Fully implantable wireless batteryless vascular electronics with printed soft sensors for multiplex sensing of hemodynamics

Recent Progress in Blood Flow Sensing

Blood plays a central role in the maintenance of the human body, and monitoring its flow rate, either invasively or non-invasively, in different parts of the circulatory is essential in the diagnosis and treatment of patients and for advancing biomedical research. This review examines the history and challenges of blood flow sensing and highlights the current state-of-the art blood flowmeters alongside the emerging tools poised to realize continuous and real-time monitoring. The clinical requirements for designing blood flow sensors are considered, including where the sensors are interfaced and their signal transduction mechanisms. Finally, the existing technological gaps are discussed and potential pathways to allow for further optimization are explored. Continued innovations in the several hundred years of evolution of blood flow sensing technology are poised to provide more timely interventions related to maintaining proper blood flow for improving patient care and outcomes.

Transforming Healthcare: Intelligent Wearable Sensors Empowered by Smart Materials and Artificial Intelligence

Intelligent wearable sensors, empowered by machine learning and innovative smart materials, enable rapid, accurate disease diagnosis, personalized therapy, and continuous health monitoring without disrupting daily life. This integration facilitates a shift from traditional, hospital-centered healthcare to a more decentralized, patient-centric model, where wearable sensors can collect real-time physiological data, provide deep analysis of these data streams, and generate actionable insights for point-of-care precise diagnostics and personalized therapy. Despite rapid advancements in smart materials, machine learning, and wearable sensing technologies, there is a lack of comprehensive reviews that systematically examine the intersection of these fields. This review addresses this gap, providing a critical analysis of wearable sensing technologies empowered by smart advanced materials and artificial Intelligence. The state-of-the-art smart materials-including self-healing, metamaterials, and responsive materials-that enhance sensor functionality are first examined. Advanced machine learning methodologies integrated into wearable devices are discussed, and their role in biomedical applications is highlighted. The combined impact of wearable sensors, empowered by smart materials and machine learning, and their applications in intelligent diagnostics and therapeutics are also examined. Finally, existing challenges, including technical and compliance issues, information security concerns, and regulatory considerations are addressed, and future directions for advancing intelligent healthcare are proposed.

Non-Surgical, In-Stent Membrane Bioelectronics for Long-Term Intracranial Pressure Monitoring

Traditional intracranial pressure (ICP) monitoring methods, using intraventricular catheters, face significant limitations, including high invasiveness, discrete data, calibration complexities, and drift issues, which hinder long-term and stable monitoring. Here, a non-surgical, in-stent membrane bioelectronic system is presented for continuous and reliable ICP monitoring. This platform integrates a capacitive thin-film sensor with a stent, enabling precise real-time detection of pressure fluctuations directly within the dural venous sinus without requiring skull penetration or frequent recalibration. The sensor demonstrates a high sensitivity of 0.052%/mmHg and a broad, readable pressure range of 3-30 mmHg while maintaining calibration-free and drift-free performance. A series of in vivo studies highlight the system's superior sensitivity, rapid sampling rate, and long-term stability compared to conventional microcatheters. Statistical analyses reveal a strong agreement between the device and clinical reference, underscoring its potential to revolutionize ICP monitoring. These advancements pave the way for broader clinical applications, minimizing complications and improving patient outcomes in neurocritical care.

Miniaturized Designs of Implantable and Wireless Hemodynamic Pressure Monitoring Capsules

OBJECTIVE

Hemodynamic pressure (HP) monitoring is critical for managing cardiovascular diseases. Clinical Doppler echocardiography and invasive catheter monitoring cannot realize remote continuous monitoring in daily life. Current implantable wireless equipment depends on custom chips or indirect sensing, presenting challenges in cost-effective and precise applications. Here, we present systematic design strategies for implantable, wireless, and battery-free capsule-like HP monitoring under near and middle-distance circumstances.

METHODS

The systems were composed of completely non-customized devices, with extremely compact volumes (<0.4 cm3). Near-distance monitoring utilized Near Field Communication with a piezoresistive sensor and foldable circuit designs. Middle-distance monitoring employed dual-winding antennas based on magnetic resonance (∼600 kHz) and Bluetooth. The power feedback circuit was optimized through human model electromagnetic simulations. Validation involved in vitro and in vivo experiments.

RESULTS

Near-distance system achieved 0.35 mmHg omnidirectional pressure accuracy under 5 mm tissue shielding. Middle-distance system attained the longest wireless power transfer distance (7.5 cm) via electromagnetic fields, supporting a capacitive sensor with 0.4 mmHg accuracy. In vitro tests in artificial tissue demonstrated stable data/energy transfer, accommodating axial misalignments up to ±45°. In vivo experiments on the beagle demonstrated real-time, wireless monitoring of left atrial pressure, whose rhythm synchronized with electrocardiograph recordings. The interatrial septum interventional installation was also validated.

CONCLUSION

The wireless and implantable capsules enable near and middle-distance hemodynamic pressure monitoring, even in dynamic swinging intracardiac situations. and has been validated in animal experiments.

SIGNIFICANCE

The designs provide a universal method for in vivo fully-implantable pressure monitor development.

Advancements in Bio-Integrated Flexible Electronics for Hemodynamic Monitoring in Cardiovascular Healthcare

Cardiovascular diseases (CVDs) remain the leading cause of global mortality, highlighting the urgent need for effective monitoring and prevention strategies. The rapid advancement of flexible sensing technology and the development of conformal sensors have attracted significant attention due to their potential for continuous, real-time assessment of cardiovascular health over extended periods. This review outlines recent advancements in bio-integrated flexible electronics designed for hemodynamic monitoring and broader CVD healthcare applications. It introduces key physiological indicators relevant to hemodynamics, including heart rate, blood pressure, blood flow velocity, and cardiac output. Next, it discusses flexible bio-integrated electronics engineering strategies, such as working principles and configuration designs. Various non-invasive and invasive bio-integrated devices for monitoring these hemodynamic indicators are then presented. Additionally, the review highlights the role of artificial intelligence algorithms and their practical applications in bio-integrated electronics for hemodynamic detection. Finally, it proposes future directions and addresses potential challenges in the field.

