A review of organic and inorganic biomaterials for neural interfaces

Effect of electrical stimulation generated by self-powered systems for tissue repair

Bioelectricity plays an important role in tissue repair. Nanogenerators can harvest biomechanical energy and convert it into electrical signals, producing electrical stimulation (ES) for diverse biomedical applications including sensing, tissue repair, cardiac pacing, etc. This review focuses on the overview of the single or multifunctional role of ES generated by self-powered nanogenerators in bone and tendon, nerve, skin, and myocardial tissue repair. Particularly, to elucidate the differential cellular responses and effects on endogenous electric fields between conventional repair and ES-enhanced tissue regeneration, the possible mechanisms by which ES promotes repair in different tissues are summarized. Eventually, the ES parameters and the matching between the type of ES produced by the nanogenerator and the practical application scenario of biological tissue are discussed. The main challenges and future perspectives of nanogenerators in tissue therapy are also proposed, expecting to promote the development of this emerging restoration method. STATEMENT OF SIGNIFICANCE: As miniature devices for tissue repair, self-powered nanogenerators can achieve the ambitious goal of self-supplying energy and efficient tissue repair. This review article details the electrical stimulation generated by self-powered nanogenerators in different tissue repair by simulating and augmenting endogenous bioelectrical signals. Introducing the classification and mechanisms of nanogenerators and reviewing the influence of the electrical stimulation and electric field in bone and tendon, nerve, skin, and myocardial tissue repair. Notably, the possible mechanisms by which electrical stimulation acts on different tissues are concluded. Lastly, the match between types of nanogenerators and different tissues is proposed, and the main challenges and perspectives of nanogenerators in tissue therapy are also discussed.

Electrode Arrays for Detecting and Modulating Deep Brain Neural Information in Primates: A Review

Primates possess a more developed central nervous system and a higher level of intelligence than rodents. Detecting and modulating deep brain activity in primates enhances our understanding of neural mechanisms, facilitates the study of major brain diseases, enables brain-computer interactions, and supports advancements in artificial intelligence. Traditional imaging methods such as magnetic resonance imaging, positron emission computed tomography, and scalp electroencephalogram are limited in spatial resolution. They cannot accurately capture deep brain signals from individual neurons. With the progress of microelectromechanical systems and other micromachining technologies, single-neuron level detection and stimulation technology in rodents based on microelectrodes has made important progress. However, compared with rodents, human and nonhuman primates have larger brain volume that needs deeper implantation depth, and the test object has higher safety and device preparation requirements. Therefore, high-resolution devices suitable for long-term detection in the brains of primates are urgently needed. This paper reviewed electrode array devices used for electrophysiological and electrochemical detections in primates' deep brains. The research progress of neural recording and stimulation technologies was introduced from the perspective of electrode type and device structures, and their potential value in neuroscience research and clinical disease treatments was discussed. Finally, it is speculated that future electrodes will have a lot of room for development in terms of flexibility, high resolution, deep brain, and high throughput. The improvements in electrode forms and preparation process will expand our understanding of deep brain neural activities, and bring new opportunities and challenges for the further development of neuroscience.

Bioelectronics hydrogels for implantable cardiac and brain disease medical treatment application

Hydrogel-based bioelectronic systems offer significant benefits for point-of-care diagnosis, treatment of cardiac and cerebral disease, surgical procedures, and other medical applications, ushering in a new era of advancements in medical technology. Progress in hydrogel-based bioelectronics has advanced from basic instrument and sensing capabilities to sophisticated multimodal perceptions and feedback systems. Addressing challenges related to immune responses and inflammation regulation after implantation, physiological dynamic mechanism, biological toxicology as well as device size, power consumption, stability, and signal conversion is crucial for the practical implementation of hydrogel-based bioelectronics in medical implants. Therefore, further exploration of hydrogel-based bioelectronics is imperative, and a comprehensive review is necessary to steer the development of these technologies for use in implantable therapies for cardiac and brain/neural conditions. In this review, a concise overview is provided on the fundamental principles underlying ionic electronic and ionic bioelectronic mechanisms. Additionally, a comprehensive examination is conducted on various bioelectronic materials integrated within hydrogels for applications in implantable medical treatments. The analysis encompasses a detailed discussion on the representative structures and physical attributes of hydrogels. This includes an exploration of their intrinsic properties such as mechanical strength, dynamic capabilities, shape-memory features, stability, stretchability, and water retention characteristics. Moreover, the discussion extends to properties related to interactions with tissues or the environment, such as adhesiveness, responsiveness, and degradability. The intricate relationships between the structure and properties of hydrogels are thoroughly examined, along with an elucidation of how these properties influence their applications in implantable medical treatments. The review also delves into the processing techniques and characterization methods employed for hydrogels. Furthermore, recent breakthroughs in the applications of hydrogels are logically explored, covering aspects such as materials, structure, properties, functions, fabrication procedures, and hybridization with other materials. Finally, the review concludes by outlining the future prospects and challenges associated with hydrogels-based bioelectronics systems.

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.

Modulation of biomaterial-induced foreign body response by regulating the differentiation and migration of Treg cells through the CXCL12-CXCR4/7 axis

Tissue exposure to implanted biomaterials triggers a foreign body response (FBR), which is a stepwise immunological process involving innate immune cells and tissue repair cells. Although the regulatory T (Treg) cells play a crucial role in inflammation and tissue repair, their function in the process of FBR has not been well investigated. In this study, as titanium (Ti) exhibits better biocompatibility and induces milder FBR than polymethyl methacrylate (PMMA), we analyzed the characteristics of Treg cells during FBR caused by the two types of biomaterials. In a rat femur implantation model, we found that the number of Treg cells around titanium implants was much more than that in the PMMA-implanted group. Meanwhile, the expression of CXCR4 in tissues around Ti implants was significantly higher, and the expression of CXCR7 was lower. When co-cultured with biomaterials and macrophages, the differentiation and migration of Treg cells in the Ti-implanted group were promoted, and this effect could be modulated by CXCR4/7 inhibitors. Moreover, targeting CXCR4/7 influenced the amount of Treg cells in vivo and then reversed the FBR induced by PMMA or Ti implants. In summary, our findings revealed the role of CXCR4/CXCR7 in regulating the migration and differentiation of Treg cells during FBR and suggested that the CXCL12-CXCR4/CXCR7 axis may serve as a potential therapeutic target for immunomodulating foreign body response.

