Penetrating Electrode Research Articles

The effects of neuron morphology and spatial distribution on the selectivity of dorsal root ganglion stimulation

Objective.For prosthesis users, sensory feedback that appears to come from the missing limb can improve function, confidence, and phantom limb pain. Numerous pre-clinical studies have considered stimulation via penetrating microelectrodes at the dorsal root ganglion (DRG) as a potential approach for somatosensory neuroprostheses. However, to develop clinically translatable neuroprosthetic devices, a less invasive approach, such as stimulation via epineural macroelectrodes, would be preferable. This work explores the feasibility of using such electrodes to deliver focal sensory feedback by examining the mechanisms of selective activation in response to stimulation via epineural electrodes compared with penetrating electrodes.Approach.We developed computational models of the DRG, representing the biophysical properties of the DRG and surrounding tissue to evaluate neural responses to stimulation via penetrating microelectrodes and epineural macroelectrodes. To assess the role of properties such as neuron morphology and spatial arrangement we designed three models, including one that contained only axons (axon only), one with pseudounipolar neurons arranged randomly (random), and one with pseudounipolar neurons placed according to a realistic spatial distribution (realistic).Main results.Our models demonstrate that activation in response to stimulation via epineural electrodes in a realistic model is commonly initiated in the axon initial segment adjacent to the cell body, whereas penetrating electrodes commonly elicit responses in t-junctions and axons. Moreover, we see a wider dynamic range for epineural electrodes compared with penetrating electrodes. This difference appears to be driven by the spatial organization and neuron morphology of the realistic DRG.Significance.We demonstrate that the anatomical features of the DRG make it a potentially effective target for epineural stimulation to deliver focal sensations from the limbs. Specifically, we show that epineural stimulation at the DRG can be highly selective thanks to the neuroanatomical arrangement of the DRG, making this a promising approach for future neuroprosthetic development.

Spatial‐coupled Ampere‐level Electrochemical Propylene Epoxidation over RuO2/Ti Hollow‐fiber Penetration Electrodes

AbstractThe electrochemical propylene epoxidation reaction (PER) provides a promising route for ecofriendly propylene oxide (PO) production, instantly generating active halogen/oxygen species to alleviate chloride contamination inherent in traditional PER. However, the complex processes and unsatisfactory PO yield for current electrochemical PER falls short of meeting industrial application requirements. Herein, a spatial‐coupling strategy over RuO2/Ti hollow‐fiber penetration electrode (HPE) is adopted to facilitate efficient PO production, significantly improving PER performance to ampere level (achieving over 80 % PO faradaic efficiency and a maximum PO current density of 859 mA cm−2). The synergetic combination of the penetration effect of HPE and the spatial‐coupled reaction sequence, enables the realization of ampere‐level PO production with high specificity, exhibiting significant potentials for economically viable PER applications.

Spatial-coupled Ampere-level Electrochemical Propylene Epoxidation over RuO2/Ti Hollow-fiber Penetration Electrodes.

The electrochemical propylene epoxidation reaction (PER) provides a promising route for ecofriendly propylene oxide (PO) production, instantly generating active halogen/oxygen species to alleviate chloride contamination inherent in traditional PER. However, the complex processes and unsatisfactory PO yield for current electrochemical PER falls short of meeting industrial application requirements. Herein, a spatial-coupling strategy over RuO2/Ti hollow-fiber penetration electrode (HPE) is adopted to facilitate efficient PO production, significantly improving PER performance to ampere level (achieving over 80 % PO faradaic efficiency and a maximum PO current density of 859 mA cm-2). The synergetic combination of the penetration effect of HPE and the spatial-coupled reaction sequence, enables the realization of ampere-level PO production with high specificity, exhibiting significant potentials for economically viable PER applications.