Materials Advances in Devices for Heart Disease Interventions

Heart disease encompasses a range of conditions that affect the heart, including coronary artery disease, arrhythmias, congenital heart defects, heart valve disease, and conditions that affect the heart muscle. Intervention strategies can be categorized according to when they are administered and include: 1) Monitoring cardiac function using sensor technology to inform diagnosis and treatment, 2) Managing symptoms by restoring cardiac output, electrophysiology, and hemodynamics, and often serving as bridge-to-recovery or bridge-to-transplantation strategies, and 3) Repairing damaged tissue, including myocardium and heart valves, when management strategies are insufficient. Each intervention approach and technology require specific material properties to function optimally, relying on materials that support their action and interface with the body, with new technologies increasingly depending on advances in materials science and engineering. This review explores material properties and requirements driving innovation in advanced intervention strategies for heart disease and highlights key examples of recent progress in the field driven by advances in materials research.

An implantable hydrogel-based phononic crystal for continuous and wireless monitoring of internal tissue strains

Conventional implantable electronic sensors for continuous monitoring of internal tissue strains are yet to match the biomechanics of tissues while maintaining biodegradability, biocompatibility and wireless monitoring capability. Here we present a two-dimensional phononic crystal composed of periodic air columns in soft hydrogel, which was named ultrasonic metagel, and we demonstrate its use as implantable sensor for continuous and wireless monitoring of internal tissue strains. The metagel's deformation shifts its ultrasonic bandgap, which can be wirelessly detected by an external ultrasonic probe. We demonstrate ex vivo the ability of the metagel sensor for monitoring tissue strains on porcine tendon, wounded tissue and heart. In live pigs, we further demonstrate the ability of the metagel to monitor tendon stretching, respiration and heartbeat, working stably during 30 days of implantation, and we loaded the metagel with growth factors to achieve different healing rates in subcutaneous wounds. The metagel results almost completely degraded 12 weeks after implantation. Our finding highlights the clinical potential of the ultrasonic sensor for tendon rehabilitation monitoring and drug delivery efficacy evaluation.

Polyelectrolyte-based wireless and drift-free iontronic sensors for orthodontic sensing

The real-time monitoring of health conditions of humans is a long-lasting topic, but there are two major challenges. First, many biomedical applications accept only implanted sensors. Second, tissue-like soft sensors often suffer from viscoelasticity-induced signal drift, causing inaccurate measurements. Here, we report a wireless and drift-free sensory system enabled by a low-creep polyelectrolyte elastomer. The system consists of the iontronic pressure sensors incorporating inductance-capacitance (LC) oscillators, exhibiting combined low drift ratio, high Q factor, high robustness to interferences, and wide-range measurement, superior to other capacitive sensors using regular dielectrics or ionogels. We have recorded 14-day orthodontic loads of two subjects using the system, showing pressure decreasing from 300 to 50 kPa and torque from 12.5 to 0.5 N·mm. The wireless, drift-free sensory system may be extended to other implants for long-term and accurate sensing.

Bio-Inspired Ionic Sensors: Transforming Natural Mechanisms into Sensory Technologies

Many natural organisms have evolved unique sensory systems over millions of years that have allowed them to detect various changes in their surrounding environments. Sensory systems feature numerous receptors-such as photoreceptors, mechanoreceptors, and chemoreceptors-that detect various types of external stimuli, including light, pressure, vibration, sound, and chemical substances. These stimuli are converted into electrochemical signals, which are transmitted to the brain to produce the sensations of sight, touch, hearing, taste, and smell. Inspired by the biological principles of sensory systems, recent advancements in electronics have led to a wide range of applications in artificial sensors. In the current review, we highlight recent developments in artificial sensors inspired by biological sensory systems utilizing soft ionic materials. The versatile characteristics of these ionic materials are introduced while focusing on their mechanical and electrical properties. The features and working principles of natural and artificial sensing systems are investigated in terms of six categories: vision, tactile, hearing, gustatory, olfactory, and proximity sensing. Lastly, we explore several challenges that must be overcome while outlining future research directions in the field of soft ionic sensors.

Biointerface engineering of flexible and wearable electronics

Biointerface sensing is a cutting-edge interdisciplinary field that merges conceptual and practical aspects. Wearable bioelectronics enable efficient interaction and close contact with biological components such as tissues and organs, paving the way for a wide range of medical applications, including personal health monitoring and medical intervention. To be applicable in real-world settings, the patches must be stable and adhere to the skin without causing discomfort or allergies in both wet and dry conditions, as well as other desirable features such as being ultra-soft, thin, flexible, and stretchable. Biosensors have emerged as promising tools primarily used to directly detect biological and electrophysiological signals, enhancing the efficacy of personalized medical treatments and enabling accurate tracking of human well-being. This review highlights the engineering of skin-tissue surfaces/interfaces and their interactions with wearable patches, aiming for both a broad and in-depth understanding of the mechanical and physicochemical properties required for the advancement of flexible and wearable skin patches. Specifically, the advantages of flexible bioelectronics and sensors with optimized surface geometry for long-term diagnosis are discussed. This insight aims to guide the future development of functional materials that can interact with human tissue in a controlled manner. Finally, we provide perspectives on the challenges and potential applications of biointerface engineering in wearable devices.