Multi-material Electrohydrodynamic Printing of Bioelectronics with Sub-Microscale 3D Gold Pillars for In Vitro Extra- and Intra-Cellular Electrophysiological Recordings

Micro/nanoscale 3D bioelectrodes gain increasing interest for electrophysiological recording of electroactive cells. Although 3D printing has shown promise to flexibly fabricate 3D bioelectronics compared with conventional microfabrication, relatively-low resolution limits the printed bioelectrode for high-quality signal monitoring. Here, a novel multi-material electrohydrodynamic printing (EHDP) strategy is proposed to fabricate bioelectronics with sub-microscale 3D gold pillars for in vitro electrophysiological recordings. EHDP is employed to fabricate conductive circuits for signal transmission, which are passivated by polyimide via extrusion-based printing. Laser-assisted EHDP is developed to produce 3D gold pillars featuring a diameter of 0.64 ± 0.04 µm. The 3D gold pillars demonstrate stable conductivity under the cell-culture environment. Living cells can conformally grow onto these sub-microscale 3D pillars with a height below 5 µm, which facilitates the highly-sensitive recording of extracellular signals with amplitudes <15 µV. The 3D pillars can apply electroporation currents to reversibly open the cellular membrane for intracellular recording, facilitating the measurement of subtle cellular electrophysiological activities. As a proof-of-concept demonstration, fully-printed chips with multiple culturing chambers and sensing bioelectronics are fabricated for zone-specific electrophysiological recording in drug testing. The proposed multi-material EHDP strategy enables rapid prototyping of organ-on-a-chip systems with 3D bioelectronics for high-quality electrophysiological recordings.

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.

Transparent, flexible graphene-ITO-based neural microelectrodes for simultaneous electrophysiology recording and calcium imaging of intracortical neural activity in freely moving mice

To understand the complex dynamics of neural activity in the brain across various temporal and spatial scales, it is crucial to record intracortical multimodal neural activity by combining electrophysiological recording and calcium imaging techniques. This poses significant constraints on the geometrical, mechanical, and optical properties of the electrodes. Here, transparent flexible graphene-ITO-based neural microelectrodes with small feature sizes are developed and validated for simultaneous electrophysiology recording and calcium imaging in the hippocampus of freely moving mice. A micro-etching technique and an oxygen plasma pre-treating method are introduced to facilitate large-area graphene transfer and establish stable low-impedance contacts between graphene and metals, leading to the batch production of high-quality microelectrodes with interconnect widths of 10 μm and recording sites diameters of 20 μm. These electrodes exhibit appropriate impedance and sufficient transparency in the field of view, enabling simultaneous recording of intracortical local field potentials and even action potentials along with calcium imaging in freely moving mice. Both types of electrophysiological signals are found to correlate with calcium activity. This proof-of-concept work demonstrates that transparent flexible graphene-ITO-based neural microelectrodes are promising tools for multimodal neuroscience research.

Biomaterials for neuroengineering: applications and challenges

Neurological injuries and diseases are a leading cause of disability worldwide, underscoring the urgent need for effective therapies. Neural regaining and enhancement therapies are seen as the most promising strategies for restoring neural function, offering hope for individuals affected by these conditions. Despite their promise, the path from animal research to clinical application is fraught with challenges. Neuroengineering, particularly through the use of biomaterials, has emerged as a key field that is paving the way for innovative solutions to these challenges. It seeks to understand and treat neurological disorders, unravel the nature of consciousness, and explore the mechanisms of memory and the brain's relationship with behavior, offering solutions for neural tissue engineering, neural interfaces and targeted drug delivery systems. These biomaterials, including both natural and synthetic types, are designed to replicate the cellular environment of the brain, thereby facilitating neural repair. This review aims to provide a comprehensive overview for biomaterials in neuroengineering, highlighting their application in neural functional regaining and enhancement across both basic research and clinical practice. It covers recent developments in biomaterial-based products, including 2D to 3D bioprinted scaffolds for cell and organoid culture, brain-on-a-chip systems, biomimetic electrodes and brain-computer interfaces. It also explores artificial synapses and neural networks, discussing their applications in modeling neural microenvironments for repair and regeneration, neural modulation and manipulation and the integration of traditional Chinese medicine. This review serves as a comprehensive guide to the role of biomaterials in advancing neuroengineering solutions, providing insights into the ongoing efforts to bridge the gap between innovation and clinical application.

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.

Soft-Actuated Cuff Electrodes with Minimal Contact for Bidirectional Peripheral Interfaces

Neural interfaces with embedded electrical functions, such as cuff electrodes, are essential for monitoring and stimulating peripheral nerves. Still, several challenges remain with cuff electrodes because sutured devices can damage the nerve by high pressure and the secured contact of electrodes with the nerve is hard to accomplish, which however is essential in maintaining electrical performance. Here, a sutureless soft-actuated cuff electrodes (SACE) that can envelop the nerve conveniently by creating a bent shape controlled upon fluid injection, is introduced. Moreover, fluid injection protrudes part of the device where electrodes are formed, thereby achieving minimized, soft but secure contact between the electrodes and the nerve. In vivo results demonstrate the successful recording and stimulation of peripheral nerves over time up to 6 weeks. While securing contact with the nerve, the implanted electrodes can preserve the nerve intact with no reduction in blood flow, thereby indicating only minimal compressive force applied to the nerve. The SACE is expected to be a promising tool for recording and stimulation of peripheral nerves toward bidirectional neuroprostheses.

Designing Silk Biomaterials toward Better Future Healthcare: The Development and Application of Silk-Based Implantable Electronic Devices in Clinical Diagnosis and Therapy

Implantable medical electronic devices (IMEDs) have attracted great attention and shown versatility for solving clinical problems ranging from real-time monitoring of physiological/ pathological states to electrical stimulation therapy and from monitoring brain cell activity to deep brain stimulation. The ongoing challenge is to select appropriate materials in target device configuration for biomedical applications. Currently, silk-based biomaterials have been developed for the design of diagnostic and therapeutic electronic devices due to their excellent properties and abundant active sites in the structure. Herein, the aim is to summarize the structural characteristics, physicochemical properties, and bioactivities of natural silk biomaterials as well as their derived materials, with a particular focus on the silk-based implantable biomedical electronic devices, such as implantable devices for invasive brain-computer interfaces, neural recording, and in vivo electrostimulation. In addition, future opportunities and challenges are also envisioned, hoping to spark the interests of researchers in interdisciplinary fields such as biomaterials, clinical medicine, and electronics.

Bioelectronic Medicines-A Novel Approach of Therapeutics in Current Epoch

BACKGROUND

Bioelectronic medicines aim to diagnose and treat a wide range of illnesses and ailments, including cancer, rheumatoid arthritis, inflammatory bowel disease, obesity, diabetes, asthma, paralysis, blindness, bleeding, ischemia, organ transplantation, cardiovascular disease, and neurodegenerative diseases. The focus of bioelectronic medicine is on electrical signaling of the nervous system. Understanding the nervous system's regulatory roles and developing technologies that record, activate, or inhibit neural signaling to influence particular biological pathways.

OBJECTIVE

Bioelectronic medicine is an emerging therapeutic option with the interconnection between molecular medicine, neuroscience, and bioengineering. The creation of nerve stimulating devices that communicate with both the central and peripheral nervous systems has the potential to completely transform how we treat disorders. Although early clinical applications have been largely effective across entire nerves, the ultimate goal is to create implantable, miniature closed-loop systems that can precisely identify and modulate individual nerve fibers to treat a wide range of disorders.

METHODOLOGY

The data bases such as PubMed, and Clinicaltrial.gov.in were searched for scientific research, review and clinical trials on bioelectronic medicine.

