Bioresorbable silicon electronic sensors for the brain

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.

Stretchable and biodegradable self-healing conductors for multifunctional electronics

As the regenerative mechanisms of biological organisms, self-healing provides useful functions for soft electronics or associated systems. However, there have been few examples of soft electronics where all components have self-healing properties while also ensuring compatibility between components to achieve multifunctional and resilient bio-integrated electronics. Here, we introduce a stretchable, biodegradable, self-healing conductor constructed by combination of two layers: (i) synthetic self-healing elastomer and (ii) self-healing conductive composite with additives. Abundant dynamic disulfide and hydrogen bonds of the elastomer and conductive composite enable rapid and complete recovery of electrical conductivity (~1000 siemens per centimeter) and stretchability (~500%) in response to repetitive damages, and chemical interactions of interpenetrated polymer chains of these components facilitate robust adhesion strength, even under extreme mechanical stress. System-level demonstration of soft, self-healing electronics with diagnostic/therapeutic functions for the urinary bladder validates the possibility for versatile, practical uses in biomedical research areas.

Soft bioelectronics for diagnostic and therapeutic applications in neurological diseases

Physical and chemical signals in the central nervous system yield crucial information that is clinically relevant under both physiological and pathological conditions. The emerging field of bioelectronics focuses on the monitoring and manipulation of neurophysiological signals with high spatiotemporal resolution and minimal invasiveness. Significant advances have been realized through innovations in materials and structural design, which have markedly enhanced mechanical and electrical properties, biocompatibility, and overall device performance. The diagnostic and therapeutic potential of soft bioelectronics has been corroborated across a diverse array of pre-clinical settings. This review summarizes recent studies that underscore the developments and applications of soft bioelectronics in neurological disorders, including neuromonitoring, neuromodulation, tumor treatment, and biosensing. Limitations and outlooks of soft devices are also discussed in terms of power supply, wireless control, biocompatibility, and the integration of artificial intelligence. This review highlights the potential of soft bioelectronics as a future platform to promote deciphering brain functions and clinical outcomes of neurological diseases.

Injectable 2D Material-Based Sensor Array for Minimally Invasive Neural Implants

Intracranial implants for diagnosis and treatment of brain diseases have been developed over the past few decades. However, the platform of conventional implantable devices still relies on invasive probes and bulky sensors in conjunction with large-area craniotomy and provides only limited biometric information. Here, an implantable multi-modal sensor array that can be injected through a small hole in the skull and inherently spread out for conformal contact with the cortical surface is reported. The injectable sensor array, composed of graphene multi-channel electrodes for neural recording and electrical stimulation and MoS2-based sensors for monitoring intracranial temperature and pressure, is designed based on a mesh structure whose elastic restoring force enables the contracted device to spread out. It is demonstrated that the sensor array injected into a rabbit's head can detect epileptic discharges on the surface of the cortex and mitigate it by electrical stimulation while monitoring both intracranial temperature and pressure. This method provides good potential for implanting a variety of functional devices via minimally invasive surgery.

Creep-free polyelectrolyte elastomer for drift-free iontronic sensing

Artificial pressure sensors often use soft materials to achieve skin-like softness, but the viscoelastic creep of soft materials and the ion leakage, specifically for ionic conductors, cause signal drift and inaccurate measurement. Here we report drift-free iontronic sensing by designing and copolymerizing a leakage-free and creep-free polyelectrolyte elastomer containing two types of segments: charged segments having fixed cations to prevent ion leakage and neutral slippery segments with a high crosslink density for low creep. We show that an iontronic sensor using the polyelectrolyte elastomer barely drifts under an ultrahigh static pressure of 500 kPa (close to its Young's modulus), exhibits a drift rate two to three orders of magnitude lower than that of the sensors adopting conventional ionic conductors and enables steady and accurate control for robotic manipulation. Such drift-free iontronic sensing represents a step towards highly accurate sensing in robotics and beyond.

Biodegradable Ferroelectric Molecular Plastic Crystal HOCH2(CF2)7CH2OH Structurally Inspired by Polyvinylidene Fluoride

Ferroelectric materials, traditionally comprising inorganic ceramics and polymers, are commonly used in medical implantable devices. However, their nondegradable nature often necessitates secondary surgeries for removal. In contrast, ferroelectric molecular crystals have the advantages of easy solution processing, lightweight, and good biocompatibility, which are promising candidates for transient (short-term) implantable devices. Despite these benefits, the discovered biodegradable ferroelectric materials remain limited due to the absence of efficient design strategies. Here, inspired by the polar structure of polyvinylidene fluoride (PVDF), a ferroelectric molecular crystal 1H,1H,9H,9H-perfluoro-1,9-nonanediol (PFND), which undergoes a cubic-to-monoclinic ferroelectric plastic phase transition at 339 K, is discovered. This transition is facilitated by a 2D hydrogen bond network formed through O-H···O interactions among the oriented PFND molecules, which is crucial for the manifestation of ferroelectric properties. In this sense, by reducing the number of -CF2- groups from ≈5 000 in PVDF to seven in PFND, it is demonstrated that this ferroelectric compound only needs simple solution processing while maintaining excellent biosafety, biocompatibility, and biodegradability. This work illuminates the path toward the development of new biodegradable ferroelectric molecular crystals, offering promising avenues for biomedical applications.

Beyond 25 years of biomedical innovation in nano-bioelectronics

Nano-bioelectronics, which blend the precision of nanotechnology with the complexity of biological systems, are evolving with innovations such as silicon nanowires, carbon nanotubes, and graphene. These elements serve applications from biochemical sensing to brain-machine interfacing. This review examines nano-bioelectronics' role in advancing biomedical interventions and discusses their potential in environmental monitoring, agricultural productivity, energy efficiency, and creative fields. The field is transitioning from molecular to ecosystem-level applications, with research exploring complex cellular mechanisms and communication. This fosters understanding of biological interactions at various levels, such as suggesting transformative approaches for ecosystem management and food security. Future research is expected to focus on refining nano-bioelectronic devices for integration with biological systems and on scalable manufacturing to broaden their reach and functionality.