Advancements in Passive Wireless Sensing Systems in Monitoring Harsh Environment and Healthcare Applications

Recent advancements in passive wireless sensor technology have significantly extended the application scope of sensing, particularly in challenging environments for monitoring industry and healthcare applications. These systems are equipped with battery-free operation, wireless connectivity, and are designed to be both miniaturized and lightweight. Such features enable the safe, real-time monitoring of industrial environments and support high-precision physiological measurements in confined internal body spaces and on wearable epidermal devices. Despite the exploration into diverse application environments, the development of a systematic and comprehensive research framework for system architecture remains elusive, which hampers further optimization of these systems. This review, therefore, begins with an examination of application scenarios, progresses to evaluate current system architectures, and discusses the function of each component-specifically, the passive sensor module, the wireless communication model, and the readout module-within the context of key implementations in target sensing systems. Furthermore, we present case studies that demonstrate the feasibility of proposed classified components for sensing scenarios, derived from this systematic approach. By outlining a research trajectory for the application of passive wireless systems in sensing technologies, this paper aims to establish a foundation for more advanced, user-friendly applications.

Recent advances in bio-integrated electrochemical sensors for neuroengineering

Detecting and diagnosing neurological diseases in modern healthcare presents substantial challenges that directly impact patient outcomes. The complex nature of these conditions demands precise and quantitative monitoring of disease-associated biomarkers in a continuous, real-time manner. Current chemical sensing strategies exhibit restricted clinical effectiveness due to labor-intensive laboratory analysis prerequisites, dependence on clinician expertise, and prolonged and recurrent interventions. Bio-integrated electronics for chemical sensing is an emerging, multidisciplinary field enabled by rapid advances in electrical engineering, biosensing, materials science, analytical chemistry, and biomedical engineering. This review presents an overview of recent progress in bio-integrated electrochemical sensors, with an emphasis on their relevance to neuroengineering and neuromodulation. It traverses vital neurological biomarkers and explores bio-recognition elements, sensing strategies, transducer designs, and wireless signal transmission methods. The integration of in vivo biochemical sensors is showcased through applications. The review concludes by outlining future trends and advancements in in vivo electrochemical sensing, and highlighting ongoing research and technological innovation, which aims to provide inspiring and practical instructions for future research.

Recent advances in materials and manufacturing of implantable devices for continuous health monitoring

Implantable devices are vital in healthcare, enabling continuous monitoring, early disease detection, informed decision-making, enhanced outcomes, cost reduction, and chronic condition management. These devices provide real-time data, allowing proactive healthcare interventions, and contribute to overall improvements in patient care and quality of life. The success of implantable devices relies on the careful selection of materials and manufacturing methods. Recent materials research and manufacturing advancements have yielded implantable devices with enhanced biocompatibility, reliability, and functionality, benefiting human healthcare. This paper provides a comprehensive overview of the latest developments in implantable medical devices, emphasizing the importance of material selection and manufacturing methods, including biocompatibility, self-healing capabilities, corrosion resistance, mechanical properties, and conductivity. It explores various manufacturing techniques such as microfabrication, 3D printing, laser micromachining, electrospinning, screen printing, inkjet printing, and nanofabrication. The paper also discusses challenges and limitations in the field, including biocompatibility concerns, privacy and data security issues, and regulatory hurdles for implantable devices.

Conformal printed electronics on flexible substrates and inflatable catheters using lathe-based aerosol jet printing

With the growth of additive manufacturing (AM), there has been increasing demand for fabricating conformal electronics that directly integrate with larger components to enable unique functionality. However, fabrication of conformal electronics is challenging because devices must merge with host substrates regardless of curvilinearity, topography, or substrate material. In this work, we employ aerosol jet (AJ) printing, an AM method for jet printing electronics using ink-based materials, and a custom-made lathe mechanism for mounting flexible substrates and 3D objects on a rotating axis. Using this method of lathe-based AJ printing, conformal electronics are printed around the circumference of rotational bodies with 3D curvilinear surfaces through cylindrical-coordinate motion. We characterize the diverse capabilities of lathe AJ (LAJ) printing and demonstrate flexible conformal electronics including multilayer carbon nanotube transistors. Lastly, a graphene sensor is conformally printed on an inflated catheter balloon for temperature and inflation monitoring, thus highlighting the versatilities of LAJ printing.

Softening implantable bioelectronics: Material designs, applications, and future directions

Implantable bioelectronics, integrated directly within the body, represent a potent biomedical solution for monitoring and treating a range of medical conditions, including chronic diseases, neural disorders, and cardiac conditions, through personalized medical interventions. Nevertheless, contemporary implantable bioelectronics rely heavily on rigid materials (e.g., inorganic materials and metals), leading to inflammatory responses and tissue damage due to a mechanical mismatch with biological tissues. Recently, soft electronics with mechanical properties comparable to those of biological tissues have been introduced to alleviate fatal immune responses and improve tissue conformity. Despite their myriad advantages, substantial challenges persist in surgical handling and precise positioning due to their high compliance. To surmount these obstacles, softening implantable bioelectronics has garnered significant attention as it embraces the benefits of both rigid and soft bioelectronics. These devices are rigid for easy standalone implantation, transitioning to a soft state in vivo in response to environmental stimuli, which effectively overcomes functional/biological problems inherent in the static mechanical properties of conventional implants. This article reviews recent research and development in softening materials and designs for implantable bioelectronics. Examples featuring tissue-penetrating and conformal softening devices highlight the promising potential of these approaches in biomedical applications. A concluding section delves into current challenges and outlines future directions for softening implantable device technologies, underscoring their pivotal role in propelling the evolution of next-generation bioelectronics.

