Energy extraction from the biologic battery in the inner ear

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.

Miniature battery-free bioelectronics

Miniature wireless bioelectronic implants that can operate for extended periods of time can transform how we treat disorders by acting rapidly on precise nerves and organs in a way that drugs cannot. To reach this goal, materials and methods are needed to wirelessly transfer energy through the body or harvest energy from the body itself. We review some of the capabilities of emerging energy transfer methods to identify the performance envelope for existing technology and discover where opportunities lie to improve how much-and how efficiently-we can deliver energy to the tiny bioelectronic implants that can support emerging medical technologies.

Piezoelectric nanogenerators for self-powered wearable and implantable bioelectronic devices

One of the recent innovations in the field of personalized healthcare is the piezoelectric nanogenerators (PENGs) for various clinical applications, including self-powered sensors, drug delivery, tissue regeneration etc. Such innovations are perceived to potentially address some of the unmet clinical needs, e.g., limited life-span of implantable biomedical devices (e.g., pacemaker) and replacement related complications. To this end, the generation of green energy from biomechanical sources for wearable and implantable bioelectronic devices gained considerable attention in the scientific community. In this perspective, this article provides a comprehensive state-of-the-art review on the recent developments in the processing, applications and associated concerns of piezoelectric materials (synthetic/biological) for personalized healthcare applications. In particular, this review briefly discusses the concepts of piezoelectric energy harvesting, piezoelectric materials (ceramics, polymers, nature-inspired), and the various applications of piezoelectric nanogenerators, such as, self-powered sensors, self-powered pacemakers, deep brain stimulators etc. Important distinction has been made in terms of the potential clinical applications of PENGs, either as wearable or implantable bioelectronic devices. While discussing the potential applications as implantable devices, the biocompatibility of the several hybrid devices using large animal models is summarized. This review closes with the futuristic vision of integrating data science approaches in developmental pipeline of PENGs as well as clinical translation of the next generation PENGs. STATEMENT OF SIGNIFICANCE: Piezoelectric nanogenerators (PENGs) hold great promise for transforming personalized healthcare through self-powered sensors, drug delivery systems, and tissue regeneration. The limited battery life of implantable devices like pacemakers presents a significant challenge, leading to complications from repititive surgeries. To address such a critical issue, researchers are focusing on generating green energy from biomechanical sources to power wearable and implantable bioelectronic devices. This comprehensive review critically examines the latest advancements in synthetic and nature-inspired piezoelectric materials for PENGs in personalized healthcare. Moreover, it discusses the potential of piezoelectric materials and data science approaches to enhance the efficiency and reliability of personalized healthcare devices for clinical applications.

Wireless and battery-free technologies for neuroengineering

Tethered and battery-powered devices that interface with neural tissues can restrict natural motions and prevent social interactions in animal models, thereby limiting the utility of these devices in behavioural neuroscience research. In this Review Article, we discuss recent progress in the development of miniaturized and ultralightweight devices as neuroengineering platforms that are wireless, battery-free and fully implantable, with capabilities that match or exceed those of wired or battery-powered alternatives. Such classes of advanced neural interfaces with optical, electrical or fluidic functionality can also combine recording and stimulation modalities for closed-loop applications in basic studies or in the practical treatment of abnormal physiological processes.

The bioelectrical properties of bone tissue

Understanding the bioelectrical properties of bone tissue is key to developing new treatment strategies for bone diseases and injuries, as well as improving the design and fabrication of scaffold implants for bone tissue engineering. The bioelectrical properties of bone tissue can be attributed to the interaction of its various cell lineages (osteocyte, osteoblast and osteoclast) with the surrounding extracellular matrix, in the presence of various biomechanical stimuli arising from routine physical activities; and is best described as a combination and overlap of dielectric, piezoelectric, pyroelectric and ferroelectric properties, together with streaming potential and electro-osmosis. There is close interdependence and interaction of the various electroactive and electrosensitive components of bone tissue, including cell membrane potential, voltage-gated ion channels, intracellular signaling pathways, and cell surface receptors, together with various matrix components such as collagen, hydroxyapatite, proteoglycans and glycosaminoglycans. It is the remarkably complex web of interactive cross-talk between the organic and non-organic components of bone that define its electrophysiological properties, which in turn exerts a profound influence on its metabolism, homeostasis and regeneration in health and disease. This has spurred increasing interest in application of electroactive scaffolds in bone tissue engineering, to recapitulate the natural electrophysiological microenvironment of healthy bone tissue to facilitate bone defect repair.

NFC-Powered Implantable Device for On-Body Parameters Monitoring With Secure Data Exchange Link to a Medical Blockchain Type of Network

Implantable devices represent the future of remote medical monitoring and administration of both chemical and physical therapies to the patients. Although some of these devices are already in the market, the security mechanisms deployed inside them to withstand deliberate external influence are still decades away from the robust digital data security schemes employed in modern distributed networks these days. Medical data theft, spoofing, and disclosure pose serious threats that can ultimately lead to individual and social stigmas or even death. In this article, we present a small-form and batteryless implantable device with acquisition channels for biopotential (30-dB gain and 16-Hz bandwidth), arterial pulse oximetry, and temperature (0.12°C accuracy) recordings, suitable for cardiovascular, neuronal, and endocrine parameters assessment. The proposed device is powered by the near-field communication (NFC) interface with an external mobile phone, with a power consumption of 0.9 mW and achieving the full operation for distances close to 1 cm under the skin. In situ encryption of the acquired physiological signals is performed by a lightweight and short-term symmetric-key distribution scheme with data stream hopping, in order to ensure secure data transference over the air between the patient and trusted entities only, complemented by data storage, processing, and recovery through a medical blockchain type of network that involves the main stakeholders inside a medical community.