CONCLUSION

The field of bioelectronic medicine is trending at present. In recent years, researchers have extended the field's applications, undertaken promising clinical trials, and begun delivering therapies to patients, thus creating the groundwork for significant future advancements. Countries and organizations must collaborate across industries and regions to establish an atmosphere and guidelines that foster the advancement of the field and the fulfillment of its prospective advantages.

A Flexible, Implantable, Bioelectronic Electroporation Device for Targeted Ablation of Seizure Foci in the Mouse Brain

The primary method of treatment for patients suffering from drug-resistant focal-onset epilepsy is resective surgery, which adversely impacts neurocognitive function. Radio frequency (RF) ablation and laser ablation are the methods with the most promise, achieving seizure-free rates similar to resection but with less negative impact on neurocognitive function. However, there remains a number of concerns and open technical questions about these two methods of thermal ablation, with the primary ones: (1) heating; (2) hemorrhage and bleeding; and (3) poor directionality. Irreversible electroporation (IRE) is a proven method of focal ablation, which circumvents all three of the primary concerns regarding focal RF and laser ablation. Here, we demonstrate the in vivo application of a flexible implant with organic electrodes for focal ablation of epilepsy foci using high-frequency IRE (H-FIRE) in mice. Our results show that local, targeted ablation is possible in the close neighborhood of the electrode, paving the way for the clinical application in the treatment of focal epilepsy.

Hydrogels in wearable neural interfaces

The integration of wearable neural interfaces (WNIs) with the human nervous system has marked a significant progression, enabling progress in medical treatments and technology integration. Hydrogels, distinguished by their high-water content, low interfacial impedance, conductivity, adhesion, and mechanical compliance, effectively address the rigidity and biocompatibility issues common in traditional materials. This review highlights their important parameters-biocompatibility, interfacial impedance, conductivity, and adhesiveness-that are integral to their function in WNIs. The applications of hydrogels in wearable neural recording and neurostimulation are discussed in detail. Finally, the opportunities and challenges faced by hydrogels for WNIs are summarized and prospected. This review aims to offer a thorough examination of hydrogel technology's present landscape and to encourage continued exploration and innovation. As developments progress, hydrogels are poised to revolutionize wearable neural interfaces, offering significant enhancements in healthcare and technological applications.

Graphical Abstract

Implantable Self-Powered Systems for Electrical Stimulation Medical Devices

With the integration of bioelectronics and materials science, implantable self-powered systems for electrical stimulation medical devices have emerged as an innovative therapeutic approach, garnering significant attention in medical research. These devices achieve self-powering through integrated energy conversion modules, such as triboelectric nanogenerators (TENGs) and piezoelectric nanogenerators (PENGs), significantly enhancing the portability and long-term efficacy of therapeutic equipment. This review delves into the design strategies and clinical applications of implantable self-powered systems, encompassing the design and optimization of energy harvesting modules, the selection and fabrication of adaptable electrode materials, innovations in systematic design strategies, and the extensive utilization of implantable self-powered systems in biological therapies, including the treatment of neurological disorders, tissue regeneration engineering, drug delivery, and tumor therapy. Through a comprehensive analysis of the latest research progress, technical challenges, and future directions in these areas, this paper aims to provide valuable insights and inspiration for further research and clinical applications of implantable self-powered systems.

Deciphering platinum dissolution in neural stimulation electrodes: Electrochemistry or biology?

Platinum (Pt) is the metal of choice for electrodes in implantable neural prostheses like the cochlear implants, deep brain stimulating devices, and brain-computer interfacing technologies. However, it is well known since the 1970s that Pt dissolution occurs with electrical stimulation. More recent clinical and in vivo studies have shown signs of corrosion in explanted electrode arrays and the presence of Pt-containing particulates in tissue samples. The process of degradation and release of metallic ions and particles can significantly impact on device performance. Moreover, the effects of Pt dissolution products on tissue health and function are still largely unknown. This is due to the highly complex chemistry underlying the dissolution process and the difficulty in decoupling electrical and chemical effects on biological responses. Understanding the mechanisms and effects of Pt dissolution proves challenging as the dissolution process can be influenced by electrical, chemical, physical, and biological factors, all of them highly variable between experimental settings. By evaluating comprehensive findings on Pt dissolution mechanisms reported in the fuel cell field, this review presents a critical analysis of the possible mechanisms that drive Pt dissolution in neural stimulation in vitro and in vivo. Stimulation parameters, such as aggregate charge, charge density, and electrochemical potential can all impact the levels of dissolved Pt. However, chemical factors such as electrolyte types, dissolved gases, and pH can all influence dissolution, confounding the findings of in vitro studies with multiple variables. Biological factors, such as proteins, have been documented to exhibit a mitigating effect on the dissolution process. Other biological factors like cells and fibro-proliferative responses, such as fibrosis and gliosis, impact on electrode properties and are suspected to impact on Pt dissolution. However, the relationship between electrical properties of stimulating electrodes and Pt dissolution remains contentious. Host responses to Pt degradation products are also controversial due to the unknown chemistry of Pt compounds formed and the lack of understanding of Pt distribution in clinical scenarios. The cytotoxicity of Pt produced via electrical stimulation appears similar to Pt-based compounds, including hexachloroplatinates and chemotherapeutic agents like cisplatin. While the levels of Pt produced under clinical and acute stimulation regimes were typically an order of magnitude lower than toxic concentrations observed in vitro, further research is needed to accurately assess the mass balance and type of Pt produced during long-term stimulation and its impact on tissue response. Finally, approaches to mitigating the dissolution process are reviewed. A wide variety of approaches, including stimulation strategies, coating electrode materials, and surface modification techniques to avoid excess charge during stimulation and minimise tissue response, may ultimately support long-term and safe operation of neural stimulating devices.

Elevating Platinum to Volumetric Capacitance: High Surface Area Electrodes through Reactive Pt Sputtering

Platinum is the most widespread electrode material used for implantable biomedical and neuroelectronic devices, motivating exploring ways to improve its performance and understand its fundamental properties. Using reactive magnetron sputtering, PtOx is prepared, which upon partial reduction yields a porous thin-film form of platinum with favorable properties, notably record-low impedance values outcompeting other reports for platinum-based electrodes. It is established that its high electrochemical capacitance scales with thickness, in the way of volumetric capacitor materials like IrOx and poly(3,4-ethylenedioxythiophene), PEDOT. Unlike these two well-known analogs, however, it is found that PtOx capacitance is not caused by reversible pseudofaradaic reactions but rather due to high surface area. In contrast to IrOx, PtOx is not a reversible valence-change oxide, but rather a porous form of platinum. The findings show that this oxygen-containing form of Pt can place Pt electrodes on a level competitive with IrOx and PEDOT. Due to its relatively low cost and ease of preparation, PtOx can be a good choice for microfabricated bioelectronic devices.