Recent advances in implantable sensors and electronics using printable materials for advanced healthcare

This review article focuses on the recent printing technological progress in healthcare, underscoring the significant potential of implantable devices across diverse applications. Printing technologies have widespread use in developing health monitoring devices, diagnostic systems, and surgical devices. Recent years have witnessed remarkable progress in fabricating low-profile implantable devices, driven by advancements in printing technologies and nanomaterials. The importance of implantable biosensors and bioelectronics is highlighted, specifically exploring printing tools using bio-printable inks for practical applications, including a detailed examination of fabrication processes and essential parameters. This review also justifies the need for mechanical and electrical compatibility between bioelectronics and biological tissues. In addition to technological aspects, this article delves into the importance of appropriate packaging methods to enhance implantable devices' performance, compatibility, and longevity, which are made possible by integrating cutting-edge printing technology. Collectively, we aim to shed light on the holistic landscape of implantable biosensors and bioelectronics, showcasing their evolving role in advancing healthcare through innovative printing technologies.

Global trends in clinical trials involving engineered biomaterials

Engineered biomaterials are materials specifically designed to interact with biological systems for biomedical applications. This paper offers the comprehensive analysis of global clinical trial trends involving such materials. We surveyed 834 studies in the ClinicalTrials.gov database and explored biomaterial types, their initiation points, and durations in clinical trials. Predominantly, synthetic and natural polymers, particularly silicone and collagen, are used. Trials, focusing on ophthalmology, dentistry, and vascular medicine, are primarily conducted in the United States, Canada, and Italy. These trials encompass a broad demographic, and trials enrolled fewer than 100 participants. The study duration varied ranging from 0.5 to 4.5 years. These biomaterials are mainly bioresorbable or bioinert, with the integration of cells in biomaterials remaining an underexplored area. Our findings shed light on current practices and future potentials of engineered biomaterials in clinical research, offering insights for advancing this dynamic field globally.

Wireless Technologies in Flexible and Wearable Sensing: From Materials Design, System Integration to Applications

Wireless and wearable sensors attract considerable interest in personalized healthcare by providing a unique approach for remote, noncontact, and continuous monitoring of various health-related signals without interference with daily life. Recent advances in wireless technologies and wearable sensors have promoted practical applications due to their significantly improved characteristics, such as reduction in size and thickness, enhancement in flexibility and stretchability, and improved conformability to the human body. Currently, most researches focus on active materials and structural designs for wearable sensors, with just a few exceptions reflecting on the technologies for wireless data transmission. This review provides a comprehensive overview of the state-of-the-art wireless technologies and related studies on empowering wearable sensors. The emerging functional nanomaterials utilized for designing unique wireless modules are highlighted, which include metals, carbons, and MXenes. Additionally, the review outlines the system-level integration of wireless modules with flexible sensors, spanning from novel design strategies for enhanced conformability to efficient transmitting data wirelessly. Furthermore, the review introduces representative applications for remote and noninvasive monitoring of physiological signals through on-skin and implantable wireless flexible sensing systems. Finally, the challenges, perspectives, and unprecedented opportunities for wireless and wearable sensors are discussed.

Detection of Blood Clots Using a Whole Stent as an Active Implantable Biosensor

Many cardiovascular problems stem from blockages that form within the vasculature and often treatment includes fitting a stent through percutaneous coronary intervention. This offers a minimally invasive therapy but re-occlusion through restenosis or thrombosis formation often occurs post-deployment. Research is ongoing into the creation of smart stents that can detect the occurrence of further problems. In this study, it is shown that selectively metalizing a non-conductive stent can create a set of electrodes that are capable of detecting a build-up of material around the stent. The associated increase in electrical impedance across the electrodes is measured, testing the stent with blood clot to mimic thrombosis. It is shown that the device is capable of sensing different amounts of occlusion. The stent can reproducibly sense the presence of clot showing a 16% +/-3% increase in impedance which is sufficient to reliably detect the clot when surrounded by explanted aorta (one sample t-test, p = 0.009, n = 9). It is demonstrated that this approach can be extended beyond the 3D printed prototypes by showing that it can be applied to a commercially available stent and it is believed that it can be further utilized by other types of medical implants.

Materials and Structural Designs toward Motion Artifact-Free Bioelectronics

Bioelectronics encompassing electronic components and circuits for accessing human information play a vital role in real-time and continuous monitoring of biophysiological signals of electrophysiology, mechanical physiology, and electrochemical physiology. However, mechanical noise, particularly motion artifacts, poses a significant challenge in accurately detecting and analyzing target signals. While software-based "postprocessing" methods and signal filtering techniques have been widely employed, challenges such as signal distortion, major requirement of accurate models for classification, power consumption, and data delay inevitably persist. This review presents an overview of noise reduction strategies in bioelectronics, focusing on reducing motion artifacts and improving the signal-to-noise ratio through hardware-based approaches such as "preprocessing". One of the main stress-avoiding strategies is reducing elastic mechanical energies applied to bioelectronics to prevent stress-induced motion artifacts. Various approaches including strain-compliance, strain-resistance, and stress-damping techniques using unique materials and structures have been explored. Future research should optimize materials and structure designs, establish stable processes and measurement methods, and develop techniques for selectively separating and processing overlapping noises. Ultimately, these advancements will contribute to the development of more reliable and effective bioelectronics for healthcare monitoring and diagnostics.

Soft mechanical sensors for wearable and implantable applications

Wearable and implantable sensing of biomechanical signals such as pressure, strain, shear, and vibration can enable a multitude of human-integrated applications, including on-skin monitoring of vital signs, motion tracking, monitoring of internal organ condition, restoration of lost/impaired mechanoreception, among many others. The mechanical conformability of such sensors to the human skin and tissue is critical to enhancing their biocompatibility and sensing accuracy. As such, in the recent decade, significant efforts have been made in the development of soft mechanical sensors. To satisfy the requirements of different wearable and implantable applications, such sensors have been imparted with various additional properties to make them better suited for the varied contexts of human-integrated applications. In this review, focusing on the four major types of soft mechanical sensors for pressure, strain, shear, and vibration, we discussed the recent material and device design innovations for achieving several important properties, including flexibility and stretchability, bioresorbability and biodegradability, self-healing properties, breathability, transparency, wireless communication capabilities, and high-density integration. We then went on to discuss the current research state of the use of such novel soft mechanical sensors in wearable and implantable applications, based on which future research needs were further discussed. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > Diagnostic Nanodevices Implantable Materials and Surgical Technologies > Nanomaterials and Implants.