Electroactive Biomaterials for Facilitating Bone Defect Repair under Pathological Conditions

Bone degeneration associated with various diseases is increasing due to rapid aging, sedentary lifestyles, and unhealthy diets. Living bone tissue has bioelectric properties critical to bone remodeling, and bone degeneration under various pathological conditions results in significant changes to these bioelectric properties. There is growing interest in utilizing biomimetic electroactive biomaterials that recapitulate the natural electrophysiological microenvironment of healthy bone tissue to promote bone repair. This review first summarizes the etiology of degenerative bone conditions associated with various diseases such as type II diabetes, osteoporosis, periodontitis, osteoarthritis, rheumatoid arthritis, osteomyelitis, and metastatic osteolysis. Next, the diverse array of natural and synthetic electroactive biomaterials with therapeutic potential are discussed. Putative mechanistic pathways by which electroactive biomaterials can mitigate bone degeneration are critically examined, including the enhancement of osteogenesis and angiogenesis, suppression of inflammation and osteoclastogenesis, as well as their anti-bacterial effects. Finally, the limited research on utilization of electroactive biomaterials in the treatment of bone degeneration associated with the aforementioned diseases are examined. Previous studies have mostly focused on using electroactive biomaterials to treat bone traumatic injuries. It is hoped that this review will encourage more research efforts on the use of electroactive biomaterials for treating degenerative bone conditions.

The remaining obstacles for a totally implantable cochlear implant

PURPOSE OF THE REVIEW

For years, the development of a totally implantable cochlear implant (TICI) has faced several technical challenges hindering any prototypes from reaching full commercialization. This article aims to review the necessary specifications for a viable TICI. An overview of the remaining challenges when designing TICIs will be provided, focusing on energy supply and implantable microphones.

RECENT FINDINGS

The literature review highlights how research efforts to generate sufficient power to supply a fully implantable CI could take advantage of microelectromechanical systems (MEMS)-based energy harvesters incorporating piezoelectric materials. Using one of the various energy sources in the vicinity of the temporal bone would allow the development of a self-sufficient implant, overcoming the limitations of electrochemical batteries. Middle ear implantable microphones could also use similar fabrication techniques and transduction mechanisms to meet the sensor requirements for a TICI.

SUMMARY

Recent breakthroughs in power supply using MEMS-based energy harvesting technologies and piezoelectric implantable microphones may make TICIs become a more practical reality in the foreseeable future. Once available, TICIs will have major impact on our patients' quality of life and may help to make hearing rehabilitation a more appealing option to a greater proportion of those who fulfill our candidacy criteria.

Toward Personalized Diagnosis and Therapy for Hearing Loss: Insights From Cochlear Implants

ABSTRACT

Sensorineural hearing loss (SNHL) is the most common sensory deficit, disabling nearly half a billion people worldwide. The cochlear implant (CI) has transformed the treatment of patients with SNHL, having restored hearing to more than 800,000 people. The success of CIs has inspired multidisciplinary efforts to address the unmet need for personalized, cellular-level diagnosis, and treatment of patients with SNHL. Current limitations include an inability to safely and accurately image at high resolution and biopsy the inner ear, precluding the use of key structural and molecular information during diagnostic and treatment decisions. Furthermore, there remains a lack of pharmacological therapies for hearing loss, which can partially be attributed to challenges associated with new drug development. We highlight advances in diagnostic and therapeutic strategies for SNHL that will help accelerate the push toward precision medicine. In addition, we discuss technological improvements for the CI that will further enhance its functionality for future patients. This report highlights work that was originally presented by Dr. Stankovic as part of the Dr. John Niparko Memorial Lecture during the 2021 American Cochlear Implant Alliance annual meeting.

Powering Implantable and Ingestible Electronics

Implantable and ingestible biomedical electronic devices can be useful tools for detecting physiological and pathophysiological signals, and providing treatments that cannot be done externally. However, one major challenge in the development of these devices is the limited lifetime of their power sources. The state-of-the-art of powering technologies for implantable and ingestible electronics is reviewed here. The structure and power requirements of implantable and ingestible biomedical electronics are described to guide the development of powering technologies. These powering technologies include novel batteries that can be used as both power sources and for energy storage, devices that can harvest energy from the human body, and devices that can receive and operate with energy transferred from exogenous sources. Furthermore, potential sources of mechanical, chemical, and electromagnetic energy present around common target locations of implantable and ingestible electronics are thoroughly analyzed; energy harvesting and transfer methods befitting each energy source are also discussed. Developing power sources that are safe, compact, and have high volumetric energy densities is essential for realizing long-term in-body biomedical electronics and for enabling a new era of personalized healthcare.

Implementation of Multi-Exit Neural-Network Inferences for an Image-Based Sensing System with Energy Harvesting

Wireless sensor systems powered by batteries are widely used in a variety of applications. For applications with space limitation, their size was reduced, limiting battery energy capacity and memory storage size. A multi-exit neural network enables to overcome these limitations by filtering out data without objects of interest, thereby avoiding computing the entire neural network. This paper proposes to implement a multi-exit convolutional neural network on the ESP32-CAM embedded platform as an image-sensing system with an energy constraint. The multi-exit design saves energy by 42.7% compared with the single-exit condition. A simulation result, based on an exemplary natural outdoor light profile and measured energy consumption of the proposed system, shows that the system can sustain its operation with a 3.2 kJ (275 mAh @ 3.2 V) battery by scarifying the accuracy only by 2.7%.

Recent Advances of Energy Solutions for Implantable Bioelectronics

The emerging field of implantable bioelectronics has attracted widespread attention in modern society because it can improve treatment outcomes, reduce healthcare costs, and lead to an improvement in the quality of life. However, their continuous operation is often limited by conventional bulky and rigid batteries with a limited lifespan, which must be surgically removed after completing their missions and/or replaced after being exhausted. Herein, this paper gives a comprehensive review of recent advances in nonconventional energy solutions for implantable bioelectronics, emphasizing the miniaturized, flexible, biocompatible, and biodegradable power devices. According to their source of energy, the promising alternative energy solutions are sorted into three main categories, including energy storage devices (batteries and supercapacitors), internal energy-harvesting devices (including biofuel cells, piezoelectric/triboelectric energy harvesters, thermoelectric and biopotential power generators), and external wireless power transmission technologies (including inductive coupling/radiofrequency, ultrasound-induced, and photovoltaic devices). Their fundamentals, materials strategies, structural design, output performances, animal experiments, and typical biomedical applications are also discussed. It is expected to offer complementary power sources to extend the battery lifetime of bioelectronics while acting as an independent power supply. Thereafter, the existing challenges and perspectives associated with these powering devices are also outlined, with a focus on implantable bioelectronics.