Boosting pH-universal electrosynthesis of hydrogen peroxide by regulating three-phase interface of carbon gas penetration electrode

Electrochemical oxygen reduction is a sustainable method for onsite H2O2 production. However, pH-universal H2O2 electrosynthesis still suffered from low kinetics and efficiency. Here carbon nanotube hollow fiber (CNT-HF) with porous fiber wall is designed to enhance H2O2 electrosynthesis via tailoring the three-phase interface. The CNT-HF gas penetration electrode with enhanced local electric field is favorable for boosting oxygen mass transfer and regulating catalyst-electrolyte interfacial protons, resulting in significantly enhanced H2O2 production performance in comparison with CNT planar gas diffusion electrode under pH-universal media. Its H2O2 production efficiency is 98.1% at pH 13. Meanwhile, H2O2 production efficiency of 96.1% and high H2O2 concentration of 46.4 g L-1 are achieved at pH 1 with 20 mM K+. Experimental and simulation results reveal the boosted H2O2 electrosynthesis on CNT-HF is mainly contributed from its significantly reduced diffusion layer thickness, enhanced local electric field and interfacial proton regulation by K+ enriched at electrode surface.

Ampere-level CO2 electroreduction with single-pass conversion exceeding 85% in acid over silver penetration electrodes

Synthesis of valuable chemicals from CO2 electroreduction in acidic media is highly desirable to overcome carbonation. However, suppressing the hydrogen evolution reaction in such proton-rich environments remains a considerable challenge. The current study demonstrates the use of a hollow fiber silver penetration electrode with hierarchical micro/nanostructures to enable CO2 reduction to CO in strong acids via balanced coordination of CO2 and K+/H+ supplies. Correspondingly, a CO faradaic efficiency of 95% is achieved at a partial current density as high as 4.3 A/cm2 in a pH = 1 solution of H2SO4 and KCl, sustaining 200 h of continuous electrolysis at a current density of 2 A/cm2 with over 85% single-pass conversion of CO2. The experimental results and density functional theory calculations suggest that the controllable CO2 feeding induced by the hollow fiber penetration configuration primarily coordinate the CO2/H+ balance on Ag active sites in strong acids, favoring CO2 activation and key intermediate *COOH formation, resulting in enhanced CO formation.

Tensile‐Strained Cu Penetration Electrode Boosts Asymmetric C–C Coupling for Ampere‐Level CO2‐to‐C2+ Reduction in Acid

The synthesis of multicarbon (C2+) products remains a substantial challenge in sustainable CO2 electroreduction owing to the need for sufficient current density and faradaic efficiency alongside carbon efficiency. Herein, we demonstrate ampere‐level high‐efficiency CO2 electroreduction to C2+ products in both neutral and strongly acidic (pH = 1) electrolytes using a hierarchical Cu hollow‐fiber penetration electrode (HPE). High concentration of K+ could concurrently suppress hydrogen evolution reaction and facilitate C–C coupling, thereby promoting C2+ production in strong acid. By optimizing the K+ and H+ concentration and CO2 flow rate, a faradaic efficiency of 84.5% and a partial current density as high as 3.1 A cm–2 for C2+ products, alongside a single‐pass carbon efficiency of 81.5% and stable electrolysis for 240 h were demonstrated in a strong acidic solution of H2SO4 and KCl (pH = 1). Experimental measurements and density functional theory simulations suggested that tensile‐strained Cu HPE enhances the asymmetric C–C coupling to steer the selectivity and activity of C2+ products.

Tensile-Strained Cu Penetration Electrode Boosts Asymmetric C-C Coupling for Ampere-Level CO2-to-C2+ Reduction in Acid.

The synthesis of multicarbon (C2+) products remains a substantial challenge in sustainable CO2 electroreduction owing to the need for sufficient current density and faradaic efficiency alongside carbon efficiency. Herein, we demonstrate ampere-level high-efficiency CO2 electroreduction to C2+ products in both neutral and strongly acidic (pH=1) electrolytes using a hierarchical Cu hollow-fiber penetration electrode (HPE). High concentration of K+ could concurrently suppress hydrogen evolution reaction and facilitate C-C coupling, thereby promoting C2+ production in strong acid. By optimizing the K+ and H+ concentration and CO2 flow rate, a faradaic efficiency of 84.5 % and a partial current density as high as 3.1 A cm-2 for C2+ products, alongside a single-pass carbon efficiency of 81.5 % and stable electrolysis for 240 h were demonstrated in a strong acidic solution of H2SO4 and KCl (pH=1). Experimental measurements and density functional theory simulations suggested that tensile-strained Cu HPE enhances the asymmetric C-C coupling to steer the selectivity and activity of C2+ products.