An Era of Digital Healthcare-A Comprehensive Review of Sensor Technologies and Telehealth Advancements in Chronic Heart Failure Management

Heart failure (HF) is a multi-faceted, complex clinical syndrome characterized by significant morbidity, high mortality rate, reduced quality of life, and rapidly increasing healthcare costs. A larger proportion of these costs comprise both ambulatory and emergency department visits, as well as hospital admissions. Despite the methods used by telehealth (TH) to improve self-care and quality of life, patient outcomes remain poor. HF management is associated with numerous challenges, such as conflicting evidence from clinical trials, heterogeneity of TH devices, variability in patient inclusion and exclusion criteria, and discrepancies between healthcare systems. A growing body of evidence suggests there is an unmet need for increased individualization of in-hospital management, continuous remote monitoring of patients pre and post-hospital admission, and continuation of treatment post-discharge in order to reduce re-hospitalizations and improve long-term outcomes. This review summarizes the current state-of-the-art for HF and associated novel technologies and advancements in the most frequently used types of TH (implantable sensors), categorizing devices in their preclinical and clinical stage, bench-to-bedside implementation challenges, and future perspectives on remote HF management to improve long-term outcomes of HF patients. The Review also highlights recent advancements in non-invasive remote monitoring technologies demonstrated by a few pilot observational prospective cohort studies.

Millimeter-scale magnetic implants paired with a fully integrated wearable device for wireless biophysical and biochemical sensing

Implantable sensors can directly interface with various organs for precise evaluation of health status. However, extracting signals from such sensors mainly requires transcutaneous wires, integrated circuit chips, or cumbersome readout equipment, which increases the risks of infection, reduces biocompatibility, or limits portability. Here, we develop a set of millimeter-scale, chip-less, and battery-less magnetic implants paired with a fully integrated wearable device for measuring biophysical and biochemical signals. The wearable device can induce a large amplitude damped vibration of the magnetic implants and capture their subsequent motions wirelessly. These motions reflect the biophysical conditions surrounding the implants and the concentration of a specific biochemical depending on the surface modification. Experiments in rat models demonstrate the capabilities of measuring cerebrospinal fluid (CSF) viscosity, intracranial pressure, and CSF glucose levels. This miniaturized system opens the possibility for continuous, wireless monitoring of a wide range of biophysical and biochemical conditions within the living organism.

Wireless Battery-free and Fully Implantable Organ Interfaces

Advances in soft materials, miniaturized electronics, sensors, stimulators, radios, and battery-free power supplies are resulting in a new generation of fully implantable organ interfaces that leverage volumetric reduction and soft mechanics by eliminating electrochemical power storage. This device class offers the ability to provide high-fidelity readouts of physiological processes, enables stimulation, and allows control over organs to realize new therapeutic and diagnostic paradigms. Driven by seamless integration with connected infrastructure, these devices enable personalized digital medicine. Key to advances are carefully designed material, electrophysical, electrochemical, and electromagnetic systems that form implantables with mechanical properties closely matched to the target organ to deliver functionality that supports high-fidelity sensors and stimulators. The elimination of electrochemical power supplies enables control over device operation, anywhere from acute, to lifetimes matching the target subject with physical dimensions that supports imperceptible operation. This review provides a comprehensive overview of the basic building blocks of battery-free organ interfaces and related topics such as implantation, delivery, sterilization, and user acceptance. State of the art examples categorized by organ system and an outlook of interconnection and advanced strategies for computation leveraging the consistent power influx to elevate functionality of this device class over current battery-powered strategies is highlighted.

On-Demand 3D Spatial Distribution of Magnetic Permeability Based on Fe3 O4 Nanoparticle Liquid Toward Micro-Cavity Detectors

The change of 3D spatial distribution of magnetic permeability can lead to the generation of introduced electrical signals. However, present studies can only achieve rough regulation by simple shape deformation of magnetic elastomers such as compression, bending, or stretching. Accurate control of the 3D spatial distribution of magnetic permeability is still an open question. In this study, an on-demand 3D spatial distribution of magnetic permeability by controlled flowing of Fe3 O4 nanoparticle liquid (FNL) is demonstrated. The flowing routes of FNL are tuned by a 3D-printed cage with pre-designed hollow structure, thus changing the 3D spatial distribution of magnetic permeability. Then, eight symmetrically distributed coils under cage are used to receive characteristic induction voltage signals. Maxwell numerical simulation reveals the working mechanism of signal generation. Notably, those eight coils can detect FNL flowing status in eight directions, allowing recognition of up to 255 different FNL flowing combinations. By introducing machine learning, the micro-cavity detector based on FNL can distinguish nine kinds of micro-cavity structures with an accuracy of 98.77%. This work provides a new strategy for the adjustment of the 3D spatial distribution of the magnetic permeability and expands the application of FNL in the field of space exploration.

Free-Boundary Microfluidic Platform for Advanced Materials Manufacturing and Applications

Microfluidics, with its remarkable capacity to manipulate fluids and droplets at the microscale, has emerged as a powerful platform in numerous fields. In contrast to conventional closed microchannel microfluidic systems, free-boundary microfluidic manufacturing (FBMM) processes continuous precursor fluids into jets or droplets in a relatively spacious environment. FBMM is highly regarded for its superior flexibility, stability, economy, usability, and versatility in the manufacturing of advanced materials and architectures. In this review, a comprehensive overview of recent advancements in FBMM is provided, encompassing technical principles, advanced material manufacturing, and their applications. FBMM is categorized based on the foundational mechanisms, primarily comprising hydrodynamics, interface effects, acoustics, and electrohydrodynamic. The processes and mechanisms of fluid manipulation are thoroughly discussed. Additionally, the manufacturing of advanced materials in various dimensions ranging from zero-dimensional to three-dimensional, as well as their diverse applications in material science, biomedical engineering, and engineering are presented. Finally, current progress is summarized and future challenges are prospected. Overall, this review highlights the significant potential of FBMM as a powerful tool for advanced materials manufacturing and its wide-ranging applications.

