A measurement setup and automated calculation method to determine the charge injection capacity of implantable microelectrodes

Producción CientíficaThe design of safe stimulation protocols for functional electrostimulation requires knowledge of the “maximum reversible charge injection capacity” of the implantable microelectrodes. One of the main difficulties encountered in characterizing such microelectrodes is the calculation of the access voltage Va. This paper proposes a method to calculate Va that does not require prior knowledge of the overpotential terms and of the electrolyte (or excitable tissue) resistance, which is an advantage for in vivo electrochemical characterization of microelectrodes. To validate this method, we compare the calculated results with those obtained from conventional methods for characterizing three flexible platinum microelectrodes by cyclic voltammetry and voltage transient measurements. This paper presents the experimental setup, the required instrumentation, and the signal processing.Ministerio de Economía y Competitividad ( Research project DPI2016-80391-C3-3-R

High-Density 3D Pyramid-Shaped Microelectrode Arrays for Brain-Machine Interface Applications

RÉSUMÉ Les dispositifs médicaux dédiés aux enregistrements des activités neuronales et à la stimulation de tissus nerveux sont appelés interfaces cerveau-machines. Ils offrent un potentiel important pour restaurer diverses fonctions neurologiques perdues. Un élément clé dans la mise en œuvre des dispositifs est le réseau de microélectrodes (MEAs pour MicroElectrode Arrays en anglais) servant d’interface avec les tissus nerveux. Les MEA jouent un rôle important dans les implants lors d’expérimentations chroniques, ils doivent être fiables, stables et efficaces pour l'enregistrement et la stimulation à long terme. Les propriétés électrochimiques et la compatibilité biologique des microélectrodes sont des facteurs essentiels qui doivent être prises en compte lors de leur conception et fabrication. La présente thèse traite de la conception et la fabrication de MEA en silicium micro-usiné à haute densité et en forme de pyramides qui sont destinés à l’enregistrement et la stimulation intracorticals 3D. Nous nous concentrons principalement sur les techniques de microfabrication des électrodes et le développement de procédure du revêtement de matériaux nécessaires pour la biocompatibilité et protection des dispositifs implantables. Nous élaborons des microélectrodes à hauteur variable pour enregistrer des signaux neuronaux, sans perdre la capacité de microstimulation et tout en maintenant des impédances de faibles valeurs. Cette caractéristique est obtenue en modifiant la géométrie et la composition de matériaux utilisés, ce qui facilite l'injection de charge et la résolution spatiale élevée. Nous présentons une nouvelle technique de micro-usinage 3D à nombre réduit de masques comparé aux techniques existantes. Nous décrivons la mise en œuvre d’un MEA à haute densité (25 électrodes / 1,96 mm2) et à différentes longueurs d’électrodes. En outre, une nouvelle technique de masquage à base de film sec a été développée pour obtenir de très petites surfaces actives pour les microélectrodes qui sont à hauteur variable. Nous avons réduit les étapes du procédé de masquage de 14 à 6 par rapport à la méthode classique de masquage utilisé dans la littérature. Nous avons ensuite effectué, pour la première fois, une croissance directe sélective de nanotubes de carbone sur les têtes de microélectrodes de longueurs variables en utilisant la technique du dépôt chimique en phase vapeur assisté par plasma (Plasma-Enhanced Chemical Vapor Deposition - PECVD).----------ABSTRACT 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 mm2 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

Versatile LCP surface microelectrodes for combining electrophysiology and in vivo two-photon imaging in the murine CNS

