Neural stimulation and recording electrodes

Electrodeposited coatings for neural electrodes: A review

Neural electrodes play a pivotal role in ensuring safe stimulation and high-quality recording for various bioelectronics such as neuromodulation devices and brain-computer interfaces. With the miniaturization of electrodes and the increasing demand for multi-functionality, the incorporation of coating materials via electrodeposition to enhance electrodes performance emerges as a highly effective strategy. These coatings not only substantially improve the stimulation and recording performance of electrodes but also introduce additional functionalities. This review began by outlining the application scenarios and critical requirements of neural electrodes. It then delved into the deposition principles and key influencing factors. Furthermore, the advancements in the electrochemical performance and adhesion stability of these coatings were reviewed. Ultimately, the latest innovative works in the electrodeposited coating applications were highlighted, and future perspectives were summarized.

Nanosilica cross-linked polyurethane hybrid hydrogels to stabilize the silicone rubber based invasive electrode-neural tissue interface

An unstable electrode-neural tissue interface induced by tissue inflammatory response hinders the application of invasive brain-computer interfaces (BCIs). In this work, nanosilica cross-linked polyurethane (SiO2/PU) hybrid hydrogels were prepared to serve as the coatings and to modify silicone rubber (SR), which is a commonly used encapsulation material of invasive electrodes for neural recording/stimulation. The hydrophilicity, swelling ratio, and bulk ionic conductivity of SiO2/PU hybrid hydrogels were tailored by incorporating different amount of SiO2 serving as the cross-linking agent. Correspondingly, the optimized SiO2/PU hybrid hydrogel coatings have less impact on the electrochemical properties of invasive electrodes relative to PU hydrogel. Cell affinity assays with rat pheochromocytoma cells reveal that coatings made of SiO2/PU hybrid hydrogels are more effective in enhancing their adhesion and neurite outgrowth than those made of PU hydrogels. The adsorption amount of non-specific proteins on SR is significantly reduced by 81.6 % and 92.6 % upon coating with PU hydrogels and SiO2/PU hybrid hydrogels, respectively. Histological assessment indicates that the SR implants with a SiO2/PU hybrid hydrogel coating provoke the mildest tissue response. Collectively, the SiO2/PU hybrid hydrogel is highly promising for the stabilization of electrode-neural tissue interface, which is crucial for the development of invasive BCIs.

Biomechanics characterization of an implantable ultrathin intracortical electrode through finite element method

Neural electrodes are widely used in brain-computer interfaces and neuroprosthesis for the treatment of various neurological disorders. However, as components that come into direct contact with neural tissue, implanted neural electrodes could cause mechanical damage during surgical insertions or while inside the brain. Thus, accurately and timely assessing this damage was vital for chronic implantation, which posed a significant challenge. This study aimed to evaluate the biomechanical effects and clinical application risks of a polyimide-based ultrathin flexible intracortical microelectrode through the finite element method (FEM). It analyzed the electrode-brain biomechanical effects during the electrode's insertion process and under steady-state acceleration with the electrode inside the brain. Furthermore, the study examined the impact of factors including implantation depth (ranging from 5 to 5000 μm), cortical thickness (0.5 mm, 2.5 mm, and 4.5 mm), step displacement (from 1 to 5 μm) during insertion, and acceleration direction (vertical and horizontal) on the electrode's biomechanical effects. The primary findings showed that the 98th percentile Von Mises Strain (ε98) and Von Mises Stress (σ98) in the region of interest (ROI) decreased dual-exponentially with increasing implantation depth and increased linearly with larger step displacements. Compared to the Von Mises strain threshold of 14.65%, as proposed by Sahoo et al., indicating a 50% risk of diffuse axonal injury (DAI), it was recommended to limit the initial step displacement during insertion to 1 μm, increasing to 5 μm at deeper locations (over 500 μm) to balance safety and efficiency. Additionally, it was found that cortical thickness had a negligible impact during insertion and while experiencing steady-state acceleration in vivo, with the three fitted curves almost coinciding when cortical thicknesses were 0.5 mm, 2.5 mm, and 4.5 mm. The flexible electrode exhibited excellent mechanical performance under steady-state acceleration in vivo, with ε98 being less than 0.3% and σ98 being less than 50 Pa, although it was more sensitive to horizontal acceleration. Thus, it could be concluded that during long-duration accelerations from transportation modes such as elevators and high-speed trains, the electrode's mechanical effects on brain tissue could be neglected, demonstrating long-term mechanical stability. This research was significant for guiding surgical insertion and clinical applications of flexible electrodes.

Soft Bioelectronic Interfaces for Continuous Peripheral Neural Signal Recording and Robust Cross-Subject Decoding

Accurate decoding of peripheral nerve signals is essential for advancing neuroscience research, developing therapeutics for neurological disorders, and creating reliable human-machine interfaces. However, the poor mechanical compliance of conventional metal electrodes and limited generalization of existing decoding models have significantly hindered progress in understanding peripheral nerve function. This study introduces low-impedance, soft-conducting polymer electrodes capable of forming stable, intimate contacts with peripheral nerve tissues, allowing for continuous and reliable recording of neural activity in awake animals. Using this unique dataset of neurophysiological signals, a neural network model that integrates both handcrafted and deep learning-derived features, while incorporating parameter-sharing and adaptation training strategies, is developed. This approach significantly improves the generalizability of the decoding model across subjects, reducing the reliance on extensive training data. The findings not only deepen the understanding of peripheral nerve function but also open avenues for developing advanced interventions to augment and restore neurological functions.

The Role of Scalp EEG Recordings During Cortical Visual Prosthesis Testing

INTRODUCTION

This article highlights the value of recording scalp electroencephalogram (EEG) from two individuals with blindness who received intracortical visual stimulators to create artificial vision. Given the known risk of cortical stimulation inducing seizures, we recorded occipital scalp EEG as a safety precaution. Over a 3-year period, over 330 h of EEG data were collected.

METHODS

Twenty-five wireless floating microelectrode arrays (WFMAs), each containing 16 stimulating electrodes, were implanted in the right dorsolateral occipital cortex of the first participant, totaling 400 independently controlled stimulating electrodes. Similarly, 32 WFMAs were implanted in the second participant's cortex, totaling 512 electrodes. Phosphenes were characterized and mapped to align their locations in the visual field to create camera-driven imagery of the visual environment.

RESULTS

Scalp EEG recordings during intracortical stimulation provided early warning of impending epileptic activity, reducing the risk of stimulation-induced seizures. In two instances, seizures occurred during direct cortical stimulation and were visible in the scalp EEG recordings. Normal electrically evoked potentials (eEPs) were also evident in the EEG records.

CONCLUSION

Scalp EEG can be valuable to alert researchers to impending seizures. However, it is not required for conditions in which low levels of stimulation are employed.

TRIAL REGISTRATION

Clinical Trial Number NCT04634383.

Advances in Electrode Design and Physiological Considerations for Retinal Implants

Until now, the ultimate solution for blind people has not been achieved, because challenges still exist. Retinal implants have emerged as a promising solution for restoring vision in individuals suffering from retinal degenerative diseases such as retinitis pigmentosa and age-related macular degeneration. Central to the efficacy of these implants is the design and functionality of the electrode arrays responsible for stimulating retinal neurons. This review evaluates the evolution of retinal implants, with particular emphasis on electrode specifications, physiological considerations for electrical stimulation, and recent advancements in electrode design. A comprehensive analysis of state-of-the-art published studies provides a detailed cross-comparison of electrode characteristics, offering insights into current state-of-the-art technologies and future directions.

