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Micromachines
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Implantable Neural Interfaces
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Implantable Neural Interfaces

A special issue of Micromachines (ISSN 2072-666X). This special issue belongs to the section "B：Biology and Biomedicine".

Deadline for manuscript submissions: closed (31 October 2021) | Viewed by 23698

Special Issue Editor

Prof. Dr. Sang Beom Jun

E-Mail Website
Guest Editor
Department of Brain and Cognitive Sciences, Ewha Womans University, Seoul 03760, Korea
Interests: bioelectronics; neural engineering; neuroelectrophysiology

Special Issue Information

Dear Colleagues,

Neural interfaces are connections that enable the two-way exchange of information with the nervous system. These connections can occur at multiple levels, including with the peripheral nerves, the spinal cord, or the brain; in many instances, fundamental biophysical and biological challenges are shared across these levels. There are several issues to be considered: selectivity, stability, resolution versus invasiveness, implant-induced injury, and the host-interface response. The engineered solutions to these challenges include electrode designs and geometry, stimulation waveforms, materials, and surface modifications. The emerging opportunities to improve neural interfaces include cellular-level silicon to neuron connections, optical stimulation, and approaches to control inflammation. Overcoming the biophysical and biological challenges will enable effective high-density neural interfaces for stimulation and recording. This Special Issue will promote new ideas, approaches, and paradigms toward the development of the next generation of implantable neural interfaces.

Prof. Dr. Sang Beom Jun
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • neural implants
  • neural interface devices
  • neural electrodes

Published Papers (6 papers)