Neurons and astrocytes are highly interconnected and form a complex cellular network for signal processing in the brain. The electrical activity of neurons and astroglial Ca2+ signals are tightly coupled. Parallel recording of electrical activity and Ca2+ signals can help to identify the molecular mechanisms of neuron-glia communications. In this work, flexible liquid crystal polymer microelectrode arrays for electrical recordings and stimulations during two-photon laser-scanning microscopy (2P-LSM) were developed. The arrays were designed for standard craniotomies used for cortical 2P-LSM in vivo imaging. Being of low weight, thin and flexible, they can be easily positioned between the dura mater and the glass coverslip. Three different designs were constructed: arrays (1) with eight circular electrodes (arranged in a matrix of three by three elements, sparing the center), (2) with sixteen circular electrodes (four by four matrix) and (3) with eight rectangular electrodes (placed in four groups of 2 single sites). The initial contact sites of gold were coated with nanoporous platinum to decrease the impedance of the electrode tissue contacts and to increase the charge transfer capability. The biocompatibility of the electrodes was confirmed by immuno-histochemistry. Electrical recordings and Ca2+-imaging were performed in mice with neuronal or astroglial expression of the genetically encoded Ca2+-sensor GCaMP3. With the sixteen channel electrode arrays, an estimation of the spatially resolved electrical activity pattern within the cranial window could be described. The eight channel arrays were used in studies for simultaneous acquisition of Ca2+ (using 2P-LSM) and electrical signals. In addition, Ca2+ signals could be elicited by electrical stimulation. Using different stimulation intensities and depth of anesthesia, the change of brain activity during transition from anesthetized to awake state was investigated. In addition, the LCP technology was transferred from the cortical to a spinal cord application.Neurone und Astrozyten bilden ein komplexes interagierendes zellulares Netzwerk zur Signalverarbeitung im Gehirn. Dabei sind die elektrische Aktivitäten der Nervenzellen und die Ca2+ Signale der Astrozyten eng aneinander gekoppelt. Parallele Aufzeichnungen der elektrischen Aktivität und der Ca2+ Signale können helfen, die molekularen Mechanismen der Neuron-Glia-Kommunikation zu identifizieren. Innerhalb dieser Arbeit wurden flexible Flüssigkristall-Polymer-Mikroelektrodenarrays für elektrische Aufzeichnungen und Stimulationen für die Zwei-Photonen-Laserscan- Mikroskopie (2P-LSM) entwickelt. Die Elektrodenarrays wurden für Standard-Kraniotomien entwickelt, die für die kortikale in vivo 2P-LSM verwendet werden. Sie sind dünn, flexibel und von geringem Gewicht und können leicht auf der Dura positioniert werden. Drei verschiedene Designs wurden konstruiert: Arrays (1) mit acht runden Elektroden (angeordnet in einer drei mal drei Matrix, ohne die mittlere Elektrode), (2) mit sechzehn kreisförmigen Elektroden (vier mal vier Matrix) und (3) mit acht rechteckigen Elektroden (angeordnet in vier Gruppen von zwei einzelnen Standorten). Die ursprünglichen Elektrodenkontakte aus Gold wurden mit nanoporösem Platin beschichtet, um die Gewebekontaktimpedanz zu verringern und die Ladungsübertragungsfähigkeit zu erhöhen. Die Biokompatibilität der Elektroden immunhistochemisch getestet. Elektrische Aktivität und Ca2+ Signale wurden bei Mäusen mit neuronaler oder astroglialer Expression des Ca2+-Indikators GCaMP3 aufgezeichnet. Mit den sechzehn Kanal-Elektroden-Arrays konnten die elektrische Aktivität entlang der Kortexoberfläche innerhalb der Kraniotomie charakterisiert werden. Die achtkanaligen Arrays wurden zur gleichzeitigen Erfassung von Ca2+ (mit 2P-LSM) und elektrischen Signalen verwendet. Darüber hinaus konnten Ca2+ Signale durch elektrische Stimulation hervorgerufen werden. Mit verschiedenen Stimulationsintensitäten und der Tiefe der Anästhesie (Isofluran) wurde die Veränderung der Hirnaktivität beim Übergang von anästhesiert zu wach beobachtet. Zusätzlich konnte die Flüssigkristall-Polymer -Technologie von der kortikalen auf die spinale Anwendung übertragen werden.- European Union / EUGlia-PhD - European Union / Neurofibre

Design and development of an implantable biohybrid device for muscle stimulation following lower motor neuron injury

