Soft subdermal implant capable of wireless battery charging and programmable controls for applications in optogenetics

Genetics-Based Targeting Strategies for Precise Neuromodulation

Genetics-based neuromodulation schemes are capable of selectively manipulating the activity of defined cell populations with high temporal-spatial resolution, providing unprecedented opportunities for probing cellular biological mechanisms, resolving neuronal projection pathways, mapping neural profiles, and precisely treating neurological and psychiatric disorders. Multimodal implementation schemes, which involve the use of exogenous stimuli such as light, heat, mechanical force, chemicals, electricity, and magnetic stimulation in combination with specific genetically engineered effectors, greatly expand their application space and scenarios. In particular, advanced wireless stimulation schemes have enabled low-invasive targeted neuromodulation through local delivery of navigable micro- and nanosized stimulators. In this review, the fundamental principles and implementation protocols of genetics-based precision neuromodulation are first introduced.The implementation schemes are systematically summarized, including optical, thermal, force, chemical, electrical, and magnetic stimulation, with an emphasis on those wireless and low-invasive strategies. Representative studies are dissected and analyzed for their advantages and disadvantages. Finally, the significance of genetics-based precision neuromodulation is emphasized and the open challenges and future perspectives are concluded.

Harnessing Dynamic Electrostatic Fields for Energy Generation with Diode Cells

Harvesting energy from distributed mechanical motions has garnered significance in future power sources for small electronics and sensors. Although technologies like triboelectric nanogenerators have shown promising results, their efficacy hinges on the alignment of motion vectors and device architectures. Here, an approach employing stationary diode cells (DiCes) to generate electricity is presented. This approach leverages dynamically changing electrostatic fields to induce potential differences across diode junctions via electrostatic induction, which is verified theoretically and experimentally. DiCes constructed with multiple diodes can directly output DC voltage and current. A 0.02 m2 sized DiCe contains 360 diodes can supply a DC voltage and current of maximum 490 V and 1.08 mA, respectively, which equals a DC power density of 26.5 W·m-2. Capable of functioning in both contact and non-contact modes, DiCes offer versatile applications, from wirelessly powering implanted medical devices to harvesting energy from vehicles and roads.

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

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

Theoretical Model of the Island Effect in Flexible Electronics under Equal Biaxial Stretching

Island-bridge architecture represents a widely used structural design strategy in the field of stretchable inorganic electronics, where flexible serpentine interconnects function as bridges to accommodate most of the deformation, while the islands residing functional devices exhibit minimal deformation. The mismatch of Young's modulus between the elastic substrate and the rigid islands usually leads to stress concentration, which is named the island effect. This phenomenon can significantly increase the risk of interfacial damage, such as debonding and tearing failure near the island. In this work, the mechanical model of the island effect under equal biaxial stretching is developed based on theoretical analysis, simulation, and experimental measurement. The scaling law of the displacement and strain distributions on the substrate surface illustrates that the ratio of the island radius to the substrate length is the main controlling parameter of the island effect, proved by the experimental and numerical results. The criterion distinguishing whether the island effect problem is axisymmetric is derived from this. Further, the deformation field in periodic array structure is predicted based on the theoretical model, demonstrating its potential for application in flexible electronic devices.

Optogenetic activation of mechanical nociceptions to enhance implant osseointegration

Orthopedic implants with high elastic modulus often suffer from poor osseointegration due to stress shielding, a phenomenon that suppresses the expression of intracellular mechanotransduction molecules (IMM) such as focal adhesion kinase (FAK). We find that reduced FAK expression under stress shielding is also mediated by decreased calcitonin gene-related peptide (CGRP) released from Piezo2+ mechanosensitive nerves surrounding the implant. To activate these nerves minimally invasively, we develop a fully implantable, wirelessly rechargeable optogenetic device. In mice engineered to express light-sensitive channels in Piezo2+ neurons, targeted stimulation of the L2-3 dorsal root ganglia (DRG) enhances localized CGRP release near the implant. This CGRP elevation activates the Protein Kinase A (PKA)/FAK signaling pathway in bone marrow mesenchymal stem cells (BMSCs), thereby enhancing osteogenesis and improving osseointegration. Here we show that bioelectronic modulation of mechanosensitive nerves offers a strategy to address implant failure, bridging neuroregulation and bone bioengineering.

An Efficient MEMS Microelectrode Array with Reliable Interelectrode Insulation Processes for In Vivo Neural Recording

Microelectrode arrays, particularly Utah arrays, offer irreplaceable advantages in clinical applications and play a crucial role in advancing brain-computer interactions. However, the glass-fused monolithic structure of Utah arrays limits functional expansion, and the glass insulation process is complex, costly, and time-intensive. This paper presents a microelectrode array with a simple and time-saving fabrication process, utilizing low-resistance silicon and borosilicate glass wafers as electrodes and insulation substrates, respectively. The utilization of the anodic bonding process improves production efficiency and enhances process compatibility. A one-step static wet etching process is used to form microneedle morphology to further simplify the fabrication process. Sputtered iridium oxide, as the electrode interface material, significantly reduces electrochemical impedance, and cellular experiments have confirmed its non-cytotoxicity. Moreover, the implantation into the primary visual cortex of mice has demonstrated the ability of the electrode to record in vivo electrical signals within 15 days. Movement trajectory experiments demonstrate that the mice exhibit good behavior activities following electrode implantation. The bonded microelectrode array (BMEA) presented in this work provides a universal and effective tool for neural recording, with prospective applications in multi-physiological monitoring and microelectromechanical system integration.

A biodegradable capacitive-coupling neurostimulator for wireless electroceutical treatment of inflammatory bowel diseases

Electroceuticals based on peripheral nerve stimulation offer promising treatment for refractory inflammatory diseases such as inflammatory bowel diseases (IBDs). For pediatric IBD (PIBD) patients, wireless, biodegradable miniaturized bioelectronic devices are crucial to prevent neural damage and support neural development during and after therapy. Here we demonstrate a battery-free, miniaturized neurostimulator based on biodegradable materials and capacitive-coupling wireless power transfer. The biodegradable capacitive-coupling (BCC) neurostimulator consists of molybdenum (Mo) electronic components and self-healing biodegradable polyurethane elastomer (SBPUE) encapsulations. The self-healing property of SBPUE enables a stable neural interface. Capacitive coupling wirelessly transfers high-frequency electric fields through a single capacitor between wearable transmitters and implanted BCC neurostimulators. Programmed electrical stimulation of the vagus nerve alleviates PIBD symptoms by restoring CD4+ T cell balance, enhancing anti-inflammatory effects and suppressing pro-inflammatory effects in the intestines.