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.

Evolution of Musculoskeletal Electronics

The musculoskeletal system, constituting the largest human physiological system, plays a critical role in providing structural support to the body, facilitating intricate movements, and safeguarding internal organs. By virtue of advancements in revolutionized materials and devices, particularly in the realms of motion capture, health monitoring, and postoperative rehabilitation, "musculoskeletal electronics" has actually emerged as an infancy area, but has not yet been explicitly proposed. In this review, the concept of musculoskeletal electronics is elucidated, and the evolution history, representative progress, and key strategies of the involved materials and state-of-the-art devices are summarized. Therefore, the fundamentals of musculoskeletal electronics and key functionality categories are introduced. Subsequently, recent advances in musculoskeletal electronics are presented from the perspectives of "in vitro" to "in vivo" signal detection, interactive modulation, and therapeutic interventions for healing and recovery. Additionally, nine strategy avenues for the development of advanced musculoskeletal electronic materials and devices are proposed. Finally, concise summaries and perspectives are proposed to highlight the directions that deserve focused attention in this booming field.

Implantable, Bioresorbable Radio Frequency Resonant Circuits for Magnetic Resonance Imaging

Magnetic resonance imaging (MRI) is widely used in clinical care and medical research. The signal-to-noise ratio (SNR) in the measurement affects parameters that determine the diagnostic value of the image, such as the spatial resolution, contrast, and scan time. Surgically implanted radiofrequency coils can increase SNR of subsequent MRI studies of adjacent tissues. The resulting benefits in SNR are, however, balanced by significant risks associated with surgically removing these coils or with leaving them in place permanently. As an alternative, here the authors report classes of implantable inductor-capacitor circuits made entirely of bioresorbable organic and inorganic materials. Engineering choices for the designs of an inductor and a capacitor provide the ability to select the resonant frequency of the devices to meet MRI specifications (e.g., 200 MHz at 4.7 T MRI). Such devices enhance the SNR and improve the associated imaging capabilities. These simple, small bioelectronic systems function over clinically relevant time frames (up to 1 month) at physiological conditions and then disappear completely by natural mechanisms of bioresorption, thereby eliminating the need for surgical extraction. Imaging demonstrations in a nerve phantom and a human cadaver suggest that this technology has broad potential for post-surgical monitoring/evaluation of recovery processes.

A biodegradable and flexible neural interface for transdermal optoelectronic modulation and regeneration of peripheral nerves

Optoelectronic neural interfaces can leverage the photovoltaic effect to convert light into electrical current, inducing charge redistribution and enabling nerve stimulation. This method offers a non-genetic and remote approach for neuromodulation. Developing biodegradable and efficient optoelectronic neural interfaces is important for achieving transdermal stimulation while minimizing infection risks associated with device retrieval, thereby maximizing therapeutic outcomes. We propose a biodegradable, flexible, and miniaturized silicon-based neural interface capable of transdermal optoelectronic stimulation for neural modulation and nerve regeneration. Enhancing the device interface with thin-film molybdenum significantly improves the efficacy of neural stimulation. Our study demonstrates successful activation of the sciatic nerve in rodents and the facial nerve in rabbits. Moreover, transdermal optoelectronic stimulation accelerates the functional recovery of injured facial nerves.

Injectable ultrasonic sensor for wireless monitoring of intracranial signals

Direct and precise monitoring of intracranial physiology holds immense importance in delineating injuries, prognostication and averting disease1. Wired clinical instruments that use percutaneous leads are accurate but are susceptible to infection, patient mobility constraints and potential surgical complications during removal2. Wireless implantable devices provide greater operational freedom but include issues such as limited detection range, poor degradation and difficulty in size reduction in the human body3. Here we present an injectable, bioresorbable and wireless metastructured hydrogel (metagel) sensor for ultrasonic monitoring of intracranial signals. The metagel sensors are cubes 2 × 2 × 2 mm3 in size that encompass both biodegradable and stimulus-responsive hydrogels and periodically aligned air columns with a specific acoustic reflection spectrum. Implanted into intracranial space with a puncture needle, the metagel deforms in response to physiological environmental changes, causing peak frequency shifts of reflected ultrasound waves that can be wirelessly measured by an external ultrasound probe. The metagel sensor can independently detect intracranial pressure, temperature, pH and flow rate, realize a detection depth of 10 cm and almost fully degrade within 18 weeks. Animal experiments on rats and pigs indicate promising multiparametric sensing performances on a par with conventional non-resorbable wired clinical benchmarks.

Advances in conductive hydrogels for neural recording and stimulation

The brain-computer interface (BCI) allows the human or animal brain to directly interact with the external environment through the neural interfaces, thus playing the role of monitoring, protecting, improving/restoring, enhancing, and replacing. Recording electrophysiological information such as brain neural signals is of great importance in health monitoring and disease diagnosis. According to the electrode position, it can be divided into non-implantable, semi-implantable, and implantable. Among them, implantable neural electrodes can obtain the highest-quality electrophysiological information, so they have the most promising application. However, due to the chemo-mechanical mismatch between devices and tissues, the adverse foreign body response and performance loss over time seriously restrict the development and application of implantable neural electrodes. Given the challenges, conductive hydrogel-based neural electrodes have recently attracted much attention, owing to many advantages such as good mechanical match with the native tissues, negligible foreign body response, and minimal signal attenuation. This review mainly focuses on the current development of conductive hydrogels as a biocompatible framework for neural tissue and conductivity-supporting substrates for the transmission of electrical signals of neural tissue to speed up electrical regeneration and their applications in neural sensing and recording as well as stimulation.