In the absence of innervation caused by complete lower motor neuron injuries, skeletal muscle undergoes an inexorable course of degeneration and atrophy. The most apparent and debilitating clinical outcome of denervation is the immediate loss of voluntary use of muscle. However, these injuries are associated with secondary complications of bones, skin and cardiovascular system that, if untreated, may be fatal. Electrical stimulation has been implemented as a clinical rehabilitation technique in patients with denervated degenerated muscles offering remarkable improvements in muscle function. Nevertheless, this approach has limitations and side effects triggered by the delivery of high intensity electrical pulses. Combining innovative approaches in the fields of cell therapy and implanted electronics offers the opportunity to develop a biohybrid device to stimulate muscles in patients with lower motor neuron injuries. Incorporation of stem cell-derived motor neurons into implantable electrodes, could allow muscles to be stimulated in a physiological manner and circumvent problems associated with direct stimulation of muscle. The hypothesis underpinning this project is that artificially-grown motor neurons can serve as an intermediate between stimulator and muscle, converting the electrical stimulus into a biological action potential and re-innervating muscle via neuromuscular interaction. Here, a suitable stem cell candidate with therapeutic potential was identified and a differentiation protocol developed to generate motor neuron-like cells. Thick-film technology and laser micromachining were implemented to manufacture electrode arrays with features and dimensions suitable for implantation. Manufactured electrodes were electrochemically characterised, and motor neuron-like cells incorporated to create biohybrid devices. In vitro results indicate manufactured electrodes support motor neuron-like cell growth and neurite extension. Moreover, electrochemical characterisation suggests electrodes are suitable for stimulation. Preliminary in vivo testing explored implantation in a rat muscle denervation model. Overall, this thesis demonstrates initial development of a novel approach for fabricating biohybrid devices that may improve stimulation of denervated muscles

A Wireless, High-Voltage Compliant, and Energy-Efficient Visual Intracortical Microstimulator

RÉSUMÉ L’objectif général de ce projet de recherche est la conception, la mise en oeuvre et la validation d’une interface sans fil intracorticale implantable en technologie CMOS avancée pour aider les personnes ayant une déficience visuelle. Les défis majeurs de cette recherche sont de répondre à la conformité à haute tension nécessaire à travers l’interface d’électrode-tissu (IET), augmenter la flexibilité dans la microstimulation et la surveillance multicanale, minimiser le budget de puissance pour un dispositif biomédical implantable, réduire la taille de l’implant et améliorer le taux de transmission sans fil des données. Par conséquent, nous présentons dans cette thèse un système de microstimulation intracorticale multi-puce basée sur une nouvelle architecture pour la transmission des données sans fil et le transfert de l’énergie se servant de couplages inductifs et capacitifs. Une première puce, un générateur de stimuli (SG) éconergétique, et une autre qui est un amplificateur de haute impédance se connectant au réseau de microélectrodes de l’étage de sortie. Les 4 canaux de générateurs de stimuli produisent des impulsions rectangulaires, demi-sinus (DS), plateau-sinus (PS) et autres types d’impulsions de courant à haut rendement énergétique. Le SG comporte un contrôleur de faible puissance, des convertisseurs numérique-analogiques (DAC) opérant en mode courant, générateurs multi-forme d’ondes et miroirs de courants alimentés sous 1.2 et 3.3V se servant pour l’interface entre les deux technologies utilisées. Le courant de stimulation du SG varie entre 2.32 et 220μA pour chaque canal. La deuxième puce (pilote de microélectrodes (MED)), une interface entre le SG et de l’arrangement de microélectrodes (MEA), fournit quatre niveaux différents de courant avec la valeur maximale de 400μA par entrée et 100μA par canal de sortie simultanément pour 8 à 16 sites de stimulation à travers les microélectrodes, connectés soit en configuration bipolaire ou monopolaire. Cette étage de sortie est hautement configurable et capable de délivrer une tension élevée pour satisfaire les conditions de l’interface à travers l’impédance de IET par rapport aux systèmes précédemment rapportés. Les valeurs nominales de plus grandes tensions d’alimentation sont de ±10V. La sortie de tension mesurée est conformément 10V/phase (anodique ou cathodique) pour les tensions d’alimentation spécifiées. L’incrémentation de tensions d’alimentation à ±13V permet de produire un courant de stimulation de 220μA par canal de sortie permettant d’élever la tension de sortie jusqu’au 20V par phase. Cet étage de sortie regroupe un commutateur haute tension pour interfacer une matrice des miroirs de courant (3.3V /20V), un registre à décalage de 32-bits à entrée sérielle, sortie parallèle, et un circuit dédié pour bloquer des états interdits.----------ABSTRACT The general objective of this research project is the design, implementation and validation of an implantable wireless intracortical interface in advanced CMOS technology to aid the visually impaired people. The major challenges in this research are to meet the required highvoltage compliance across electrode-tissue interface (ETI), increase lexibility in multichannel microstimulation and monitoring, minimize power budget for an implantable biomedical device, reduce the implant size, and enhance the data rate in wireless transmission. Therefore, we present in this thesis a multi-chip intracortical microstimulation system based on a novel architecture for wireless data and power transmission comprising inductive and capacitive couplings. The first chip is an energy-efficient stimuli generator (SG) and the second one is a highimpedance microelectrode array driver output-stage. The 4-channel stimuli-generator produces rectangular, half-sine (HS), plateau-sine (PS), and other types of energy-efficient current pulse. The SG is featured with low-power controller, current mode source- and sinkdigital- to-analog converters (DACs), multi-waveform generators, and 1.2V/3.3V interface current mirrors. The stimulation current per channel of the SG ranges from 2.32 to 220μA per channel. The second chip (microelectrode driver (MED)), an interface between the SG and the microelectrode array (MEA), supplies four different current levels with the maximum value of 400μA per input and 100μA per output channel. These currents can be delivered simultaneously to 8 to 16 stimulation sites through microelectrodes, connected either in bipolar or monopolar configuration. This output stage is highly-configurable and able to deliver higher compliance voltage across ETI impedance compared to previously reported designs. The nominal values of largest supply voltages are ±10V. The measured output compliance voltage is 10V/phase (anodic or cathodic) for the specified supply voltages. Increment of supply voltages to ±13V allows 220μA stimulation current per output channel enhancing the output compliance voltage up to 20V per phase. This output-stage is featured with a high-voltage switch-matrix, 3.3V/20V current mirrors, an on-chip 32-bit serial-in parallel-out shift register, and the forbidden state logic building blocks. The SG and MED chips have been designed and fabricated in IBM 0.13μm CMOS and Teledyne DALSA 0.8μm 5V/20V CMOS/DMOS technologies with silicon areas occupied by them 1.75 x 1.75mm2 and 4 x 4mm2 respectively. The measured DC power budgets consumed by low-and mid-voltage microchips are 2.56 and 2.1mW consecutively

