Microelectrodes with three-dimensional structures for improved neural interfacing (original) (raw)
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Design and Fabrication of a Flexible Substrate Microelectrode Array for Brain Machine Interfaces
2006
We report a neural microelectrode array design that leverages the recording properties of conventional microwire electrode arrays with the additional features of precise control of the electrode geometries. Using microfabrication techniques, a neural probe array is fabricated that possesses a flexible polyimide-based cable. The performance of the design was tested with electrochemical impedance spectroscopy and in vivo studies. The gold-plated electrode site has an impedance value of 0.9 MΩ at 1 kHz. Acute neural recording provided high neuronal yields, peak-topeak amplitudes (as high as 100 µV), and signal-to-noise ratios (27dB).
High-density 3D pyramid-shaped microelectrode arrays for brain-machine interface applications
2014 IEEE Biomedical Circuits and Systems Conference (BioCAS) Proceedings, 2014
Neuroprosthetic devices that can record neural activities and stimulate the central nervous system (CNS), called brain-machine interfaces (BMI), offer significant potential to restore various lost neurologic functions. A key element in functions restoration is Microelectrode arrays (MEAs) implanted in neural tissues. MEAs, which act as an interface between bioelectronic devices and neural tissues, play an important role in chronic implants and must be reliable, stable, and efficient for long-term recording and stimulation. Electrochemical properties and biological compatibility of chronic microelectrodes are essential factors that must be taken into account in their design and fabrication. The present thesis deals with the design and fabrication of silicon micromachined, high-density, pyramid-shaped neural MEAs for intracortical 3D recording and stimulation. The focused is mainly on the MEAs fabrication techniques and development of coating materials process required with implantable devices with an ultimate purpose: elaborate variable-height microelectrodes to obtain consistent recording signals from small groups of neurons without losing microstimulation capabilities, while maintaining low-impedance pathways for charge injection, high charge transfer, and high-spatial resolution by altering the geometries and material compositions of the array. In the first part of the thesis, we present a new 3D micromachining technique with a single masking step in a time and cost effective manner. A high density 25 electrodes/ 1.96 mm 2 MEA with varying lengths electrodes to access neurons that are located in different depths of cortical tissue was designed and fabricated. Furthermore, a novel dry-film based masking technique for procuring extremely small active area for variable-height electrodes has been developed. With this technology, we have reduced the masking process steps from 14 to 6 compared to the conventional masking method. We have then reported for the first time a selective direct growth of carbon nanotubes (CNTs) on the tips of 3D MEAs using Plasma Enhanced Chemical Vapor Deposition (PECVD) that could enhance electrical properties of the electrodes significantly. The CNT coating led to a 5-fold decrease in impedance and a 600-fold increase in charge transfer compared with Pt electrode. Finally, we have highlighted the importance of the coating MEAs with bioactive molecules (Poly-D-lysine) and polyethylene glycol (PEG) hydrogels to minimize the immune response of the neural tissue to implanted MEAs by in vitro cell-culture tests.
Flexible three-dimensional microelectrode array for neural applications
Sensors and Actuators A: Physical, 2014
A neural electrode array design is proposed with 3 mm long sharpened pillars made from an aluminumbased substrate. The array is composed by 25 electrically insulated pillars in a 5 x 5 matrix, in which each aluminum pillar was precisely machined via dicing saw technique. The result is an aluminum structure with high-aspect-ratio pillars (19:1), each with a tip radius of 10 µm. A thin-film of platinum was deposited via sputtering technique to perform the ionic signal transduction. Each pillar was encapsulated with an epoxy resin insulating the entire pillar excluding the tip. This process resulted in mechanically robust electrodes each capable of withstanding loads up to 200 mN before bending. The array implantation tests were conducted on agar gel at speeds of 50 mm/s, 120 mm/s and 180 mm/s which resulted in average implantation forces of 119 mN, 145 mN and 150 mN respectively. Insertion and withdrawal tests were also performed in porcine cadaver brain showing a necessary force of 66 mN for successful explantation. A three point flexural test demonstrated a displacement of 0.8 mm before array's breakage. The electrode's impedance was characterized showing a near resistive impedance of 385 Ω in the frequency range from 2 kHz to 125 kHz. The resultant array, as well as the fabrication technique, is an innovative alternative to silicon-based electrode solutions, avoiding some fabrication methods and limitations related to silicon and increasing the mechanical flexibility of the array.
Recent Progress on Microelectrodes in Neural Interfaces
Materials (Basel, Switzerland), 2018
Brain‒machine interface (BMI) is a promising technology that looks set to contribute to the development of artificial limbs and new input devices by integrating various recent technological advances, including neural electrodes, wireless communication, signal analysis, and robot control. Neural electrodes are a key technological component of BMI, as they can record the rapid and numerous signals emitted by neurons. To receive stable, consistent, and accurate signals, electrodes are designed in accordance with various templates using diverse materials. With the development of microelectromechanical systems (MEMS) technology, electrodes have become more integrated, and their performance has gradually evolved through surface modification and advances in biotechnology. In this paper, we review the development of the extracellular/intracellular type of in vitro microelectrode array (MEA) to investigate neural interface technology and the penetrating/surface (non-penetrating) type of in v...