Rugged Island-Bridge Inorganic Electronics Mounted on Locally Strain-Isolated Substrates

Various strain isolation strategies that combine rigid and stretchable regions for stretchable electronics were recently proposed, but the vulnerability of inorganic materials to mechanical stress has emerged as a major impediment to their performance. We report a strain-isolation system that combines heteropolymers with different elastic moduli (i.e., hybrid stretchable polymers) and utilize it to construct a rugged island-bridge inorganic electronics system. Two types of prepolymers were simultaneously cross-linked to form an interpenetrating polymer network at the rigid-stretchable interface, resulting in a hybrid stretchable polymer that exhibited efficient strain isolation and mechanical stability. The system, including stretchable micro-LEDs and microheaters, demonstrated consistent operation under external strain, suggesting that the rugged island-bridge inorganic electronics mounted on a locally strain-isolated substrate offer a promising solution for replacing conventional stretchable electronics, enabling devices with a variety of form factors.

Design and Development of Transient Sensing Devices for Healthcare Applications

With the ever-growing requirements in the healthcare sector aimed at personalized diagnostics and treatment, continuous and real-time monitoring of relevant parameters is gaining significant traction. In many applications, health status monitoring may be carried out by dedicated wearable or implantable sensing devices only within a defined period and followed by sensor removal without additional risks for the patient. At the same time, disposal of the increasing number of conventional portable electronic devices with short life cycles raises serious environmental concerns due to the dangerous accumulation of electronic and chemical waste. An attractive solution to address these complex and contradictory demands is offered by biodegradable sensing devices. Such devices may be able to perform required tests within a programmed period and then disappear by safe resorption in the body or harmless degradation in the environment. This work critically assesses the design and development concepts related to biodegradable and bioresorbable sensors for healthcare applications. Different aspects are comprehensively addressed, from fundamental material properties and sensing principles to application-tailored designs, fabrication techniques, and device implementations. The emerging approaches spanning the last 5 years are emphasized and a broad insight into the most important challenges and future perspectives of biodegradable sensors in healthcare are provided.

Silicon-based transient electronics: principles, devices and applications

Recent advances in materials science, device designs and advanced fabrication technologies have enabled the rapid development of transient electronics, which represents a class of devices or systems that their functionalities and constitutions can be partially/completely degraded via chemical reaction or physical disintegration over a stable operation. Therefore, numerous potentials, including zero/reduced waste electronics, bioresorbable electronic implants, hardware security, and others, are expected. In particular, transient electronics with biocompatible and bioresorbable properties could completely eliminate the secondary retrieval surgical procedure after their in-body operation, thus offering significant potentials for biomedical applications. In terms of material strategies for the manufacturing of transient electronics, silicon nanomembranes (SiNMs) are of great interest because of their good physical/chemical properties, modest mechanical flexibility (depending on their dimensions), robust and outstanding device performances, and state-of-the-art manufacturing technologies. As a result, continuous efforts have been made to develop silicon-based transient electronics, mainly focusing on designing manufacturing strategies, fabricating various devices with different functionalities, investigating degradation or failure mechanisms, and exploring their applications. In this review, we will summarize the recent progresses of silicon-based transient electronics, with an emphasis on the manufacturing of SiNMs, devices, as well as their applications. After a brief introduction, strategies and basics for utilizing SiNMs for transient electronics will be discussed. Then, various silicon-based transient electronic devices with different functionalities are described. After that, several examples regarding on the applications, with an emphasis on the biomedical engineering, of silicon-based transient electronics are presented. Finally, summary and perspectives on transient electronics are exhibited.

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.

Bioresorbable Multilayer Organic-Inorganic Films for Bioelectronic Systems

Bioresorbable electronic devices as temporary biomedical implants represent an emerging class of technology relevant to a range of patient conditions currently addressed with technologies that require surgical explantation after a desired period of use. Obtaining reliable performance and favorable degradation behavior demands materials that can serve as biofluid barriers in encapsulating structures that avoid premature degradation of active electronic components. Here, this work presents a materials design that addresses this need, with properties in water impermeability, mechanical flexibility, and processability that are superior to alternatives. The approach uses multilayer assemblies of alternating films of polyanhydride and silicon oxynitride formed by spin-coating and plasma-enhanced chemical vapor deposition , respectively. Experimental and theoretical studies investigate the effects of material composition and multilayer structure on water barrier performance, water distribution, and degradation behavior. Demonstrations with inductor-capacitor circuits, wireless power transfer systems, and wireless optoelectronic devices illustrate the performance of this materials system as a bioresorbable encapsulating structure.

Bioresorbable, wireless, passive sensors for continuous pH measurements and early detection of gastric leakage

Continuous monitoring of biomarkers at locations adjacent to targeted internal organs can provide actionable information about postoperative status beyond conventional diagnostic methods. As an example, changes in pH in the intra-abdominal space after gastric surgeries can serve as direct indicators of potentially life-threatening leakage events, in contrast to symptomatic reactions that may delay treatment. Here, we report a bioresorbable, wireless, passive sensor that addresses this clinical need, designed to locally monitor pH for early detection of gastric leakage. A pH-responsive hydrogel serves as a transducer that couples to a mechanically optimized inductor-capacitor circuit for wireless readout. This platform enables real-time monitoring of pH with fast response time (within 1 hour) over a clinically relevant period (up to 7 days) and timely detection of simulated gastric leaks in animal models. These concepts have broad potential applications for temporary sensing of relevant biomarkers during critical risk periods following diverse types of surgeries.