Memristor-Based Artificial Chips

Memristors, promising nanoelectronic devices with in-memory resistive switching behavior that is assembled with a physically integrated core processing unit (CPU) and memory unit and even possesses highly possible multistate electrical behavior, could avoid the von Neumann bottleneck of traditional computing devices and show a highly efficient ability of parallel computation and high information storage. These advantages position them as potential candidates for future data-centric computing requirements and add remarkable vigor to the research of next-generation artificial intelligence (AI) systems, particularly those that involve brain-like intelligence applications. This work provides an overview of the evolution of memristor-based devices, from their initial use in creating artificial synapses and neural networks to their application in developing advanced AI systems and brain-like chips. It offers a broad perspective of the key device primitives enabling their special applications from the view of materials, nanostructure, and mechanism models. We highlight these demonstrations of memristor-based nanoelectronic devices that have potential for use in the field of brain-like AI, point out the existing challenges of memristor-based nanodevices toward brain-like chips, and propose the guiding principle and promising outlook for future device promotion and system optimization in the biomedical AI field.

Unconstrained Piezoelectric Vascular Electronics for Wireless Monitoring of Hemodynamics and Cardiovascular Health

The patient-centered healthcare requires timely disease diagnosis and prognostic assessment, calling for individualized physiological monitoring. To assess the postoperative hemodynamic status of patients, implantable blood flow monitoring devices are highly expected to deliver real time, long-term, sensitive, and reliable hemodynamic signals, which can accurately reflect multiple physiological conditions. Herein, an implantable and unconstrained vascular electronic system based on a piezoelectric sensor immobilized is presented by a "growable" sheath around continuously growing arterial vessels for real-timely and wirelessly monitoring of hemodynamics. The piezoelectric sensor made of circumferentially aligned polyvinylidene fluoride nanofibers around pulsating artery can sensitively perceive mechanical signals, and the growable sheath bioinspired by the structure and function of leaf sheath has elasticity and conformal shape adaptive to the dynamically growing arterial vessels to avoid growth constriction. With this integrated and smart design, long-term, wireless, and sensitive monitoring of hemodynamics are achieved and demonstrated in rats and rabbits. It provides a simple and versatile strategy for designing implantable sensors in a less invasive way.

3D-Printed Biohybrid Microstructures Enable Transplantation and Vascularization of Microtissues in the Anterior Chamber of the Eye

Hybridizing biological cells with man-made sensors enable the detection of a wide range of weak physiological responses with high specificity. The anterior chamber of the eye (ACE) is an ideal transplantation site due to its ocular immune privilege and optical transparency, which enable superior noninvasive longitudinal analyses of cells and microtissues. Engraftment of biohybrid microstructures in the ACE may, however, be affected by the pupillary response and dynamics. Here, sutureless transplantation of biohybrid microstructures, 3D printed in IP-Visio photoresin, containing a precisely localized pancreatic islet to the ACE of mice is presented. The biohybrid microstructures allow mechanical fixation in the ACE, independent of iris dynamics. After transplantation, islets in the microstructures successfully sustain their functionality for over 20 weeks and become vascularized despite physical separation from the vessel source (iris) and immersion in a low-viscous liquid (aqueous humor) with continuous circulation and clearance. This approach opens new perspectives in biohybrid microtissue transplantation in the ACE, advancing monitoring of microtissue-host interactions, disease modeling, treatment outcomes, and vascularization in engineered tissues.

A dual-mode fiber-shaped flexible capacitive strain sensor fabricated by direct ink writing technology for wearable and implantable health monitoring applications

Flexible fiber-shaped strain sensors show tremendous potential in wearable health monitoring and human‒machine interactions due to their compatibility with everyday clothing. However, the conductive and sensitive materials generated by traditional manufacturing methods to fabricate fiber-shaped strain sensors, including sequential coating and solution extrusion, exhibit limited stretchability, resulting in a limited stretch range and potential interface delamination. To address this issue, we fabricate a fiber-shaped flexible capacitive strain sensor (FSFCSS) by direct ink writing technology. Through this technology, we print parallel helical Ag electrodes on the surface of TPU tube fibers and encapsulate them with a high dielectric material BTO@Ecoflex, endowing FSFCSS with excellent dual-mode sensing performance. The FSFCSS can sense dual-model strain, namely, axial tensile strain and radial expansion strain. For axial tensile strain sensing, FSFCSS exhibits a wide detection range of 178%, a significant sensitivity of 0.924, a low detection limit of 0.6%, a low hysteresis coefficient of 1.44%, and outstanding mechanical stability. For radial expansion strain sensing, FSFCSS demonstrates a sensitivity of 0.00086 mmHg-1 and exhibits excellent responsiveness to static and dynamic expansion strain. Furthermore, FSFCSS was combined with a portable data acquisition circuit board for the acquisition of physiological signals and human‒machine interaction in a wearable wireless sensing system. To measure blood pressure and heart rate, FSFCSS was combined with a printed RF coil in series to fabricate a wireless hemodynamic sensor. This work enables simultaneous application in wearable and implantable health monitoring, thereby advancing the development of smart textiles.