Proceedings of the 25th Annual International Conference of the IEEE Engineering in Medicine and Biology Society (IEEE Cat. No.03CH37439), 2003
Absfracf-Microelectrode arrays are likely to play an field relies primarily on arrays of microelectrodes embedded important role in the implementation of brainmachine into the brain. The major limitation of these microelectrode interfaces. One of the major obstacles is to make existing arrays, and the main reason that prevents them from being microelectrode arrays much less invasive. In this aim, novel used as potential brain-machine interfaces, is that all approaches for the implementation of these microelectrode versions produced so far are highly invasive, Existing arrays of microelectrodes [4] are based on three arrays will be required. This paper suggests the use structurally bi-stable electrodes based on deployable main approaches. A first approach relies on an array of microstructures which minimize the overall dimensions during insertion into the cortex and then deploy to increase microelectrodes machined from a single piece of material. A recording surface and lower the electrical impedance. Other second approach Stacks 2D sihn-based microelectrodes design alternatives and issues such as new methods of and electronics created using lithography to form a 3D array. implantation, tracking, and additional features that could Finally, in the simplest form, individual wires or bundles of make microelectrodes less invasive are also briefly described. wires are used to form the array. In all of these approaches, the size of the microelectrodes is the same during the initial insertion into the as Once fully implanted into the brain, All of these approaches may result in substantial KeywordsMicroelectrode, minimally invasive, bi-stable, size reduction, deployable structures, methods of implantation
Journal of Microelectromechanical Systems, 2000
This paper describes the design and microassembly process of a low-profile 3-D microelectrode array for mapping the functional organization of targeted areas of the central nervous system and for possible application in neural prostheses. The array consists of multiple planar complimentary metal-oxide-semiconductor stimulating probes and 3-D assembly components. Parylene-encapsulated gold beams supported by etch-stopped silicon braces allow the backends of the probes to be folded over to reduce the height of the array above the cortical surface. A process permitting parylene to be used at wafer level with bulk-silicon wet release has been reported. Spacers are used to fix the microassembled probes in position and are equipped with interlocking structures to facilitate the assembly process and increase yield. Four-probe 256-site 3-D arrays operate from ±5 V with an average per-channel power dissipation of 97 µW at full range stimulation with pulse widths of 100 µs at 500-Hz frequency. Thirty-two sites can be stimulated simultaneously with maximum currents of ±127 µA and a current resolution of ±1 µA. The microassembly techniques allow a variety of 3-D microstructures to be created from planar components. [2006-0133] Index Terms-Biomedical electrodes, microassembly.
Novel multi-sided, microelectrode arrays for implantable neural applications
Biomedical Microdevices, 2011
A new parylene-based microfabrication process is presented for neural recordingand drug delivery applications. We introduce a large design space for electrode placement and structural flexibility with a six mask process. By using chemical mechanical polishing, electrode sites may be created top-side, backside, or on the edge of the device having three exposed sides. Added surface area was achieved on the exposed edge through electroplating. Poly(3,4-ethylenedioxythiophene) (PEDOT) modified edge electrodes having an 85 µm 2 footprint resulted in an impedance of 200 kΩ at 1kHz. Edge electrodes were able to successfully record single unit activity in acute animal studies. A finite element model of planar and edge electrodes relative to neuron position reveals that edge electrodes should be beneficial for increasing the volume of tissue being sampled in recording applications. .
Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces
Medical & Biological Engineering & Computing, 2010
Microelectrode arrays (MEAs) are designed to monitor and/or stimulate extracellularly neuronal activity. However, the biomechanical and structural mismatch between current MEAs and neural tissues remains a challenge for neural interfaces. This article describes a material strategy to prepare neural electrodes with improved mechanical compliance that relies on thin metal film electrodes embedded in polymeric substrates. The electrode impedance of micro-electrodes on polymer is comparable to that of MEA on glass substrates. Furthermore, MEAs on plastic can be flexed and rolled offering improved structural interface with brain and nerves in vivo.
Method of Thin Flexible Microelectrode Insertion in Deep Brain Region for Chronic Neural Recording
2019
Reliable chronic neural recording from focal deep brain structures is impeded by insertion injury and foreign body response, the magnitude of which is correlated with the mechanical mismatch between the electrode and tissue. Thin and flexible neural electrodes cause less glial scarring and record longer than stiff electrodes. However, the insertion of flexible microelectrodes in the brain has been a challenge. A novel insertion method is proposed, and demonstrated, for precise targeting deep brain structures using flexible micro-wire electrodes. A novel electrode guiding system is designed based on the principles governing the buckling strength of electrodes. The proposed guide significantly increases the critical buckling force of the microelectrode. The electrode insertion mechanism involves spinning of the electrode during insertion. The spinning electrode is slowly inserted in the brain through the electrode guide. The electrode guide does not penetrate into cortex. The electrod...
IEEE transactions on neural systems and rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society, 2014
We introduce a new 3-D flexible microelectrode array for high performance electrographic neural signal recording and stimulation. The microelectrode architecture maximizes the number of channels on each shank and minimizes its footprint. The electrode was implemented on flexible polyimide substrate using microfabrication and thin-film processing. The electrode has a planar layout and comprises multiple shanks. Each shank is three mm in length and carries six gold pads representing the neuro-interfacing channels. The channels are used in recording important precursors with potential clinical relevance and consequent electrical stimulation to perturb the clinical condition. The polyimide structure satisfied the mechanical characteristics required for the proper electrode implantation and operation. Pad postprocessing technique was developed to improve the electrode electrical performance. The planar electrodes were used for creating 3-D "Waterloo Array" microelectrode with c...