Halide-modulated Hollow-Fiber Cu penetration electrode boosts Ampere-Level CO2 electroreduction to multicarbon products

Electroreduction of CO2 to chemical fuels is desirable for the economically viable use of CO2 and consumption of renewable electricity. Efficient production of C2+ on Cu-based catalysts remains a challenge. Herein, a copper hollow fiber penetration electrode with a striking C–C coupling capability by virtue of modulating the electronic states through halide ion coordinated adsorption. An efficient C2+ production with a FE of 68.8 % at 2.1 A cm−2 in 3.0 M KI and remained stable during 120-h electrolysis at 2.0 A cm−2, outperforming reported catalytic performance, which is the result of combined effect of penetration effect and halide ion coordinated adsorption, which promotes the transfer of electrons to CO2, reduces the C–C coupling energy and suppresses proton adsorption, thereby reducing hydrogen evolution.

Study on liquid dielectrophoresis based on double flexible electrodes simulating interdigitated pattern electrodes

Dielectrophoresis affects the surface wettability by applying a non-uniform electric field to dipoles inside dielectric liquid, achieving adjustable droplet contact angle and overcoming the saturation limitation of contact angle caused by the electrowettability effect. However, it is difficult to realize useful three-dimensional tunable optical devices because most of the driving electrodes need to be patterned. In this work, a model of double flexible electrodes simulating planar interdigitated pattern electrodes is proposed based on the dielectrophoresis. Double flexible electrodes, which are wrapped with an insulating dielectric layer and are not conductive to each other are arranged at close intervals and wound along the plane substrate to form a two-dimensional planar line wall. A hydrophobic layer is used to fill the gap and increase the initial contact angle. Ultimately, the “droplet-interdigitated planar line wall” dielectrophoresis driven-droplet model is formed after the dielectric droplets have been deposited on the line wall surface. Firstly, considering the influence of penetration depth and electrode gap area, Young’s equation is theoretically modified to adapt to this model. Then, the finite element algorithm simulation is used to used to comparatively analyze the potential distribution of this model and the planar interdigitated pattern electrode model. The field strength distributions of the electrodes with different wire diameters and insulating layer thickness values are analyzed. It can be found that with the increase of the diameter of the electrode wire and the thickness of the insulating layer, the morphology of the model changes from the tip electrode into the planar electrode, the surface field strength attenuates exponentially and the peak value decreases. This shows that the structure of this electrode in this model is superior to that of the planar electrode. After that, the contact angle of the model is measured experimentally in a range of 58°－90° under 0–250 <i>V</i><sub>rms</sub> voltage, which is in line with the theoretical expectation. At the same time, neither obvious contact angle lag nor saturation is observed in the experiment. Finally, the new electrophoretic driving droplet model constructed in this paper transforms the dielectric electrophoretic driving mode from a two-dimensional planar electrode to a one-dimensional flexible linear electrode. Because of its flexibility and plasticity, it is convenient to form a three-dimensional cavity and can be applied to more complex device structures.

Hollow penetration electrode of Bi with dislocated lattice enabling ampere-level reduction of CO2 exclusively to formate

CO2 electroreduction to valuable chemicals using renewable energy is a prospective strategy for realizing carbon neutrality, however, exclusive production of formate under high industry current densities (> 200 mA cm−2) remains challenging. Herein, we presented a lattice-dislocated hollow-fiber Bi via in situ reconstruction to make a breakthrough for such issue. A nearly perfect formate Faradaic efficiency of > 99.5 % was realized with a current density of 1 A cm−2, completely suppressing CO and hydrogen generation. Finite element simulations showed high-concentration CO2 feeding was realized even though at ampere-level current density. And density functional theory calculations revealed that the abundant dislocated lattice acting as the active sites boosted the production of OCHO* . Thus, the synergistic combination of penetration and strain effects induced by the lattice-dislocated Bi hollow penetration electrode is responsible for such remarkable activities. This work represents a large step toward the application of direct conversion of CO2.