Bioelectronics for electrical stimulation: materials, devices and biomedical applications

Bioelectronics is a hot research topic, yet an important tool, as it facilitates the creation of advanced medical devices that interact with biological systems to effectively diagnose, monitor and treat a broad spectrum of health conditions. Electrical stimulation (ES) is a pivotal technique in bioelectronics, offering a precise, non-pharmacological means to modulate and control biological processes across molecular, cellular, tissue, and organ levels. This method holds the potential to restore or enhance physiological functions compromised by diseases or injuries by integrating sophisticated electrical signals, device interfaces, and designs tailored to specific biological mechanisms. This review explains the mechanisms by which ES influences cellular behaviors, introduces the essential stimulation principles, discusses the performance requirements for optimal ES systems, and highlights the representative applications. From this review, we can realize the potential of ES based bioelectronics in therapy, regenerative medicine and rehabilitation engineering technologies, ranging from tissue engineering to neurological technologies, and the modulation of cardiovascular and cognitive functions. This review underscores the versatility of ES in various biomedical contexts and emphasizes the need to adapt to complex biological and clinical landscapes it addresses.

Graphene and its hybrid nanocomposite: A Metamorphoses elevation in the field of tissue engineering

In this discourse, we delve into the manifold applications of graphene-based nanomaterials (GBNs) in the realm of biomedicine. Graphene, characterized by its two-dimensional planar structure, superconductivity, mechanical robustness, chemical inertness, extensive surface area, and propitious biocompatibility, stands as an exemplary candidate for diverse biomedical utility. Graphene include various distinctive characteristics of its two-dimensional planar structure, enormous surface area, mechanical and chemical stability, high conductivity, and exceptional biocompatibility. We investigate graphene and its diverse derivatives, which include reduced graphene oxides (rGOs), graphene oxides (GOs), and graphene composites, with a focus on elucidating the unique attributes relevant to their biomedical utility. In this review article it highlighted the unique properties of graphene, synthesis methods of graphene and functionalization methods of graphene. In the quest for novel materials to advance regenerative medicine, researchers have increasingly turned their attention to graphene-based materials, which have emerged as a prominent innovation in recent years. Notably, it highlights their applications in the regeneration of various tissues, including nerves, skeletal muscle, bones, skin, cardiac tissue, cartilage, and adipose tissue, as well as their influence on induced pluripotent stem cells, marking significant breakthroughs in the field of regenerative medicine. Additionally, this review article explores future prospects in this evolving area of study.

Biomaterial-enhanced treg cell immunotherapy: A promising approach for transplant medicine and autoimmune disease treatment

Regulatory T cells (Tregs) are crucial for preserving tolerance in the body, rendering Treg immunotherapy a promising treatment option for both organ transplants and autoimmune diseases. Presently, organ transplant recipients must undergo lifelong immunosuppression to prevent allograft rejection, while autoimmune disorders lack definitive cures. In the last years, there has been notable advancement in comprehending the biology of both antigen-specific and polyclonal Tregs. Clinical trials involving Tregs have demonstrated their safety and effectiveness. To maximize the efficacy of Treg immunotherapy, it is essential for these cells to migrate to specific target tissues, maintain stability within local organs, bolster their suppressive capabilities, and ensure their intended function's longevity. In pursuit of these goals, the utilization of biomaterials emerges as an attractive supportive strategy for Treg immunotherapy in addressing these challenges. As a result, the prospect of employing biomaterial-enhanced Treg immunotherapy holds tremendous promise as a treatment option for organ transplant recipients and individuals grappling with autoimmune diseases in the near future. This paper introduces strategies based on biomaterial-assisted Treg immunotherapy to enhance transplant medicine and autoimmune treatments.

Bioelectronic Neural Interfaces: Improving Neuromodulation Through Organic Conductive Coatings

Integration of bioelectronic devices in clinical practice is expanding rapidly, focusing on conditions ranging from sensory to neurological and mental health disorders. While platinum (Pt) electrodes in neuromodulation devices such as cochlear implants and deep brain stimulators have shown promising results, challenges still affect their long-term performance. Key among these are electrode and device longevity in vivo, and formation of encapsulating fibrous tissue. To overcome these challenges, organic conductors with unique chemical and physical properties are being explored. They hold great promise as coatings for neural interfaces, offering more rapid regulatory pathways and clinical implementation than standalone bioelectronics. This study provides a comprehensive review of the potential benefits of organic coatings in neuromodulation electrodes and the challenges that limit their effective integration into existing devices. It discusses issues related to metallic electrode use and introduces physical, electrical, and biological properties of organic coatings applied in neuromodulation. Furthermore, previously reported challenges related to organic coating stability, durability, manufacturing, and biocompatibility are thoroughly reviewed and proposed coating adhesion mechanisms are summarized. Understanding organic coating properties, modifications, and current challenges of organic coatings in clinical and industrial settings is expected to provide valuable insights for their future development and integration into organic bioelectronics.

Ion detection in a DNA nanopore FET device

An ion detection device that combines a DNA-origami nanopore and a field-effect transistor (FET) was designed and modeled to determine sensitivity of the nanodevice to the local cellular environment. Such devices could be integrated into a live cell, creating an abiotic-biotic interface integrated with semiconductor electronics. A continuum model is used to describe the behavior of ions in an electrolyte solution. The drift-diffusion equations are employed to model the ion distribution, taking into account the electric fields and concentration gradients. This was matched to the results from electric double layer theory to verify applicability of the model to a bio-sensing environment. The FET device combined with the nanopore is shown to have high sensitivity to ion concentration and nanopore geometry, with the electrical double layer behavior governing the device characteristics. A logarithmic relationship was found between ion concentration and a single FET current, generating up to 200 nA of current difference with a small applied bias.

Carbon Nanotube-Based Printed All-Organic Microelectrode Arrays for Neural Stimulation and Recording

In this paper, we report a low-cost printing process of carbon nanotube (CNT)-based, all-organic microelectrode arrays (MEAs) suitable for in vitro neural stimulation and recording. Conventional MEAs have been mainly composed of expensive metals and manufactured through high-cost and complex lithographic processes, which have limited their accessibility for neuroscience experiments and their application in various studies. Here, we demonstrate a printing-based fabrication method for microelectrodes using organic CNT/paraffin ink, coupled with the deposition of an insulating layer featuring single-cell-sized sensing apertures. The simple microfabrication processes utilizing the economic and readily available ink offer potential for cost reduction and improved accessibility of MEAs. Biocompatibility of the fabricated microelectrode was suggested through a live/dead assay of cultured neural cells, and its large electric double layer capacitance was revealed by cyclic voltammetry that was crucial for preventing cytotoxic electrolysis during electric neural stimulation. Furthermore, the electrode exhibited sufficiently low electric impedance of 2.49 Ω·cm2 for high signal-to-noise ratio neural recording, and successfully captured model electric waves in physiological saline solution. These results suggest the easily producible and low-cost printed all-organic microelectrodes are available for neural stimulation and recording, and we believe that they can expand the application of MEA in various neuroscience research.

Flexible high-density microelectrode arrays for closed-loop brain-machine interfaces: a review

Flexible high-density microelectrode arrays (HDMEAs) are emerging as a key component in closed-loop brain-machine interfaces (BMIs), providing high-resolution functionality for recording, stimulation, or both. The flexibility of these arrays provides advantages over rigid ones, such as reduced mismatch between interface and tissue, resilience to micromotion, and sustained long-term performance. This review summarizes the recent developments and applications of flexible HDMEAs in closed-loop BMI systems. It delves into the various challenges encountered in the development of ideal flexible HDMEAs for closed-loop BMI systems and highlights the latest methodologies and breakthroughs to address these challenges. These insights could be instrumental in guiding the creation of future generations of flexible HDMEAs, specifically tailored for use in closed-loop BMIs. The review thoroughly explores both the current state and prospects of these advanced arrays, emphasizing their potential in enhancing BMI technology.