Exploration of carbon nanotube composites and piezoelectric materials for implantable devices

This thesis describes an exploration of carbon nanotube (CNT) nanocomposites for application in implantable medical devices. The focus here is on materials and structures of interest as components of devices incorporating electrodes. Electrodes for implantable devices are commonly required to interface between an electrical system, where the charge carriers are electrons presented through a metal, and human tissue, where the charge carriers are ions as well as electrons not in a metal. These interfaces are found to be prone to issues such as fibrosis and rejection. The properties of carbon nanomaterials, piezoelectric peptides/polymers and their composites suggest them as promising candidate materials that could resolve these issues. The superior conductivity, mechanical properties and chemical stability of carbon nanotubes have been explored in recent years for potential application in biomedical sensors and devices. This work has explored piezoelectric materials, carbon nanotubes, polymers and nanocomposites of these as potential components of implantable devices. Diphenylalanine is a chiral, amphiphilic dipeptide molecule which has the ability to self-assemble into piezoelectric microtubules. The self-assembly process of diphenylalanine microtubules has been explored and its properties have been compared to the properties of poly[vinylidenefluoride-co-trifluoroethylene] (P[VDF-TrFE]) electrospun nanofibres. Later parts of this work considered the deposition of electrodes by printing. The development of CNT-polymer nanocomposites as printable inks for the fabrication of electrodes was explored. The structure and properties of the piezoelectric nano/ micro-materials, CNT-peptide complex and conductive CNT-polymer printable inks were characterised by a range of microscopic and spectroscopic techniques. The viability of neural cells on the developed functional materials and electrodes were tested by metabolic activity measurements and immunochemical staining microscopy. A CNT-polymer ink demonstrated good conductivity and dimensional stability when printed by 3D printer. Good biocompatibility of all the functional materials developed have been demonstrated in vitro, showing promise for further development of soft electrodes and applications in nanostructure piezoelectric sensors and implantable devices

Building And Validating Next-Generation Neurodevices Using Novel Materials, Fabrication, And Analytic Strategies