Wireless Modular Implantable Neural Device with One-touch Magnetic Assembly for Versatile Neuromodulation

Multimodal neural interfaces open new opportunities in brain research by enabling more sophisticated and systematic neural circuit dissection. Integrating complementary features across distinct functional domains, these multifunctional neural probes have greatly advanced the interrogation of complex neural circuitry. However, introducing multiple functionalities into a compact form factor for freely behaving animals presents substantial design hurdles that complicate the device or require more than one device. Moreover, fixed functionality poses challenges in meeting the dynamic needs of chronic neuroscience inquiry, such as replacing consumable parts like batteries or drugs. To address these limitations, the modular implantable neural device (MIND) is introduced with a one-touch magnetic assembly mechanism. Leveraging the seamless exchange of neural interface modules such as optical stimulation, drug delivery, and electrical stimulation, MIND ensures functional adaptability, reusability, and scalability. The versatile design of MIND will facilitate brain research by enabling simplified access to multiple functional modalities as needed.

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.

The mechanisms of electrical neuromodulation

The central and peripheral nervous systems are specialized to conduct electrical currents that underlie behaviour. When this multidimensional electrical system is disrupted by degeneration, damage, or disuse, externally applied electrical currents may act to modulate neural structures and provide therapeutic benefit. The administration of electrical stimulation can exert precise and multi-faceted effects at cellular, circuit and systems levels to restore or enhance the functionality of the central nervous system by providing an access route to target specific cells, fibres of passage, neurotransmitter systems, and/or afferent/efferent communication to enable positive changes in behaviour. Here we examine the neural mechanisms that are thought to underlie the therapeutic effects seen with current neuromodulation technologies. To gain further insights into the mechanisms associated with electrical stimulation, we summarize recent findings from genetic dissection studies conducted in animal models. KEY POINTS: Electricity is everywhere around us and is essential for how our nerves communicate within our bodies. When nerves are damaged or not working properly, using exogenous electricity can help improve their function at distinct levels - inside individual cells, within neural circuits, and across entire systems. This method can be tailored to target specific types of cells, nerve fibres, neurotransmitters and communication pathways, offering significant therapeutic potential. This overview explains how exogenous electricity affects nerve function and its potential benefits, based on research in animal studies. Understanding these effects is important because electrical neuromodulation plays a key role in medical treatments for neurological conditions.

Wireless Optogenetic Targeting Nociceptors Helps Host Cells Win the Competitive Colonization in Implant-Associated Infections

The role of nociceptive nerves in modulating immune responses to harmful stimuli via pain or itch induction remains controversial. Compared to conventional surgery, various implant surgeries are more prone to infections even with low bacterial loads. In this study, an optogenetic technique is introduced for selectively activating peripheral nociceptive nerves using a fully implantable, wirelessly rechargeable optogenetic device. By targeting nociceptors in the limbs of awake, freely moving mice, it is found that activation induces anticipatory immunity in the innervated territory and enhances the adhesion of various host cells to the implant surface. This effect mediates acute immune cell-mediated killing of Staphylococcus aureus on implants and enables the host to win "implant surface competition" against Staphylococcus aureus. This finding provides new strategies for preventing and treating implant-associated infections.

A Robust Backscatter Modulation Scheme for Uninterrupted Ultrasonic Powering and Back-Communication of Deep Implants

Traditionally, implants are powered by batteries, which have to be recharged by an inductive power link. In the recent years, ultrasonic power links are being investigated, promising more available power for deeply implanted miniaturized devices. These implants often need to transfer back information. For ultrasonically powered implants, this is usually achieved with on-off keying (OOK) based on backscatter modulation, or active driving of a secondary transducer. In this article, we propose to superimpose subcarriers, effectively leveraging frequency-shift keying (FSK), which increases the robustness of the link against interference and fading. It also allows for simultaneous powering and communication, and inherently provides the possibility of frequency domain multiplexing for implant networks. The modulation scheme can be implemented in miniaturized application-specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), and microcontrollers. We have validated this modulation scheme in a water tank during continuous ultrasound and movement. We achieved symbol rates of up to 104 kBd, and were able to transfer data through 20 cm of water and through a 5 cm tissue phantom with additional misalignment and during movements. This approach could provide a robust uplink for miniaturized implants that are located deep inside the body and need continuous ultrasonic powering.

Wireless optogenetic stimulation on the prelimbic to the nucleus accumbens core circuit attenuates cocaine-induced behavioral sensitization

Behavioral sensitization is defined as the heightened and persistent behavioral response to repeated drug exposure as a manifestation of drug craving. Psychomotor stimulants such as cocaine can induce strong behavioral sensitization. In this study, we explored the effects of optogenetic stimulation of the prelimbic (PL) to the nucleus accumbnes (NAc) core on the expression of cocaine-induced behavioral sensitization. Using wireless optogenetics, we selectively stimulated the PL-NAc core circuit, and assessed the effects of this treatment on cocaine-induced locomotor activity and accompanying changes in neuronal activation and dendritic spine density. Our findings revealed that optogenetic stimulation of the PL-NAc core circuit effectively suppressed the cocaine-induced locomotor sensitization, accompanied by a reduction in c-Fos expression within the NAc core. Moreover, optogenetic stimulation led to reduction in dendritic spine density, particularly thin and mushroom spine densities, in the NAc core. This study demonstrates that cocaine-induced locomotor sensitization can be regulated by optogenetic stimulation of the PL-NAc core circuit, providing insights into the crucial role of this circuit in psychomotor stimulant addiction.