Statistical field theory of polarizable polymer chains with nonlocal dipolar interactions

The electromechanical response of polymeric soft matter to applied electric fields is of fundamental scientific interest as well as relevant to technologies for sensing and actuation. Several existing theoretical and numerical approaches for polarizable polymers subject to a combined applied electric field and stretch are based on discrete monomer models. In these models, accounting for the interactions between the induced dipoles on monomers is challenging due to the nonlocality of these interactions. On the other hand, the framework of statistical field theory provides a continuous description of polymer chains that potentially enables a tractable way to account for these interactions. However, prior formulations using this framework have been restricted to the case of weak anisotropy of the monomer polarizability. This paper formulates a general approach based in the framework of statistical field theory to account for the nonlocal nature of the dipolar interactions without any restrictions on the anisotropy or nonlinearity of the polarizability of the monomer. The approach is based on three key elements: (1) the statistical field theory framework, in which the discrete monomers are regularized to a continuous dipole distribution, (2) a replacement of the nonlocal dipole-dipole interactions by the local electrostatics partial differential equation with the continuous dipole distribution as the forcing, and (3) the use of a completely general relation between the polarization and the local electric field. Rather than treat the dipole-dipole interactions directly, the continuous description in the field theory enables the computationally tractable nonlocal-to-local transformation. Further, it enables the use of a realistic statistical-mechanical ensemble wherein the average far-field applied electric field is prescribed, rather than prescribing the applied field at every point in the polymer domain. The model is applied, using the finite element method, to study the electromechanical response of a polymer chain in the ensemble with fixed far-field applied electric field and fixed chain stretch. The nonlocal dipolar interactions are found to increase, over the case where dipole-dipole interactions are neglected, the magnitudes of the polarization and electric field by orders of magnitude as well as significantly change their spatial distributions. Next, the effect of the relative orientation between the applied field and the chain on the local electric field and polarization is studied. The model predicts that the elastic response of the polymer chain is linear, consistent with the Gaussian approximation, and largely unchanged by the orientation of the applied electric field, though the polarization and local electric field distributions are significantly impacted.

Recent Progress and Challenges of Implantable Biodegradable Biosensors

Implantable biosensors have evolved to the cutting-edge technology of personalized health care and provide promise for future directions in precision medicine. This is the reason why these devices stand to revolutionize our approach to health and disease management and offer insights into our bodily functions in ways that have never been possible before. This review article tries to delve into the important developments, new materials, and multifarious applications of these biosensors, along with a frank discussion on the challenges that the devices will face in their clinical deployment. In addition, techniques that have been employed for the improvement of the sensitivity and specificity of the biosensors alike are focused on in this article, like new biomarkers and advanced computational and data communicational models. A significant challenge of miniaturized in situ implants is that they need to be removed after serving their purpose. Surgical expulsion provokes discomfort to patients, potentially leading to post-operative complications. Therefore, the biodegradability of implants is an alternative method for removal through natural biological processes. This includes biocompatible materials to develop sensors that remain in the body over longer periods with a much-reduced immune response and better device longevity. However, the biodegradability of implantable sensors is still in its infancy compared to conventional non-biodegradable ones. Sensor design, morphology, fabrication, power, electronics, and data transmission all play a pivotal role in developing medically approved implantable biodegradable biosensors. Advanced material science and nanotechnology extended the capacity of different research groups to implement novel courses of action to design implantable and biodegradable sensor components. But the actualization of such potential for the transformative nature of the health sector, in the first place, will have to surmount the challenges related to biofouling, managing power, guaranteeing data security, and meeting today's rules and regulations. Solving these problems will, therefore, not only enhance the performance and reliability of implantable biodegradable biosensors but also facilitate the translation of laboratory development into clinics, serving patients worldwide in their better disease management and personalized therapeutic interventions.

Biodegradable Mg-Mo2C MXene Air Batteries for Transient Energy Storage

Primary batteries are the fundamental power sources in small electronic gadgets and bio/ecoresorbable batteries. They are fabricated from benign and biodegradable materials and are of interest in environmental sensing and implants because of their low toxicity toward the environment and human body during decomposition. However, current bio/ecoresorbable batteries suffer from low operating voltages and output powers because of the occurrence of undesired hydrogen evolution reactions (HERs) at cathodes. Herein, Mo2C MXene was used as a cathode to achieve high operating voltage and areal power. Mo2C provides energy barriers for HERs in alkaline solutions, and such barriers suppress HERs and allow the oxygen reduction reaction to dominate at the cathode. The fabricated battery exhibits an operating voltage and areal power of 1.4 V and 0.92 mW cm-2, respectively. Degradation tests show that the full cell completely degrades within 123 days, leaving only Mo fragments from the electrode and biodegradable encapsulation. This study provides insights into bio/ecoresorbable batteries with high power and operating voltage, which can be used for environmental sensing.

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.

Fully bioresorbable hybrid opto-electronic neural implant system for simultaneous electrophysiological recording and optogenetic stimulation

Bioresorbable neural implants based on emerging classes of biodegradable materials offer a promising solution to the challenges of secondary surgeries for removal of implanted devices required for existing neural implants. In this study, we introduce a fully bioresorbable flexible hybrid opto-electronic system for simultaneous electrophysiological recording and optogenetic stimulation. The flexible and soft device, composed of biodegradable materials, has a direct optical and electrical interface with the curved cerebral cortex surface while exhibiting excellent biocompatibility. Optimized to minimize light transmission losses and photoelectric artifact interference, the device was chronically implanted in the brain of transgenic mice and performed to photo-stimulate the somatosensory area while recording local field potentials. Thus, the presented hybrid neural implant system, comprising biodegradable materials, promises to provide monitoring and therapy modalities for versatile applications in biomedicine.

