications are reviewed, including integrated diagnostics, tissue repair, cardiac pacing, and neurostimulation. In addition to the material, device, and system issues, the challenges and trends in symbiotic bioresorbable electronics are discussed.

Ultrathin, Lightweight Materials Enabled Wireless Data and Power Transmission in Chip-Less Flexible Electronics

The surge of flexible, biointegrated electronics has inspired continued research efforts in designing and developing chip-less and wireless devices as soft and mechanically compliant interfaces to the living systems. In recent years, innovations in materials, devices, and systems have been reported to address challenges surrounding this topic to empower their reliable operation for monitoring physiological signals. This perspective provides a brief overview of recent works reporting various chip-less electronics for sensing and actuation in diverse application scenarios. We summarize wireless signal/data/power transmission strategies, key considerations in materials design and selection, as well as successful demonstrations of sensors and actuators in wearable and implantable forms. The final section provides an outlook to the future direction down the road for performance improvement and optimization. These versatile, inexpensive, and low-power device concepts can serve as alternative strategies to existing digital wireless electronics, which will find broad applications as bidirectional biointerfaces in basic biomedical research and clinical practices.

Dual-Site Biomacromolecule Doped Poly(3, 4-Ethylenedioxythiophene) for Bosting Both Anticoagulant and Electrochemical Performances

Poly(3, 4-ethylenedioxythiophene) (PEDOT) as a new generation of intelligent conductive polymers, is attracting much attention in the field of tissue engineering. However, its water dispersibility, conductivity, and biocompatibility are incompatible, which limit its further development. In this work, biocompatible electrode material of PEDOT doped with sodium sulfonated alginate (SS) which contains two functional groups of sulfonic acid and carboxylic acid per repeat unit of the macromolecule. The as dual-site doping strategy simultaneously boosts anticoagulant and electrochemical performances, for example, good hydrophilicity (water contact angle of 59.40°), well dispersibility (dispersion solution unstratified in 30 days), high conductivity (4.45 S m-1), and enhanced anticoagulant property (extended activated partial thrombin time value of 59.0 s), forming an adjustable PEDOT: biomacromolecule interface; this fills the technical gap of implantable bioelectronics in terms of coagulation and thrombosis risk. At the same time, the assembled all-in-one supercapacitor with anticoagulant properties is prepared by PEDOT: sodium sulfonated alginate as electrode material and sodium alginate hydrogel as electrolyte layer. The dual-site doping strategy provides a new opinion for the design and optimization of functional conductive polymers and its applications in implantable energy storage fields.

Dynamic Imine Chemistry Enables Paintable Biogel Electrolytes to Shield On-Body Zinc-Ion Batteries from Interfacial Interference

On-body batteries with hydrogel electrolytes are a pivotal enabling technology to drive bioelectronics for healthcare and sports, yet they are prone to failure due to dynamic interfacial interference, accompanied by e-waste production. Here, dynamic imine chemistry is proposed to design on-electrode paintable biogel electrolytes that feature temperature-controlled reversible phase transition (gelling within 1.5 min) and ultrafast self-healing capability (6 s), establishing a dynamically self-adaptive interface on cyclically deforming electrodes for shielding on-body Zn-ion batteries from interfacial interference. Consequently, the deformed Zn anode shows an exceptional cycling stability of 400 h regardless of the bending radius, and the as-assembled Zn-I2 battery delivers sufficient durability to endure 5000 deformation cycles, together extending to 1300 h and 15 000 deformation cycles via dynamically restarting the interfacial electric field, respectively. Also, the features of recyclability, biodegradation, and biocompatibility make the proposed on-body Zn-I2 batteries appealing in terms of sustainability and biosafety, enabling their successful power supply of heart rate monitors in sports. This work demonstrates the promise of dynamic biogel chemistry for green and biorelated energy-storage systems.

An anticoagulant supercapacitor for implantable applications

With the rapid advancement of implantable electronic medical devices, implantable supercapacitors have emerged as popular energy storage devices. However, supercapacitors inevitably come into direct contact with blood when implanted, potentially causing adverse clinical reactions such as coagulation and thrombosis, impairing the performance of implanted energy storage devices, and posing a serious threat to human health. Therefore, this work aims to design an anticoagulant supercapacitor by heparin doped poly(3, 4-ethylenedioxythiophene) (PEDOT) for possible applications in implantable bioelectronics. Heparin (Hep), the as-known anticoagulant macromolecule acts as the counterion for PEDOT doping to enhance its conductivity, and the bioelectrode material PEDOT: Hep with anticoagulant activity is synthesized via chemical oxidation polymerization. Concurrently, the anticoagulant supercapacitor is constructed through in-situ polymerization, where PEDOT: Hep and bacterial cellulose as electrode material and electrolyte layer, respectively. Owing to the incorporation of heparin, the supercapacitor exhibits high hemocompatibility with hemolysis rate <5 %, good anticoagulant performance with coagulation time of 63.4 s, reasonable cycle stability with capacitance retention rate of 76.24 % after 20, 000 cycles, and supplies power for implanted heart rate sensors in female mice. This work provides a platform for implantable electronics to achieve anticoagulant activity in vivo.