Transcranial optogenetic brain modulator for precise bimodal neuromodulation in multiple brain regions

Transcranial brain stimulation is a promising technology for safe modulation of brain function without invasive procedures. Recent advances in transcranial optogenetic techniques with external light sources, using upconversion particles and highly sensitive opsins, have shown promise for precise neuromodulation with improved spatial resolution in deeper brain regions. However, these methods have not yet been used to selectively excite or inhibit specific neural populations in multiple brain regions. In this study, we created a wireless transcranial optogenetic brain modulator that combines highly sensitive opsins and upconversion particles and allows for precise bimodal neuromodulation of multiple brain regions without optical crosstalk. We demonstrate the feasibility of our approach in freely behaving mice. Furthermore, we demonstrate its usefulness in studies of complex behaviors and brain dysfunction by controlling extorting behavior in mice in food competition tests and alleviating the symptoms of Parkinson's disease. Our approach has potential applications in the study of neural circuits and development of treatments for various brain disorders.

Multifunctional hydrogel electronics for closed-loop antiepileptic treatment

Closed-loop strategies offer advanced therapeutic potential through intelligent disease management. Here, we develop a hydrogel-based, single-component, organic electronic device for closed-loop neurotherapy. Fabricated out of conductive hydrogels, the device consists of a flexible array of microneedle electrodes, each of which can be individually addressed to perform electrical recording and control chemical release with sophisticated spatiotemporal control, thus pioneering a smart antiseizure therapeutic system by combining electrical and pharmacological interventions. The recorded neural signal acts as the trigger for a voltage-driven drug release in detected pathological conditions predicted by real-time electrophysiology analysis. When implanted into epileptic animals, the device enables autonomous antiseizure management, where the dosing of antiepileptic drug is controlled in a time-sensitive, region-selective, and dose-adaptive manner, allowing the inhibition of seizure outbursts through the delivery of just-necessary drug dosages. The side effects are minimized with dosages three orders of magnitude lower than the usage in approaches simulating existing clinical treatments.

A stealthy neural recorder for the study of behaviour in primates

By monitoring brain neural signals, neural recorders allow for the study of neurological mechanisms underlying specific behavioural and cognitive states. However, the large brain volumes of non-human primates and their extensive range of uncontrolled movements and inherent wildness make it difficult to carry out covert and long-term recording and analysis of deep-brain neural signals. Here we report the development and performance of a stealthy neural recorder for the study of naturalistic behaviours in non-human primates. The neural recorder includes a fully implantable wireless and battery-free module for the recording of local field potentials and accelerometry data in real time, a flexible 32-electrode neural probe with a resorbable insertion shuttle, and a repeater coil-based wireless-power-transfer system operating at the body scale. We used the device to record neurobehavioural data for over 1 month in a freely moving monkey and leveraged the recorded data to train an artificial intelligence model for the classification of the animals' eating behaviours.

A review of temporal interference, nanoparticles, ultrasound, gene therapy, and designer receptors for Parkinson disease

In this review, we summarize preclinical and clinical trials investigating innovative neuromodulatory approaches for Parkinson disease (PD) motor symptom management. We highlight the following technologies: temporal interference, nanoparticles for drug delivery, blood-brain barrier opening, gene therapy, optogenetics, upconversion nanoparticles, magnetothermal nanoparticles, magnetoelectric nanoparticles, ultrasound-responsive nanoparticles, and designer receptors exclusively activated by designer drugs. These studies establish the basis for novel and promising neuromodulatory treatments for PD motor symptoms.

Advances in Biointegrated Wearable and Implantable Optoelectronic Devices for Cardiac Healthcare

With the prevalence of cardiovascular disease, it is imperative that medical monitoring and treatment become more instantaneous and comfortable for patients. Recently, wearable and implantable optoelectronic devices can be seamlessly integrated into human body to enable physiological monitoring and treatment in an imperceptible and spatiotemporally unconstrained manner, opening countless possibilities for the intelligent healthcare paradigm. To achieve biointegrated cardiac healthcare, researchers have focused on novel strategies for the construction of flexible/stretchable optoelectronic devices and systems. Here, we overview the progress of biointegrated flexible and stretchable optoelectronics for wearable and implantable cardiac healthcare devices. Firstly, the device design is addressed, including the mechanical design, interface adhesion, and encapsulation strategies. Next, the practical applications of optoelectronic devices for cardiac physiological monitoring, cardiac optogenetics, and nongenetic stimulation are presented. Finally, an outlook on biointegrated flexible and stretchable optoelectronic devices and systems for intelligent cardiac healthcare is discussed.

Magnetoelectrics for Implantable Bioelectronics: Progress to Date

The coupling of magnetic and electric properties manifested in magnetoelectric (ME) materials has unlocked numerous possibilities for advancing technologies like energy harvesting, memory devices, and medical technologies. Due to this unique coupling, the magnetic properties of these materials can be tuned by an electric field; conversely, their electric polarization can be manipulated through a magnetic field. Over the past seven years, our lab work has focused on leveraging these materials to engineer implantable bioelectronics for various neuromodulation applications. One of the main challenges for bioelectronics is to design miniaturized solutions that can be delivered with minimally invasive procedures and yet can receive sufficient power to directly stimulate tissue or power electronics to perform functions like communication and sensing. Magnetoelectric coupling in ME materials is strongest when the driving field matches a mechanical resonant mode. However, miniaturized ME transducers typically have resonance frequencies >100 kHz, which is too high for direct neuromodulation as neurons only respond to low frequencies (typically <1 kHz). We discuss two approaches that have been proposed to overcome this frequency mismatch: operating off-resonance and rectification. The off-resonance approach is most common for magnetoelectric nanoparticles (MENPs) that typically have resonance frequencies in the gigahertz range. In vivo experiments on rat models have shown that MENPs could induce changes in neural activity upon excitation with <200 Hz magnetic fields. However, the neural response has latencies of several seconds due to the weak coupling in the off-resonance regime. To stimulate neural responses with millisecond precision, we developed methods to rectify the ME response so that we could drive the materials at their resonant frequency but still produce the slowly varying voltages needed for direct neural stimulation. The first version of the stimulator combined a ME transducer and analog electronics for rectification. To create even smaller solutions, we introduced the first magnetoelectric metamaterial (MNM) that exhibits self-rectification. Both designs have effectively induced neural modulation in rat models with less than 5 ms latency. Based on our experience with in vivo testing of the rectified ME stimulators, we found it challenging to deliver the precisely controlled therapy required for clinical applications, given the ME transducer's sensitivity to the external transmitter alignment. To overcome this challenge, we developed the ME-BIT (MagnetoElectric BioImplanT), a digitally programmable stimulator that receives wireless power and data through the ME link. We further expanded the utility of this technology to neuromodulation applications that require high stimulation thresholds by introducing the DOT (Digitally programmable Overbrain Therapeutic). The DOT has voltage compliance up to 14.5 V. We have demonstrated the efficacy of these designs through various in vivo studies for applications like peripheral nerve stimulation and epidural cortical stimulation. To further improve these systems to be adaptive and enable a network of coordinated devices, we developed a bidirectional communication system to transmit data to and from the implant. To enable even greater miniaturization, we developed a way to use the same ME transducer for wireless power and data communication by developing the first ME backscatter communication protocol.