Quantifying physical degradation alongside recording and stimulation performance of 980 intracortical microelectrodes chronically implanted in three humans for 956-2130 days

The clinical success of brain computer interfaces (BCI) depends on overcoming both biological and material challenges to ensure a long-term stable connection for neural recording and stimulation. This study systematically quantified damage that microelectrodes sustained during chronical implantation in three people with tetraplegia for 956-2130 days. Using scanning electron microscopy (SEM), we imaged 980 microelectrodes from eleven Neuroport arrays tipped with platinum (Pt, n = 8) and sputtered iridium oxide film (SIROF, n = 3). Arrays were implanted/explanted from posterior parietal, motor and somatosensory cortices across three clinical sites (Caltech/UCLA, Caltech/USC, APL/Johns Hopkins). From the electron micrographs, we quantified and correlated physical damage with functional outcomes measured in vivo, prior to explant (recording quality, noise, impedance and stimulation ability). Despite greater physical degradation, SIROF electrodes were twice as likely to record neural activity than Pt (measured by SNR). For SIROF, 1 kHz impedance significantly correlated with all physical damage metrics, recording metrics, and stimulation performance, suggesting a reliable measurement of in vivo degradation. We observed a new degradation type, primarily on stimulated electrodes ("pockmarked" vs "cracked") electrodes; however, no significant degradation due to stimulation or amount of charge delivered. We hypothesize erosion of the silicon shank accelerates damage to the electrode / tissue interface, following damage to the tip metal. These findings link quantitative measurements to the microelectrodes' physical condition and their capacity to record/stimulate. These data could lead to improved manufacturing processes or novel electrode designs to improve long-term performance of BCIs, making them vitally important as multi-year clinical trials of BCIs are becoming more common. STATEMENT OF SIGNIFICANCE: Long-term performance stability of the electrode-tissue interface is essential for clinical viability of brain computer interface (BCI) devices; currently, materials degradation is a critical component for performance loss. Across three human participants, ten micro-electrode arrays (plus one control) were implanted for 956-2130 days. Using scanning electron microscopy (SEM), we analyzed degradation of 980 electrodes, comparing two types of commonly implanted electrode tip metals: Platinum (Pt) and Sputtered Iridium Oxide Film (SIROF). We correlated observed degradation with in vivo electrode performance: recording (signal-to-noise ratio, noise, impedance) and stimulation (evoked somatosensory percepts). We hypothesize penetration of the electrode tip by biotic processes leads to erosion of the supporting silicon core, which then accelerates further tip metal damage. These data could lead to improved manufacturing processes or novel electrode designs towards the goal of a stable BCI electrical interface, spanning a multi-decade participant lifetime.

Biomimetic stimulation patterns drive natural artificial touch percepts using intracortical microstimulation in humans

Objective.Intracortical microstimulation (ICMS) of human somatosensory cortex evokes tactile percepts that people describe as originating from their own body, but are not always described as feeling natural. It remains unclear whether stimulation parameters such as amplitude, frequency, and spatiotemporal patterns across electrodes can be chosen to increase the naturalness of these artificial tactile percepts.Approach.In this study, we investigated whether biomimetic stimulation patterns-ICMS patterns that reproduce essential features of natural neural activity-increased the perceived naturalness of ICMS-evoked sensations compared to a non-biomimetic pattern in three people with cervical spinal cord injuries. All participants had electrode arrays implanted in their somatosensory cortices. Rather than qualitatively asking which pattern felt more natural, participants directly compared natural residual percepts, delivered by mechanical indentation on a sensate region of their hand, to artificial percepts evoked by ICMS and were asked whether linear non-biomimetic or biomimetic stimulation felt most like the mechanical indentation.Main results.We show that simple biomimetic ICMS, which modulated the stimulation amplitude on a single electrode, was perceived as being more like a mechanical indentation reference on 32% of the electrodes. We also tested an advanced biomimetic stimulation scheme that captured more of the spatiotemporal dynamics of cortical activity using co-modulated stimulation amplitudes and frequencies across four electrodes. Here, ICMS felt more like the mechanical reference for 75% of the electrode groups. Finally, biomimetic stimulus trains required less charge than their non-biomimetic counterparts to create an intensity-matched sensation.Significance.We conclude that ICMS encoding schemes that mimic naturally occurring neural spatiotemporal activation patterns in the somatosensory cortex feel more like an actual touch than non-biomimetic encoding schemes. This also suggests that using key elements of neuronal activity can be a useful conceptual guide to constrain the large stimulus parameter space when designing future stimulation strategies. This work is a part of Clinical Trial NCT01894802.

Foldable 3D opto-electro array for optogenetic neuromodulation and physiology recording

This paper presents a thin-film, three-dimensional (3D) opto-electro array featuring four addressable microscale light-emitting diodes (LEDs) for surface cortex illumination and nine penetrating electrodes for simultaneous recording of light-evoked neural activities. Inspired by the origami concept, we have developed a meticulously designed "bridge+trench" structure that facilitates the transformation of the array from 2D to 3D while preventing damage to the thin film metal. Prior to device transformation, the shape and dimensions of the 2D array can be customized, enhancing its versatility for various applications. In addition, the arched base offers strong mechanical support to facilitate the direct insertion of the probe into tissue without any mechanical reinforcement. The array was encapsulated using polyimide and epoxy to ensure mechanical flexibility and biocompatibility of the device. The efficacy of the device was evaluated through comprehensive in vitro and in vivo characterization.

Bioelectric and physicochemical foundations of bioelectronics in tissue regeneration

Understanding and exploiting bioelectric signaling pathways and physicochemical properties of materials that interface with living tissues is central to advancing tissue regeneration. In particular, the emerging field of bioelectronics leverages these principles to develop personalized, minimally invasive therapeutic strategies tailored to the dynamic demands of individual patients. By integrating sensing and actuation modules into flexible, biocompatible devices, clinicians can continuously monitor and modulate local electrical microenvironments, thereby guiding regenerative processes without extensive surgical interventions. This review provides a critical examination of how fundamental bioelectric cues and physicochemical considerations drive the design and engineering of next-generation bioelectronic platforms. These platforms not only promote the formation and maturation of new tissues across neural, cardiac, musculoskeletal, skin, and gastrointestinal systems but also precisely align therapies with the unique structural, functional, and electrophysiological characteristics of each tissue type. Collectively, these insights and innovations represent a convergence of biology, electronics, and materials science that holds tremendous promise for enhancing the efficacy, specificity, and long-term stability of regenerative treatments, ushering in a new era of advanced tissue engineering and patient-centered regenerative medicine.

Differences and Commonalities of Electrical Stimulation Paradigms After Central Paralysis and Amputation

BACKGROUND

Patients with spinal cord injury (SCI) or with severe brain stroke suffer from life-lasting functional and sensory impairments. Other traumatic injuries such as limb loss after an accident or disease also affect motor function and sensory feedback and impair quality of life in those individuals. Invasive and non-invasive functional electrical stimulation (FES) is a well-established method to partially restore function and sensory feedback of paralyzed and phantom limbs. It is also a supporting technology for the rehabilitation of the neuromuscular system and for complementing assistive devices.

METHODS

This work reviews the current state-of-the-art of FES as a technology for restoring function and supporting rehabilitation therapy and assistive devices.

RESULTS

Electrodes, electrical stimulation, use of brain signals for rehabilitation and control, and sensory feedback are covered as parts of the whole. A perspective is given on how clinical and research protocols developed for patients with SCI and brain injuries can be translated to the treatment of patients with an amputation and vice versa. We further elaborate on how motor learning strategies with quantitative electrophysiological and kinematic measurements may help caregivers in the rehabilitation process. Insights from practitioners (collected during a workshop of the IFESS 2025) have been integrated to summarize common needs, open questions, and challenges.

CONCLUSIONS

The information from the literature and from practitioners was integrated to propose the next steps towards establishing common guidelines and measures of FES in clinical practice towards evidence-driven treatment and objective assessments.

Hydrogel Adhesive Integrated-Microstructured Electrodes for Cuff-Free, Less-Invasive, and Stable Interface for Vagus Nerve Stimulation

Vagus nerve stimulation (VNS) is a recognized treatment for neurological disorders, yet the surgical procedure carries significant risks. During the process of isolating or cuffing the vagus nerve, there is a danger of damaging the nerve itself or the adjacent carotid artery or jugular vein. To minimize this risk, here we introduce a novel hydrogel adhesive-integrated and stretchable microdevice that provides a less invasive,  cuff-free option for interfacing with the vagus nerve. The device features a novel hydrogel adhesive formulation that enables crosslinking on biological tissue. The inclusion of kirigami structures within the thin-film microdevice creates space for uniform hydrogel-to-epineurium contact while accommodating the stiffness changes of the hydrogel upon hydration. Using a rodent model, we demonstrate a robust device adhesion on a partially exposed vagus nerve in physiological fluid even without the vagus nerve isolation and cuffing process. Our device elicted stable and clear evoked compound action potential (~1500 µV peak-to-peak) in C-fibers with a current amplitude of 0.4 mA. We believe this innovative platform provides a novel, less-risky approach to interface with fragile nerve and vascular structures during VNS implantation.