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Research

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12 pages, 1758 KiB  
Communication
A Hydrogel-Based Microfluidic Nerve Cuff for Neuromodulation of Peripheral Nerves
by Raviraj Thakur, Felix P. Aplin and Gene Y. Fridman
Micromachines 2021, 12(12), 1522; https://doi.org/10.3390/mi12121522 - 8 Dec 2021
Cited by 7 | Viewed by 3636
Abstract
Implantable neuromodulation devices typically have metal in contact with soft, ion-conducting nerves. These neural interfaces excite neurons using short-duration electrical pulses. While this approach has been extremely successful for multiple clinical applications, it is limited in delivering long-duration pulses or direct current (DC), [...] Read more.
Implantable neuromodulation devices typically have metal in contact with soft, ion-conducting nerves. These neural interfaces excite neurons using short-duration electrical pulses. While this approach has been extremely successful for multiple clinical applications, it is limited in delivering long-duration pulses or direct current (DC), even for acute term studies. When the charge injection capacity of electrodes is exceeded, irreversible electrochemical processes occur, and toxic byproducts are discharged directly onto the nerve, causing biological damage. Hydrogel coatings on electrodes improve the overall charge injection limit and provide a mechanically pliable interface. To further extend this idea, we developed a silicone-based nerve cuff lead with a hydrogel microfluidic conduit. It serves as a thin, soft and flexible interconnection and provides a greater spatial separation between metal electrodes and the target nerve. In an in vivo rat model, we used this cuff to stimulate and record from sciatic nerves, with performance comparable to that of metal electrodes. Further, we delivered DC through the lead in an acute manner to induce nerve block that is reversible. In contrast to most metallic cuff electrodes, which need microfabrication equipment, we built this cuff using a consumer-grade digital cutter and a simplified molding process. Overall, the device will be beneficial to neuromodulation researchers as a general-purpose nerve cuff electrode for peripheral neuromodulation experiments. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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13 pages, 2183 KiB  
Article
A Flexible a-SiC-Based Neural Interface Utilizing Pyrolyzed-Photoresist Film (C) Active Sites
by Chenyin Feng, Christopher L. Frewin, Md Rubayat-E Tanjil, Richard Everly, Jay Bieber, Ashok Kumar, Michael Cai Wang and Stephen E. Saddow
Micromachines 2021, 12(7), 821; https://doi.org/10.3390/mi12070821 - 13 Jul 2021
Cited by 10 | Viewed by 3010
Abstract
Carbon containing materials, such as graphene, carbon-nanotubes (CNT), and graphene oxide, have gained prominence as possible electrodes in implantable neural interfaces due to their excellent conductive properties. While carbon is a promising electrochemical interface, many fabrication processes are difficult to perform, leading to [...] Read more.
Carbon containing materials, such as graphene, carbon-nanotubes (CNT), and graphene oxide, have gained prominence as possible electrodes in implantable neural interfaces due to their excellent conductive properties. While carbon is a promising electrochemical interface, many fabrication processes are difficult to perform, leading to issues with large scale device production and overall repeatability. Here we demonstrate that carbon electrodes and traces constructed from pyrolyzed-photoresist-film (PPF) when combined with amorphous silicon carbide (a-SiC) insulation could be fabricated with repeatable processes which use tools easily available in most semiconductor facilities. Directly forming PPF on a-SiC simplified the fabrication process which eliminates noble metal evaporation/sputtering and lift-off processes on small features. PPF electrodes in oxygenated phosphate buffered solution at pH 7.4 demonstrated excellent electrochemical charge storage capacity (CSC) of 14.16 C/cm2, an impedance of 24.8 ± 0.4 kΩ, and phase angle of −35.9 ± 0.6° at 1 kHz with a 1.9 kµm2 recording site area. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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16 pages, 5291 KiB  
Article
Manufacturable 32-Channel Cochlear Electrode Array and Preliminary Assessment of Its Feasibility for Clinical Use
by Soowon Shin, Yoonhee Ha, Gwangjin Choi, Junewoo Hyun, Sangwoo Kim, Seung-Ha Oh and Kyou-Sik Min
Micromachines 2021, 12(7), 778; https://doi.org/10.3390/mi12070778 - 30 Jun 2021
Cited by 9 | Viewed by 5607
Abstract
(1) Background: In this study, we introduce a manufacturable 32-channel cochlear electrode array. In contrast to conventional cochlear electrode arrays manufactured by manual processes that consist of electrode-wire welding, the placement of each electrode, and silicone molding over wired structures, the proposed cochlear [...] Read more.
(1) Background: In this study, we introduce a manufacturable 32-channel cochlear electrode array. In contrast to conventional cochlear electrode arrays manufactured by manual processes that consist of electrode-wire welding, the placement of each electrode, and silicone molding over wired structures, the proposed cochlear electrode array is manufactured by semi-automated laser micro-structuring and a mass-produced layer-by-layer silicone deposition scheme similar to the semiconductor fabrication process. (2) Methods: The proposed 32-channel electrode array has 32 electrode contacts with a length of 24 mm and 0.75 mm spacing between contacts. The width of the electrode array is 0.45 mm at its apex and 0.8 mm at its base, and it has a three-layered arrangement consisting of a 32-channel electrode layer and two 16-lead wire layers. To assess its feasibility, we conducted an electrochemical evaluation, stiffness measurements, and insertion force measurements. (3) Results: The electrochemical impedance and charge storage capacity are 3.11 ± 0.89 kOhm at 1 kHz and 5.09 mC/cm2, respectively. The V/H ratio, which indicates how large the vertical stiffness is compared to the horizontal stiffness, is 1.26. The insertion force is 17.4 mN at 8 mm from the round window, and the maximum extraction force is 61.4 mN. (4) Conclusions: The results of the preliminary feasibility assessment of the proposed 32-channel cochlear electrode array are presented. After further assessments are performed, a 32-channel cochlear implant system consisting of the proposed 32-channel electrode array, 32-channel neural stimulation and recording IC, titanium-based hermetic package, and sound processor with wireless power and signal transmission coil will be completed. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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10 pages, 4246 KiB  
Article
Implantable Optrode Array for Optogenetic Modulation and Electrical Neural Recording
by Saeyeong Jeon, Youjin Lee, Daeho Ryu, Yoon Kyung Cho, Yena Lee, Sang Beom Jun and Chang-Hyeon Ji
Micromachines 2021, 12(6), 725; https://doi.org/10.3390/mi12060725 - 19 Jun 2021
Cited by 6 | Viewed by 3079
Abstract
During the last decade, optogenetics has become an essential tool for neuroscience research due to its unrivaled feature of cell-type-specific neuromodulation. There have been several technological advances in light delivery devices. Among them, the combination of optogenetics and electrophysiology provides an opportunity for [...] Read more.
During the last decade, optogenetics has become an essential tool for neuroscience research due to its unrivaled feature of cell-type-specific neuromodulation. There have been several technological advances in light delivery devices. Among them, the combination of optogenetics and electrophysiology provides an opportunity for facilitating optogenetic approaches. In this study, a novel design of an optrode array was proposed for realizing optical modulation and electrophysiological recording. A 4 × 4 optrode array and five-channel recording electrodes were assembled as a disposable part, while a reusable part comprised an LED (light-emitting diode) source and a power line. After the characterization of the intensity of the light delivered at the fiber tips, in vivo animal experiment was performed with transgenic mice expressing channelrhodopsin, showing the effectiveness of optical activation and neural recording. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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14 pages, 7061 KiB  
Article
Numerical Evaluation on Residual Thermal Stress-Induced Delamination at PDMS–Metal Interface of Neural Prostheses
by Yuyang Mao, Ivan Pechenizkiy, Thomas Stieglitz and Theodor Doll
Micromachines 2021, 12(6), 669; https://doi.org/10.3390/mi12060669 - 8 Jun 2021
Cited by 5 | Viewed by 3027
Abstract
The most common failure mode of implantable neural implants has been delamination of layers in compound structures and encapsulations in a wet body environment. Current knowledge of failure mechanisms of adhesion and its standardized test procedures are lacking and must be established. This [...] Read more.
The most common failure mode of implantable neural implants has been delamination of layers in compound structures and encapsulations in a wet body environment. Current knowledge of failure mechanisms of adhesion and its standardized test procedures are lacking and must be established. This study demonstrated a combined experimental and numerical method to investigate the residual stresses from one of the most common encapsulation materials, silicone rubber (polydimethylsiloxane-PDMS) during the coating process at elevated temperatures. Measured shrinkage of test specimen correlates well to a modified shrinkage model using thermal-mechanical finite element method (FEM) simulation. All simulated interfacial stresses show stress concentration at the PDMS coating front depending on curing temperature and coating thickness, while Griffith’s condition estimated the delamination of the coating front. This study emphasizes the understanding of the interfacial delamination giving the possibility to predict failure mode of neural interface. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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Review

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25 pages, 1141 KiB  
Review
Current Review of Optical Neural Interfaces for Clinical Applications
by Younghoon Park, Sung-Yun Park and Kyungsik Eom
Micromachines 2021, 12(8), 925; https://doi.org/10.3390/mi12080925 - 2 Aug 2021
Cited by 7 | Viewed by 3914
Abstract
Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities [...] Read more.
Neural interfaces, which enable the recording and stimulation of living neurons, have emerged as valuable tools in understanding the brain in health and disease, as well as serving as neural prostheses. While neural interfaces are typically based on electrical transduction, alternative energy modalities have been explored to create safe and effective approaches. Among these approaches, optical methods of linking neurons to the outside world have gained attention because light offers high spatial selectivity and decreased invasiveness. Here, we review the current state-of-art of optical neural interfaces and their clinical applications. Optical neural interfaces can be categorized into optical control and optical readout, each of which can be divided into intrinsic and extrinsic approaches. We discuss the advantages and disadvantages of each of these methods and offer a comparison of relative performance. Future directions, including their clinical opportunities, are discussed with regard to the optical properties of biological tissue. Full article
(This article belongs to the Special Issue Implantable Neural Interfaces)
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