3D Printed Integrated Sensors: From Fabrication to Applications-A Review

The integration of 3D printed sensors into hosting structures has become a growing area of research due to simplified assembly procedures, reduced system complexity, and lower fabrication cost. Embedding 3D printed sensors into structures or bonding the sensors on surfaces are the two techniques for the integration of sensors. This review extensively discusses the fabrication of sensors through different additive manufacturing techniques. Various additive manufacturing techniques dedicated to manufacture sensors as well as their integration techniques during the manufacturing process will be discussed. This review will also discuss the basic sensing mechanisms of integrated sensors and their applications. It has been proven that integrating 3D printed sensors into infrastructures can open new possibilities for research and development in additive manufacturing and sensor materials for smart goods and the Internet of Things.

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.

Recent Advances in Sensor-Actuator Hybrid Soft Systems: Core Advantages, Intelligent Applications, and Future Perspectives

The growing demand for soft intelligent systems, which have the potential to be used in a variety of fields such as wearable technology and human-robot interaction systems, has spurred the development of advanced soft transducers. Among soft systems, sensor-actuator hybrid systems are considered the most promising due to their effective and efficient performance, resulting from the synergistic and complementary interaction between their sensor and actuator components. Recent research on integrated sensor and actuator systems has resulted in a range of conceptual and practical soft systems. This review article provides a comprehensive analysis of recent advances in sensor and actuator integrated systems, which are grouped into three categories based on their primary functions: i) actuator-assisted sensors for intelligent detection, ii) sensor-assisted actuators for intelligent movement, and iii) sensor-actuator interactive devices for a hybrid of intelligent detection and movement. In addition, several bottlenecks in current studies are discussed, and prospective outlooks, including potential applications, are presented. This categorization and analysis will pave the way for the advancement and commercialization of sensor and actuator-integrated systems.

Actuation-enhanced multifunctional sensing and information recognition by magnetic artificial cilia arrays

Artificial cilia integrating both actuation and sensing functions allow simultaneously sensing environmental properties and manipulating fluids in situ, which are promising for environment monitoring and fluidic applications. However, existing artificial cilia have limited ability to sense environmental cues in fluid flows that have versatile information encoded. This limits their potential to work in complex and dynamic fluid-filled environments. Here, we propose a generic actuation-enhanced sensing mechanism to sense complex environmental cues through the active interaction between artificial cilia and the surrounding fluidic environments. The proposed mechanism is based on fluid-cilia interaction by integrating soft robotic artificial cilia with flexible sensors. With a machine learning-based approach, complex environmental cues such as liquid viscosity, environment boundaries, and distributed fluid flows of a wide range of velocities can be sensed, which is beyond the capability of existing artificial cilia. As a proof of concept, we implement this mechanism on magnetically actuated cilia with integrated laser-induced graphene-based sensors and demonstrate sensing fluid apparent viscosity, environment boundaries, and fluid flow speed with a reconfigurable sensitivity and range. The same principle could be potentially applied to other soft robotic systems integrating other actuation and sensing modalities for diverse environmental and fluidic applications.

Beyond Tissue replacement: The Emerging role of smart implants in healthcare

Smart implants are increasingly used to treat various diseases, track patient status, and restore tissue and organ function. These devices support internal organs, actively stimulate nerves, and monitor essential functions. With continuous monitoring or stimulation, patient observation quality and subsequent treatment can be improved. Additionally, using biodegradable and entirely excreted implant materials eliminates the need for surgical removal, providing a patient-friendly solution. In this review, we classify smart implants and discuss the latest prototypes, materials, and technologies employed in their creation. Our focus lies in exploring medical devices beyond replacing an organ or tissue and incorporating new functionality through sensors and electronic circuits. We also examine the advantages, opportunities, and challenges of creating implantable devices that preserve all critical functions. By presenting an in-depth overview of the current state-of-the-art smart implants, we shed light on persistent issues and limitations while discussing potential avenues for future advancements in materials used for these devices.

Development and Prospective Applications of 3D Membranes as a Sensor for Monitoring and Inducing Tissue Regeneration

For decades, tissue regeneration has been a challenging issue in scientific modeling and human practices. Although many conventional therapies are already used to treat burns, muscle injuries, bone defects, and hair follicle injuries, there remains an urgent need for better healing effects in skin, bone, and other unique tissues. Recent advances in three-dimensional (3D) printing and real-time monitoring technologies have enabled the creation of tissue-like membranes and the provision of an appropriate microenvironment. Using tissue engineering methods incorporating 3D printing technologies and biomaterials for the extracellular matrix (ECM) containing scaffolds can be used to construct a precisely distributed artificial membrane. Moreover, advances in smart sensors have facilitated the development of tissue regeneration. Various smart sensors may monitor the recovery of the wound process in different aspects, and some may spontaneously give feedback to the wound sites by releasing biological factors. The combination of the detection of smart sensors and individualized membrane design in the healing process shows enormous potential for wound dressings. Here, we provide an overview of the advantages of 3D printing and conventional therapies in tissue engineering. We also shed light on different types of 3D printing technology, biomaterials, and sensors to describe effective methods for use in skin and other tissue regeneration, highlighting their strengths and limitations. Finally, we highlight the value of 3D bioengineered membranes in various fields, including the modeling of disease, organ-on-a-chip, and drug development.

Wearable Transmitter Coil Design for Inductive Wireless Power Transfer to Implantable Devices

Wireless endovascular sensors and stimulators are emerging biomedical technologies for applications such as endovascular pressure monitoring, hyperthermia, and neural stimulations. Recently, coil-shaped stents have been proposed for inductive power transfer to endovascular devices using the stent as a receiver. However, less work has been done on the external transmitter components, so the maximum power transferable remains unknown. In this work, we design and evaluate a wearable transmitter coil that allows 50 mW power transfer in simulation.Clinical Relevance-This allows more accurate measurements and precise control of endovascular devices.