Bioaugmented design and functional evaluation of low damage implantable array electrodes

Implantable neural electrodes are key components of brain-computer interfaces (BCI), but the mismatch in mechanical and biological properties between electrode materials and brain tissue can lead to foreign body reactions and glial scarring, and subsequently compromise the long-term stability of electrical signal transmission. In this study, we proposed a new concept for the design and bioaugmentation of implantable electrodes (bio-array electrodes) featuring a heterogeneous gradient structure. Different composite polyaniline-gelatin-alginate based conductive hydrogel formulations were developed for electrode surface coating. In addition, the design, materials, and performance of the developed electrode was optimized through a combination of numerical simulations and physio-chemical characterizations. The long-term biological performance of the bio-array electrodes were investigated in vivo using a C57 mouse model. It was found that compared to metal array electrodes, the surface charge of the bio-array electrodes increased by 1.74 times, and the impedance at 1 kHz decreased by 63.17 %, with a doubling of the average capacitance. Long-term animal experiments showed that the bio-array electrodes could consistently record 2.5 times more signals than those of the metal array electrodes, and the signal-to-noise ratio based on action potentials was 2.1 times higher. The study investigated the mechanisms of suppressing the scarring effect by the bioaugmented design, revealing reduces brain damage as a result of the interface biocompatibility between the bio-array electrodes and brain tissue, and confirmed the long-term in vivo stability of the bio-array electrodes.

Conveying tactile object characteristics through customized intracortical microstimulation of the human somatosensory cortex

Microstimulation of the somatosensory cortex can evoke tactile percepts in people with spinal cord injury, providing a means to restore touch. While location and intensity can be reliably conveyed, two issues that prevent creating more complex naturalistic sensations are a lack of methods to effectively scan the large stimulus parameter space and difficulties with assessing percept quality. Here, we address both challenges with an experimental paradigm that enables three male individuals with tetraplegia to control their stimulation parameters in a blinded fashion to create sensations for different virtual objects. Using this method, participants can reliably create object-specific sensations and report vivid object-appropriate characteristics. Moreover, both linear classifiers and participants can match stimulus profiles with their respective objects significantly above chance without any visual cues. Confusion between two sensations increases as the associated objects share more tactile characteristics. We conclude that while visual information contributes to the experience of the artificially evoked sensations, microstimulation in the somatosensory cortex itself can evoke intuitive percepts with a variety of tactile properties. This self-guided stimulation approach may be used to effectively characterize percepts from future stimulation paradigms.

Supracortical Microstimulation: Advances in Microelectrode Design and In Vivo Validation

Electrical stimulation of the brain is being developed as a treatment for an increasing number of neurological disorders. Technologies for delivering electrical stimulation are advancing rapidly and vary in specificity, coverage, and invasiveness. Supracortical microstimulation (SCMS), characterized by microelectrode contacts placed on the epidural or subdural cortical surface, achieves a balance between the advantages and limitations of other electrical stimulation technologies by delivering spatially precise activation without disrupting the integrity of the cortex. However, in vivo experiments involving SCMS have not been comprehensively summarized. Here, we review the field of SCMS, focusing on recent advances, to guide the development of clinically translatable supracortical microelectrodes. We also highlight the gaps in our understanding of the biophysical effects of this technology. Future work investigating the unique electrochemical properties of supracortical microelectrodes and validating SCMS in nonhuman primate preclinical studies can enable rapid clinical translation of innovative treatments for humans with neurological disorders.

Soft neural interface with color adjusted PDMS encapsulation layer for spinal cord stimulation

BACKGROUND

Spinal cord stimulation (SCS) plays a crucial role in treating various neurological diseases. Utilizing soft spinal cord electrodes in SCS allows for a better fit with the physiological structure of the spinal cord and reduces tissue damage. Polydimethylsiloxane (PDMS) has emerged as an ideal material for soft bioelectronics. However, micromachining soft PDMS bioelectronics devices with low thermal effects and high uniformity remains challenging.

NEW METHOD

Here, we demonstrated a fully laser-micromachined soft neural interface for SCS. The native and color adjusted PDMS with variable absorbance characteristics were investigated in laser processing. In addition, we systematically evaluated the impact of electrode sizes on the electrochemical performance of neural interface. By fitting the equivalent circuit model, the electrochemical process of neural interface was revealed and the performance of the electrode was evaluated. The biocompatibility of color adjusted PDMS was confirmed by cytotoxicity assays. Finally, we validated the neural interface in mice.

RESULTS

Color adjusted PDMS has good biocompatibility and can significantly reduce the damage caused by thermal effects, enhancing the electrochemical performance of bioelectronic devices. The soft neural interface with color adjusted PDMS encapsulation layer can activate the motor function safely.

COMPARISON WITH EXISTING METHODS

The fully laser-micromachined soft neural interface was proposed for the first time. Compared with existing methods, this method showed low thermal effects, high uniformity, and could be easily scaled up.

CONCLUSIONS

The fully laser-micromachined soft neural interface device with color adjusted PDMS encapsulation layer shows great promise for applications in SCS.

Soft 3D Bioelectrodes for Intraorganoid Signal Monitoring in Cardiac Models

Continuous monitoring of physiological activities within the internal regions of three-dimensional (3D) organoids holds significant promise for advancing organoid-based research. However, conventional methods are constrained to capturing signals from the peripheral surfaces of organoids, limiting insights into internal dynamics. Here, we present a soft 3D bioelectrode platform for continuous intraorganoid signal monitoring. These bioelectrodes, formed via 3D printing of liquid metal, are designed with customizable geometric parameters, including height and diameter, to adapt to various organoid structures. The tissue-comparable softness of the electrodes minimizes damage to cardiac organoids, ensuring a stable interface for reliable signal recording even under dynamic deformations caused by rhythmic contractions or displacements in aqueous environments. The array configuration enables simultaneous electrocardiogram (ECG) recordings from 32 organoids. Demonstrating real-time monitoring of drug-induced ECG responses, this scalable platform highlights its potential for high-throughput drug screening.

A Neuroelectronic Interface with Microstructured Substrates for Spiral Ganglion Neurons Cultured In Vitro: Proof of Concept

In this study, we present a proof-of-concept neuroelectronic interface (NEI) for extracellular stimulation and recording of neurophysiological activity in spiral ganglion neurons (SGNs) cultured in vitro on three-dimensional, micro-patterned substrates with customized microtopographies, integrated within a 196-channel microelectrode array (MEA). This approach enables mechanotaxis-driven neuronal contact guidance, promoting SGN growth and development, which is highly sensitive to artificial in vitro environments. The microtopography geometry was optimized based on our previous studies to enhance SGN alignment and neuron-electrode interactions. The NEI was validated using SGNs dissociated from rat pups in the prehearing period and cultured for seven days in vitro (DIV). We observed viable and proliferative cellular cultures with robust neurophysiological responses in the form of local field potentials (LFPs) resembling action potentials (APs), elicited both spontaneously and through electrical stimulation. These findings provide deeper insights into SGN behavior and neuron-microenvironment interactions, laying the groundwork for further advancements in neuroelectronic systems.

Biodegradable stimulating electrodes for resident neural stem cell activation in vivo

Brain stimulation has been recognized as a clinically effective strategy for treating neurological disorders. Endogenous brain neural precursor cells (NPCs) have been shown to be electrosensitive cells that respond to electrical stimulation by expanding in number, undergoing directed cathodal migration, and differentiating into neural phenotypes in vivo, supporting the application of electrical stimulation to promote neural repair. In this study, we present the design of a flexible and biodegradable brain stimulation electrode for temporally regulated neuromodulation of NPCs. Leveraging the cathodally skewed electrochemical window of molybdenum and the volumetric charge transfer properties of conductive polymer, we engineered the electrodes with high charge injection capacity for the delivery of biphasic monopolar stimulation. We demonstrate that the electrodes are biocompatible and can deliver an electric field sufficient for NPC activation for 7 days post implantation before undergoing resorption in physiological conditions, thereby eliminating the need for surgical extraction. The biodegradable electrode demonstrated its potential to be used for NPC-based neural repair strategies.