Local contribution to the somatosensory evoked potentials in rat's thalamus

Local Field Potential (LFP), despite its name, often reflects remote activity. Depending on the orientation and synchrony of their sources, both oscillations and more complex waves may passively spread in brain tissue over long distances and be falsely interpreted as local activity at such distant recording sites. Here we show that the whisker-evoked potentials in the thalamic nuclei are of local origin up to around 6 ms post stimulus, but the later (7-15 ms) wave is overshadowed by a negative component reaching from cortex. This component can be analytically removed and local thalamic LFP can be recovered reliably using Current Source Density analysis. We used model-based kernel CSD (kCSD) method which allowed us to study the contribution of local and distant currents to LFP from rat thalamic nuclei and barrel cortex recorded with multiple, non-linear and non-regular multichannel probes. Importantly, we verified that concurrent recordings from the cortex are not essential for reliable thalamic CSD estimation. The proposed framework can be used to analyze LFP from other brain areas and has consequences for general LFP interpretation and analysis.

Biophysical Principles and Computational Modeling of Deep Brain Stimulation

BACKGROUND

Deep brain stimulation (DBS) has revolutionized the treatment of neurological disorders, yet the mechanisms of DBS are still under investigation. Computational models are important in silico tools for elucidating these underlying principles and potentially for personalizing DBS therapy to individual patients. The basic principles underlying neurostimulation computational models, however, are not well known in the clinical neuromodulation community.

OBJECTIVE

In this study, we present a tutorial on the derivation of computational models of DBS and outline the biophysical contributions of electrodes, stimulation parameters, and tissue substrates to the effects of DBS.

RESULTS

Given that many aspects of DBS are difficult to characterize experimentally, computational models have played an important role in understanding how material, size, shape, and contact segmentation influence device biocompatibility, energy efficiency, the spatial spread of the electric field, and the specificity of neural activation. Neural activation is dictated by stimulation parameters including frequency, current vs voltage control, amplitude, pulse width, polarity configurations, and waveform. These parameters also affect the potential for tissue damage, energy efficiency, the spatial spread of the electric field, and the specificity of neural activation. Activation of the neural substrate also is influenced by the encapsulation layer surrounding the electrode, the conductivity of the surrounding tissue, and the size and orientation of white matter fibers. These properties modulate the effects of the electric field and determine the ultimate therapeutic response.

CONCLUSION

This article describes biophysical principles that are useful for understanding the mechanisms of neurostimulation.

Revealing an important role of piezoelectric polymers in nervous-tissue regeneration: A review

Nerve injuries pose a drastic threat to nerve mobility and sensitivity and lead to permanent dysfunction due to low regenerative capacity of mature neurons. The electrical stimuli that can be provided by electroactive materials are some of the most effective tools for the formation of soft tissues, including nerves. Electric output can provide a distinctly favorable bioelectrical microenvironment, which is especially relevant for the nervous system. Piezoelectric biomaterials have attracted attention in the field of neural tissue engineering owing to their biocompatibility and ability to generate piezoelectric surface charges. In this review, an outlook of the most recent achievements in the field of piezoelectric biomaterials is described with an emphasis on piezoelectric polymers for neural tissue engineering. First, general recommendations for the design of an optimal nerve scaffold are discussed. Then, specific mechanisms determining nerve regeneration via piezoelectric stimulation are considered. Activation of piezoelectric responses via natural body movements, ultrasound, and magnetic fillers is also examined. The use of magnetoelectric materials in combination with alternating magnetic fields is thought to be the most promising due to controllable reproducible cyclic deformations and deep tissue permeation by magnetic fields without tissue heating. In vitro and in vivo applications of nerve guidance scaffolds and conduits made of various piezopolymers are reviewed too. Finally, challenges and prospective research directions regarding piezoelectric biomaterials promoting nerve regeneration are discussed. Thus, the most relevant scientific findings and strategies in neural tissue engineering are described here, and this review may serve as a guideline both for researchers and clinicians.

Resorbable conductive materials for optimally interfacing medical devices with the living

Implantable and wearable bioelectronic systems are arising growing interest in the medical field. Linking the microelectronic (electronic conductivity) and biological (ionic conductivity) worlds, the biocompatible conductive materials at the electrode/tissue interface are key components in these systems. We herein focus more particularly on resorbable bioelectronic systems, which can safely degrade in the biological environment once they have completed their purpose, namely, stimulating or sensing biological activity in the tissues. Resorbable conductive materials are also explored in the fields of tissue engineering and 3D cell culture. After a short description of polymer-based substrates and scaffolds, and resorbable electrical conductors, we review how they can be combined to design resorbable conductive materials. Although these materials are still emerging, various medical and biomedical applications are already taking shape that can profoundly modify post-operative and wound healing follow-up. Future challenges and perspectives in the field are proposed.

Electrogelated drug-embedded silk/gelatin/rGO degradable electrode for anti-inflammatory applications in brain-implant systems

Implantable electrodes have raised great interest over the last years with the increasing incidence of neurodegenerative disorders. For brain implant devices, some key factors resulting in the formation of glial scars, such as mechanical mismatch and acute injury-induced inflammation, should be considered for material design. Therefore, in this study, a new biocompatible flexible electrode (e-SgG) with arbitrary shapes on a positive electrode was developed via electrogelation by applying a direct electrical voltage on a silk fibroin/gelatin/reduced graphene oxide composite hydrogel. The implantable flexible e-SgG-2 film with 1.23% rGO content showed high Young's modulus (11-150 MPa), which was sufficient for penetration under dried conditions but subsequently became a biomimetic brain tissue with low Young's modulus (50-3200 kPa) after insertion in the brain. At the same time, an anti-inflammatory drug (DEX) incorporated into the e-SgG-2 film can be electrically stimulated to exhibit two-stage release to overcome tissue inflammation during cyclic voltammetry via degradation by applying an AC field. The results of cell response to the SF/gelatin/rGO/DEX composite film showed that the released DEX could interrupt astrocyte growth to reduce the inflammatory response but showed non-toxicity toward neurons, which demonstrated a great potential for the application of the biocompatible and degradable e-SgG-D electrodes in the improvement of nerve tissue repair.

System of Implantable Electrodes for Neural Signal Acquisition and Stimulation for Wirelessly Connected Forearm Prosthesis

There is great interest in the development of prosthetic limbs capable of complex activities that are wirelessly connected to the patient's neural system. Although some progress has been achieved in this area, one of the main problems encountered is the selective acquisition of nerve impulses and the closing of the automation loop through the selective stimulation of the sensitive branches of the patient. Large-scale research and development have achieved so-called "cuff electrodes"; however, they present a big disadvantage: they are not selective. In this article, we present the progress made in the development of an implantable system of plug neural microelectrodes that relate to the biological nerve tissue and can be used for the selective acquisition of neuronal signals and for the stimulation of specific nerve fascicles. The developed plug electrodes are also advantageous due to their small thickness, as they do not trigger nerve inflammation. In addition, the results of the conducted tests on a sous scrofa subject are presented.