High-speed and large-scale intrinsically stretchable integrated circuits

Intrinsically stretchable electronics with skin-like mechanical properties have been identified as a promising platform for emerging applications ranging from continuous physiological monitoring to real-time analysis of health conditions, to closed-loop delivery of autonomous medical treatment1-7. However, current technologies could only reach electrical performance at amorphous-silicon level (that is, charge-carrier mobility of about 1 cm2 V-1 s-1), low integration scale (for example, 54 transistors per circuit) and limited functionalities8-11. Here we report high-density, intrinsically stretchable transistors and integrated circuits with high driving ability, high operation speed and large-scale integration. They were enabled by a combination of innovations in materials, fabrication process design, device engineering and circuit design. Our intrinsically stretchable transistors exhibit an average field-effect mobility of more than 20 cm2 V-1 s-1 under 100% strain, a device density of 100,000 transistors per cm2, including interconnects and a high drive current of around 2 μA μm-1 at a supply voltage of 5 V. Notably, these achieved parameters are on par with state-of-the-art flexible transistors based on metal-oxide, carbon nanotube and polycrystalline silicon materials on plastic substrates12-14. Furthermore, we realize a large-scale integrated circuit with more than 1,000 transistors and a stage-switching frequency greater than 1 MHz, for the first time, to our knowledge, in intrinsically stretchable electronics. Moreover, we demonstrate a high-throughput braille recognition system that surpasses human skin sensing ability, enabled by an active-matrix tactile sensor array with a record-high density of 2,500 units per cm2, and a light-emitting diode display with a high refreshing speed of 60 Hz and excellent mechanical robustness. The above advancements in device performance have substantially enhanced the abilities of skin-like electronics.

In Situ Polymer-Solution-Processed Graphene-PDMS Nanocomposites for Application in Intracranial Pressure Sensors

Polydimethylsiloxane (PDMS) has emerged as a promising candidate for the dielectric layer in implantable sensors due to its exceptional biocompatibility, stability, and flexibility. This study introduces an innovative approach to produce graphene-reinforced PDMS (Gr-PDMS), where graphite powders are exfoliated into mono- and few-layer graphene sheets within the polymer solution, concurrently forming cross-linkages with PDMS. This method yields a uniformly distributed graphene within the polymer matrix with improved interfaces between graphene and PDMS, significantly reducing the percolation threshold of graphene dispersed in PDMS from 10% to 5%. As-synthesized Gr-PDMS exhibits improved mechanical and electrical properties, tested for potential use in capacitive pressure sensors. The results demonstrate an impressive pressure sensitivity up to 0.0273 kpa-1, 45 times higher than that of pristine PDMS and 2.5 times higher than the reported literature value. The Gr-PDMS showcases excellent pressure sensing ability and stability, fulfilling the requirements for implantable intracranial pressure (ICP) sensors.

Recent Advances in Implantable Neural Interfaces for Multimodal Electrical Neuromodulation

Electrical neuromodulation plays a pivotal role in enhancing patient outcomes among individuals suffering from neurological disorders. Implantable neural interfaces are vital components of the electrical neuromodulation system to ensure desirable performance; However, conventional devices are limited to a single function and are constructed with bulky and rigid materials, which often leads to mechanical incompatibility with soft tissue and an inability to adapt to the dynamic and complex 3D structures of biological systems. In addition, current implantable neural interfaces utilized in clinical settings primarily rely on wire-based techniques, which are associated with complications such as increased risk of infection, limited positioning options, and movement restrictions. Here, the state-of-art applications of electrical neuromodulation are presented. Material schemes and device structures that can be employed to develop robust and multifunctional neural interfaces, including flexibility, stretchability, biodegradability, self-healing, self-rolling, or morphing are discussed. Furthermore, multimodal wireless neuromodulation techniques, including optoelectronics, mechano-electrics, magnetoelectrics, inductive coupling, and electrochemically based self-powered devices are reviewed. In the end, future perspectives are given.

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

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

Anti-friction gold-based stretchable electronics enabled by interfacial diffusion-induced cohesion

Stretchable electronics that prevalently adopt chemically inert metals as sensing layers and interconnect wires have enabled high-fidelity signal acquisition for on-skin applications. However, the weak interfacial interaction between inert metals and elastomers limit the tolerance of the device to external friction interferences. Here, we report an interfacial diffusion-induced cohesion strategy that utilizes hydrophilic polyurethane to wet gold (Au) grains and render them wrapped by strong hydrogen bonding, resulting in a high interfacial binding strength of 1017.6 N/m. By further constructing a nanoscale rough configuration of the polyurethane (RPU), the binding strength of Au-RPU device increases to 1243.4 N/m, which is 100 and 4 times higher than that of conventional polydimethylsiloxane and styrene-ethylene-butylene-styrene-based devices, respectively. The stretchable Au-RPU device can remain good electrical conductivity after 1022 frictions at 130 kPa pressure, and reliably record high-fidelity electrophysiological signals. Furthermore, an anti-friction pressure sensor array is constructed based on Au-RPU interconnect wires, demonstrating a superior mechanical durability for concentrated large pressure acquisition. This chemical modification-free approach of interfacial strengthening for chemically inert metal-based stretchable electronics is promising for three-dimensional integration and on-chip interconnection.

Materials, Designs, and Implementations of Wearable Antennas and Circuits for Biomedical Applications: A Review

The intersection of biomedicine and radio frequency (RF) engineering has fundamentally transformed self-health monitoring by leveraging soft and wearable electronic devices. This paradigm shift presents a critical challenge, requiring these devices and systems to possess exceptional flexibility, biocompatibility, and functionality. To meet these requirements, traditional electronic systems, such as sensors and antennas made from rigid and bulky materials, must be adapted through material science and schematic design. Notably, in recent years, extensive research efforts have focused on this field, and this review article will concentrate on recent advancements. We will explore the traditional/emerging materials for highly flexible and electrically efficient wearable electronics, followed by systematic designs for improved functionality and performance. Additionally, we will briefly overview several remarkable applications of wearable electronics in biomedical sensing. Finally, we provide an outlook on potential future directions in this developing area.