Nitrogen-Doped Ultrananocrystalline Diamond - Optoelectronic Biointerface for Wireless Neuronal Stimulation

This study presents a semiconducting optoelectronic system for light-controlled non-genetic neuronal stimulation using visible light. The system architecture is entirely wireless, comprising a thin film of nitrogen-doped ultrananocrystalline diamond directly grown on a semiconducting silicon substrate. When immersed in a physiological medium and subjected to pulsed illumination in the visible (595 nm) or near-infrared wavelength (808 nm) range, charge accumulation at the device-medium interface induces a transient ionic displacement current capable of electrically stimulating neurons with high temporal resolution. With a measured photoresponsivity of 7.5 mA W-1, the efficacy of this biointerface is demonstrated through optoelectronic stimulation of degenerate rat retinas using 595 nm irradiation, pulse durations of 50-500 ms, and irradiance levels of 1.1-4.3 mW mm-2, all below the safe ocular threshold. This work presents the pioneering utilization of a diamond-based optoelectronic platform, capable of generating sufficiently large photocurrents for neuronal stimulation in the retina.

A General Strategy for Exceptionally Robust Conducting Polymer-Based Bioelectrodes with Multimodal Capabilities Through Decoupled Charge Transport Mechanisms

Bioelectrodes function as a critical interface for signal transduction between living organisms and electronics. Conducting polymers (CPs), particularly poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), are among the most promising materials for bioelectrodes, due to their electrical performance, high compactness, and ease of processing, but often suffer from degradation or de-doping even in some common environments (e.g., electrical stimulation, chemicals, and high temperatures). This instability therefore severely undermines their reliability in practical application. To resolve this critical issue, a novel strategy of separating electron transfer from electron-ion transduction is proposed. Specifically, chemically derived holey graphene (HG), serving as an ultra-stable mixed ion-electron conductor, is introduced into the CP matrix. The HG can restore the CP's destructed conductive pathways, whilst its porosity and its intercalation by the CP synergically preserve fast ionic and molecular diffusion. The resulting bioelectrode therefore exhibits excellent low impedance, high charge injection capacity, electrochemical activity, and outstanding resilience to various harsh conditions, outperforming HG, reduced graphene oxide, CP, or graphene-coated CP electrodes. Furthermore, this strategy also exhibits broad compatibility with various processing techniques and proves adaptable to other electrode systems, such as stretchable electrodes, paving the way for practical applications in electrophysical capture, neuron modulation, and biochemical analysis.

Graphene-based materials: an innovative approach for neural regeneration and spinal cord injury repair

Spinal cord injury (SCI), the most serious disease affecting the central nervous system (CNS), is one of contemporary medicine's most difficult challenges, causing patients to suffer physically, emotionally, and socially. However, due to recent advances in medical science and biomaterials, graphene-based materials (GBMs) have tremendous potential in SCI therapy due to their wonderful and valuable properties, such as physicochemical properties, extraordinary electrical conductivity, distinct morphology, and high mechanical strength. This review discusses SCI pathology and GBM characteristics, as well as recent in vitro and in vivo findings on graphenic scaffolds, electrodes, and injectable achievements for SCI improvement using neuroprotective and neuroregenerative techniques to improve neural structural and functional repair. Additionally, it suggests possible ideas and desirable products for graphene-based technological advances, intending to reach therapeutic importance for SCI.

Interfacing with the Brain: How Nanotechnology Can Contribute

Interfacing artificial devices with the human brain is the central goal of neurotechnology. Yet, our imaginations are often limited by currently available paradigms and technologies. Suggestions for brain-machine interfaces have changed over time, along with the available technology. Mechanical levers and cable winches were used to move parts of the brain during the mechanical age. Sophisticated electronic wiring and remote control have arisen during the electronic age, ultimately leading to plug-and-play computer interfaces. Nonetheless, our brains are so complex that these visions, until recently, largely remained unreachable dreams. The general problem, thus far, is that most of our technology is mechanically and/or electrically engineered, whereas the brain is a living, dynamic entity. As a result, these worlds are difficult to interface with one another. Nanotechnology, which encompasses engineered solid-state objects and integrated circuits, excels at small length scales of single to a few hundred nanometers and, thus, matches the sizes of biomolecules, biomolecular assemblies, and parts of cells. Consequently, we envision nanomaterials and nanotools as opportunities to interface with the brain in alternative ways. Here, we review the existing literature on the use of nanotechnology in brain-machine interfaces and look forward in discussing perspectives and limitations based on the authors' expertise across a range of complementary disciplines─from neuroscience, engineering, physics, and chemistry to biology and medicine, computer science and mathematics, and social science and jurisprudence. We focus on nanotechnology but also include information from related fields when useful and complementary.

Flexible graphene-based neurotechnology for high-precision deep brain mapping and neuromodulation in Parkinsonian rats

Deep brain stimulation (DBS) is a neuroelectronic therapy for the treatment of a broad range of neurological disorders, including Parkinson's disease. Current DBS technologies face important limitations, such as large electrode size, invasiveness, and lack of adaptive therapy based on biomarker monitoring. In this study, we investigate the potential benefits of using nanoporous reduced graphene oxide (rGO) technology in DBS, by implanting a flexible high-density array of rGO microelectrodes (25 µm diameter) in the subthalamic nucleus (STN) of healthy and hemi-parkinsonian rats. We demonstrate that these microelectrodes record action potentials with a high signal-to-noise ratio, allowing the precise localization of the STN and the tracking of multiunit-based Parkinsonian biomarkers. The bidirectional capability to deliver high-density focal stimulation and to record high-fidelity signals unlocks the visualization of local neuromodulation of the multiunit biomarker. These findings demonstrate the potential of bidirectional high-resolution neural interfaces to investigate closed-loop DBS in preclinical models.

Soft, stretchable conductive hydrogels for high-performance electronic implants

Conductive hydrogels are emerging as promising materials for electronic implants owing to their favorable mechanical and electrical properties. Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) hydrogels are particularly attractive, but their preparation often requires toxic additives. Here, we introduced a nutritive sweetener, d-sorbitol, as a nontoxic additive to create soft and stretchable PEDOT:PSS conductive hydrogels. These hydrogels exhibit mechanical properties comparable with biological tissues, reducing adverse immune responses. The hydrogels can be patterned on elastic substrates using a simple, low-cost micromolding technique to fabricate soft and stretchable implantable devices for electrical stimulation and recording. The hydrogel electrodes show much lower electrochemical impedance and higher charge storage and injection capacity compared to platinum electrodes. In addition, the properties of hydrogels and devices remain stable after long-term storage and exposure to extreme conditions. We demonstrate the use of soft hydrogel-based electronic devices for effective electrical stimulation and high-quality electrical recordings in live animal models.

Long-Term Stability of Spatial Distribution and Peak Dynamics of Subthalamic Beta Power in Parkinson's Disease Patients

BACKGROUND

Subthalamic beta oscillations are a biomarker for bradykinesia and rigidity in Parkinson's disease (PD), incorporated as a feedback signal in adaptive deep brain stimulation with potential for guiding electrode contact selection. Understanding their longitudinal stability is essential for successful clinical implementation.

OBJECTIVES

We aimed to analyze the long-term dynamics of beta peak parameters and beta power distribution along electrodes.

METHODS

We recorded local field potentials from 12 channels per hemisphere of 33 PD patients at rest, in a therapy-off state at two to four sessions (0, 3, 12, 18-44 months) post-surgery. We analyzed bipolar beta power (13-35 Hz) and estimated monopolar beta power in subgroups with consistent recordings.