A Review on Biomaterials for Neural Interfaces: Enhancing Brain-Machine Interfaces

Biomaterials are essential to the development of neural interfaces, including brainmachine interfaces. Biomaterial methods improve neural interface functionality, compatibility, and longevity, enabling brain-device communication. An extensive investigation of biomaterials utilized in brain electrode arrays, neural probes, & implantable devices rely on how materials affect neural signals recording, stimulation, & tissue contact. It also investigates how biomaterials, bioelectronics and 3D printing could improve neural interfaces. Biomaterials modulate neuroinflammatory responses, enhance brain tissue regeneration, and promote neural interface longevity. This study shows the potential for change of biomaterial-based neural interfaces in neuroprosthetics, neurological rehabilitation, and fundamental neuroscience research, addressing the need for brain-machine relationship and neurotechnology innovation. These findings suggest expanding biomaterials research and development to advance and sustain neural interface technologies for future use.

Recent Advancements in Bioelectronic Medicine: A Review

Bioelectronic medicine is a multidisciplinary field that combines molecular medicine, neurology, engineering, and computer science to design devices for diagnosing and treating diseases. The advancements in bioelectronic medicine can improve the precision and personalization of illness treatment. Bioelectronic medicine can produce, suppress, and measure electrical activity in excitable tissue. Bioelectronic devices modify specific neural circuits using electrons rather than pharmaceuticals and uses of bioelectronic processes to regulate the biological processes underlining various diseases. This promotes the potential to address the underlying causes of illnesses, reduce adverse effects, and lower costs compared to conventional medication. The current review presents different important aspects of bioelectronic medicines with recent advancements. The area of bioelectronic medicine has a lot of potential for treating diseases, enabling non-invasive therapeutic intervention by regulating brain impulses. Bioelectronic medicine uses electricity to control biological processes, treat illnesses, or regain lost capability. These new classes of medicines are designed by the technological developments in the detection and regulation of electrical signaling methods in the nervous system. Peripheral nervous system regulates a wide range of processes in chronic diseases; it involves implanting small devices onto specific peripheral nerves, which read and regulate the brain signaling patterns to achieve therapeutic effects specific to the signal capacity of a particular organ. The potential for bioelectronic medicine field is vast, as it investigates for treatment of various diseases, including rheumatoid arthritis, diabetes, hypertension, paralysis, chronic illnesses, blindness, etc.

Advances in electrode interface materials and modification technologies for brain-computer interfaces

Recent advances in neuroelectrode interface materials and modification technologies are reviewed. Brain-computer interface is the new method of human-computer interaction, which not only can realise the exchange of information between the human brain and external devices, but also provides a brand-new means for the diagnosis and treatment of brain-related diseases. The neural electrode interface part of brain-computer interface is an important area for electrical, optical and chemical signal transmission between brain tissue system and external electronic devices, which determines the performance of brain-computer interface. In order to solve the problems of insufficient flexibility, insufficient signal recognition ability and insufficient biocompatibility of traditional rigid electrodes, researchers have carried out extensive studies on the neuroelectrode interface in terms of materials and modification techniques. This paper introduces the biological reactions that occur in neuroelectrodes after implantation into brain tissue and the decisive role of the electrode interface for electrode function. Following this, the latest research progress on neuroelectrode materials and interface materials is reviewed from the aspects of neuroelectrode materials and modification technologies, firstly taking materials as a clue, and then focusing on the preparation process of neuroelectrode coatings and the design scheme of functionalised structures.

Interfacing neural cells with typical microelectronics materials for future manufacturing

The biocompatibility of materials used in electronic devices is critical for the development of implantable devices like pacemakers and neuroprosthetics, as well as in future biomanufacturing. Biocompatibility refers to the ability of these materials to interact with living cells and tissues without causing an adverse response. Therefore, it is essential to evaluate the biocompatibility of metals and semiconductor materials used in electronic devices to ensure their safe use in medical applications. Here, we evaluated the biocompatibility of a collection of diced silicon chips coated with a variety of metal thin films, interfacing them with different cell types, including murine mastocytoma cells in suspension culture, adherent NIH 3T3 fibroblasts, and human induced pluripotent stem cell (iPSC)-derived neural progenitor cells (NPCs). All materials tested were biocompatible and showed the potential to support neural differentiation of iPSC-NPCs, creating an opportunity to use these materials in a scalable production of a range of biohybrid devices such as electronic devices to study neural behaviors and neuropathies.

A Review on Electroactive Polymer-Metal Composites: Development and Applications for Tissue Regeneration

Electroactive polymer-metal composites (EAPMCs) have gained significant attention in tissue engineering owing to their exceptional mechanical and electrical properties. EAPMCs develop by combining an electroactive polymer matrix and a conductive metal. The design considerations include choosing an appropriate metal that provides mechanical strength and electrical conductivity and selecting an electroactive polymer that displays biocompatibility and electrical responsiveness. Interface engineering and surface modification techniques are also crucial for enhancing the adhesion and biocompatibility of composites. The potential of EAPMC-based tissue engineering revolves around its ability to promote cellular responses, such as cell adhesion, proliferation, and differentiation, through electrical stimulation. The electrical properties of these composites can be used to mimic natural electrical signals within tissues and organs, thereby aiding tissue regeneration. Furthermore, the mechanical characteristics of the metallic components provide structural reinforcement and can be modified to align with the distinct demands of various tissues. EAPMCs have extraordinary potential as regenerative biomaterials owing to their ability to promote beneficial effects in numerous electrically responsive cells. This study emphasizes the characteristics and applications of EAPMCs in tissue engineering.

Functional material-mediated wireless physical stimulation for neuro-modulation and regeneration

Nerve injuries and neurological diseases remain intractable clinical challenges. Despite the advantages of stem cell therapy in treating neurological disorders, uncontrollable cell fates and loss of cell function in vivo are still challenging. Recently, increasing attention has been given to the roles of external physical signals, such as electricity and ultrasound, in regulating stem cell fate as well as activating or inhibiting neuronal activity, which provides new insights for the treatment of neurological disorders. However, direct physical stimulations in vivo are short in accuracy and safety. Functional materials that can absorb energy from a specific physical field exerted in a wireless way and then release another localized physical signal hold great advantages in mediating noninvasive or minimally invasive accurate indirect physical stimulations to promote the therapeutic effect on neurological disorders. In this review, the mechanism by which various physical signals regulate stem cell fate and neuronal activity is summarized. Based on these concepts, the approaches of using functional materials to mediate indirect wireless physical stimulation for neuro-modulation and regeneration are systematically reviewed. We expect that this review will contribute to developing wireless platforms for neural stimulation as an assistance for the treatment of neurological diseases and injuries.