Electroactive Biomaterials and Systems for Cell Fate Determination and Tissue Regeneration: Design and Applications

During natural tissue regeneration, tissue microenvironment and stem cell niche including cell-cell interaction, soluble factors, and extracellular matrix (ECM) provide a train of biochemical and biophysical cues for modulation of cell behaviors and tissue functions. Design of functional biomaterials to mimic the tissue/cell microenvironment have great potentials for tissue regeneration applications. Recently, electroactive biomaterials have drawn increasing attentions not only as scaffolds for cell adhesion and structural support, but also as modulators to regulate cell/tissue behaviors and function, especially for electrically excitable cells and tissues. More importantly, electrostimulation can further modulate a myriad of biological processes, from cell cycle, migration, proliferation and differentiation to neural conduction, muscle contraction, embryogenesis, and tissue regeneration. In this review, endogenous bioelectricity and piezoelectricity are introduced. Then, design rationale of electroactive biomaterials is discussed for imitating dynamic cell microenvironment, as well as their mediated electrostimulation and the applying pathways. Recent advances in electroactive biomaterials are systematically overviewed for modulation of stem cell fate and tissue regeneration, mainly including nerve regeneration, bone tissue engineering, and cardiac tissue engineering. Finally, the significance for simulating the native tissue microenvironment is emphasized and the open challenges and future perspectives of electroactive biomaterials are concluded.

The Green Lean Amine Machine: Harvesting Electric Power While Capturing Carbon Dioxide from Breath

As wearable technologies redefine the way people exchange information, receive entertainment, and monitor health, the development of sustainable power sources that capture energy from the user's everyday activities garners increasing interest. Electric fishes, such as the electric eel and the torpedo ray, provide inspiration for such a power source with their ability to generate massive discharges of electricity solely from the metabolic processes within their bodies. Inspired by their example, the device presented in this work harnesses electric power from ion gradients established by capturing the carbon dioxide (CO₂ ) from human breath. Upon localized exposure to CO₂ , this novel adaptation of reverse electrodialysis chemically generates ion gradients from a single initial solution uniformly distributed throughout the device instead of requiring the active circulation of two different external solutions. A thorough analysis of the relationship between electrical output and the concentration of carbon capture agent (monoethanolamine, MEA), the amount of CO₂ captured, and the device geometry informs device design. The prototype device presented here harvests enough energy from a breath-generated ion gradient to power small electronic devices, such as a light-emitting diode (LED).

Mechanical Energy Sensing and Harvesting in Micromachined Polymer-Based Piezoelectric Transducers for Fully Implanted Hearing Systems: A Review

The paper presents a comprehensive review of mechanical energy harvesters and microphone sensors for totally implanted hearing systems. The studies on hearing mechanisms, hearing losses and hearing solutions are first introduced to bring to light the necessity of creating and integrating the in vivo energy harvester and implantable microphone into a single chip. The in vivo energy harvester can continuously harness energy from the biomechanical motion of the internal organs. The implantable microphone executes mechanoelectrical transduction, and an array of such structures can filter sound frequency directly without an analogue-to-digital converter. The revision of the available transduction mechanisms, device configuration structures and piezoelectric material characteristics reveals the advantage of adopting the polymer-based piezoelectric transducers. A dual function of sensing the sound signal and simultaneously harvesting vibration energy to power up its system can be attained from a single transducer. Advanced process technology incorporates polymers into piezoelectric materials, initiating the invention of a self-powered and flexible transducer that is compatible with the human body, magnetic resonance imaging system (MRI) and the standard complementary metal-oxide-semiconductor (CMOS) processes. The polymer-based piezoelectric is a promising material that satisfies many of the requirements for obtaining high performance implantable microphones and in vivo piezoelectric energy harvesters.

Soft, Wireless and subdermally implantable recording and neuromodulation tools

Progress in understanding neuronal interaction and circuit behavior of the central and peripheral nervous system strongly relies on the advancement of tools that record and stimulate with high fidelity and specificity. Currently, devices used in exploratory research predominantly utilize cables or tethers to provide pathways for power supply, data communication, stimulus delivery and recording, which constrains the scope and use of such devices. In particular, the tethered connection, mechanical mismatch to surrounding soft tissues and bones frustrate the interface leading to irritation and limitation of motion of the subject, which in the case of fundamental and preclinical studies, impacts naturalistic behaviors of animals and precludes the use in experiments involving social interaction and ethologically relevant three-dimensional environments, limiting the use of current tools to mostly rodents and exclude species such as birds and fish. This review explores the current state-of-the-art in wireless, subdermally implantable tools that quantitively expand capabilities in analysis and perturbation of the central and peripheral nervous system by removing tethers and externalized features of implantable neuromodulation and recording tools. Specifically, the review explores power harvesting strategies, wireless communication schemes, and soft materials and mechanics that enable the creation of such devices and discuss their capabilities in the context of freely-behaving subjects. Highlights of this class of devices includes wireless battery-free and fully implantable operation with capabilities in cell specific recording, multimodal neural stimulation and electrical, optogenetic and pharmacological neuromodulation capabilities. We conclude with discussion on translation of such technologies which promises routes towards broad dissemination.