Soft Bioelectronics for Heart Monitoring

Cardiovascular diseases (CVDs) are a predominant global health concern, accounting for over 17.9 million deaths in 2019, representing approximately 32% of all global fatalities. In North America and Europe, over a million adults undergo cardiac surgeries annually. Despite the benefits, such surgeries pose risks and require precise postsurgery monitoring. However, during the postdischarge period, where monitoring infrastructures are limited, continuous monitoring of vital signals is hindered. In this area, the introduction of implantable electronics is altering medical practices by enabling real-time and out-of-hospital monitoring of physiological signals and biological information postsurgery. The multimodal implantable bioelectronic platforms have the capability of continuous heart sensing and stimulation, in both postsurgery and out-of-hospital settings. Furthermore, with the emergence of machine learning algorithms into healthcare devices, next-generation implantables will benefit artificial intelligence (AI) and connectivity with skin-interfaced electronics to provide more precise and user-specific results. This Review outlines recent advancements in implantable bioelectronics and their utilization in cardiovascular health monitoring, highlighting their transformative deployment in sensing and stimulation to the heart toward reaching truly personalized healthcare platforms compatible with the Sustainable Development Goal 3.4 of the WHO 2030 observatory roadmap. This Review also discusses the challenges and future prospects of these devices.

An Opto-electrophysiology Neural Probe with Photoelectric Artifact-Free for Advanced Single-Neuron Analysis

Opto-electrophysiology neural probes targeting single-cell levels offer an important avenue for elucidating the intrinsic mechanisms of the nervous system using different physical quantities, representing a significant future direction for brain-computer interface (BCI) devices. However, the highly integrated structure poses significant challenges to fabrication processes and the presence of photoelectric artifacts complicates the extraction and analysis of target signals. Here, we propose a highly miniaturized and integrated opto-electrophysiology neural probe for electrical recording and optical stimulation at the single-cell/subcellular level. The design of a total internal reflection layer addresses the photoelectric artifacts that are more pronounced in single-cell devices compared to conventional implantable BCI devices. Finite element simulations and electrical signal tests demonstrate that the opto-electrophysiology neural probe eliminates the photoelectric artifacts in the time domain, which represents a significant breakthrough for optoelectrical integrated BCI devices. Our proposed opto-electrophysiology neural probe holds substantial potential for promoting the development of in vivo BCI devices and developing advanced therapeutic strategies for neurological disorders.

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.

Implantable Zinc Ion Battery and Osteogenesis-Immunoregulation Bifunction of Its Catabolite

Biocompatible batteries can power implantable electronic devices and have broad applications in medicine. However, the controlled degradation of implantable batteries, the impact of battery catabolites on surrounding tissues, and wireless charging designs are often overlooked. Here, we designed an implantable zinc ion battery (ZIB) using a gelatin/polycaprolactone-based composite gel electrolyte. The prepared ZIBs deliver a high specific capacity of 244.0 mA h g-1 (0.5C) and long cycling stability of 300 cycles (4C). ZIBs were completely degraded within 8 weeks in rats and 30 days in a phosphate-buffered saline lipase solution, demonstrating good biocompatibility and degradability. ZIBs catabolites induced macrophage M2 polarization and exhibited anti-inflammatory properties, with mRNA levels of the M2 markers Arg-1 and CD206 up-regulated 15.8-fold and 13.4-fold, respectively, compared to the blank control group. Meanwhile, the expressions of two typical osteogenic markers, osteopontin and osteocalcin, were up-regulated by 3.6-fold and 5.6-fold, respectively, demonstrating that designed ZIBs promoted osteogenic differentiation of bone marrow mesenchymal stem cells. Additionally, a wireless energy transmission module was designed using 3D printing technology to realize real-time charging of the ZIB in rats. The designed ZIB is a promising power source for implantable medical electronic devices and also serves as a functional material to accelerate bone repair.

Self-adaptive rotational electromagnetic energy generation as an alternative to triboelectric and piezoelectric transductions

Triboelectric and piezoelectric energy harvesters can hardly power most microelectronic systems. Rotational electromagnetic harvesters are very promising alternatives, but their performance is highly dependent on the varying mechanical sources. This study presents an innovative approach to significantly increase the performance of rotational harvesters, based on dynamic coil switching strategies for optimization of the coil connection architecture during energy generation. Both analytical and experimental validations of the concept of self-adaptive rotational harvester were carried out. The adaptive harvester was able to provide an average power increase of 63.3% and 79.5% when compared to a non-adaptive 16-coil harvester for harmonic translation and harmonic swaying excitations, respectively, and 83.5% and 87.2% when compared to a non-adaptive 8-coil harvester. The estimated energy conversion efficiency was also enhanced from ~80% to 90%. This study unravels an emerging technological approach to power a wide range of applications that cannot be powered by other vibrationally driven harvesters.

Modelling of negative equivalent magnetic reluctance structure and its application in weak-coupling wireless power transmission

In weak-coupling wireless power transmission, increasing operating frequency, and incorporating metamaterials, resonance structures or ferrite cores have been explored as effective solutions to enhance power efficiency. However, these solutions present significant challenges that need to be addressed. The increased operating frequency boosts ferrite core losses when it exceeds the working frequency range of the material. Existing metamaterial-based solutions present challenges in terms of requiring additional space for slab installation, resulting in increased overall size. In addition, limitations are faced in using Snell's law for explaining the effects of metamaterial-based solutions outside the transmission path, where the magnetic field can not be reflected or refracted. To address these issues, in this work, the concept of a negative equivalent magnetic reluctance structure is proposed and the metamaterial theory is extended with the proposed magnetic reluctance modelling method. Especially, the negative equivalent magnetic reluctance structure is effectively employed in the weak-coupling wireless power transfer system. The proposed negative equivalent magnetic reluctance structure is verified by the stacked negative equivalent magnetic reluctance structure-based transformer experiments and two-coil mutual inductance experiments. Besides, the transmission gain, power experiments and loss analysis experiments verify the effectiveness of the proposed structure in the weak-coupling wireless power transfer system.