Dual-Conductive and Stiffness-Morphing Microneedle Patch Enables Continuous In Planta Monitoring of Electrophysiological Signal and Ion Fluctuation

The use of conductive microneedles presents a promising solution for achieving high-fidelity electrophysiological recordings with minimal impact on the interfaced tissue. However, a conventional metal-based microneedle suffers from high electrochemical impedance and mechanical mismatch. In this paper, we report a dual-conductive (i.e., both ionic and electronic conductive) and stiffness-morphing microneedle patch (DSMNP) for high-fidelity electrophysiological recordings with reduced tissue damage. The polymeric network of the DSMNP facilitates electrolyte absorption and therefore allows the transition of stiffness from 6.82 to 0.5139 N m-1. Furthermore, the nanoporous conductive polymer increases the specific electrochemical surface area after tissue penetration, resulting in an ultralow specific impedance of 893.13 Ω mm2 at 100 Hz. DSMNPs detect variation potential and action potential in real time and cation fluctuations in plants in response to environmental stimuli. After swelling, DSMNPs mechanically "lock" into biological tissues and prevent motion artifact by providing a stable interface. These results demonstrate the potential of DSMNPs for various applications in the field of plant physiology research and smart agriculture.

Conducting Polymer-Hydrogel Interpenetrating Networks for Improving the Electrode-Neural Interface

Implantable neural microelectrodes are recognized as a bridge for information exchange between inner organisms and outer devices. Combined with novel modulation technologies such as optogenetics, it offers a highly precise methodology for the dissection of brain functions. However, achieving chronically effective and stable microelectrodes to explore the electrophysiological characteristics of specific neurons in free-behaving animals continually poses great challenges. To resolve this, poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)/poly(vinyl alcohol) (PEDOT/PSS/PVA) interpenetrating conducting polymer networks (ICPN) are fabricated via a hydrogel scaffold precoating and electrochemical polymerization process to improve the performance of neural microelectrodes. The ICPN films exhibit robust interfacial adhesion, a significantly lower electrochemical impedance, superior mechanical properties, and improved electrochemical stability compared to the pure poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate)(PEDOT/PSS) films, which may be attributed to the three-dimensional (3D) porous microstructure of the ICPN. Hippocampal neurons and rat pheochromocytoma cells (PC12 cells) adhesion on ICPN and neurite outgrowth are observed, indicating enhanced biocompatibility. Furthermore, alleviated tissue response at the electrode-neural tissue interface and improved recording signal quality are confirmed by histological and electrophysiological studies, respectively. Owing to these merits, optogenetic modulations and electrophysiological recordings are performed in vivo, and an anxiolytic effect of hippocampal glutamatergic neurons on behavior is shown. This study demonstrates the effectiveness and advantages of ICPN-modified neural implants for in vivo applications.

The Impact of Biomaterial Surface Properties on Engineering Neural Tissue for Spinal Cord Regeneration

Tissue engineering for spinal cord injury (SCI) remains a complex and challenging task. Biomaterial scaffolds have been suggested as a potential solution for supporting cell survival and differentiation at the injury site. However, different biomaterials display multiple properties that significantly impact neural tissue at a cellular level. Here, we evaluated the behavior of different cell lines seeded on chitosan (CHI), poly (ε-caprolactone) (PCL), and poly (L-lactic acid) (PLLA) scaffolds. We demonstrated that the surface properties of a material play a crucial role in cell morphology and differentiation. While the direct contact of a polymer with the cells did not cause cytotoxicity or inhibit the spread of neural progenitor cells derived from neurospheres (NPCdn), neonatal rat spinal cord cells (SCC) and NPCdn only attached and matured on PCL and PLLA surfaces. Scanning electron microscopy and computational analysis suggested that cells attached to the material's surface emerged into distinct morphological populations. Flow cytometry revealed a higher differentiation of neural progenitor cells derived from human induced pluripotent stem cells (hiPSC-NPC) into glial cells on all biomaterials. Immunofluorescence assays demonstrated that PCL and PLLA guided neuronal differentiation and network development in SCC. Our data emphasize the importance of selecting appropriate biomaterials for tissue engineering in SCI treatment.

Combining PEDOT:PSS Polymer Coating with Metallic 3D Nanowires Electrodes to Achieve High Electrochemical Performances for Neuronal Interfacing Applications

This study presents a novel approach to improve the performance of microelectrode arrays (MEAs) used for electrophysiological studies of neuronal networks. The integration of 3D nanowires (NWs) with MEAs increases the surface-to-volume ratio, which enables subcellular interactions and high-resolution neuronal signal recording. However, these devices suffer from high initial interface impedance and limited charge transfer capacity due to their small effective area. To overcome these limitations, the integration of conductive polymer coatings, poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is investigated as a mean of improving the charge transfer capacity and biocompatibility of MEAs. The study combines platinum silicide-based metallic 3D nanowires electrodes with electrodeposited PEDOT:PSS coatings to deposit ultra-thin (<50 nm) layers of conductive polymer onto metallic electrodes with very high selectivity. The polymer-coated electrodes were fully characterized electrochemically and morphologically to establish a direct relationship between synthesis conditions, morphology, and conductive features. Results show that PEDOT-coated electrodes exhibit thickness-dependent improved stimulation and recording performances, offering new perspectives for neuronal interfacing with optimal cell engulfment to enable the study of neuronal activity with acute spatial and signal resolution at the sub-cellular level.

Printed Silk Microelectrode Arrays for Electrophysiological Recording and Controlled Drug Delivery

The use of soft and flexible bioelectronic interfaces can enhance the quality for recording cells' electrical activity by ensuring a continuous and intimate contact with the smooth, curving surfaces found in the physiological environment. This work develops soft microelectrode arrays (MEAs) made of silk fibroin (SF) films for recording interfaces that can also serve as a drug delivery system. Inkjet printing is used as a tool to deposit the substrate, conductive electrode, and insulator, as well as a drug-delivery nanocomposite film. This approach is highly versatile, as shown in the fabrication of carbon microelectrodes, sandwiched between a silk substrate and a silk insulator. The technique permits the development of thin-film devices that can be employed for in vitro extracellular recordings of HL-1 cell action potentials. The tuning of SF by applying an electrical stimulus to produce a permeable layer that can be used in on-demand drug delivery systems is also demonstrated. The multifunctional MEA developed here can pave the way for in vitro drug screening by applying time-resolved and localized chemical stimuli.

Highly Sensitive and Omnidirectionally Stretchable Bioelectrode Arrays for In Vivo Neural Interfacing

Flexible electrode array, a new-generation neural microelectrode, is a crucial tool for information exchange between living tissues and external electronics. Till date, advances in flexible neural microelectrodes are limited because of their high impedance and poor mechanical consistency at tissue interfaces. Herein, a highly sensitive and omnidirectionally stretchable polymeric electrode array (PEA) is introduced. Micropyramid-nanowire composite structures are constructed to increase the effective surface area of PEA, achieving an exponential reduction in impedance compared with gold (Au) and flat polypyrrole electrodes. Moreover, for the first time, a suspended umbrella structure to enable PEA with omnidirectional stretchability of up to ≈20% is designed. The PEA can withstand 1000 cycles of mechanical loads without decrease in performance. As a proof of concept, PEA is conformally attached to a rat heart and tibialis anterior muscle, and electrophysiological signals (electrocardiogram and electromyogram) of the rat are successfully recorded. This strategy provides a new perspective toward highly sensitive and omnidirectionally stretchable PEA that can facilitate the practical application of neural electrodes.