16.8 nW Ultra-Low-Power Energy Harvester IC for Tiny Ingestible Sensors Sustained by Bio-Galvanic Energy Source

Herein, we present a 16.8 nW ultra-low-power (ULP) energy harvester integrated circuit (IC) for ingestible biomedical sensors. The energy harvester can be powered from the electro-galvanic operation inside a human body, which provides a sustainable and long-term energy source. The challenge of dealing with relatively high input impedance (∼kΩ) of the bio-galvanic energy source is addressed by introducing two design techniques. The first technique is an adaptive V_MPP-controlled algorithm (AVCA) for a maximum power point tracking (MPPT) controller, and the second technique is a ULP delay-line-based zero current switching (ZCS) controller. Different from the conventional fractional open-circuit voltage (FOCV) method for MPPT, the proposed AVCA allows continuous source tracking without detachment of the harvester from the source. The ZCS operation is achieved using a delay-line controller without using either a comparator or an opamp. The proposed AVCA is realized using a 12.1 nW MPPT controller. Successful ZCS operation is achieved using a 2.1 nW delay controller. Overall power consumption of the IC is 16.8 nW. The converter has been fabricated in a 0.18 μm CMOS process with 2 μm thick top-metal option. The measured result shows that the converter achieves a peak efficiency of 72.1% to generate 507 nW output power. The ULP operation allows a significant reduction in electrode size down to the submillimeter scale (∼0.4 mm²), demonstrating the good potential of the proposed energy harvester IC.

Mobile In-Ear Power Sensor for Jaw Joint Activity

In only a short time, in-ear wearables have gone from hearing aids to a host of electronic devices such as wireless earbuds and digital earplugs. To operate, these devices rely exclusively on batteries, which are not only cumbersome but known for several drawbacks. In this paper, the earcanal dynamic movements generated by jaw activity are evaluated as an alternative source of energy that could replace batteries. A mobile in-ear power sensor device capable of measuring jaw activity metrics is prototyped and tested on three test subjects. The test results are subsequently analyzed using a detection algorithm to detect the jaw activity based on the captured audio signals and to classify them into four main categories, namely chewing, swallowing, coughing and talking. The mean power associated with each category of activity is then calculated by using the pressure signals as measured by a water-inflated earplug subjected to earcanal dynamic movement. The results show that 3.8 mW of power, achieved mainly by the chewing movement, is readily available on average from within the earcanal.

A self-powered analog sensor-data-logging device based on Fowler-Nordheim dynamical systems

Continuous, battery-free operation of sensor nodes requires ultra-low-power sensing and data-logging techniques. Here we report that by directly coupling a sensor/transducer signal into globally asymptotically stable monotonic dynamical systems based on Fowler-Nordheim quantum tunneling, one can achieve self-powered sensing at an energy budget that is currently unachievable using conventional energy harvesting methods. The proposed device uses a differential architecture to compensate for environmental variations and the device can retain sensed information for durations ranging from hours to days. With a theoretical operating energy budget less than 10 attojoules, we demonstrate that when integrated with a miniature piezoelectric transducer the proposed sensor-data-logger can measure cumulative "action" due to ambient mechanical acceleration without any additional external power.

Electrochemical glucose sensors in diabetes management: an updated review (2010-2020)

While over half a century has passed since the introduction of enzyme glucose biosensors by Clark and Lyons, this important field has continued to be the focus of immense research activity. Extensive efforts during the past decade have led to major scientific and technological innovations towards tight monitoring of diabetes. Such continued progress toward advanced continuous glucose monitoring platforms, either minimal- or non-invasive, holds considerable promise for addressing the limitations of finger-prick blood testing toward tracking glucose trends over time, optimal therapeutic interventions, and improving the life of diabetes patients. However, despite these major developments, the field of glucose biosensors is still facing major challenges. The scope of this review is to present the key scientific and technological advances in electrochemical glucose biosensing over the past decade (2010-present), along with current obstacles and prospects towards the ultimate goal of highly stable and reliable real-time minimally-invasive or non-invasive glucose monitoring. After an introduction to electrochemical glucose biosensors, we highlight recent progress based on using advanced nanomaterials at the electrode-enzyme interface of three generations of glucose sensors. Subsequently, we cover recent activity and challenges towards next-generation wearable non-invasive glucose monitoring devices based on innovative sensing principles, alternative body fluids, advanced flexible materials, and novel platforms. This is followed by highlighting the latest progress in the field of minimally-invasive continuous glucose monitoring (CGM) which offers real-time information about interstitial glucose levels, by focusing on the challenges toward developing biocompatible membrane coatings to protect electrochemical glucose sensors against surface biofouling. Subsequent sections cover new analytical concepts of self-powered glucose sensors, paper-based glucose sensing and multiplexed detection of diabetes-related biomarkers. Finally, we will cover the latest advances in commercially available devices along with the upcoming future technologies.

Self-powered cardiovascular electronic devices and systems

Cardiovascular electronic devices have enormous benefits for health and quality of life but the long-term operation of these implantable and wearable devices remains a huge challenge owing to the limited life of batteries, which increases the risk of device failure and causes uncertainty among patients. A possible approach to overcoming the challenge of limited battery life is to harvest energy from the body and its ambient environment, including biomechanical, solar, thermal and biochemical energy, so that the devices can be self-powered. This strategy could allow the development of advanced features for cardiovascular electronic devices, such as extended life, miniaturization to improve comfort and conformability, and functions that integrate with real-time data transmission, mobile data processing and smart power utilization. In this Review, we present an update on self-powered cardiovascular implantable electronic devices and wearable active sensors. We summarize the existing self-powered technologies and their fundamental features. We then review the current applications of self-powered electronic devices in the cardiovascular field, which have two main goals. The first is to harvest energy from the body as a sustainable power source for cardiovascular electronic devices, such as cardiac pacemakers. The second is to use self-powered devices with low power consumption and high performance as active sensors to monitor physiological signals (for example, for active endocardial monitoring). Finally, we present the current challenges and future perspectives for the field.