Kinetic and in Situ Analysis for Ion Transport Process in Copper Electrodeposition Using Polyelectrolyte Membranes

Electrodeposition of metals has been one of the most important techniques for fabrication of microelectronics and semiconductor elements in printed circuit boards and electronics device manufacturing. From the industrial perspective, the management of electrodeposition bath is crucial to maintain product quality, productivity and long-term stability of the bath, the subject of which includes bath temperature, concentration of metal salts, supporting electrolytes, and various additives. Although these parameters have been optimized to achieve desirable deposition rate, depending on the product type and morphology, some environmental issues regarding with generating mist, sludges, and waste effluent during electrodeposition process are becoming apparent. Additionally, current electrodeposition process has been developed for substrates with large surface area and for large scale production of electronic components and could not be suitable for recent demand of small-lot, site-selective and multiproduct device microfabrication. Therefore, high-performance deposition system, allowing site-selective electrodeposition of metals without generation of large amount of effluents, needs to be developed to impact above environmental and cost perspectives. Recently, we reported a novel method for electrodeposition of metals using polyelectrolyte films attached on cathode substrate (solid electrodeposition: SED) [1]. The SED process enables one to deposit metals directly on the cathode surface from metal ions inside solid polyelectrolyte membranes and has desirable advantages including higher deposition rate, site-selectivity, and deposition using lower concentration electrolyte solution without additives. In this SED process, thin polyelectrolyte membrane sandwiched between electrodes effectively concentrates metal ions through interfacial penetration, which increases the conductance between the electrodes and realizes solid-state electrodeposition that produces no mist, sludge, or even waste effluent.In this study, we present mechanistic analysis of the SED process, including transport kinetics and equilibrium reaction of copper ions at solution/membrane interface (Figure A). We show that both detailed experimental results and theoretical calculations reveal that ion transfer in the present electrodeposition system is a penetration-controlled process at the solution/polyelectrolyte interface, providing an inherently different ion-transport mechanism compared to that of conventional diffusion-controlled electrodeposition. Several parameters including penetration rate constant, electrode geometry, and distance between polyelectrolyte and anode are varied to investigate the ion-transport process in the SED system. When the anode is slightly apart from polyelectrolyte film to introduce electrolyte layer but is closer as far as possible to it, greater current density for copper electrodeposition is achieved at steady state than that for the systemwhere the membrane is sandwiched by electrodes (Figure B). This can be due to maximum ion penetration rate and minimum resistivity of electrolyte layer, providing better deposition setup for high performance electrodeposition. Additionally, we also performed in situ analysis of concentration of copper ions inside polyelectrolyte film via visible absorption spectroscopy using a miscofiber during electrodeposition. As a result, concentration of copper in the polyelectrolyte film decreased initially and then became constant (steady state) as the deposition proceeded, a fashion of which was quite similar with that of current-time curves simultaneously acquired during constant-voltage electrodeposition.The developed deposition setup demonstrates stable electrodeposition of copper using aqueous copper sulfate solution with no supporting electrolytes and/or additives at deposition rate of few micrometers per minute. As a site-selective deposition tool, the SED process can be used to fabricate microelectronic and even semiconductor circuit elements in a manner that resembles stamping deposition, and is suitable for small-lot, on-demand, and multi-product microfabrication.Reference:[1] K. Akamatsu, S. Nakano, K. Kimura, Y. Takashima, T. Tsuruoka, H. Nawafune, Y. Sato, J. Murai, H. Yanagimoto, ACS Appl. Mater. Interfaces, 13 (2021) 13896-13906. Figure 1

Emerging Penetrating Neural Electrodes: In Pursuit of Large Scale and Longevity.