Rational Fabrication of Ionic Covalent Organic Frameworks for Chemical Analysis Applications

The rapid development of advanced material science boosts novel chemical analytical technologies for effective pretreatment and sensitive sensing applications in the fields of environmental monitoring, food security, biomedicines, and human health. Ionic covalent organic frameworks (iCOFs) emerge as a class of covalent organic frameworks (COFs) with electrically charged frames or pores as well as predesigned molecular and topological structures, large specific surface area, high crystallinity, and good stability. Benefiting from the pore size interception effect, electrostatic interaction, ion exchange, and recognizing group load, iCOFs exhibit the promising ability to extract specific analytes and enrich trace substances from samples for accurate analysis. On the other hand, the stimuli response of iCOFs and their composites to electrochemical, electric, or photo-irradiating sources endows them as potential transducers for biosensing, environmental analysis, surroundings monitoring, etc. In this review, we summarized the typical construction of iCOFs and focused on their rational structure design for analytical extraction/enrichment and sensing applications in recent years. The important role of iCOFs in the chemical analysis was fully highlighted. Finally, the opportunities and challenges of iCOF-based analytical technologies were also discussed, which may be beneficial to provide a solid foundation for further design and application of iCOFs.

Evaluation of Polymer-Coated Carbon Nanotube Flexible Microelectrodes for Biomedical Applications

The demand for electrically insulated microwires and microfibers in biomedical applications is rapidly increasing. Polymer protective coatings with high electrical resistivity, good chemical resistance, and a long shelf-life are critical to ensure continuous device operation during chronic applications. As soft and flexible electrodes can minimize mechanical mismatch between tissues and electronics, designs based on flexible conductive microfibers, such as carbon nanotube (CNT) fibers, and soft polymer insulation have been proposed. In this study, a continuous dip-coating approach was adopted to insulate meters-long CNT fibers with hydrogenated nitrile butadiene rubber (HNBR), a soft and rubbery insulating polymer. Using this method, 4.8 m long CNT fibers with diameters of 25-66 µm were continuously coated with HNBR without defects or interruptions. The coated CNT fibers were found to be uniform, pinhole free, and biocompatible. Furthermore, the HNBR coating had better high-temperature tolerance than conventional insulating materials. Microelectrodes prepared using the HNBR-coated CNT fibers exhibited stable electrochemical properties, with a specific impedance of 27.0 ± 9.4 MΩ µm2 at 1.0 kHz and a cathodal charge storage capacity of 487.6 ± 49.8 mC cm-2. Thus, the developed electrodes express characteristics that made them suitable for use in implantable medical devices for chronic in vivo applications.

Polymer nanofiber network reinforced gold electrode array for neural activity recording

Flexible and stretchable neural electrodes are promising tools for high-fidelity interfacing with soft and curvilinear brain surface. Here, we describe a flexible and stretchable neural electrode array that consists of polyacrylonitrile (PAN) nanofiber network reinforced gold (Au) film electrodes. Under stretching, the interweaving PAN nanofibers effectively terminate the formation of propagating cracks in the Au films and thus enable the formation of a dynamically stable electrode-tissue interface. Moreover, the PAN nanofibers increase the surface roughness and active surface areas of the Au electrodes, leading to reduced electrochemical impedance and improved signal-to-noise ratio. As a result, PAN nanofiber network reinforced Au electrode arrays can allow for reliable in vivo multichannel recording of epileptiform activities in rats.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13534-022-00257-5.

A Nonswelling Hydrogel with Regenerable High Wet Tissue Adhesion for Bioelectronics

Reducing the swelling of tissue-adhesive hydrogels is crucial for maintaining stable tissue adhesion and inhibiting tissue inflammation. However, reported strategies for reducing swelling always result in a simultaneous decrease in the tissue adhesive strength of the hydrogel. Furthermore, once the covalent bonds break in the currently reported hydrogels, they cannot be rebuilt, and the hydrogel loses its tissue adhesive ability. In this work, a nonswelling hydrogel (named as "PAACP") possessing regenerable high tissue adhesion is synthesized by copolymerizing and crosslinking poly(vinyl butyral) with acrylic acid, gelatin, and chitosan-grafted N-acetyl-l-cysteine. The tissue adhesive strength of the obtained PAACP reaches 211.4 kPa, which is approximately ten times higher than that of the reported nonswelling hydrogels, and the hydrogel can be reused for multiple cycles. The as-prepared hydrogel shows great potential in soft bioelectronics, as muscle fatigue is successfully monitored via the electrode array and strain sensor integrated on PAACP substrates. The success of these bioelectronics offers potential applicability in the long-term diagnosis of muscle-related health conditions and prosthetic manipulations.

Recent Progress and Perspectives on Neural Chip Platforms Integrating PDMS-Based Microfluidic Devices and Microelectrode Arrays

Recent years have witnessed a spurt of progress in the application of the encoding and decoding of neural activities to drug screening, diseases diagnosis, and brain-computer interactions. To overcome the constraints of the complexity of the brain and the ethical considerations of in vivo research, neural chip platforms integrating microfluidic devices and microelectrode arrays have been raised, which can not only customize growth paths for neurons in vitro but also monitor and modulate the specialized neural networks grown on chips. Therefore, this article reviews the developmental history of chip platforms integrating microfluidic devices and microelectrode arrays. First, we review the design and application of advanced microelectrode arrays and microfluidic devices. After, we introduce the fabrication process of neural chip platforms. Finally, we highlight the recent progress on this type of chip platform as a research tool in the field of brain science and neuroscience, focusing on neuropharmacology, neurological diseases, and simplified brain models. This is a detailed and comprehensive review of neural chip platforms. This work aims to fulfill the following three goals: (1) summarize the latest design patterns and fabrication schemes of such platforms, providing a reference for the development of other new platforms; (2) generalize several important applications of chip platforms in the field of neurology, which will attract the attention of scientists in the field; and (3) propose the developmental direction of neural chip platforms integrating microfluidic devices and microelectrode arrays.

A Short Review on Nanostructured Carbon Containing Biopolymer Derived Composites for Tissue Engineering Applications

The development of new scaffolds and materials for tissue engineering is a wide and open realm of material science. Among solutions, the use of biopolymers represents a particularly interesting area of study due to their great chemical complexity that enables creation of specific molecular architectures. However, biopolymers do not exhibit the properties required for direct application in tissue repair-such as mechanical and electrical properties-but they do show very attractive chemical functionalities which are difficult to produce through in vitro synthesis. The combination of biopolymers with nanostructured carbon fillers could represent a robust solution to enhance composite properties, producing composites with new and unique features, particularly relating to electronic conduction. In this paper, we provide a review of the field of carbonaceous nanostructure-containing biopolymer composites, limiting our investigation to tissue-engineering applications, and providing a complete overview of the recent and most outstanding achievements.