RESULTS

During the initial 3 months, beta peak power increased (P < 0.0001). While detection of high-beta peaks was more consistent, low- and high-beta peak frequencies shifted substantially in some hemispheres during all periods. Spatial distribution of beta power correlated over time. Maximal beta power across segmented contact levels and directions was significantly stable compared with chance and increased in stability over time. Active contacts for therapeutic stimulation showed consistently higher normalized beta power than inactive contacts (P < 0.0001).

CONCLUSIONS

Our findings indicate that beta power is a stable chronic biomarker usable for beta-guided programming. For adaptive stimulation, high-beta peaks might be more reliable over time. Greater stability of beta power, center frequency, and spatial distribution beyond an initial stabilization period suggests that the microlesional effect significantly impacts neuronal oscillations, which should be considered in routine clinical practice when using beta activity for automated programming algorithms. © 2025 The Author(s). Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Softening, Conformable, and Stretchable Conductors for Implantable Bioelectronics Interfaces

Neural implantable devices serve as electronic interfaces facilitating communication between the body and external electronic systems. These bioelectronic systems ideally possess stable electrical conductivity, flexibility, and stretchability to accommodate dynamic movements within the body. However, achieving both high electrical conductivity and mechanical compatibility remains a challenge. Effective electrical conductors tend to be rigid and stiff, leading to a substantial mechanical mismatch with bodily tissues. On the other hand, highly stretchable polymers, while mechanically compatible, often suffer from limited compatibility with lithography techniques and reduced electrical stability. Therefore, there exists a pressing need to develop electromechanically stable neural interfaces that enable precise communication with biological tissues. In this study, a polymer that is softening, flexible, conformal, and compatible with lithography to microfabricate perforated thin-film architectures was utilized. These architectures offer stretchability and improved mechanical compatibility. Three distinct geometries were evaluated both mechanically and electrically under in-vitro conditions that simulate physiological environments. Notably, the Peano structure demonstrates minimal changes in resistance, varying less than 1.5× even when subjected to almost 150% strain. Furthermore, devices exhibit a maximum mechanical elongation before fracture, reaching 220%. Finally, the application of multi-electrode spinal cord leads employing titanium nitride for neural stimulation in rat models was demonstrated.

Overcoming failure: improving acceptance and success of implanted neural interfaces

Implanted neural interfaces are electronic devices that stimulate or record from neurons with the purpose of improving the quality of life of people who suffer from neural injury or disease. Devices have been designed to interact with neurons throughout the body to treat a growing variety of conditions. The development and use of implanted neural interfaces is increasing steadily and has shown great success, with implants lasting for years to decades and improving the health and quality of life of many patient populations. Despite these successes, implanted neural interfaces face a multitude of challenges to remain effective for the lifetime of their users. The devices are comprised of several electronic and mechanical components that each may be susceptible to failure. Furthermore, implanted neural interfaces, like any foreign body, will evoke an immune response. The immune response will differ for implants in the central nervous system and peripheral nervous system, as well as over time, ultimately resulting in encapsulation of the device. This review describes the challenges faced by developers of neural interface systems, particularly devices already in use in humans. The mechanical and technological failure modes of each component of an implant system is described. The acute and chronic reactions to devices in the peripheral and central nervous system and how they affect system performance are depicted. Further, physical challenges such as micro and macro movements are reviewed. The clinical implications of device failures are summarized and a guide for determining the severity of complication was developed and provided. Common methods to diagnose and examine mechanical, technological, and biological failure modes at various stages of development and testing are outlined, with an emphasis on chronic in vivo characterization of implant systems. Finally, this review concludes with an overview of some of the innovative solutions developed to reduce or resolve the challenges faced by implanted neural interface systems.

Multi-layered electrode constructs for neural tissue engineering

Although neural tissue engineering holds great therapeutic potential for multiple clinical applications, one important challenge is the development of scaffolds that provide cues required for neural tissue development. To achieve this, biomaterial systems can be leveraged to present appropriate biological, mechanical, topographical and electrical cues that could direct cell fate. In this study, a multi-layered electrode construct was engineered to be used as a platform for 3D cell encapsulation for in vitro applications. The first layer is a conductive hydrogel coating, that improves electrical conductivity from the underlying platinum electrode. The second layer is a biosynthetic hydrogel, specifically tailored to support neural development. This layered electrode construct was electrochemically characterised, and a numerical model was applied to study electrical stimuli reaching the biosynthetic hydrogel layer. The construct was shown to effectively support the growth and proliferation of encapsulated astrocytes within the biosynthetic layer, while the numerical model will enable computational experimentation for benchmarking and study validation. This highly versatile system represents a robust tool to study the influence of electrical stimuli on neural fate, as well as investigating the development of biohybrid interfaces in vitro.

Devices for the electrical stimulation of the olfactory system: A review

The loss of olfactory function has a profound impact on quality of life, affecting not only sensory perception but also memory, emotion, and overall well-being. Despite this, advancements in olfactory prostheses have lagged significantly behind those made for vision and hearing restoration. This review offers a comprehensive analysis of the current state of devices for electrical stimulation of the olfactory system. We begin by providing an overview of the olfactory system's structure and function, emphasizing the neural pathways involved in smell perception. Following this, we explore the key challenges associated with chronic implantation and electrical stimulation, material biocompatibility, inflammation risks, and ensuring long-term functionality and durability. A detailed analysis of existing neural stimulation devices-including ECoG, intracortical, and depth electrodes-is presented, assessing their potential for application in olfactory stimulation. We also discuss the limitations and pitfalls of current approaches and explore new emerging technologies aimed at overcoming these obstacles. A comprehensive literature review about the olfactory system electrical stimulation is reported, and results are analyzed to identify the most promising routes. Finally, the review highlights emerging technologies, ongoing research, and the ethical considerations associated with olfactory implants, along with future directions for developing more effective, safe, and durable solutions to restore the sense of smell for individuals with olfactory disorders.

Neurocardiology: translational advancements and potential

In our original white paper published in the The Journal of Physiology in 2016, we set out our knowledge of the structural and functional organization of cardiac autonomic control, how it remodels during disease, and approaches to exploit such knowledge for autonomic regulation therapy. The aim of this update is to build on this original blueprint, highlighting the significant progress which has been made in the field since and major challenges and opportunities that exist with regard to translation. Imbalances in autonomic responses, while beneficial in the short term, ultimately contribute to the evolution of cardiac pathology. As our understanding emerges of where and how to target in terms of actuators (including the heart and intracardiac nervous system (ICNS), stellate ganglia, dorsal root ganglia (DRG), vagus nerve, brainstem, and even higher centres), there is also a need to develop sensor technology to respond to appropriate biomarkers (electrophysiological, mechanical, and molecular) such that closed-loop autonomic regulation therapies can evolve. The goal is to work with endogenous control systems, rather than in opposition to them, to improve outcomes.

Optimized Conditions for Electrical Tissue Stimulation with Biphasic, Charge-Balanced Impulses

The cultivation of excitable cells typically profits from continuous electrical stimulation, but electrochemical consequences are mostly harmful and must be minimized. The properties of the electrode materials and stimulation impulses are key. Here, we developed an easy method to analyze the electrochemical impact of biphasic, current-controlled impulses, applied via graphite electrodes, using phenol red as the redox indicator. We also tested the stimulation conditions for the long-term cultivation of myocardial tissue. The colorimetric assay was able to detect ±0.2% deviations in typical positive and negative pulse charges. Phenol red was best preserved (20% degradation over 24 h) by impulses of equivalent positive and negative charges (full charge balance), generated with either manual calibration, capacitive electrode coupling, or feedback regulation of electrode polarization. Feedback regulation established full charge balance at pre-pulse voltages of about 300 mV, but also provided the option to selectively compensate irreversible electrode reactions. Modifications to shape and timing did not affect the electrochemical effects of symmetric impulses. Charge-balanced stimulation maintained more than 80% of the contractility of porcine left ventricular myocardium after 10 days of culture, whereas disbalances of 2-4% provoked weakening and discoloration of the tissues. Active polarization regulation, in contrast to capacitive electrode coupling, reproduced the biological advantages of full charge balance.