Penetrating neural electrodes provide a powerful approach to decipher brain circuitry by allowing for time-resolved electrical detections of individual action potentials. This unique capability has contributed tremendously to basic and translational neuroscience, enabling both fundamental understandings of brain functions and applications of human prosthetic devices that restore crucial sensations and movements. However, conventional approaches are limited by the scarce number of available sensing channels and compromised efficacy over long-term implantations. Recording longevity and scalability have become the most sought-after improvements in emerging technologies. In this review, we discuss the technological advances in the past 5-10 years that have enabled larger-scale, more detailed, and longer-lasting recordings of neural circuits at work than ever before. We present snapshots of the latest advances in penetration electrode technology, showcase their applications in animal models and humans, and outline the underlying design principles and considerations to fuel future technological development.

Highly Efficient CO2 Reduction at Steady 2 A cm-2 by Surface Reconstruction of Silver Penetration Electrode.

Electroreduction of CO2 to CO is a promising route for greenhouse gas resource utilization, but it still suffers from impractical current density and poor durability. Here, a nanosheet shell (NS) vertically standing on the Ag hollow fiber (NS@Ag HF) surface formed by electrochemical surface reconstruction is reported. As-prepared NS@Ag HF as a gas penetration electrode exhibited a high CO faradaic efficiency of 97% at an ultra-high current density of 2.0 A cm-2 with a sustained performance for continuous >200h operation. The experimental and theoretical studies reveal that promoted surface electronic structures of NS@Ag HF by the nanosheets not only suppress the competitive hydrogen evolution reaction but also facilitate the CO2 reduction kinetics. This work provides a feasible strategy for fabricating robust catalysts for highly efficient and stable CO2 reduction.

Gas penetrating hollow fiber Bi with contractive bond enables industry-level CO2 electroreduction

Electrochemical conversion of carbon dioxide (CO2) to valuable fuels driven by renewable electricity exhibits significant potential for achieving carbon neutrality. Bismuth (Bi) possesses the reliable capability of electrocatalyzing CO2 to formate, and high formate faradaic efficiencies have been realized over Bi-based catalysts, but industry-level large current densities with high conversion rates at mild conditions remain challenging yet. Herein we present a bismuth hollow fiber (Bi HF) as a gas penetration electrode (GPE) that efficiently reduces CO2 with a formate faradaic efficiency of 93% and a current density of 1.13 A cm−2 at − 1.26 V (vs. RHE), corresponding to a CO2 conversion rate of 37% under ambient temperature and pressure. Finite element analysis (FEA) and density functional theory (DFT) demonstrate that the synergetic combination of unlimited CO2 feeding to triphasic interface reactions and selective reduction induced by contractive Bi-Bi bond is responsible for the superior activity of Bi HF.

Facet-oriented Cu2O and oxygen vacancies synergistically promoting CO2 electroreduction to formate on Cu-based hollow fiber

Electrochemical reduction of carbon dioxide (CO2) to value-added chemicals is an attractive route to utilize CO2 as resources and contribute carbon neutrality. As one of common products from CO2 electroreduction, formate is an economically viable liquid fuel under current techno-economic conditions. However, the current densities of CO2 electroreduction remain insufficient yet challenging due to the limited CO2 solubility and the unclear mechanisms on electrocatalyst surface. Herein, an exquisite Cu2O surface on copper-based hollow fiber (HF) was developed as a gas penetration electrode for CO2 electroreduction that can enhance mass transfer and boost three-phase interface reactions. Moreover, the (111)-oriented Cu2O and abundant oxygen vacancies synergistically promoted CO2 electrochemical reduction to formate, resulting in a high formate Faradaic efficiency of 92.3% with a partial current density of 84.4 mA·cm−2 at a potential of − 1.18 V vs. RHE. Operando Raman spectra suggested that carboxylate anion *CO2- was the key intermediate of CO2 reduction to formate, which was further reduced to formate via the subsequent proton-electron transfer.