Soft Bioelectronics for Neuroengineering: New Horizons in the Treatment of Brain Tumor and Epilepsy

Soft bioelectronic technologies for neuroengineering have shown remarkable progress, which include novel soft material technologies and device design strategies. Such technological advances that are initiated from fundamental brain science are applied to clinical neuroscience and provided meaningful promises for significant improvement in the diagnosis efficiency and therapeutic efficacy of various brain diseases recently. System-level integration strategies in consideration of specific disease circumstances can enhance treatment effects further. Here, recent advances in soft implantable bioelectronics for neuroengineering, focusing on materials and device designs optimized for the treatment of intracranial disease environments, are reviewed. Various types of soft bioelectronics for neuroengineering are categorized and exemplified first, and then details for the sensing and stimulating device components are explained. Next, application examples of soft implantable bioelectronics to clinical neuroscience, particularly focusing on the treatment of brain tumor and epilepsy are reviewed. Finally, an ideal system of soft intracranial bioelectronics such as closed-loop-type fully-integrated systems is presented, and the remaining challenges for their clinical translation are discussed.

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 Biodegradable Green Electronic Materials and Sensor Applications

As environmental issues have become the dominant agenda worldwide, the necessity for more environmentally friendly electronics has recently emerged. Accordingly, biodegradable or nature-derived materials for green electronics have attracted increased interest. Initially, metal-green hybrid electronics are extensively studied. Although these materials are partially biodegradable, they have high utility owing to their metallic components. Subsequently, carbon-framed materials (such as graphite, cylindrical carbon nanomaterials, graphene, graphene oxide, laser-induced graphene) have been investigated. This has led to the adoption of various strategies for carbon-based materials, such as blending them with biodegradable materials. Moreover, various conductive polymers have been developed and researchers have studied their potential use in green electronics. Researchers have attempted to fabricate conductive polymer composites with high biodegradability by shortening the polymer chains. Furthermore, various physical, chemical, and biological sensors that are essential to modern society have been studied using biodegradable compounds. These recent advances in green electronics have paved the way toward their application in real life, providing a brighter future for society.

Full-Color Generation via Phototunable Mono Ink for Fast and Elaborate Printings

Unlike pigment-based colors, which are determined by their molecular structure, diverse colors can be expressed by a regular arrangement of nanomaterials. However, existing techniques for constructing such nanostructures have struggled to combine high precision and speed, resulting in a narrow gamut, and prolonged color fabrication time. Here, this work reports a phototunable mono ink that can generate a wide range of colors by controlling regularly arranged nanostructure. Core-shell growth controlled by polymerization time precisely regulates the distance between arranged particles at a nanometer-scale, enabling the generation of various colors. Moreover, the wide and thin arrangement induces constrained out-of-plane growth, thus facilitating the intricate color generation at the desired location via photopolymerization. Upon terminating polymerization by oxygen gas, the generated colors are readily fixed and kept stable. Utilizing programmed ultraviolet illumination, large-scale and high-resolution (≈1 µm) full-color printings are demonstrated at high speed (100 mm2 s-1 ).

A Bioresorbable and Conductive Scaffold Integrating Silicon Membranes for Peripheral Nerve Regeneration

Peripheral nerve injury represents one of the most common types of traumatic damage, severely impairing motor and sensory functions, and posttraumatic nerve regeneration remains a major challenge. Electrical cues are critical bioactive factors that promote nerve regrowth, and bioartificial scaffolds incorporating conductive materials to enhance the endogenous electrical field have been demonstrated to be effective. The utilization of fully biodegradable scaffolds can eliminate material residues, and circumvent the need for secondary retrieval procedures. Here, a fully bioresorbable and conductive nerve scaffold integrating N-type silicon (Si) membranes is proposed, which can deliver both structural guidance and electrical cues for the repair of nerve defects. The entire scaffold is fully biodegradable, and the introduction of N-type Si can significantly promote the proliferation and production of neurotrophic factors of Schwann cells and enhance the calcium activity of dorsal root ganglion (DRG) neurons. The conductive scaffolds enable accelerated nerve regeneration and motor functional recovery in rodents with sciatic nerve transection injuries. This work sheds light on the advancement of bioresorbable and electrically active materials to achieve desirable neural interfaces and improved therapeutic outcomes, offering essential strategies for regenerative medicine.

Bridging the Gap-Thermofluidic Designs for Precision Bioelectronics

Bioelectronics, the merging of biology and electronics, can monitor and modulate biological behaviors across length and time scales with unprecedented capability. Current bioelectronics research largely focuses on devices' mechanical properties and electronic designs. However, the thermofluidic control is often overlooked, which is noteworthy given the discipline's importance in almost all bioelectronics processes. It is believed that integrating thermofluidic designs into bioelectronics is essential to align device precision with the complexity of biofluids and biological structures. This perspective serves as a mini roadmap for researchers in both fields to introduce key principles, applications, and challenges in both bioelectronics and thermofluids domains. Important interdisciplinary opportunities for the development of future healthcare devices and precise bioelectronics will also be discussed.

Recent advances of responsive scaffolds in bone tissue engineering

The investigation of bone defect repair has been a significant focus in clinical research. The gradual progress and utilization of different scaffolds for bone repair have been facilitated by advancements in material science and tissue engineering. In recent times, the attainment of precise regulation and targeted drug release has emerged as a crucial concern in bone tissue engineering. As a result, we present a comprehensive review of recent developments in responsive scaffolds pertaining to the field of bone defect repair. The objective of this review is to provide a comprehensive summary and forecast of prospects, thereby contributing novel insights to the field of bone defect repair.

Resorbable barrier polymers for flexible bioelectronics

Resorbable, implantable bioelectronic devices are emerging as powerful tools to reliably monitor critical physiological parameters in real time over extended periods. While degradable magnesium-based electronics have pioneered this effort, relatively short functional lifetimes have slowed clinical translation. Barrier films that are both flexible and resorbable over predictable timelines would enable tunability in device lifetime and expand the viability of these devices. Herein, we present a library of stereocontrolled succinate-based copolyesters which leverage copolymer composition and processing method to afford tunability over thermomechanical, crystalline, and barrier properties. One copolymer composition within this library has extended the functional lifetime of transient bioelectronic prototypes over existing systems by several weeks-representing a considerable step towards translational devices.