A Preliminary Prototype High-Speed Feedback Control of an Artificial Cochlear Sensory Epithelium Mimicking Function of Outer Hair Cells

A novel feedback control technique for the local oscillation amplitude in an artificial cochlear sensory epithelium that mimics the functions of the outer hair cells in the cochlea is successfully developed and can be implemented with a control time on the order of hundreds of milliseconds. The prototype artificial cochlear sensory epithelium was improved from that developed in our previous study to enable the instantaneous determination of the local resonance position based on the electrical output from a bimorph piezoelectric membrane. The device contains local patterned electrodes deposited with micro electro mechanical system (MEMS) technology that is used to detect the electrical output and oscillate the device by applying local electrical stimuli. The main feature of the present feedback control system is the principle that the resonance position is recognized by simultaneously measuring the local electrical outputs of all of the electrodes and comparing their magnitudes, which drastically reduces the feedback control time. In this way, it takes 0.8 s to control the local oscillation of the device, representing the speed of control with the order of one hundred times relative to that in the previous study using the mechanical automatic stage to scan the oscillation amplitude at each electrode. Furthermore, the intrinsic difficulties in the experiment such as the electrical measurement against the electromagnetic noise, adhesion of materials, and fatigue failure mechanism of the oscillation system are also shown and discussed in detail based on the many scientific aspects. The basic knowledge of the MEMS fabrication and the experimental measurement would provide useful suggestions for future research. The proposed preliminary prototype high-speed feedback control can aid in the future development of fully implantable cochlear implants with a wider dynamic range.

Emerging Implantable Energy Harvesters and Self-Powered Implantable Medical Electronics

Implantable energy harvesters (IEHs) are the crucial component for self-powered devices. By harvesting energy from organisms such as heartbeat, respiration, and chemical energy from the redox reaction of glucose, IEHs are utilized as the power source of implantable medical electronics. In this review, we summarize the IEHs and self-powered implantable medical electronics (SIMEs). The typical IEHs are nanogenerators, biofuel cells, electromagnetic generators, and transcutaneous energy harvesting devices that are based on ultrasonic or optical energy. A benefit from these technologies of energy harvesting in vivo, SIMEs emerged, including cardiac pacemakers, nerve/muscle stimulators, and physiological sensors. We provide perspectives on the challenges and potential solutions associated with IEHs and SIMEs. Beyond the energy issue, we highlight the implanted devices that show the therapeutic function in vivo.

Materials Strategies and Device Architectures of Emerging Power Supply Devices for Implantable Bioelectronics

Implantable bioelectronics represent an emerging technology that can be integrated into the human body for diagnostic and therapeutic functions. Power supply devices are an essential component of bioelectronics to ensure their robust performance. However, conventional power sources are usually bulky, rigid, and potentially contain hazardous constituent materials. The fact that biological organisms are soft, curvilinear, and have limited accommodation space poses new challenges for power supply systems to minimize the interface mismatch and still offer sufficient power to meet clinical-grade applications. Here, recent advances in state-of-the-art nonconventional power options for implantable electronics, specifically, miniaturized, flexible, or biodegradable power systems are reviewed. Material strategies and architectural design of a broad array of power devices are discussed, including energy storage systems (batteries and supercapacitors), power devices which harvest sources from the human body (biofuel cells, devices utilizing biopotentials, piezoelectric harvesters, triboelectric devices, and thermoelectric devices), and energy transfer devices which utilize sources in the surrounding environment (ultrasonic energy harvesters, inductive coupling/radiofrequency energy harvesters, and photovoltaic devices). Finally, future challenges and perspectives are given.

Recent advances in solid-contact ion-selective electrodes: functional materials, transduction mechanisms, and development trends

This article presents a comprehensive overview of recent progress in the design and applications of solid-contact ion-selective electrodes (SC-ISEs).

NFC-Powered Flexible Chest Patch for Fast Assessment of Cardiac, Hemodynamic, and Endocrine Parameters

Cardiac-related diseases are still the number one cause of death worldwide. Methods and technologies to suppress this problem are currently being investigated by integrating electrocardiographic (ECG) monitoring with other sensing modalities in order to detect these diseases more accurately and in due course of time. In this paper, we propose a battery-less and flexible device to be worn as a chest patch for monitoring cardiac and hemodynamic parameters through electrical and acoustic measurements, combined with sweat pH level estimation and skin temperature, by swiping a smartphone over the patch area for enough time (≃5 seconds) to allow adequate acquisition and estimation of the aforementioned parameters. Fast screening of vital signals from patients in ambulatory or emergency scenarios can thus be achieved by this Near Field Communication (NFC) powered device, as well as home or office monitoring for those individuals suffering from diseases affecting the hemodynamic, cardiac and endocrine parameters detected by the proposed technology. Current consumption of the device is 1 mA for harvested levels of 1.8 V, yielding a power requirement of 1.8 mW. Within these conditions, the sensitivities achieved by each sensing modality are 42 mV/unit for pH, 0.12 °C for temperature, 48 dB SNR for ECG and -56 dBA for acoustic measurements.

A Multi-site Heart Pacing Study Using Wirelessly Powered Leadless Pacemakers

In this work, we report an energy-efficient switched capacitor based millimeter-scale pacemaker (5 mm ×7.5 mm) and a multi-receiver wireless energy transfer system operating at around 200 MHz, and use them in a proof-of-concept multi-site heart pacing study. Two pacemakers were placed on two beating Langendorff rodent heart models separately. By utilizing a single transmitter positioned 20-30 cm away, both Langendorff hearts captured the stimuli simultaneously and were electromechanically coupled. This study provides an insight for future energy-efficient and distributed cardiac pacemakers that can offer cardiac resynchronization therapies.

Differential Fowler-Nordheim Tunneling Dynamical System for Attojoule Sensing and Recording

Dynamical systems that evolve unidirectionally with respect to time provide a natural mechanism for implementing a time-domain, near-zero-threshold energy rectifier. In this paper we implement such a dynamical system using a pair of differential, leaky floating-gates and demonstrate that the circuit can sense and record signals of interest while compensating for environmental variations. A Fowler-Nordheim (FN) tunneling current has been used to implement the leakage process, which we experimentally show can be modulated by signals at energy levels below femtojoules. At this level of energy, the proposed FN-system could be self-powered using different types of biopotential energy sources like intra-cellular potentials, a feature that was not possible with previously reported recorders. Furthermore, the degree of modulation is shown to be a function of the input intensity as well as time-of-occurrence, which opens up the possibility of using reconstruction techniques to reconstruct the input signal from measurement of multiple sensing devices. Using devices fabricated in a 0.5 μm standard CMOS process, we demonstrate recording of 6 mV events with retention capability lasting over 30 minutes.