Technologies that enable scientists to record and modulate neural activity across spatial scales are advancing the way that neurological disorders are diagnosed and treated, and fueling breakthroughs in our fundamental understanding of brain function. Despite the rapid pace of technology development, significant challenges remain in realizing safe, stable, and functional interfaces between manmade electronics and soft biological tissues. Additionally, technologies that employ multimodal methods to interrogate brain function across temporal and spatial scales, from single cells to large networks, offer insights beyond what is possible with electrical monitoring alone. However, the tools and methodologies to enable these studies are still in their infancy. Recently, carbon nanomaterials have shown great promise to improve performance and multimodal capabilities of bioelectronic interfaces through their unique optical and electronic properties, flexibility, biocompatibility, and nanoscale topology. Unfortunately, their translation beyond the lab has lagged due to a lack of scalable assembly methods for incorporating such nanomaterials into functional devices. In this thesis, I leverage carbon nanomaterials to address several key limitations in the field of bioelectronic interfaces and establish scalable fabrication methods to enable their translation beyond the lab. First, I demonstrate the value of transparent, flexible electronics by analyzing simultaneous optical and electrical recordings of brain activity at the microscale using custom-fabricated graphene electronics. Second, I leverage a recently discovered 2D nanomaterial, Ti3C2 MXene, to improve the capabilities and performance of neural microelectronic devices. Third, I fabricate and validate human-scale Ti3C2 MXene epidermal electrode arrays in clinical applications. Leveraging the unique solution-processability of Ti3C2 MXene, I establish novel fabrication methods for both high-resolution microelectrode arrays and macroscale epidermal electrode arrays that are scalable and sufficiently cost-effective to allow translation of MXene bioelectronics beyond the lab and into clinical use. Thetechnologies and methodologies developed in this thesis advance bioelectronic technology for both research and clinical applications, with the goal of improving patient quality of life and illuminating complex brain dynamics across spatial scales