Recent advances in smart wearable sensors as electronic skin

Flexible and multifunctional electronic devices and soft robots inspired by human organs, such as skin, have many applications. However, the emergence of electronic skins (e-skins) or textiles in biomedical engineering has made a great revolution in a myriad of people's lives who suffer from different types of diseases and problems in which their skin and muscles lose their appropriate functions. In this review, recent advances in the sensory function of the e-skins are described. Furthermore, we have categorized them from the sensory function perspective and highlighted their advantages and limitations. The categories are tactile sensors (including capacitive, piezoresistive, piezoelectric, triboelectric, and optical), temperature, and multi-sensors. In addition, we summarized the most recent advancements in sensors and their particular features. The role of material selection and structure in sensory function and other features of the e-skins are also discussed. Finally, current challenges and future prospects of these systems towards advanced biomedical applications are elaborated.

Frictionless multiphasic interface for near-ideal aero-elastic pressure sensing

Conventional pressure sensors rely on solid sensing elements. Instead, inspired by the air entrapment phenomenon on the surfaces of submerged lotus leaves, we designed a pressure sensor that uses the solid-liquid-liquid-gas multiphasic interfaces and the trapped elastic air layer to modulate capacitance changes with pressure at the interfaces. By creating an ultraslippery interface and structuring the electrodes at the nanoscale and microscale, we achieve near-friction-free contact line motion and thus near-ideal pressure-sensing performance. Using a closed-cell pillar array structure in synergy with the ultraslippery electrode surface, our sensor achieved outstanding linearity (R2 = 0.99944 ± 0.00015; nonlinearity, 1.49 ± 0.17%) while simultaneously possessing ultralow hysteresis (1.34 ± 0.20%) and very high sensitivity (79.1 ± 4.3 pF kPa-1). The sensor can operate under turbulent flow, in in vivo biological environments and during laparoscopic procedures. We anticipate that such a strategy will enable ultrasensitive and ultraprecise pressure monitoring in complex fluid environments with performance beyond the reach of the current state-of-the-art.

Advances in Bioresorbable Materials and Electronics

Transient electronic systems represent an emerging class of technology that is defined by an ability to fully or partially dissolve, disintegrate, or otherwise disappear at controlled rates or triggered times through engineered chemical or physical processes after a required period of operation. This review highlights recent advances in materials chemistry that serve as the foundations for a subclass of transient electronics, bioresorbable electronics, that is characterized by an ability to resorb (or, equivalently, to absorb) in a biological environment. The primary use cases are in systems designed to insert into the human body, to provide sensing and/or therapeutic functions for timeframes aligned with natural biological processes. Mechanisms of bioresorption then harmlessly eliminate the devices, and their associated load on and risk to the patient, without the need of secondary removal surgeries. The core content focuses on the chemistry of the enabling electronic materials, spanning organic and inorganic compounds to hybrids and composites, along with their mechanisms of chemical reaction in biological environments. Following discussions highlight the use of these materials in bioresorbable electronic components, sensors, power supplies, and in integrated diagnostic and therapeutic systems formed using specialized methods for fabrication and assembly. A concluding section summarizes opportunities for future research.

Tissue-Matchable and Implantable Batteries Toward Biomedical Applications

Implantable electronic devices can realize real-time and reliable health monitoring, diagnosis, and treatment of human body, which are expected to overcome important bottlenecks in the biomedical field. However, the commonly used energy supply devices for them are implantable batteries based on conventional rigid device design with toxic components, which both mechanically and biologically mismatch soft biological tissues. Therefore, the development of highly soft, safe, and implantable tissue-matchable flexible batteries is of great significance and urgency for implantable bioelectronics. In this work, the recent advances of tissue-matchable and implantable flexible batteries are overviewed, focusing on the design strategies of electrodes/batteries and their biomedical applications. The mechanical flexibility, biocompatibility, and electrochemical performance in vitro and in vivo of these flexible electrodes/batteries are then discussed. Finally, perspectives are provided on the current challenges and possible directions of this field in the future.

Communication Protocols Integrating Wearables, Ingestibles, and Implantables for Closed-Loop Therapies

Body-conformal sensors and tissue interfacing robotic therapeutics enable the real-time monitoring and treatment of diabetes, wound healing, and other critical conditions. By integrating sensors and drug delivery devices, scientists and engineers have developed closed-loop drug delivery systems with on-demand therapeutic capabilities to provide just-in-time treatments that correspond to chemical, electrical, and physical signals of a target morbidity. To enable closed-loop functionality in vivo, engineers utilize various low-power means of communication that reduce the size of implants by orders of magnitude, increase device lifetime from hours to months, and ensure the secure high-speed transfer of data. In this review, we highlight how communication protocols used to integrate sensors and drug delivery devices, such as radio frequency communication (e.g., Bluetooth, near-field communication), in-body communication, and ultrasound, enable improved treatment outcomes.

Bioderived Ionic Liquids with Alkaline Metal Ions for Transient Ionics

Choline lactate, an ionic liquid composed of bioderived materials, offers an opportunity to develop biodegradable electrochemical devices. Although ionic liquids possess large potential windows, high conductivity, and are nonvolatile, they do not exhibit electrochemical characteristics such as intercalation pseudocapacitance, redox pseudocapacitance, and electrochromism. Herein, bioderived ionic liquids are developed, including metal ions, Li, Na, and Ca, to yield ionic liquid with electrochemical behavior. Differential scanning calorimetry results reveal that the ionic liquids remained in liquid state from 230.42 to 373.15 K. The conductivities of the ionic liquids with metal are lower than those of the pristine ionic liquid, whereas the capacitance change negligibly. A protocol of the Organization for Economic Co-operation and Development 301C modified MITI test (I) confirms that the pristine ionic liquid and ionic liquids with metal are readily biodegradable. Additionally, an ionic gel comprising the ionic liquid and poly(vinyl alcohol) is biodegradable. An electrochromic device is developed using an ionic liquid containing Li ions. The device successfully changes color at -2.5 V, demonstrating the intercalation of Li ions into the WO3 crystal. The results suggest that the electrochemically active ionic liquids have potential for the development of environmentally benign devices, sustainable electronics, and bioresorbable/implantable devices.