Symbiotic cardiac pacemaker

Self-powered implantable medical electronic devices that harvest biomechanical energy from cardiac motion, respiratory movement and blood flow are part of a paradigm shift that is on the horizon. Here, we demonstrate a fully implanted symbiotic pacemaker based on an implantable triboelectric nanogenerator, which achieves energy harvesting and storage as well as cardiac pacing on a large-animal scale. The symbiotic pacemaker successfully corrects sinus arrhythmia and prevents deterioration. The open circuit voltage of an implantable triboelectric nanogenerator reaches up to 65.2 V. The energy harvested from each cardiac motion cycle is 0.495 μJ, which is higher than the required endocardial pacing threshold energy (0.377 μJ). Implantable triboelectric nanogenerators for implantable medical devices offer advantages of excellent output performance, high power density, and good durability, and are expected to find application in fields of treatment and diagnosis as in vivo symbiotic bioelectronics.

Invited Article: Emerging soft bioelectronics for cardiac health diagnosis and treatment

Cardiovascular diseases are among the leading causes of death worldwide. Conventional technologies for diagnosing and treating lack the compliance and comfort necessary for those living with life-threatening conditions. Soft electronics presents a promising outlet for conformal, flexible, and stretchable devices that can overcome the mechanical mismatch that is often associated with conventional technologies. Here, we review the various methods in which electronics have been made flexible and stretchable, to better interface with the human body, both externally with the skin and internally with the outer surface of the heart. Then, we review soft, wearable, noninvasive heart monitors designed to be attached to the chest or other parts of the body for mechano-acoustic and electrophysiological sensing. A common method of treatment for various abnormal heart rhythms involves catheter ablation procedures and we review the current soft bioelectronics that can be placed on the balloon or head of the catheter. Cardiac mapping is integral to determine the state of the heart; we discuss the various parameters for sensing aside from electrophysiological sensing, such as temperature, pH, strain, and tactile sensing. Finally, we review the soft devices that harvest energy from the natural and spontaneous beating of the heart by converting its mechanical motion into electrical energy to power implants.

Using Artificial Skin Devices as Skin Replacements: Insights into Superficial Treatment

Artificial skin devices are able to mimic the flexibility and sensory perception abilities of the skin. They have thus garnered attention in the biomedical field as potential skin replacements. This Review delves into issues pertaining to these skin-deep devices. It first elaborates on the roles that these devices have to fulfill as skin replacements, and identify strategies that are used to achieve such functionality. Following which, a comparison is done between the current state of these skin-deep devices and that of natural skin. Finally, an outlook on artificial skin devices is presented, which discusses how complementary technologies can create skin enhancements, and what challenges face such devices.

Future of Implantable Auditory Devices

The advances in technology leading to rapid developments in implantable auditory devices are constantly evolving. Devices are becoming smaller, less visible, and more efficient. The ability to preserve hearing outcomes with cochlear implantation will continue to evolve as surgical techniques improve with the use of continuous feedback during the procedure as well as with intraoperative delivery of drugs and robot assistance. As engineering methods improve, there may one day be a totally implantable aid that is self-sustaining in hearing-impaired patients making them indistinguishable from patients without hearing loss.

Implantable Energy-Harvesting Devices

The sustainable operation of implanted medical devices is essential for healthcare applications. However, limited battery capacity is a key challenge for most implantable medical electronics (IMEs). The human body abounds with mechanical and chemical energy, such as the heartbeat, breathing, blood circulation, and the oxidation-reduction of glucose. Harvesting energy from the human body is a possible approach for powering IMEs. Many new methods for developing in vivo energy harvesters (IVEHs) have been proposed for powering IMEs. In this context energy harvesters based on the piezoelectric effect, triboelectric effect, automatic wristwatch devices, biofuel cells, endocochlear potential, and light, with an emphasis on fabrication, energy output, power management, durability, animal experiments, evaluation criteria, and typical applications are discussed. Importantly, the IVEHs that are discussed, are actually implanted into living things. Future challenges and perspectives are also highlighted.

Methods for powering bioelectronic microdevices

Bioelectronic microdevices are an emerging class of biomedical devices miniaturized at the scale of a millimeter or less, which promise new capabilities for monitoring and treating human disease. Although rapid progress has been made in the sensing and actuation capabilities of microdevices, a major technological challenge remains in the way that these devices are powered within the body. In this review, we revisit the power requirements of microdevices, describe current methods for storing, transferring or harvesting energy in microdevices, provide an overview of emerging powering approaches and discuss the promise of microdevices in biomedicine.

Compliant and stretchable thermoelectric coils for energy harvesting in miniature flexible devices

With accelerating trends in miniaturization of semiconductor devices, techniques for energy harvesting become increasingly important, especially in wearable technologies and sensors for the internet of things. Although thermoelectric systems have many attractive attributes in this context, maintaining large temperature differences across the device terminals and achieving low-thermal impedance interfaces to the surrounding environment become increasingly difficult to achieve as the characteristic dimensions decrease. Here, we propose and demonstrate an architectural solution to this problem, where thin-film active materials integrate into compliant, open three-dimensional (3D) forms. This approach not only enables efficient thermal impedance matching but also multiplies the heat flow through the harvester, thereby increasing the efficiencies for power conversion. Interconnected arrays of 3D thermoelectric coils built using microscale ribbons of monocrystalline silicon as the active material demonstrate these concepts. Quantitative measurements and simulations establish the basic operating principles and the key design features. The results suggest a scalable strategy for deploying hard thermoelectric thin-film materials in harvesters that can integrate effectively with soft materials systems, including those of the human body.