Nano-optogenetics for Disease Therapies

Optogenetic, known as the method of 21 centuries, combines optic and genetic engineering to precisely control photosensitive proteins for manipulation of a broad range of cellular functions, such as flux of ions, protein oligomerization and dissociation, cellular intercommunication, and so on. In this technique, light is conventionally delivered to targeted cells through optical fibers or micro light-emitting diodes, always suffering from high invasiveness, wide-field illumination facula, strong absorption, and scattering by nontargeted endogenous substance. Light-transducing nanomaterials with advantages of high spatiotemporal resolution, abundant wireless-excitation manners, and easy functionalization for recognition of specific cells, recently have been widely explored in the field of optogenetics; however, there remain a few challenges to restrain its clinical applications. This review summarized recent progress on light-responsive genetically encoded proteins and the myriad of activation strategies by use of light-transducing nanomaterials and their disease-treatment applications, which is expected for sparking helpful thought to push forward its preclinical and translational uses.

Lead-free dual-frequency ultrasound implants for wireless, biphasic deep brain stimulation

Ultrasound-driven bioelectronics could offer a wireless scheme with sustainable power supply; however, current ultrasound implantable systems present critical challenges in biocompatibility and harvesting performance related to lead/lead-free piezoelectric materials and devices. Here, we report a lead-free dual-frequency ultrasound implants for wireless, biphasic deep brain stimulation, which integrates two developed lead-free sandwich porous 1-3-type piezoelectric composite elements with enhanced harvesting performance in a flexible printed circuit board. The implant is ultrasonically powered through a portable external dual-frequency transducer and generates programmable biphasic stimulus pulses in clinically relevant frequencies. Furthermore, we demonstrate ultrasound-driven implants for long-term biosafety therapy in deep brain stimulation through an epileptic rodent model. With biocompatibility and improved electrical performance, the lead-free materials and devices presented here could provide a promising platform for developing implantable ultrasonic electronics in the future.

Ultra-low frequency magnetic energy focusing for highly effective wireless powering of deep-tissue implantable electronic devices

The limited lifespan of batteries is a challenge in the application of implantable electronic devices. Existing wireless power technologies such as ultrasound, near-infrared light and magnetic fields cannot charge devices implanted in deep tissues, resulting in energy attenuation through tissues and thermal generation. Herein, an ultra-low frequency magnetic energy focusing (ULFMEF) methodology was developed for the highly effective wireless powering of deep-tissue implantable devices. A portable transmitter was used to output the low-frequency magnetic field (<50 Hz), which remotely drives the synchronous rotation of a magnetic core integrated within the pellet-like implantable device, generating an internal rotating magnetic field to induce wireless electricity on the coupled coils of the device. The ULFMEF can achieve energy transfer across thick tissues (up to 20 cm) with excellent transferred power (4-15 mW) and non-heat effects in tissues, which is remarkably superior to existing wireless powering technologies. The ULFMEF is demonstrated to wirelessly power implantable micro-LED devices for optogenetic neuromodulation, and wirelessly charged an implantable battery for programmable electrical stimulation on the sciatic nerve. It also bypassed thick and tough protective shells to power the implanted devices. The ULFMEF thus offers a highly advanced methodology for the generation of wireless powered biodevices.

Miniaturized Implantable Fluorescence Probes Integrated with Metal-Organic Frameworks for Deep Brain Dopamine Sensing

Continuously monitoring neurotransmitter dynamics can offer profound insights into neural mechanisms and the etiology of neurological diseases. Here, we present a miniaturized implantable fluorescence probe integrated with metal-organic frameworks (MOFs) for deep brain dopamine sensing. The probe is assembled from physically thinned light-emitting diodes (LEDs) and phototransistors, along with functional surface coatings, resulting in a total thickness of 120 μm. A fluorescent MOF that specifically binds dopamine is introduced, enabling a highly sensitive dopamine measurement with a detection limit of 79.9 nM. A compact wireless circuit weighing only 0.85 g is also developed and interfaced with the probe, which was later applied to continuously monitor real-time dopamine levels during deep brain stimulation in rats, providing critical information on neurotransmitter dynamics. Cytotoxicity tests and immunofluorescence analysis further suggest a favorable biocompatibility of the probe for implantable applications. This work presents fundamental principles and techniques for integrating fluorescent MOFs and flexible electronics for brain-computer interfaces and may provide more customized platforms for applications in neuroscience, disease tracing, and smart diagnostics.

Injectable Fluorescent Neural Interfaces for Cell-Specific Stimulating and Imaging

Building on current explorations in chronic optical neural interfaces, it is essential to address the risk of photothermal damage in traditional optogenetics. By focusing on calcium fluorescence for imaging rather than stimulation, injectable fluorescent neural interfaces significantly minimize photothermal damage and improve the accuracy of neuronal imaging. Key advancements including the use of injectable microelectronics for targeted electrical stimulation and their integration with cell-specific genetically encoded calcium indicators have been discussed. These injectable electronics that allow for post-treatment retrieval offer a minimally invasive solution, enhancing both usability and reliability. Furthermore, the integration of genetically encoded fluorescent calcium indicators with injectable bioelectronics enables precise neuronal recording and imaging of individual neurons. This shift not only minimizes risks such as photothermal conversion but also boosts safety, specificity, and effectiveness of neural imaging. Embracing these advancements represents a significant leap forward in biomedical engineering and neuroscience, paving the way for advanced brain-machine interfaces.