Fabrication of Eco-Friendly Wearable Strain Sensor Arrays via Facile Contact Printing for Healthcare Applications

Wearable flexible strain sensors with spatial resolution enable the acquisition and analysis of complex actions for noninvasive personalized healthcare applications. To provide secure contact with skin and to avoid environmental pollution after usage, sensors with biocompatibility and biodegradability are highly desirable. Herein, wearable flexible strain sensors composed of crosslinked gold nanoparticle (GNP) thin films as the active conductive layer and transparent biodegradable polyurethane (PU) films as the flexible substrate are developed. The patterned GNP films (micrometer- to millimeter-scale square and rectangle geometry, alphabetic characters, and wave and array patterns) are transferred onto the biodegradable PU film via a facile, clean, rapid and high-precision contact printing method, without the need of a sacrificial polymer carrier or organic solvents. The GNP-PU strain sensor with low Young's modulus (≈17.8 MPa) and high stretchability showed good stability and durability (10 000 cycles) as well as degradability (42% weight loss after 17 days at 74 °C in water). The GNP-PU strain sensor arrays with spatiotemporal strain resolution are applied as wearable eco-friendly electronics for monitoring subtle physiological signals (e.g., mapping of arterial lines and sensing pulse waveforms) and large-strain actions (e.g., finger bending).

Battery-Free, Wireless, Cuff-Type, Multimodal Physical Sensor for Continuous Temperature and Strain Monitoring of Nerve

Peripheral nerve injuries cause various disabilities related to loss of motor and sensory functions. The treatment of these injuries typically requires surgical operations for improving functional recovery of the nerve. However, capabilities for continuous nerve monitoring remain a challenge. Herein, a battery-free, wireless, cuff-type, implantable, multimodal physical sensing platform for continuous in vivo monitoring of temperature and strain from the injured nerve is introduced. The thin, soft temperature, and strain sensors wrapped around the nerve exhibit good sensitivity, excellent stability, high linearity, and minimum hysteresis in relevant ranges. In particular, the strain sensor integrated with circuits for temperature compensation provides reliable, accurate strain monitoring with negligible temperature dependence. The system enables power harvesting and data communication to wireless, multiple implanted devices wrapped around the nerve. Experimental evaluations, verified by numerical simulations, with animal tests, demonstrate the feasibility and stability of the sensor system, which has great potential for continuous in vivo nerve monitoring from an early stage to complete regeneration.

Micropatterned Elastomeric Composites for Encapsulation of Transient Electronics

Although biodegradable, transient electronic devices must dissolve or decompose via environmental factors, an effective waterproofing or encapsulation system is essential for reliable, durable operation for a desired period of time. Existing protection approaches use multiple or alternate layers of electrically inactive organic/inorganic elements combined with polymers; however, their high mechanical stiffness is not suitable for soft, time-dynamic biological tissues/skins/organs. Here, we introduce a stretchable, bioresorbable encapsulant using nanoparticle-incorporated elastomeric composites with modifications of surface morphology. Nature-inspired micropatterns reduce the diffusion area for water molecules, and embedded nanoparticles impede water permeation, which synergistically enhances the water-barrier performance. Empirical and theoretical evaluations validate the encapsulation mechanisms under strains. Demonstration of a soft, degradable shield with an optical component under a biological solution highlights the potential applicability of the proposed encapsulation strategy.

In situ assembly of bioresorbable organic bioelectronics in the brain

Bioelectronics can potentially complement classical therapies in nonchronic treatments, such as immunotherapy and cancer. In addition to functionality, minimally invasive implantation methods and bioresorbable materials are central to nonchronic treatments. The latter avoids the need for surgical removal after disease relief. Self-organizing substrate-free organic electrodes meet these criteria and integrate seamlessly into dynamic biological systems in ways difficult for classical rigid solid-state electronics. Here we place bioresorbable electrodes with a brain-matched shear modulus-made from water-dispersed nanoparticles in the brain-in the targeted area using a capillary thinner than a human hair. Thereafter, we show that an optional auxiliary module grows dendrites from the installed conductive structure to seamlessly embed neurons and modify the electrode's volume properties. We demonstrate that these soft electrodes set off a controlled cellular response in the brain when relaying external stimuli and that the biocompatible materials show no tissue damage after bioresorption. These findings encourage further investigation of temporary organic bioelectronics for nonchronic treatments assembled in vivo.

Fully printed and self-compensated bioresorbable electrochemical devices based on galvanic coupling for continuous glucose monitoring

Real-time glucose monitoring conventionally involves non-bioresorbable semi-implantable glucose sensors, causing infection and pain during removal. Despite bioresorbable electronics serves as excellent alternatives, the bioresorbable sensor dissolves in aqueous environments with interferential biomolecules. Here, the theories to achieve stable electrode potential and accurate electrochemical detection using bioresorbable materials have been proposed, resulting in a fully printed bioresorbable electrochemical device. The adverse effect caused by material degradation has been overcome by a molybdenum-tungsten reference electrode that offers stable potential through galvanic-coupling and self-compensation modules. In vitro and in vivo glucose monitoring has been conducted for 7 and 5 days, respectively, followed by full degradation within 2 months. The device offers a glucose detection range of 0 to 25 millimolars and a sensitivity of 0.2458 microamperes per millimolar with anti-interference capability and biocompatibility, indicating the possibility of mass manufacturing high-performance bioresorbable electrochemical devices using printing and low-temperature water-sintering techniques. The mechanisms may be implemented developing more comprehensive bioresorbable sensors for chronic diseases.