An Energy-Efficient Wirelessly Powered Millimeter-Scale Neurostimulator Implant Based on Systematic Codesign of an Inductive Loop Antenna and a Custom Rectifier

In this work, a switched-capacitor-based stimulator circuit that enables efficient energy harvesting for neurostimulation applications is presented, followed by the discussion on the optimization of the inductive coupling front-end through a codesign approach. The stimulator salvages input energy and stores it in a storage capacitor, and, when the voltage reaches a threshold, releases the energy as an output stimulus. The dynamics of the circuit are automatically enabled by a positive feedback, eliminating any stimulation control circuit blocks. The IC is fabricated in a 180 nm CMOS process and achieves a quiescent current consumption of 1.8 μA. The inductive coupling front-end is optimized as a loaded resonator, in which the input impedance of the custom rectifier directly loads the inductive loop antenna. The loaded quality factor and the rectifier's efficiency determine the reception sensitivity of the stimulator, while a balance should be achieved for the robustness of the system against dielectric medium variations by increasing the reception bandwidth. The finalized stimulator adopts a 4.9 mm × 4.9 mm inductive loop antenna and achieves an overall assembly dimension of 5 mm × 7.5 mm. Operating at the resonant frequency of 198 MHz, the stimulator works at a 14 cm distance from the transmitter in the air. An animal experiment was performed, in which a fully implanted stimulator excited the sciatic nerve of a rat that consequently triggered the movement of the limb.

A New Way to Promote Molecular Drug Release during Medical Treatment: A Polyelectrolyte Matrix on a Piezoelectric-Dielectric Energy Conversion Substrate

Enhanced drug releases in a timely manner during urgent medical treatments would significantly enhance the prognosis of patients. Inspired by the facilitated molecular transports by the potentials, an enhanced drug release strategy driven by mechanical disturbances that widely exist in medical treatment processes is proposed. This strategy is enabled by a functional material comprised of multilayers of dendrimers as the drug reservoir, which are built on a piezoelectric-dielectric flexible film with reduced graphene oxide fillers. The generated voltages are higher and last longer than that in regular piezoelectric films. Photochemical crosslinking leads to a stable drug matrix which is even sustained in electric fields and high ionic strengths. The device enhances releases of positively, negatively, and zwitterionically charged molecules in response to mechanical stimuli and supports high cell viabilities. An illustrative application is demonstrated by preparing the material on the surface of a gastric lavage tube. The results show that the release of antiemetic drug increased by 200% within 60 min in response to forces mimicking human swallowing. This study contributes an integrative material that can realize electrically triggered releases that are previously only realized using complicated electrochemical setups. It is believed that this material can facilitate medicine applications in various emergent situations.

Artificial Cochlear Sensory Epithelium with Functions of Outer Hair Cells Mimicked Using Feedback Electrical Stimuli

We report a novel vibration control technique of an artificial auditory cochlear epithelium that mimics the function of outer hair cells in the organ of Corti. The proposed piezoelectric and trapezoidal membrane not only has the acoustic/electric conversion and frequency selectivity of the previous device developed mainly by one of the authors and colleagues, but also has a function to control local vibration according to sound stimuli. Vibration control is achieved by applying local electrical stimuli to patterned electrodes on an epithelium made using micro-electro-mechanical system technology. By choosing appropriate phase differences between sound and electrical stimuli, it is shown that it is possible to both amplify and dampen membrane vibration, realizing better control of the response of the artificial cochlea. To be more specific, amplification and damping are achieved when the phase difference between the membrane vibration by sound stimuli and electrical stimuli is zero and π, respectively. We also demonstrate that the developed control system responds automatically to a change in sound frequency. The proposed technique can be applied to mimic the nonlinear response of the outer hair cells in a cochlea, and to realize a high-quality human auditory system.

Energy Harvesting from the Animal/Human Body for Self-Powered Electronics

Living subjects (i.e., humans and animals) have abundant sources of energy in chemical, thermal, and mechanical forms. The use of these energies presents a viable way to overcome the battery capacity limitation that constrains the long-term operation of wearable/implantable devices. The intersection of novel materials and fabrication techniques offers boundless possibilities for the benefit of human health and well-being via various types of energy harvesters. This review summarizes the existing approaches that have been demonstrated to harvest energy from the bodies of living subjects for self-powered electronics. We present material choices, device layouts, and operation principles of these energy harvesters with a focus on in vivo applications. We discuss a broad range of energy harvesters placed in or on various body parts of human and animal models. We conclude with an outlook of future research in which the integration of various energy harvesters with advanced electronics can provide a new platform for the development of novel technologies for disease diagnostics, treatment, and prevention.

Extending the Limits of Wireless Power Transfer to Miniaturized Implantable Electronic Devices

Implantable electronic devices have been evolving at an astonishing pace, due to the development of fabrication techniques and consequent miniaturization, and a higher efficiency of sensors, actuators, processors and packaging. Implantable devices, with sensing, communication, actuation, and wireless power are of high demand, as they pave the way for new applications and therapies. Long-term and reliable powering of such devices has been a challenge since they were first introduced. This paper presents a review of representative state of the art implantable electronic devices, with wireless power capabilities, ranging from inductive coupling to ultrasounds. The different power transmission mechanisms are compared, to show that, without new methodologies, the power that can be safely transmitted to an implant is reaching its limit. Consequently, a new approach, capable of multiplying the available power inside a brain phantom for the same specific absorption rate (SAR) value, is proposed. In this paper, a setup was implemented to quadruple the power available in the implant, without breaking the SAR limits. A brain phantom was used for concept verification, with both simulation and measurement data.