Implantable Self-Powered Systems for Electrical Stimulation Medical Devices

With the integration of bioelectronics and materials science, implantable self-powered systems for electrical stimulation medical devices have emerged as an innovative therapeutic approach, garnering significant attention in medical research. These devices achieve self-powering through integrated energy conversion modules, such as triboelectric nanogenerators (TENGs) and piezoelectric nanogenerators (PENGs), significantly enhancing the portability and long-term efficacy of therapeutic equipment. This review delves into the design strategies and clinical applications of implantable self-powered systems, encompassing the design and optimization of energy harvesting modules, the selection and fabrication of adaptable electrode materials, innovations in systematic design strategies, and the extensive utilization of implantable self-powered systems in biological therapies, including the treatment of neurological disorders, tissue regeneration engineering, drug delivery, and tumor therapy. Through a comprehensive analysis of the latest research progress, technical challenges, and future directions in these areas, this paper aims to provide valuable insights and inspiration for further research and clinical applications of implantable self-powered systems.

Biodegradable and Implantable Triboelectric Nanogenerator Improved by β-Lactoglobulin Fibrils-Assisted Flexible PVA Porous Film

Triboelectric nanogenerators (TENGs) are highly promising as implantable, degradable energy sources and self-powered sensors. However, the degradable triboelectric materials are often limited in terms of contact electrification and mechanical properties. Here, a bio-macromolecule-assisted toughening strategy for PVA aerogel-based triboelectric materials is proposed. By introducing β-lactoglobulin fibrils (BF) into the PVA aerogel network, the material's mechanical properties while preserving its swelling resistance is significantly enhanced. Compared to pure PVA porous film, the BF-PVA porous film exhibits an eightfold increase in fracture strength (from 1.92 to 15.48 J) and a fourfold increase in flexibility (from 10.956 to 39.36 MPa). Additionally, the electrical output of BF-PVA in triboelectric performance tests increased nearly fivefold (from 45 to 203 V). Leveraging these enhanced properties, a biodegradable TENG (bi-TENG) for implantable muscle activity sensing is developed, achieving real-time monitoring of neuromuscular processes. This innovation holds significant potential for advancing implantable medical devices and promoting new applications in bio-integrated electronics.

Fully Printed and Sweat-Activated Micro-Batteries with Lattice-Match Zn/MoS2 Anode for Long-Duration Wearables

Aqueous zinc-ion batteries with superior operational safety have great promise to serve as wearable energy storage devices. However, the poor cycling stability and low output voltage limited their practical applications. Here, fully printable Zn/MoS2-MnO2 micro-batteries are developed and demonstrated significantly enhanced cycling stability with sweat activation. 2D MoS2 is utilized to enable lattice-matching with Zn powders to realize printed Zn anodes with desirable stability and promote electron/ion transfer. Interestingly, the mild acid epidermal sweat also contributed to eliminating the MnO2 cathode by-products and compensating for the hydrogel electrolytes' water loss. The Zn/MoS2-MnO2 micro-batteries achieve a high specific capacity of 318.9 µAh cm-2 at the current density of 0.16 mA cm-2, and an energy density of 424.6 µWh cm-2, with remarkable cycle stability of ≈90% after 250 cycles. In-battery electrochromic display of capacity level and feasible electronics charging are demonstrated. The as-printed micro-batteries with innovative sweat activation would inspire the advances of sustainable power supply for wearables.

Biomimetic Exogenous "Tissue Batteries" as Artificial Power Sources for Implantable Bioelectronic Devices Manufacturing

Implantable bioelectronic devices (IBDs) have gained attention for their capacity to conformably detect physiological and pathological signals and further provide internal therapy. However, traditional power sources integrated into these IBDs possess intricate limitations such as bulkiness, rigidity, and biotoxicity. Recently, artificial "tissue batteries" (ATBs) have diffusely developed as artificial power sources for IBDs manufacturing, enabling comprehensive biological-activity monitoring, diagnosis, and therapy. ATBs are on-demand and designed to accommodate the soft and confining curved placement space of organisms, minimizing interface discrepancies, and providing ample power for clinical applications. This review presents the near-term advancements in ATBs, with a focus on their miniaturization, flexibility, biodegradability, and power density. Furthermore, it delves into material-screening, structural-design, and energy density across three distinct categories of TBs, distinguished by power supply strategies. These types encompass innovative energy storage devices (chemical batteries and supercapacitors), power conversion devices that harness power from human-body (biofuel cells, thermoelectric nanogenerators, bio-potential devices, piezoelectric harvesters, and triboelectric devices), and energy transfer devices that receive and utilize external energy (radiofrequency-ultrasound energy harvesters, ultrasound-induced energy harvesters, and photovoltaic devices). Ultimately, future challenges and prospects emphasize ATBs with the indispensability of bio-safety, flexibility, and high-volume energy density as crucial components in long-term implantable bioelectronic devices.

Recent Development of Implantable Chemical Sensors Utilizing Flexible and Biodegradable Materials for Biomedical Applications

Implantable chemical sensors built with flexible and biodegradable materials exhibit immense potential for seamless integration with biological systems by matching the mechanical properties of soft tissues and eliminating device retraction procedures. Compared with conventional hospital-based blood tests, implantable chemical sensors have the capability to achieve real-time monitoring with high accuracy of important biomarkers such as metabolites, neurotransmitters, and proteins, offering valuable insights for clinical applications. These innovative sensors could provide essential information for preventive diagnosis and effective intervention. To date, despite extensive research on flexible and bioresorbable materials for implantable electronics, the development of chemical sensors has faced several challenges related to materials and device design, resulting in only a limited number of successful accomplishments. This review highlights recent advancements in implantable chemical sensors based on flexible and biodegradable materials, encompassing their sensing strategies, materials strategies, and geometric configurations. The following discussions focus on demonstrated detection of various objects including ions, small molecules, and a few examples of macromolecules using flexible and/or bioresorbable implantable chemical sensors. Finally, we will present current challenges and explore potential future directions.