Implantable Soft Neural Electrodes of Liquid Metals for Deep Brain Stimulation

Stimulating large volumes of neural networks using macroelectrodes can modulate disorder-associated brain circuits effectively. However, conventional solid-metal electrodes often cause unwanted brain damage due to their high mechanical stiffness. In contrast, low-modulus liquid metals provide tissue-like stiffness while maintaining macroscale electrode dimensions. Here, we present implantable soft macroelectrodes made from biocompatible liquid metals for brain stimulation. These probes can be easily fabricated by simply filling polymeric tubes with a liquid metal, offering a straightforward method for creating brain stimulation devices. They can be customized in various lengths and diameters and also serve as recording microelectrodes. The electrode tips are enhanced with platinum nanoclusters, resulting in low impedance and effective charge injection while preventing liquid metal leakage into brain tissue. In vivo experiments in neuropathic pain rat models demonstrate the stability and effectiveness of these probes for simultaneous neural stimulation and recording, demonstrating their potential for pain alleviation and behavioral control.

Bio-inspired electronics: Soft, biohybrid, and "living" neural interfaces

Neural interface technologies are increasingly evolving towards bio-inspired approaches to enhance integration and long-term functionality. Recent strategies merge soft materials with tissue engineering to realize biologically-active and/or cell-containing living layers at the tissue-device interface that enable seamless biointegration and novel cell-mediated therapeutic opportunities. This review maps the field of bio-inspired electronics and discusses key recent developments in tissue-like and regenerative bioelectronics, from soft biomaterials and surface-functionalized bioactive coatings to cell-containing 'biohybrid' and 'all-living' interfaces. We define and contextualize key terminology in this emerging field and highlight how biological and living components can bridge the gap to clinical translation.

Restore axonal conductance in a locally demyelinated axon with electromagnetic stimulation

Objective. Axonal demyelination leads to failure of axonal conduction. Current research on demyelination focuses on the promotion of remyelination. Electromagnetic stimulation is widely used to promote neural activity. We hypothesized that electromagnetic stimulation of the demyelinated area, by providing excitation to the nodes of Ranvier, could rescue locally demyelinated axons from conductance failure.Approach. We built a multi-compartment NEURON model of a myelinated axon under electromagnetic stimulation. We simulated the action potential (AP) propagation and observed conductance failure when local demyelination occurred. Conductance failure was due to current leakage and a lack of activation of the nodes in the demyelinated region. To investigate the effects of electromagnetic stimulation on locally demyelinated axons, we positioned a miniature coil next to the affected area to activate nodes in the demyelinated region.Main results. Subthreshold microcoil stimulation caused depolarization of node membranes. This depolarization, in combination with membrane depolarization induced by the invading AP, resulted in sufficient activation of nodes in the demyelinated region and restoration of axonal conductance. Efficacy of restoration was dependent on the amplitude and frequency of the stimuli, and the location of the microcoil relative to the targeted nodes. The restored axonal conductance was due to the enhanced Na+current and reduced K+current in the nodes, rather than a reduction in leakage current in the demyelinated region. Finally, we found that microcoil stimulation had no effect on axonal conductance in healthy, myelinated axons.Significance. Activation of nodes in the demyelinated region using electromagnetic stimulation provides an alternative treatment strategy to restore axonal function under local demyelination conditions. Results provide insights to the development of microcoil technology for the treatment of focal segmental demyelination cases, such as neuropraxia, spinal cord injury, and auditory nerve demyelination.

Graphene-Based Microelectrodes with Reinforced Interfaces and Tunable Porous Structures for Improved Neural Recordings

Invasive neural electrodes prepared from materials with a miniaturized geometrical size could improve the longevity of implants by reducing the chronic inflammatory response. Graphene-based microfibers with tunable porous structures have a large electrochemical surface area (ESA)/geometrical surface area (GSA) ratio that has been reported to possess low impedance and high charge injection capacity (CIC), yet control of the porous structure remains to be fully investigated. In this study, we introduce wet-spun graphene-based electrodes with pores tuned by sucrose concentrations in the coagulation bath. The electrochemical properties of thermally reduced rGO were optimized by adjusting the ratio of rGO to sucrose, resulting in significantly lower impedance, higher CIC, and higher charge storage capacity (CSC) in comparison to platinum microwires. Tensile and insertion tests confirmed that optimized electrodes had sufficient strength to ensure a 100% insertion success rate with a low angle shift, thus allowing precise implantation without the need for additional mechanical enhancement. Acute in vivo recordings from the auditory cortex found low impedance benefits from the recorded amplitude of spikes, leading to an increase in the signal-to-noise ratio (SNR). Ex vivo recordings from hippocampal brain slices demonstrate that it is possible to record and stimulate with graphene-based electrodes with good fidelity compared with conventional electrodes.

Fabrication of thin-film electrodes and organic electrochemical transistors for neural implants

Bioelectronic medicine, which involves the delivery of electrical stimulation via implantable electrodes, is poised to advance the treatment of neurological conditions. However, current hand-made devices are bulky, invasive and lack specificity. Thin-film neurotechnology devices can overcome these disadvantages. With a typical thickness in the range of micrometers, thin-film devices demonstrate high conformability, stretchability, are minimally invasive and can be fabricated using traditional lithography techniques. Despite their potential, variability and unreliability in fabrication processes hinder their wider utilization. Here, we detail a fabrication method for thin-film poly(ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) electrodes and organic electrochemical transistors. The use of organic materials makes these devices particularly well suited for bioelectronic medicine applications as they show superior mechanical and electrical matching of biological tissues compared with devices made of inorganic materials. The procedure details the entire process, including mask design, the fabrication through three photolithography stages, the integration with larger-scale electronics, implantation procedures and the expected electrical characterization metrics. The nanofabrication protocol requires at least 3 d and is suitable for those familiar with lithographic fabrication procedures. The surgery requires up to 10 h and is suitable for those familiar with in vivo implantation procedures.

Characterization of motor nerve stimulation using sinusoidal low frequency alternating currents and cuff electrodes

Objective:Direct electrical neurostimulation using continuous sinusoidal low frequency alternating currents (LFAC) is an emerging modality for neuromodulation. As opposed to the traditional rectangular pulse stimulation, there is limited background on the characteristics of peripheral nerves responses to sinusoidal LFAC stimulation; especially within the low frequency range (<50 Hz). In this study, we demonstrate LFAC activation as a means to activate motor nerves by direct bipolar nerve stimulation via cuff electrodes, and characterize the factors of activation. We study and quantify the effects of sinusoidal frequency and electrode geometry on the motor nerve activation thresholdin-vivoand in computational models,in-silico.Approach:Acutein-vivoexperiments (N= 34) were conducted on isoflurane-anaesthetized rats. A pure tone continuous sinusoidal current was applied to the rat sciatic nerve in bipolar configurations via bipolar or tripolar nerve cuff electrodes (different contact separations). LFAC activation thresholds were quantified by measuring the electromyogram (EMG) response of the triceps surae muscles and the induced twitch force to LFAC stimulation at six frequencies (1, 2, 3, 4, 8, and 20 Hz). Computationally, we utilized a volume conductor model of a bipolar cuff electrode around a single rat-size fascicle and projected the potentials to the McIntyre-Richardson-Grill models of myelinated motor nerve fibers. We compared thein-silicoresponses of a range of fiber diameters (5.7 to 16µm) to LFAC stimulation and their activation thresholds to thein-vivofindings.Main results: Sinusoidal LFAC stimulation elicited motor nerve activityin-vivoandin-silico, with a remarkable convergence of thein-silicopredictions to thein-vivoobservations. The EMG activity showed that muscle responses to LFAC stimulation were phase-locked to the sinusoidal cycle but exhibited two distinct activation modes. These modes were classified as burst and unitary, indicating the presence of two distinct patterns of muscle activation during LFAC stimulation. The LFAC motor activation threshold was significantly dependent on frequency and influenced by the contact separation of the cuff electrode, with a greater extent of reduction at a higher frequency or wider separation. Moreover, the order of fiber recruitment was suggested to be normal-physiological (small-to-large caliber) given the nature of the induced EMG activity andin-silicopredictions.Significance: These findings provide significant insights into the nature of sinusoidal LFAC stimulation, at the explored range of frequency, and the expected mammalian peripheral motor nerve responses to LFAC. The characteristics of sinusoidal LFAC stimulation would facilitate selectivity approaches in a broader range of therapeutic and rehabilitative neuromodulation applications.