Power-integrated, wireless neural recording systems on the cranium using a direct printing method for deep-brain analysis

Conventional power-integrated wireless neural recording devices suffer from bulky, rigid batteries in head-mounted configurations, hindering the precise interpretation of the subject's natural behaviors. These power sources also pose risks of material leakage and overheating. We present the direct printing of a power-integrated wireless neural recording system that seamlessly conforms to the cranium. A quasi-solid-state Zn-ion microbattery was 3D-printed as a built-in power source geometrically synchronized to the shape of a mouse skull. Soft deep-brain neural probes, interconnections, and auxiliary electronics were also printed using liquid metals on the cranium with high resolutions. In vivo studies using mice demonstrated the reliability and biocompatibility of this wireless neural recording system, enabling the monitoring of neural activities across extensive brain regions without notable heat generation. This all-printed neural interface system revolutionizes brain research, providing bio-conformable, customizable configurations for improved data quality and naturalistic experimentation.

Wireless magnetoelectrically powered organic light-emitting diodes

Compact wireless light sources are a fundamental building block for applications ranging from wireless displays to optical implants. However, their realization remains challenging because of constraints in miniaturization and the integration of power harvesting and light-emission technologies. Here, we introduce a strategy for a compact wirelessly powered light-source that consists of a magnetoelectric transducer serving as power source and substrate and an antiparallel pair of custom-designed organic light-emitting diodes. The devices operate at low-frequency ac magnetic fields (~100 kHz), which has the added benefit of allowing operation multiple centimeters deep inside watery environments. By tuning the device resonance frequency, it is possible to separately address multiple devices, e.g., to produce light of distinct colors, to address individual display pixels, or for clustered operation. By simultaneously offering small size, individual addressing, and compatibility with challenging environments, our devices pave the way for a multitude of applications in wireless displays, deep tissue treatment, sensing, and imaging.

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

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

Body-temperature softening electronic ink for additive manufacturing of transformative bioelectronics via direct writing

Mechanically transformative electronic systems (TESs) built using gallium have emerged as an innovative class of electronics due to their ability to switch between rigid and flexible states, thus expanding the versatility of electronics. However, the challenges posed by gallium's high surface tension and low viscosity have substantially hindered manufacturability, limiting high-resolution patterning of TESs. To address this challenge, we introduce a stiffness-tunable gallium-copper composite ink capable of direct ink write printing of intricate TES circuits, offering high-resolution (~50 micrometers) patterning, high conductivity, and bidirectional soft-rigid convertibility. These features enable transformative bioelectronics with design complexity akin to traditional printed circuit boards. These TESs maintain rigidity at room temperature for easy handling but soften and conform to curvilinear tissue surfaces at body temperature, adapting to dynamic tissue deformations. The proposed ink with direct ink write printing makes TES manufacturing simple and versatile, opening possibilities in wearables, implantables, consumer electronics, and robotics.

Flexible and Stretchable Light-Emitting Diodes and Photodetectors for Human-Centric Optoelectronics

Optoelectronic devices with unconventional form factors, such as flexible and stretchable light-emitting or photoresponsive devices, are core elements for the next-generation human-centric optoelectronics. For instance, these deformable devices can be utilized as closely fitted wearable sensors to acquire precise biosignals that are subsequently uploaded to the cloud for immediate examination and diagnosis, and also can be used for vision systems for human-interactive robotics. Their inception was propelled by breakthroughs in novel optoelectronic material technologies and device blueprinting methodologies, endowing flexibility and mechanical resilience to conventional rigid optoelectronic devices. This paper reviews the advancements in such soft optoelectronic device technologies, honing in on various materials, manufacturing techniques, and device design strategies. We will first highlight the general approaches for flexible and stretchable device fabrication, including the appropriate material selection for the substrate, electrodes, and insulation layers. We will then focus on the materials for flexible and stretchable light-emitting diodes, their device integration strategies, and representative application examples. Next, we will move on to the materials for flexible and stretchable photodetectors, highlighting the state-of-the-art materials and device fabrication methods, followed by their representative application examples. At the end, a brief summary will be given, and the potential challenges for further development of functional devices will be discussed as a conclusion.

Wireless closed-loop deep brain stimulation using microelectrode array probes

Deep brain stimulation (DBS), including optical stimulation and electrical stimulation, has been demonstrated considerable value in exploring pathological brain activity and developing treatments for neural disorders. Advances in DBS microsystems based on implantable microelectrode array (MEA) probes have opened up new opportunities for closed-loop DBS (CL-DBS) in situ. This technology can be used to detect damaged brain circuits and test the therapeutic potential for modulating the output of these circuits in a variety of diseases simultaneously. Despite the success and rapid utilization of MEA probe-based CL-DBS microsystems, key challenges, including excessive wired communication, need to be urgently resolved. In this review, we considered recent advances in MEA probe-based wireless CL-DBS microsystems and outlined the major issues and promising prospects in this field. This technology has the potential to offer novel therapeutic options for psychiatric disorders in the future.

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.

Radiation Patterns of RF Wireless Devices Implanted in Small Animals: Unexpected Deformations Due to Body Resonance

One challenge in designing RF wireless bioelectronic devices is the impact of the interaction between electromagnetic waves and host body tissues on far-field wireless performance. In this article, we investigate a peculiar phenomenon of implantable RF wireless devices within a small-scale host body related to the deformation of the directivity pattern. Radiation measurements of subcutaneously implanted antennas within rodent cadavers show that the direction of maximum radiation is not always identical with the direction to the closest body-air interface, as one would expect in larger-scale host bodies. For an implanted antenna in the back of a mouse, we observed the maximum directivity in the ventral direction with 4.6 dB greater gain compared to the nearest body-air interface direction. Analytic analysis within small-scale spherical body phantoms identifies two main factors for these results: the limited absorption losses due to the small body size relative to the operating wavelength and the high permittivity of the biological tissues of the host body. Due to these effects, the entire body acts as a dielectric resonator antenna, leading to deformations of the directivity pattern. These results are confirmed with the practical example of a wirelessly powered 2.4-GHz optogenetic implant, demonstrating the significance of the judicious placement of external antennas to take advantage of the deformation of the implanted antenna pattern. These findings emphasize the importance of carefully designing implantable RF wireless devices based on their placements and relative electrical dimensions in small-scale animal models.