Parameters optimization of tungsten inert gas welding process on 304L stainless steel using grey based Taguchi method

Tungsten inert gas can be used to weld stainless steel due to its offering sound weld, narrow fusion zone, precise control weld’s shape and over penetration, spatter free, slagless, stable arc and low electrode wear. The goal of this study was to offer the best process parameters for improving the mechanical characteristics of the weld joint. The experimental analysis approach was applied in this work, and the experiment was carried out on 304L stainless steel using L16. The selected welding parameters were welding travel speed, current of welding, gas flow rate, arc length, and root gap. Rockwell hardness, tensile strength, and bending strength tests were the examined mechanical properties on the weld joint. Based on the grey based Taguchi method, the optimal level-settings of welding travel speed, current of welding, flow rate of gas, arc length, and root gap were obtained 2.7 mm s−1, 160 A, 14 l min−1, 3 mm, and 1 mm, respectively. The analysis result of ANOVA showed that the current has the greatest impact and it was followed by travel speed and root gap on weld joint quality with percentage contribution of 80.77%, 10.86%, and 5.98%, respectively. According to confirmation results, the average grey relational grade of 0.863 which was found between the confidence interval of 0.800 to 1.082 for the 95% confidence level, and the maximum Rockwell hardness, tensile strength and bending strength were obtained 101.38 HRB, 1425.8 MPa and 1648.6 MPa, respectively.

Assessment of Safety of a Fully Implanted Endovascular Brain-Computer Interface for Severe Paralysis in 4 Patients

Brain-computer interface (BCI) implants have previously required craniotomy to deliver penetrating or surface electrodes to the brain. Whether a minimally invasive endovascular technique to deliver recording electrodes through the jugular vein to superior sagittal sinus is safe and feasible is unknown. To assess the safety of an endovascular BCI and feasibility of using the system to control a computer by thought. The Stentrode With Thought-Controlled Digital Switch (SWITCH) study, a single-center, prospective, first in-human study, evaluated 5 patients with severe bilateral upper-limb paralysis, with a follow-up of 12 months. From a referred sample, 4 patients with amyotrophic lateral sclerosis and 1 with primary lateral sclerosis met inclusion criteria and were enrolled in the study. Surgical procedures and follow-up visits were performed at the Royal Melbourne Hospital, Parkville, Australia. Training sessions were performed at patients' homes and at a university clinic. The study start date was May 27, 2019, and final follow-up was completed January 9, 2022. Recording devices were delivered via catheter and connected to subcutaneous electronic units. Devices communicated wirelessly to an external device for personal computer control. The primary safety end point was device-related serious adverse events resulting in death or permanent increased disability. Secondary end points were blood vessel occlusion and device migration. Exploratory end points were signal fidelity and stability over 12 months, number of distinct commands created by neuronal activity, and use of system for digital device control. Of 4 patients included in analyses, all were male, and the mean (SD) age was 61 (17) years. Patients with preserved motor cortex activity and suitable venous anatomy were implanted. Each completed 12-month follow-up with no serious adverse events and no vessel occlusion or device migration. Mean (SD) signal bandwidth was 233 (16) Hz and was stable throughout study in all 4 patients (SD range across all sessions, 7-32 Hz). At least 5 attempted movement types were decoded offline, and each patient successfully controlled a computer with the BCI. Endovascular access to the sensorimotor cortex is an alternative to placing BCI electrodes in or on the dura by open-brain surgery. These final safety and feasibility data from the first in-human SWITCH study indicate that it is possible to record neural signals from a blood vessel. The favorable safety profile could promote wider and more rapid translation of BCI to people with paralysis. ClinicalTrials.gov Identifier: NCT03834857.

Effects on Retinal Stimulation of the Geometry and the Insertion Location of Penetrating Electrodes.