Recent Progress in Flexible Microelectrode Arrays for Combined Electrophysiological and Electrochemical Sensing

Understanding brain function requires advanced neural probes to monitor electrical and chemical signaling across multiple timescales and brain regions. Microelectrode arrays (MEAs) are widely used to record neurophysiological activity across various depths and brain regions, providing single-unit resolution for extended periods. Recent advancements in flexible MEAs, built on micrometer-thick polymer substrates, have improved integration with brain tissue by mimicking the brain's soft nature, reducing mechanical trauma and inflammation. These flexible, subcellular-scale MEAs can record stable neural signals for months, making them ideal for long-term studies. In addition to electrical recording, MEAs have been functionalized for electrochemical neurotransmitter detection. Electroactive neurotransmitters, such as dopamine, serotonin, and adenosine, can be directly measured via electrochemical methods, particularly on carbon-based surfaces. For non-electroactive neurotransmitters like acetylcholine, glutamate, and γ-aminobutyric acid, alternative strategies, such as enzyme immobilization and aptamer-based recognition, are employed to generate electrochemical signals. This review highlights recent developments in flexible MEA fabrication and functionalization to achieve both electrochemical and electrophysiological recordings, minimizing sensor fowling and brain damage when implanted long-term. It covers multi-time scale neurotransmitter detection, development of conducting polymer and nanomaterial composite coatings to enhance sensitivity, incorporation of enzyme and aptamer-based recognition methods, and the integration of carbon electrodes on flexible MEAs. Finally, it summarizes strategies to acquire electrochemical and electrophysiological measurements from the same device.

Advances in Photonic Materials and Integrated Devices for Smart and Digital Healthcare: Bridging the Gap Between Materials and Systems

Recent advances in developing photonic technologies using various materials offer enhanced biosensing, therapeutic intervention, and non-invasive imaging in healthcare. Here, this article summarizes significant technological advancements in materials, photonic devices, and bio-interfaced systems, which demonstrate successful applications for impacting human healthcare via improved therapies, advanced diagnostics, and on-skin health monitoring. The details of required materials, necessary properties, and device configurations are described for next-generation healthcare systems, followed by an explanation of the working principles of light-based therapeutics and diagnostics. Next, this paper shares the recent examples of integrated photonic systems focusing on translation and immediate applications for clinical studies. In addition, the limitations of existing materials and devices and future directions for smart photonic systems are discussed. Collectively, this review article summarizes the recent focus and trends of technological advancements in developing new nanomaterials, light delivery methods, system designs, mechanical structures, material functionalization, and integrated photonic systems to advance human healthcare and digital healthcare.

A Body-Temperature-Triggered In Situ Softening Peripheral Nerve Electrode for Chronic Robust Neuromodulation

Implantable peripheral nerve electrodes are crucial for monitoring health and alleviating symptoms of chronic diseases. Advanced compliant electrodes have been developed because of their biomechanical compatibility. However, these mechanically tissue-like electrodes suffer from unmanageable operating forces, leading to high risks of nerve injury and fragile electrode-tissue interfaces. Here, a peripheral nerve electrode is developed that simultaneously fulfills the criteria of body temperature softening and tissue-like modulus (less than 0.8 MPa at 37 °C) after implantation. The central core is altered from the tri-arm crosslinker to the star-branched monomer to kill two birds (close the translation temperature to 37 °C and decrease the modulus after implantation) with one stone. Furthermore, the decreased interfacial impedance (325.1 ± 46.9 Ω at 1 kHz) and increased charge storage capacity (111.2 ± 5.8 mC cm-2) are achieved by an in situ electrografted conductive polymer on the strain-insensitive conductive network of Au nanotubes. The electrodes are readily wrapped around nerves and applied for long-term stimulation in vivo with minimal inflammation. Neuromodulation experiments demonstrate their potential clinical utility, including vagus nerve stimulation in rats to suppress seizures and alleviation of cardiac remodeling in a canine model of myocardial infarction.

Preparation and characterization of neural stem cell-loaded conductive hydrogel cochlear implant electrode coatings

Sensorineural deafness is a hearing impairment resulting from damage to the auditory nerve or inner ear hair cells. Currently, cochlear implants (CIs) are widely used as hearing aids for sensorineural deafness patients. A fundamental limitation of cochlear implants (CIs) is that spiral ganglion neurons (SGNs) cannot be replenished. This greatly restricts the rehabilitation of sensorineural deafness. Additionally, the insertion of CIs can cause secondary cochlear damage, worsening the condition of the patients' cochlear. Therefore, a new type of neural stem cells (NSCs) loaded graphene oxide-polyaniline/GelMA (GO-PAni/GelMA) conductive hydrogel electrode for cochlear implant was fabricated via in-situ radical polymerization and cyclic UV curing technique. On the one hand, the hydrogel electrode, as a direct contact layer, helps to avoid the physical hurt for cochlear. On the other hand, NSCs were supplemented via the hydrogel carrier and neuronal differentiation was induced by electrical stimulation, which was validated by the experimental results of immunofluorescence, Phalloidin Staining and RT-qPCR. Furthermore, based on RNA sequencing and transcriptome analysis, we hypothesized that the neuronal differentiation of NSCs was adjusted by the calcium signaling pathway and GABAergic synapse. Overall, our cell loading conductive hydrogel electrode may be an effective solution to sensorineural deafness. The revelation of the mechanism of neuronal differentiation promoted by electrical stimulation provides a basis for further sensorineural deafness treatment using conductive hydrogel CI electrode.

A Simple, Low-Cost Implant for Reliable Diaphragm EMG Recordings in Awake, Behaving Rats

Breathing is a complex neuromuscular process vital to sustain life. In preclinical animal models, the study of respiratory motor control is primarily accomplished through neurophysiologic recordings and functional measurements of respiratory output. Neurophysiologic recordings that target neural or muscular output via direct nerve recordings or respiratory muscle electromyography (EMG) are commonly collected during anesthetized conditions. While offering tight control of experimental preparations, the use of anesthesia results in respiratory depression, may impact cardiovascular control, eliminates the potential to record volitional nonventilatory behaviors, and can limit translation. Since the diaphragm is a unique muscle which is rhythmically active and difficult to access, placing diaphragm EMGs to collect chronic recordings in awake animals is technically challenging. Here, we describe methods for fabricating and implanting indwelling diaphragm EMG electrodes to enable recordings from awake rodents for longitudinal studies. These electrodes are relatively easy and quick to produce (∼1 h), are affordable, and provide high-quality and reproducible diaphragm signals using a tethered system that allows animals to ad libitum behave. This system is also designed to work in conjunction with whole-body plethysmography to facilitate simultaneous recordings of diaphragm EMG and ventilation. We include detailed instructions and considerations for electrode fabrication and surgical implantation. We also provide a brief discussion on data acquisition, material considerations for implant fabrication, and the physiological implications of the diaphragm EMG signal.

From innovation to clinic: Emerging strategies harnessing electrically conductive polymers to enhance electrically stimulated peripheral nerve repair

Peripheral nerve repair (PNR) is a major healthcare challenge due to the limited regenerative capacity of the nervous system, often leading to severe functional impairments. While nerve autografts are the gold standard, their implications are constrained by issues such as donor site morbidity and limited availability, necessitating innovative alternatives like nerve guidance conduits (NGCs). However, the inherently slow nerve growth rate (∼1 mm/day) and prolonged neuroinflammation, delay recovery even with the use of passive (no-conductive) NGCs, resulting in muscle atrophy and loss of locomotor function. Electrical stimulation (ES) has the ability to enhance nerve regeneration rate by modulating the innate bioelectrical microenvironment of nerve tissue while simultaneously fostering a reparative environment through immunoregulation. In this context, electrically conductive polymer (ECP)-based biomaterials offer unique advantages for nerve repair combining their flexibility, akin to traditional plastics, and mixed ionic-electronic conductivity, similar to ionically conductive nerve tissue, as well as their biocompatibility and ease of fabrication. This review focuses on the progress, challenges, and emerging techniques for integrating ECP based NGCs with ES for functional nerve regeneration. It critically evaluates the various approaches using ECP based scaffolds, identifying gaps that have hindered clinical translation. Key challenges discussed include designing effective 3D NGCs with high electroactivity, optimizing ES modules, and better understanding of immunoregulation during nerve repair. The review also explores innovative strategies in material development and wireless, self-powered ES methods. Furthermore, it emphasizes the need for non-invasive ES delivery methods combined with hybrid ECP based neural scaffolds, highlighting future directions for advancing preclinical and clinical translation. Together, ECP based NGCs combined with ES represent a promising avenue for advancing PNR and improving patient outcomes.