Skin preparation-free, stretchable microneedle adhesive patches for reliable electrophysiological sensing and exoskeleton robot control

High-fidelity and comfortable recording of electrophysiological (EP) signals with on-the-fly setup is essential for health care and human-machine interfaces (HMIs). Microneedle electrodes allow direct access to the epidermis and eliminate time-consuming skin preparation. However, existing microneedle electrodes lack elasticity and reliability required for robust skin interfacing, thereby making long-term, high-quality EP sensing challenging during body movement. Here, we introduce a stretchable microneedle adhesive patch (SNAP) providing excellent skin penetrability and a robust electromechanical skin interface for prolonged and reliable EP monitoring under varying skin conditions. Results demonstrate that the SNAP can substantially reduce skin contact impedance under skin contamination and enhance wearing comfort during motion, outperforming gel and flexible microneedle electrodes. Our wireless SNAP demonstration for exoskeleton robot control shows its potential for highly reliable HMIs, even under time-dynamic skin conditions. We envision that the SNAP will open new opportunities for wearable EP sensing and its real-world applications in HMIs.

High-Performing and Capacitive-Matched Triboelectric Implants Driven by Ultrasound

In implantable bioelectronics, which aim for semipermanent use of devices, biosafe energy sources and packaging materials to protect devices are essential elements. However, research so far has been conducted in a direction where they cannot coexist. Here, the development of capacitance-matched triboelectric implants driven is reported by ultrasound under 500 mW cm-2 safe intensity and realize a battery-free, miniatured, and wireless neurostimulator with full titanium (Ti) packaging. The triboelectric implant with high dielectric composite, which has ultralow output impedance, can efficiently deliver sufficient power to generate the stimulation pulse without an energy-storing battery, despite ultrasound attenuation due to the Ti, and has the highest energy transmission efficiency among those reported so far. In vivo study using a rat model demonstrated that the proposed device system is an effective solution for relieving urinary symptoms. These achievements provide a significant step toward permanently implantable devices for controlling human organs and treating various diseases.

Versatile On-Chip Programming of Circuit Hardware for Wearable and Implantable Biomedical Microdevices

Wearable and implantable microscale electronic sensors have been developed for a range of biomedical applications. The sensors, typically millimeter size silicon microchips, are sought for multiple sensing functions but are severely constrained by size and power. To address these challenges, a hardware programmable application-specific integrated circuit design is proposed and post-process methodology is exemplified by the design of battery-less wireless microchips. Specifically, both mixed-signal and radio frequency circuits are designed by incorporating metal fuses and anti-fuses on the top metal layer to enable programmability of any number of features in hardware of the system-on-chip (SoC) designs. This is accomplished in post-foundry editing by combining laser ablation and focused ion beam processing. The programmability provided by the technique can significantly accelerate the SoC chip development process by enabling the exploration of multiple internal circuit parameters without the requirement of additional programming pads or extra power consumption. As examples, experimental results are described for sub-millimeter size complementary metal-oxide-semiconductor microchips being developed for wireless electroencephalogram sensors and as implantable microstimulators for neural interfaces. The editing technique can be broadly applicable for miniaturized biomedical wearables and implants, opening up new possibilities for their expedited development and adoption in the field of smart healthcare.

Lifetime engineering of bioelectronic implants with mechanically reliable thin film encapsulations

While the importance of thin form factor and mechanical tissue biocompatibility has been made clear for next generation bioelectronic implants, material systems meeting these criteria still have not demonstrated sufficient long-term durability. This review provides an update on the materials used in modern bioelectronic implants as substrates and protective encapsulations, with a particular focus on flexible and conformable devices. We review how thin film encapsulations are known to fail due to mechanical stresses and environmental surroundings under processing and operating conditions. This information is then reflected in recommending state-of-the-art encapsulation strategies for designing mechanically reliable thin film bioelectronic interfaces. Finally, we assess the methods used to evaluate novel bioelectronic implant devices and the current state of their longevity based on encapsulation and substrate materials. We also provide insights for future testing to engineer long-lived bioelectronic implants more effectively and to make implantable bioelectronics a viable option for chronic diseases in accordance with each patient's therapeutic timescale.

Brainmask: an ultrasoft and moist micro-electrocorticography electrode for accurate positioning and long-lasting recordings

Bacterial cellulose (BC), a natural biomaterial synthesized by bacteria, has a unique structure of a cellulose nanofiber-weaved three-dimensional reticulated network. BC films can be ultrasoft with sufficient mechanical strength, strong water absorption and moisture retention and have been widely used in facial masks. These films have the potential to be applied to implantable neural interfaces due to their conformality and moisture, which are two critical issues for traditional polymer or silicone electrodes. In this work, we propose a micro-electrocorticography (micro-ECoG) electrode named "Brainmask", which comprises a BC film as the substrate and separated multichannel parylene-C microelectrodes bonded on the top surface. Brainmask can not only guarantee the precise position of microelectrode sites attached to any nonplanar epidural surface but also improve the long-lasting signal quality during acute implantation with an exposed cranial window for at least one hour, as well as the in vivo recording validated for one week. This novel ultrasoft and moist device stands as a next-generation neural interface regardless of complex surface or time of duration.

Illuminating the Brain: Advances and Perspectives in Optoelectronics for Neural Activity Monitoring and Modulation

Optogenetic modulation of brain neural activity that combines optical and electrical modes in a unitary neural system has recently gained robust momentum. Controlling illumination spatial coverage, designing light-activated modulators, and developing wireless light delivery and data transmission are crucial for maximizing the use of optical neuromodulation. To this end, biocompatible electrodes with enhanced optoelectrical performance, device integration for multiplexed addressing, wireless transmission, and multimodal operation in soft systems have been developed. This review provides an outlook for uniformly illuminating large brain areas while spatiotemporally imaging the neural responses upon optoelectrical stimulation with little artifacts. Representative concepts and important breakthroughs, such as head-mounted illumination, multiple implanted optical fibers, and micro-light-delivery devices, are discussed. Examples of techniques that incorporate electrophysiological monitoring and optoelectrical stimulation are presented. Challenges and perspectives are posed for further research efforts toward high-density optoelectrical neural interface modulation, with the potential for nonpharmacological neurological disease treatments and wireless optoelectrical stimulation.