Technology Roadmap for Flexible Sensors

Humans rely increasingly on sensors to address grand challenges and to improve quality of life in the era of digitalization and big data. For ubiquitous sensing, flexible sensors are developed to overcome the limitations of conventional rigid counterparts. Despite rapid advancement in bench-side research over the last decade, the market adoption of flexible sensors remains limited. To ease and to expedite their deployment, here, we identify bottlenecks hindering the maturation of flexible sensors and propose promising solutions. We first analyze challenges in achieving satisfactory sensing performance for real-world applications and then summarize issues in compatible sensor-biology interfaces, followed by brief discussions on powering and connecting sensor networks. Issues en route to commercialization and for sustainable growth of the sector are also analyzed, highlighting environmental concerns and emphasizing nontechnical issues such as business, regulatory, and ethical considerations. Additionally, we look at future intelligent flexible sensors. In proposing a comprehensive roadmap, we hope to steer research efforts towards common goals and to guide coordinated development strategies from disparate communities. Through such collaborative efforts, scientific breakthroughs can be made sooner and capitalized for the betterment of humanity.

Droplets Patterning of Structurally Integrated 3D Conductive Networks-Based Flexible Strain Sensors for Healthcare Monitoring

Flexible strain sensors with significant extensibility, stability, and durability are essential for public healthcare due to their ability to monitor vital health signals noninvasively. However, thus far, the conductive networks have been plagued by the inconsistent interface states of the conductive components, which hampered the ultimate sensitivity performance. Here, we demonstrate structurally integrated 3D conductive networks-based flexible strain sensors of hybrid Ag nanorods/nanoparticles(AgNRs/NPs) by combining a droplet-based aerosol jet printing(AJP) process and a feasible transfer process. Structurally integrated 3D conductive networks have been intentionally developed by tweaking droplets deposition behaviors at multi-scale for efficient hybridization and ordered assembly of AgNRs/NPs. The hybrid AgNRs/NPs enhance interfacial conduction and mechanical properties during stretching. In a strain range of 25%, the developed sensor demonstrates an ideal gauge factor of 23.18. When real-time monitoring of finger bending, arm bending, squatting, and vocalization, the fabricated sensors revealed effective responses to human movements. Our findings demonstrate the efficient droplet-based AJP process is particularly capable of developing advanced flexible devices for optoelectronics and wearable electronics applications.

Ultrasoft and Biocompatible Magnetic-Hydrogel-Based Strain Sensors for Wireless Passive Biomechanical Monitoring

Implantable flexible mechanical sensors have exhibited great potential in health monitoring and disease diagnosis due to continuous and real-time monitoring capability. However, the wires and power supply required in current devices cause inconvenience and potential risks. Magnetic-based devices have demonstrated advantages in wireless and passive sensing, but the mismatched mechanical properties, poor biocompatibility, and insufficient sensitivity have limited their applications in biomechanical monitoring. Here, a wireless and passive flexible magnetic-based strain sensor based on a gelatin methacrylate/Fe₃O₄ magnetic hydrogel has been fabricated. The sensor exhibits ultrasoft mechanical properties, strong magnetic properties, and long-term stability in saline solution and can monitor strains down to 50 μm. A model of the sensing process is established to identify the optimal detection location and the relation between the relative magnetic permeability and the sensitivity of the sensors. Moreover, an in vitro tissue model is developed to investigate the potential of the sensor in detecting subtle biomechanical signals and avoiding interference with bioactivities. Furthermore, a real-time and high-throughput biomonitoring platform is built and implements passive wireless monitoring of the drug response and cultural status of the cardiomyocytes. This work demonstrates the potential of applying magnetic sensing for biomechanical monitoring and provides ideas for the design of wireless and passive implantable devices.

Biomechanical Sensing Systems for Cardiac Activity Monitoring

Cardiovascular disease is consistently ranked high among the causes of death on a global scale. Monitoring of cardiovascular signs throughout the course of a long period of time and in real time is necessary in order to discover anomalies and begin early intervention at the appropriate time. To this purpose, a significant amount of interest among researchers has been directed toward the creation of flexible sensors that may be worn or implanted and are capable of constant, immediate observation of a variety of main physiological indicators. The real-time readings of the heart and arteries' pressure fluctuations can be reflected directly by mechanical sensors, which are one of the many types of sensors. Potential benefits of mechanical sensors include excellent accuracy and considerable versatility. Capacitive, piezoresistive, piezoelectric, and triboelectric principles are the foundations of the four types of mechanical sensors that are discussed in this article as recent developments for the purpose of monitoring the cardiovascular system. The biomechanical systems that are present in the cardiovascular system are then detailed, along with their monitoring, and this includes blood and endocardial pressure, pulse wave, and heart rhythm. In conclusion, we examine the usefulness of the use of continuous health monitoring for the treatment of vascular disease and highlight the difficulties associated with its translation into clinical practice.

Mechanical Sensors for Cardiovascular Monitoring: From Battery-Powered to Self-Powered

Cardiovascular disease is one of the leading causes of death worldwide. Long-term and real-time monitoring of cardiovascular indicators is required to detect abnormalities and conduct early intervention in time. To this end, the development of flexible wearable/implantable sensors for real-time monitoring of various vital signs has aroused extensive interest among researchers. Among the different kinds of sensors, mechanical sensors can reflect the direct information of pressure fluctuations in the cardiovascular system with the advantages of high sensitivity and suitable flexibility. Herein, we first introduce the recent advances of four kinds of mechanical sensors for cardiovascular system monitoring, based on capacitive, piezoresistive, piezoelectric, and triboelectric principles. Then, the physio-mechanical mechanisms in the cardiovascular system and their monitoring are described, including pulse wave, blood pressure, heart rhythm, endocardial pressure, etc. Finally, we emphasize the importance of real-time physiological monitoring in the treatment of cardiovascular disease and discuss its challenges in clinical translation.