Parasitic Capacitance in High-Density Neural Electrode Arrays: Sources and Evaluation Methods

OBJECTIVE

This study aims to identify sources of parasitic capacitance in high-density neural electrode arrays and to provide an approach for evaluating their associated capacitance values. We also represent the effect of parasitic capacitance on the electrochemical properties of electrodes.

METHODS

Electrochemical impedance spectroscopy (EIS) and voltage transient (VT) measurements were employed to assess the parasitic capacitance of a 16-channel ultramicro-sized electrode array (UMEA) (8 × 25 µm2 electrode sites). The effect of parasitic capacitance on cyclic voltammetry (CV), EIS, and VT measurements of 20-µm diameter electrodes was assessed by comparing two different array designs: narrow and wide trace arrays.

RESULTS

The capacitive leakage currents and charge during CV measurements were not significant, however, during current pulsing 34% underestimation of the maximum charge injection capacity corresponded to capacitive leakage. Capacitive leakage during EIS resulted in an underestimation of the electrode impedance at frequencies >1.5 kHz.

CONCLUSION

The electrode design and insulation thickness can play a significant role in determining the amount of capacitive leakage during current pulsing and EIS at higher frequencies.

SIGNIFICANCE

Determining the sources and levels of capacitive leakage current in high-density neural electrode arrays, enables us to correct the measured value for the leakage current and thus estimate the electrode impedance and stimulation thresholds more accurately. This study highlights the importance of electrode design in developing high-density arrays with minimum capacitive leakage.

Flexible Electrode Arrays Based on a Wide Bandgap Semiconductors for Chronic Implantable Multiplexed Sensing and Heart Pacemakers

Implantable systems with chronic stability, high sensing performance, and extensive spatial-temporal resolution are a growing focus for monitoring and treating several diseases such as epilepsy, Parkinson's disease, chronic pain, and cardiac arrhythmias. These systems demand exceptional bendability, scalable size, durable electrode materials, and well-encapsulated metal interconnects. However, existing chronic implantable bioelectronic systems largely rely on materials prone to corrosion in biofluids, such as silicon nanomembranes or metals. This study introduces a multielectrode array featuring a wide bandgap (WBG) material as electrodes, demonstrating its suitability for chronic implantable applications. Our devices exhibit excellent flexibility and longevity, taking advantage of the low bending stiffness and chemical inertness in WBG nanomembranes and multimodalities for physical health monitoring, including temperature, strain, and impedance sensing. Our top-down manufacturing process enables the formation of distributed electrode arrays that can be seamlessly integrated onto the curvilinear surfaces of skins. As proof of concept for chronic cardiac pacing applications, we demonstrate the effective pacing functionality of our devices on rabbit hearts through a set of ex vivo experiments. The engineering approach proposed in this study overcomes the drawbacks of prior WBG material fabrication techniques, resulting in an implantable system with high bendability, effective pacing, and high-performance sensing.

Electric field stimulation directs target-specific axon regeneration and partial restoration of vision after optic nerve crush injury

Failure of central nervous system (CNS) axons to regenerate after injury results in permanent disability. Several molecular neuro-protective and neuro-regenerative strategies have been proposed as potential treatments but do not provide the directional cues needed to direct target-specific axon regeneration. Here, we demonstrate that applying an external guidance cue in the form of electric field stimulation to adult rats after optic nerve crush injury was effective at directing long-distance, target-specific retinal ganglion cell (RGC) axon regeneration to native targets in the diencephalon. Stimulation was performed with asymmetric charged-balanced (ACB) waveforms that are safer than direct current and more effective than traditional, symmetric biphasic waveforms. In addition to partial anatomical restoration, ACB waveforms conferred partial restoration of visual function as measured by pattern electroretinogram recordings and local field potential recordings in the superior colliculus-and did so without the need for genetic manipulation. Our work suggests that exogenous electric field application can override cell-intrinsic and cell-extrinsic barriers to axon regeneration, and that electrical stimulation performed with specific ACB waveforms may be an effective strategy for directing anatomical and functional restoration after CNS injury.

Quantification of safe operation conditions for large-area platinum-iridium electrodes in neurostimulation application

OBJECTIVE

Using electrochemical characterization methods of stimulation electrodes as well as accelerated stimulation examinations, a safe operating field for stimulation is investigated for particularly very large Pt-Ir macroelectrodes in a Laplace configuration.

APPROACH

Traditional methods such as Electrochemical Impedance Spectroscopy, Cyclic Voltammetry and biphasic, charge balanced current pulses were applied on Pt-Ir macroelectrodes in phosphate buffered saline solution to investigate reversible boundaries. These experiments were adapted to approach realistic working conditions.

MAIN RESULTS

Investigating operational conditions close to realistic use cases have shown an anti-correlation between higher scan rates and the occurrence of irreversible reactions. In addition, at higher current pulse amplitudes (>3 mA), the voltage dropping across the phase boundary (Ema and Emc) saturated. The value of the residual voltage depends on the degree of charge balance of the biphasic pulse. Thus, we have been able to detect more dissolved platinum at high residual voltages-objected by mass spectroscopic measurement.

SIGNIFICANCE

Residual voltage plays a greater role concerning reversibility in prolonged stimulation and charge imbalance of applied biphasic current pulses. The Ema saturation is suggested as a new marker for the occurrence of irreversible reactions which needs further investigation. Current amplitudes of 1 mA for the considered single electrode configuration did not lead to a capacitive voltage saturation nor a considerable dissolution of platinum ions and is thus considered as a safe operation configuration.

Electroceuticals: Unlocking the promise of therapies

OBJECTIVES

Electroceuticals refers to the constantly growing disciplines of bioelectric and bioelectronic medication. These include a broad variety of devices that have been invented and are now being utilized in medical implants, wearable medical electronics, and bioelectronics. The primary aim of this study is to encompass several facets of electroceuticals, their applications, and recent advancements in the field of medical challenges.

EVIDENCE ACQUISITIONS

A complete literature study was conducted, which included a comprehensive review of globally recognized scientific research databases.

RESULTS

The progressive refinement and diminution of technology, in conjunction with swift advancements in comprehending the role of electrical pathways in the human body, have rendered it progressively viable to manipulate these pathways for therapeutic purposes.

DISCUSSION AND CONCLUSION

Electrical stimulation impacts and modifies biological functioning and pathological processes in the body. In the contemporary era of medicine, health care practitioners from a variety of fields utilize electricity to cure disease or injury or to assess and diagnose using a variety of electrically driven medical tools.

Enhanced control of a brain-computer interface by tetraplegic participants via neural-network-mediated feature extraction

To infer intent, brain-computer interfaces must extract features that accurately estimate neural activity. However, the degradation of signal quality over time hinders the use of feature-engineering techniques to recover functional information. By using neural data recorded from electrode arrays implanted in the cortices of three human participants, here we show that a convolutional neural network can be used to map electrical signals to neural features by jointly optimizing feature extraction and decoding under the constraint that all the electrodes must use the same neural-network parameters. In all three participants, the neural network led to offline and online performance improvements in a cursor-control task across all metrics, outperforming the rate of threshold crossings and wavelet decomposition of the broadband neural data (among other feature-extraction techniques). We also show that the trained neural network can be used without modification for new datasets, brain areas and participants.