A wireless, solar-powered, optoelectronic system for spatial restriction-free long-term optogenetic neuromodulations

Numerous wireless optogenetic systems have been reported for practical tether-free optogenetics in freely moving animals. However, most devices rely on battery-powered or coil-powered systems requiring periodic battery replacement or bulky, high-cost charging equipment with delicate antenna design. This leads to spatiotemporal constraints, such as limited experimental duration due to battery life or animals' restricted movement within specific areas to maintain wireless power transmission. In this study, we present a wireless, solar-powered, flexible optoelectronic device for neuromodulation of the complete freely behaving subject. This device provides chronic operation without battery replacement or other external settings including impedance matching technique and radio frequency generators. Our device uses high-efficiency, thin InGaP/GaAs tandem flexible photovoltaics to harvest energy from various light sources, which powers Bluetooth system to facilitate long-term, on-demand use. Observation of sustained locomotion behaviors for a month in mice via secondary motor cortex area stimulation demonstrates the notable capabilities of our device, highlighting its potential for space-free neuromodulating applications.

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.

Hierarchical Serpentine-Helix Combination for 3D Stretchable Electronics

3D stretchable electronics attract growing interest due to their new and more complex functionalities compared to 1D or 2D counterparts. Among all 3D configuration designs, a 3D helical structure is commonly used as it can be designed to achieve outstanding stretching ratios as well as highly robust mechanical performance. However, the stretching ratio that mainly focuses on the axis direction hinders its applications. Inspired by hierarchies in a tendon, a novel structural design of hierarchical 3D serpentine-helix combination is proposed. The structural design constructed by a sequence with repeating small units winding in a helical manner around the axis can enable large mechanical forces transferred down to a smaller scale with the dissipation of potentially damaging stresses by microscale buckling, thereby endowing the electronic components made from high-performance but hard-to-stretch materials with large stretchability (≥200%) in x-, y-, or z-axis direction, high structural stability, and extraordinary electromechanical performance. Two applications including a wireless charging patch and an epidermal electronic system are demonstrated. The epidermal electronic system made of several hierarchical 3D serpentine-helix combinations allows for high-fidelity monitoring of electrophysiological signals, galvanic skin response, and finger-movement-induced electrical signals, which can achieve good tactile pattern recognition when combined with an artificial neural network.

Soft monolithic infrared neural interface for simultaneous neurostimulation and electrophysiology

Controlling neuronal activity using implantable neural interfaces constitutes an important tool to understand and develop novel strategies against brain diseases. Infrared neurostimulation is a promising alternative to optogenetics for controlling the neuronal circuitry with high spatial resolution. However, bi-directional interfaces capable of simultaneously delivering infrared light and recording electrical signals from the brain with minimal inflammation have not yet been reported. Here, we have developed a soft fibre-based device using high-performance polymers which are >100-fold softer than conventional silica glass used in standard optical fibres. The developed implant is capable of stimulating the brain activity in localized cortical domains by delivering laser pulses in the 2 μm spectral region while recording electrophysiological signals. Action and local field potentials were recorded in vivo from the motor cortex and hippocampus in acute and chronic settings, respectively. Immunohistochemical analysis of the brain tissue indicated insignificant inflammatory response to the infrared pulses while the signal-to-noise ratio of recordings still remained high. Our neural interface constitutes a step forward in expanding infrared neurostimulation as a versatile approach for fundamental research and clinically translatable therapies.

Biocompatible Material-Based Flexible Biosensors: From Materials Design to Wearable/Implantable Devices and Integrated Sensing Systems

Human beings have a greater need to pursue life and manage personal or family health in the context of the rapid growth of artificial intelligence, big data, the Internet of Things, and 5G/6G technologies. The application of micro biosensing devices is crucial in connecting technology and personalized medicine. Here, the progress and current status from biocompatible inorganic materials to organic materials and composites are reviewed and the material-to-device processing is described. Next, the operating principles of pressure, chemical, optical, and temperature sensors are dissected and the application of these flexible biosensors in wearable/implantable devices is discussed. Different biosensing systems acting in vivo and in vitro, including signal communication and energy supply are then illustrated. The potential of in-sensor computing for applications in sensing systems is also discussed. Finally, some essential needs for commercial translation are highlighted and future opportunities for flexible biosensors are considered.

Adolescent Parvalbumin Expression in the Left Orbitofrontal Cortex Shapes Sociability in Female Mice

The adolescent social experience is essential for the maturation of the prefrontal cortex in mammalian species. However, it still needs to be determined which cortical circuits mature with such experience and how it shapes adult social behaviors in a sex-specific manner. Here, we examined social-approaching behaviors in male and female mice after postweaning social isolation (PWSI), which deprives social experience during adolescence. We found that the PWSI, particularly isolation during late adolescence, caused an abnormal increase in social approaches (hypersociability) only in female mice. We further found that the PWSI female mice showed reduced parvalbumin (PV) expression in the left orbitofrontal cortex (OFCL). When we measured neural activity in the female OFCL, a substantial number of neurons showed higher activity when mice sniffed other mice (social sniffing) than when they sniffed an object (object sniffing). Interestingly, the PWSI significantly reduced both the number of activated neurons and the activity level during social sniffing in female mice. Similarly, the CRISPR/Cas9-mediated knockdown of PV in the OFCL during late adolescence enhanced sociability and reduced the social sniffing-induced activity in adult female mice via decreased excitability of PV+ neurons and reduced synaptic inhibition in the OFCL Moreover, optogenetic activation of excitatory neurons or optogenetic inhibition of PV+ neurons in the OFCL enhanced sociability in female mice. Our data demonstrate that the adolescent social experience is critical for the maturation of PV+ inhibitory circuits in the OFCL; this maturation shapes female social behavior via enhancing social representation in the OFCL SIGNIFICANCE STATEMENT Adolescent social isolation often changes adult social behaviors in mammals. Yet, we do not fully understand the sex-specific effects of social isolation and the brain areas and circuits that mediate such changes. Here, we found that adolescent social isolation causes three abnormal phenotypes in female but not male mice: hypersociability, decreased PV+ neurons in the left orbitofrontal cortex (OFCL), and decreased socially evoked activity in the OFCL Moreover, parvalbumin (PV) deletion in the OFCL in vivo caused the same phenotypes in female mice by increasing excitation compared with inhibition within the OFCL Our data suggest that adolescent social experience is required for PV maturation in the OFCL, which is critical for evoking OFCL activity that shapes social behaviors in female mice.