Retinal implants have been developed and implanted to restore vision from outer retinal degeneration, but their performance is still limited due to the poor spatial resolution. To improve the localization of stimulation, microelectrodes in various three-dimensional (3D) shapes have been investigated. In particular, computational simulation is crucial for optimizing the performance of a novel microelectrode design before actual fabrication. However, most previous studies have assumed a uniform conductivity for the entire retina without testing the effect of electrodes placement in different layers. In this study, we used the finite element method to simulate electric fields created by 3D microelectrodes of three different designs in a retina model with a stratified conductivity profile. The three electrode designs included two conventional shapes - a conical electrode (CE) and a pillar electrode (PE); we also proposed a novel structure of pillar electrode with an insulating wall (PEIW). A quantitative comparison of these designs shows the PEIW generates a stronger and more confined electric field with the same current injection, which is preferred for high-resolution retinal prostheses. Moreover, our results demonstrate both the magnitude and the shape of potential distribution generated by a penetrating electrode depend not only on the geometry, but also substantially on the insertion depth of the electrode. Although epiretinal insertions are mainly discussed, we also compared results for subretinal insertions. The results provide valuable insights for improving the spatial resolution of retinal implants using 3D penetrating microelectrodes and highlight the importance of considering the heterogeneity of conductivities in the retina.

Selective neuromodulation of retinal ganglion cells via a hybrid optic-nerve and retinal neuroprosthesis for visual restoration.

A visual neuroprosthesis delivers electrical stimulation to the surviving neural cells of the visual pathway to produce prosthetic vision. While the retina is often chosen as the stimulation site, current retinal prostheses are hindered by the lack of functional selectivity that impairs the resolution. A possible strategy to improve the resolution is to combine the retinal stimulation and the stimulation of the optic nerve bundle, which contains myelinated fibres of retinal ganglion cells (RGCs) axons that vary in diameter. In this study, we used a computational model of retinal ganglion cells (RGCs) with myelinated axons to predict whether the frequency of electrical stimulation delivered to the optic nerve can be modulated to preferentially inhibit a subset of optic nerve fibres classified by diameter. The model combined a finite element model of bipolar penetrating electrodes delivering sinusoidal stimulation in the range of 25-10000 Hz to the optic nerve, and a double-cable model, to represent an optic nerve fibre. We found that the diameter of the axon fibre and ion kinetic properties of the RGC affect the neuron's frequency response, demonstrating the potential of an optic nerve stimulation to produce selective inhibition based on the axon fibre size. Clinical Relevance-This establishes the importance of considering the size of the nerve cell axons, as well as the functional type of the RGC, in stimulating the optic nerve. This can be exploited to facilitate functionally selective neuromodulation when used in conjunction with retinal stimulation.

Ultraflexible and Stretchable Intrafascicular Peripheral Nerve Recording Device with Axon-Dimension, Cuff-Less Microneedle Electrode Array.

Peripheral nerve mapping tools with higher spatial resolution are needed to advance systems neuroscience, and potentially provide a closed-loop biomarker in neuromodulation applications. Two critical challenges of microscale neural interfaces are 1) how to apply them to small peripheral nerves, and 2) how to minimize chronic reactivity. A flexible microneedle nerve array (MINA) is developed, which is the first high-density penetrating electrode array made with axon-sized silicon microneedles embedded in low-modulus thin silicone. The design, fabrication, acute recording, and chronic reactivity to an implanted MINA, are presented. Distinctive units are identified in the rat peroneal nerve. The authors also demonstrate a long-term, cuff-free, and suture-free fixation manner using rose bengal as a light-activated adhesive for two time-points. The tissue response is investigated at 1-week and 6-week time-points, including two sham groups and two MINA-implanted groups. These conditions are quantified in the left vagus nerve of rats using histomorphometry. Micro computed tomography (micro-CT) is added to visualize and quantify tissue encapsulation around the implant. MINA demonstrates a reduction in encapsulation thickness over previously quantified interfascicular methods. Future challenges include techniques for precise insertion of the microneedle electrodes and demonstrating long-term recording.