Gene-Embedded Nanostructural Biotic-Abiotic Optoelectrode Arrays Applied for Synchronous Brain Optogenetics and Neural Signal Recording

Recent Progress of Soft and Bioactive Materials in Flexible Bioelectronics

Materials that establish functional, stable interfaces to targeted tissues for long-term monitoring/stimulation equipped with diagnostic/therapeutic capabilities represent breakthroughs in biomedical research and clinical medicine. A fundamental challenge is the mechanical and chemical mismatch between tissues and implants that ultimately results in device failure for corrosion by biofluids and associated foreign body response. Of particular interest is in the development of bioactive materials at the level of chemistry and mechanics for high-performance, minimally invasive function, simultaneously with tissue-like compliance and in vivo biocompatibility. This review summarizes the most recent progress for these purposes, with an emphasis on material properties such as foreign body response, on integration schemes with biological tissues, and on their use as bioelectronic platforms. The article begins with an overview of emerging classes of material platforms for bio-integration with proven utility in live animal models, as high performance and stable interfaces with different form factors. Subsequent sections review various classes of flexible, soft tissue-like materials, ranging from self-healing hydrogel/elastomer to bio-adhesive composites and to bioactive materials. Additional discussions highlight examples of active bioelectronic systems that support electrophysiological mapping, stimulation, and drug delivery as treatments of related diseases, at spatiotemporal resolutions that span from the cellular level to organ-scale dimension. Envisioned applications involve advanced implants for brain, cardiac, and other organ systems, with capabilities of bioactive materials that offer stability for human subjects and live animal models. Results will inspire continuing advancements in functions and benign interfaces to biological systems, thus yielding therapy and diagnostics for human healthcare.

Implantable hydrogels as pioneering materials for next-generation brain-computer interfaces

Use of brain-computer interfaces (BCIs) is rapidly becoming a transformative approach for diagnosing and treating various brain disorders. By facilitating direct communication between the brain and external devices, BCIs have the potential to revolutionize neural activity monitoring, targeted neuromodulation strategies, and the restoration of brain functions. However, BCI technology faces significant challenges in achieving long-term, stable, high-quality recordings and accurately modulating neural activity. Traditional implantable electrodes, primarily made from rigid materials like metal, silicon, and carbon, provide excellent conductivity but encounter serious issues such as foreign body rejection, neural signal attenuation, and micromotion with brain tissue. To address these limitations, hydrogels are emerging as promising candidates for BCIs, given their mechanical and chemical similarities to brain tissues. These hydrogels are particularly suitable for implantable neural electrodes due to their three-dimensional water-rich structures, soft elastomeric properties, biocompatibility, and enhanced electrochemical characteristics. These exceptional features make them ideal for signal recording, neural modulation, and effective therapies for neurological conditions. This review highlights the current advancements in implantable hydrogel electrodes, focusing on their unique properties for neural signal recording and neuromodulation technologies, with the ultimate aim of treating brain disorders. A comprehensive overview is provided to encourage future progress in this field. Implantable hydrogel electrodes for BCIs have enormous potential to influence the broader scientific landscape and drive groundbreaking innovations across various sectors.

Design, Fabrication, and Implantation of Invasive Microelectrode Arrays as in vivo Brain Machine Interfaces: A Comprehensive Review

Invasive Microelectrode Arrays (MEAs) have been a significant and useful tool for us to gain a fundamental understanding of how the brain works through high spatiotemporal resolution neuron-level recordings and/or stimulations. Through decades of research, various types of microwire, silicon, and flexible substrate-based MEAs have been developed using the evolving new materials, novel design concepts, and cutting-edge advanced manufacturing capabilities. Surgical implantation of the latest minimal damaging flexible MEAs through the hard-to-penetrate brain membranes introduces new challenges and thus the development of implantation strategies and instruments for the latest MEAs. In this paper, studies on the design considerations and enabling manufacturing processes of various invasive MEAs as in vivo brain-machine interfaces have been reviewed to facilitate the development as well as the state-of-art of such brain-machine interfaces from an engineering perspective. The challenges and solution strategies developed for surgically implanting such interfaces into the brain have also been evaluated and summarized. Finally, the research gaps have been identified in the design, manufacturing, and implantation perspectives, and future research prospects in invasive MEA development have been proposed.

Chiral Nanostructured Glycerohydrogel Sol-Gel Plates of Chitosan L- and D-Aspartate: Supramolecular Ordering and Optical Properties

A comprehensive study was performed on the supramolecular ordering and optical properties of thin nanostructured glycerohydrogel sol-gel plates based on chitosan L- and D-aspartate and their individual components in the X-ray, UV, visible, and IR ranges. Our comparative analysis of chiroptical characteristics, optical collimated transmittance, the average cosine of the scattering angle, microrelief and surface asymmetry, and the level of structuring shows a significant influence of the wavelength range of electromagnetic radiation and the enantiomeric form of aspartic acid on the functional characteristics of the sol-gel materials. At the macrolevel of the supramolecular organization, a complex topography of the surface layer and a dense amorphous-crystalline ordering of polymeric substances were revealed, while at the nanolevel, there were two forms of voluminous scattering domains: nanospheres with diameters of 60-120 nm (L-) and 45-55 nm (D-), anisometric particles of lengths within ~100-160 (L-) and ~85-125 nm (D-), and widths within ~10-20 (L-) and ~20-30 nm (D-). The effect of optical clearing on glass coated with a thin layer of chitosan L-(D-)aspartate in the near-UV region was discovered (observed for the first time for chitosan-based materials). The resulting nanocomposite shape-stable glycerohydrogels seem promising for sensorics and photonics.