Biomimetic Artificial Basilar Membranes for Next-Generation Cochlear Implants

Patients with sensorineural hearing loss can recover their hearing using a cochlear implant (CI). However, there is a need to develop next-generation CIs to overcome the limitations of conventional CIs caused by extracorporeal devices. Recently, artificial basilar membranes (ABMs) are actively studied for next-generation CIs. The ABM is an acoustic transducer that mimics the mechanical frequency selectivity of the BM and acoustic-to-electrical energy conversion of hair cells. This paper presents recent progress in biomimetic ABMs. First, the characteristics of frequency selectivity of the ABMs by the trapezoidal membrane and beam array are addressed. Second, to reflect the latest research of energy conversion technologies, ABMs using various piezoelectric materials and triboelectric-based ABMs are discussed. Third, in vivo evaluations of the ABMs in animal models are discussed according to the target position for implantation. Finally, future perspectives of ABM studies for the development of practical hearing devices are discussed.

High-performance wireless powering for peripheral nerve neuromodulation systems

Neuromodulation of peripheral nerves with bioelectronic devices is a promising approach for treating a wide range of disorders. Wireless powering could enable long-term operation of these devices, but achieving high performance for miniaturized and deeply placed devices remains a technological challenge. We report the miniaturized integration of a wireless powering system in soft neuromodulation device (15 mm length, 2.7 mm diameter) and demonstrate high performance (about 10%) during in vivo wireless stimulation of the vagus nerve in a porcine animal model. The increased performance is enabled by the generation of a focused and circularly polarized field that enhances efficiency and provides immunity to polarization misalignment. These performance characteristics establish the clinical potential of wireless powering for emerging therapies based on neuromodulation.

Recent Progress on Piezoelectric and Triboelectric Energy Harvesters in Biomedical Systems

Implantable medical devices (IMDs) have become indispensable medical tools for improving the quality of life and prolonging the patient's lifespan. The minimization and extension of lifetime are main challenges for the development of IMDs. Current innovative research on this topic is focused on internal charging using the energy generated by the physiological environment or natural body activity. To harvest biomechanical energy efficiently, piezoelectric and triboelectric energy harvesters with sophisticated structural and material design have been developed. Energy from body movement, muscle contraction/relaxation, cardiac/lung motions, and blood circulation is captured and used for powering medical devices. Other recent progress in this field includes using PENGs and TENGs for our cognition of the biological processes by biological pressure/strain sensing, or direct intervention of them for some special self-powered treatments. Future opportunities lie in the fabrication of intelligent, flexible, stretchable, and/or fully biodegradable self-powered medical systems for monitoring biological signals and treatment of various diseases in vitro and in vivo.

Near-Zero-Power Temperature Sensing via Tunneling Currents Through Complementary Metal-Oxide-Semiconductor Transistors

Temperature sensors are routinely found in devices used to monitor the environment, the human body, industrial equipment, and beyond. In many such applications, the energy available from batteries or the power available from energy harvesters is extremely limited due to limited available volume, and thus the power consumption of sensing should be minimized in order to maximize operational lifetime. Here we present a new method to transduce and digitize temperature at very low power levels. Specifically, two pA current references are generated via small tunneling-current metal-oxide-semiconductor field effect transistors (MOSFETs) that are independent and proportional to temperature, respectively, which are then used to charge digitally-controllable banks of metal-insulator-metal (MIM) capacitors that, via a discrete-time feedback loop that equalizes charging time, digitize temperature directly. The proposed temperature sensor was integrated into a silicon microchip and occupied 0.15 mm² of area. Four tested microchips were measured to consume only 113 pW with a resolution of 0.21 °C and an inaccuracy of ±1.65 °C, which represents a 628× reduction in power compared to prior-art without a significant reduction in performance.

A Self-Powered Implantable Drug-Delivery System Using Biokinetic Energy

The first triboelectric-nanogenerator (TENG)-based self-powered implantable drug-delivery system is presented. Pumping flow rates from 5.3 to 40 µL min^-1 under different rotating speeds of the TENG are realized. The implantable drug-delivery system can be powered with a TENG device rotated by human hand motion. Ex vivo trans-sclera drug delivery in porcine eyes is demonstrated by utilizing the biokinetic energies of human hands.

Prolonged energy harvesting for ingestible devices

Ingestible electronics have revolutionized the standard of care for a variety of health conditions. Extending the capacity and safety of these devices, and reducing the costs of powering them, could enable broad deployment of prolonged monitoring systems for patients. Although prior biocompatible power harvesting systems for in vivo use have demonstrated short minute-long bursts of power from the stomach, not much is known about the capacity to power electronics in the longer term and throughout the gastrointestinal tract. Here, we report the design and operation of an energy-harvesting galvanic cell for continuous in vivo temperature sensing and wireless communication. The device delivered an average power of 0.23 μW per mm² of electrode area for an average of 6.1 days of temperature measurements in the gastrointestinal tract of pigs. This power-harvesting cell has the capacity to provide power for prolonged periods of time to the next generation of ingestible electronic devices located in the gastrointestinal tract.

Developing and Evaluating a Flexible Wireless Microcoil Array Based Integrated Interface for Epidural Cortical Stimulation

Stroke leads to serious long-term disability. Electrical epidural cortical stimulation has made significant improvements in stroke rehabilitation therapy. We developed a preliminary wireless implantable passive interface, which consists of a stimulating surface electrode, receiving coil, and single flexible passive demodulated circuit printed by flexible printed circuit (FPC) technique and output pulse voltage stimulus by inductively coupling an external circuit. The wireless implantable board was implanted in cats’ unilateral epidural space for electrical stimulation of the primary visual cortex (V1) while the evoked responses were recorded on the contralateral V1 using a needle electrode. The wireless implantable board output stable monophasic voltage stimuli. The amplitude of the monophasic voltage output could be adjusted by controlling the voltage of the transmitter circuit within a range of 5–20 V. In acute experiment, cortico-cortical evoked potential (CCEP) response was recorded on the contralateral V1. The amplitude of N2 in CCEP was modulated by adjusting the stimulation intensity of the wireless interface. These results demonstrated that a wireless interface based on a microcoil array can offer a valuable tool for researchers to explore electrical stimulation in research and the dura mater-electrode interface can effectively transmit electrical stimulation.