Carbohydrate based biomaterials for neural interface applications

Neuroprosthetic devices that record and modulate neural activities have demonstrated immense potential for bypassing or restoring lost neurological functions due to neural injuries and disorders. However, implantable electrical devices interfacing with brain tissue are susceptible to a series of inflammatory tissue responses along with mechanical or electrical failures which can affect the device performance over time. Several biomaterial strategies have been implemented to improve device-tissue integration for high quality and stable performance. Ranging from developing smaller, softer, and more flexible electrode designs to introducing bioactive coatings and drug-eluting layers on the electrode surface, such strategies have shown different degrees of success but with limitations. With their hydrophilic properties and specific bioactivities, carbohydrates offer a potential solution for addressing some of the limitations of the existing biomolecular approaches. In this review, we summarize the role of polysaccharides in the central nervous system, with a primary focus on glycoproteins and proteoglycans, to shed light on their untapped potential as biomaterials for neural implants. Utilization of glycosaminoglycans for neural interface and tissue regeneration applications is comprehensively reviewed to provide the current state of carbohydrate-based biomaterials for neural implants. Finally, we will discuss the challenges and opportunities of applying carbohydrate-based biomaterials for neural tissue interfaces.

Bio-integrative design of the neural tissue-device interface

Neural implants enable bidirectional communications with nervous tissue and have demonstrated tremendous potential in research and clinical applications. To obtain high fidelity and stable information exchange, we need to minimize the undesired host responses and achieve intimate neuron-device interaction. This paper highlights the key bio-integrative strategies aimed at seamless integration through intelligent device designs to minimize the immune responses, as well as incorporate bioactive elements to actively modulate cellular reactions. These approaches span from surface modification and bioactive agent delivery, to biomorphic and biohybrid designs. Many of these strategies have shown effectiveness in functional outcome measures, others are exploratory but with fascinating potentials. The combination of bio-integrative strategies may synergistically promote the next generation of neural interfaces.

Electroresponsive Hydrogels for Therapeutic Applications in the Brain

Electroresponsive hydrogels possess a conducting material component and respond to electric stimulation through reversible absorption and expulsion of water. The high level of hydration, soft elastomeric compliance, biocompatibility, and enhanced electrochemical properties render these hydrogels suitable for implantation in the brain to enhance the transmission of neural electric signals and ion transport. This review provides an overview of critical electroresponsive hydrogel properties for augmenting electric stimulation in the brain. A background on electric stimulation in the brain through electroresponsive hydrogels is provided. Common conducting materials and general techniques to integrate them into hydrogels are briefly discussed. This review focuses on and summarizes advances in electric stimulation of electroconductive hydrogels for therapeutic applications in the brain, such as for controlling delivery of drugs, directing neural stem cell differentiation and neurogenesis, improving neural biosensor capabilities, and enhancing neural electrode-tissue interfaces. The key challenges in each of these applications are discussed and recommendations for future research are also provided.

In Vivo Optogenetic Modulation with Simultaneous Neural Detection Using Microelectrode Array Integrated with Optical Fiber

The detection of neuroelectrophysiology while performing optogenetic modulation can provide more reliable and useful information for neural research. In this study, an optical fiber and a microelectrode array were integrated through hot-melt adhesive bonding, which combined optogenetics and electrophysiological detection technology to achieve neuromodulation and neuronal activity recording. We carried out the experiments on the activation and electrophysiological detection of infected neurons at the depth range of 900-1250 μm in the brain which covers hippocampal CA1 and a part of the upper cortical area, analyzed a possible local inhibition circuit by combining opotogenetic modulation and electrophysiological characteristics and explored the effects of different optical patterns and light powers on the neuromodulation. It was found that optogenetics, combined with neural recording technology, could provide more information and ideas for neural circuit recognition. In this study, the optical stimulation with low frequency and large duty cycle induces more intense neuronal activity and larger light power induced more action potentials of neurons within a certain power range (1.032 mW-1.584 mW). The present study provided an efficient method for the detection and modulation of neurons in vivo and an effective tool to study neural circuit in the brain.

Novel Platform for Surface-Mediated Gene Delivery Assisted with Visible-Light Illumination

Surface-mediated gene delivery has attracted more and more attentions in biomedical research and applications because of its characteristics of low toxicity and localized delivery. Herein, a novel visible-light-regulated, surface-mediated gene-delivery platform is exhibited, arising from the photoinduced surface-charge accumulation on silicon. Silicon with a pn junction is used and tested subsequently for the behavior of surface-mediated gene delivery under visible-light illumination. It is found that positive-charge accumulation under light illumination changes the surface potential and then facilitates the delivery of gene-loaded carriers. As a result, the gene-expression efficiency shows a significant improvement from 6% to 28% under a 10 min visible-light illumination. Such improvement is ascribed to the increase in surface potential caused by light illumination, which promotes both the release of gene-loaded carriers and the cellular uptake. This work suggests that silicon with photovoltaic effect could offer a new strategy for surface-mediated, gene-delivery-related biomedical research and applications.

Multimaterial and multifunctional neural interfaces: from surface-type and implantable electrodes to fiber-based devices

Development of neural interfaces from surface electrodes to fibers with various type, functionality, and materials.