완전 이식형 시각 보철 시스템을 위한 연구

학위논문(박사)--서울대학교 대학원 :공과대학 전기·정보공학부,2020. 2. 김성준.A visual prosthetic system typically consists of a neural stimulator, which is a surgically implantable device for electrical stimulation intended to restore the partial vision of blind patients, and peripheral external devices including an image sensor, a controller, and a processor. Although several visual prosthetic systems, such as retinal prostheses or retinal implants, have already been commercialized, there are still many issues on them (e.g., substrate materials for implantable units, electrode configurations, the use of external hardware, power supply and data transmission methods, design and fabrication approaches, etc.) to be dealt with for an improved visual prosthetic system. In this dissertation, a totally implantable visual prosthetic system is suggested with four motivations, which are thought to be important, as in the following: 1) simple fabrication of implantable parts, such as micro-sized electrodes and a case, for a neural stimulator based on polymer without semiconductor techniques, 2) multi-polar stimulation for virtual channel generation to overcome a limited number of physical electrodes in a confined space, 3) a new image acquisition strategy using an implantable camera, and 4) power supply as well as data transmission to a neural stimulator without hindering patients various activities. First, polymer materials have been widely used to develop various implantable devices for visual prosthetic systems because of their outstanding advantages including flexibility and applicability to microfabrication, compared with metal, silicon, or ceramic. Most polymer-based implantable devices have been fabricated by the semiconductor technology based on metal deposition and photolithography. This technology provides high accuracy and precision for metal patterning on a polymer substrate. However, the technology is also complicated and time-consuming as it requires masks for photolithography and vacuum for metal deposition as well as huge fabrication facilities. This is the reason why biocompatible cyclic olefin polymer (COP) with low water absorption (<0.01 %) and high light transmission (92 %) was chosen as a new substrate material of an implantable device in this study. Based on COP, simple fabrication process of an implantable device was developed without masks, vacuum, and huge fabrication facilities. COP is characterized by strong adhesion to gold and high ultraviolet (UV) transparency as well. Because of such adhesion and UV transparency, a gold thin film can be thermally laminated on a COP substrate with no adhesion layer and micromachined by a UV laser without damaging the substrate. Using the developed COP-based process, a depth-type microprobe was fabricated first, and its electrochemical and mechanical properties as well as functionality were evaluated by impedance measurements, buckling tests, and in vivo neural signal recording, respectively. Furthermore, the long-term reliability of COP encapsulation formed by the developed process was estimated through leakage current measurements during accelerated aging in saline solution, to show the feasibility of the encapsulation using COP as well. Second, even if stimulation electrodes become sufficiently small, it is demanding to arrange them for precise stimulation on individual neurons due to electrical crosstalk, which is the spatial superposition of electric fields generated by simultaneous stimuli. Hence, an adequate spacing between adjacent electrodes is required, and this causes a limited number of physical electrodes in a confined space such as in the brain or in the retina. To overcome this limitation, many researchers have proposed stimulation strategies using virtual channels, which are intermediate areas with large magnitudes of electric fields between physical electrodes. Such virtual channels can be created by multi-polar stimulation that can combine stimuli output from two or more electrodes at the same time. To produce more delicate stimulation patterns using virtual channels herein, penta-polar stimulation with a grid-shaped arrangement of electrodes was leveraged specially to generate them in two dimensions. This penta-polar stimulation was realized using a custom-designed integrated circuit with five different current sources and surface-type electrodes fabricated by the developed COP-based process. The effectiveness of the penta-polar stimulation was firstly evaluated by focusing electric fields in comparison to mono-polar stimulation. In addition, the distribution of electric fields changed by the penta-polar stimulation, which indicated virtual channel generation, was estimated in accordance with an amplitude ratio between stimuli of the two adjacent electrodes and a distance from them, through both finite element analysis and in vitro evaluation. Third, an implantable camera is herein proposed as a new image acquisition approach capturing real-time images while implanted in the eye, to construct a totally implantable visual prosthetic system. This implantable camera has distinct advantages in that it can provide blind patients with benefits to perform several ordinary activities, such as sleep, shower, or running, while focusing on objects in accordance with natural eye movements. These advantages are impossible to be achieved using a wearing unit such as a glasses-mounted camera used in a conventional partially implantable visual prosthetic system. Moreover, the implantable camera also has a merit of garnering a variety of image information using the complete structure of a camera, compared with a micro-photodiode array of a retinal implant. To fulfill these advantageous features, after having been coated with a biocompatible epoxy to prevent moisture penetration and sealed using a medical-grade silicone elastomer to gain biocompatibility as well as flexibility, the implantable camera was fabricated enough to be inserted into the eye. Its operation was assessed by wireless image acquisition that displayed a processed black and white image. In addition, to estimate reliable wireless communication ranges of the implantable camera in the body, signal-to-noise ratio measurements were conducted while it was covered by an 8-mm-thick biological medium that mimicked an in vivo environment. Lastly, external hardware attached on the body has been generally used in conventional visual prosthetic systems to stably deliver power and data to implanted units and to acquire image signals outside the body. However, there are common problems caused by this external hardware, including functional failure due to external damages, unavailability during sleep, in the shower, or while running or swimming, and cosmetic issues. Especially, an external coil for power and data transmission in a conventional visual prosthetic system is connected to a controller and processor through a wire, which makes the coil more vulnerable to the problems. To solve this issue, a totally implantable neural stimulation system controlled by a handheld remote controller is presented. This handheld remote controller can control a totally implantable stimulator powered by a rechargeable battery through low-power but relatively long-range ZigBee wireless communication. Moreover, two more functions can be performed by the handheld controller for expanded applications; one is percutaneous stimulation, and the other is inductive charging of the rechargeable battery. Additionally, simple switches on the handheld controller enable users to modulate parameters of stimuli like a gamepad. These handheld and user-friendly interfaces can make it easy to use the controller under various circumstances. The functionality of the controller was evaluated in vivo, through percutaneous stimulation and remote control especially for avian navigation, as well as in vitro. Results of both in vivo experiments were compared in order to verify the feasibility of remote control of neural stimulation using the controller. In conclusion, several discussions on results of this study, including the COP-based simple fabrication process, the penta-polar stimulation, the implantable camera, and the multi-functional handheld remote controller, are addressed. Based on these findings and discussions, how the researches in this thesis can be applied to the realization of a totally implantable visual prosthetic system is elucidated at the end of this dissertation.시각 보철 시스템은 일반적으로 실명 환자들의 부분 시력을 전기 자극으로 회복시키기 위하여 수술적으로 이식될 수 있는 장치인 신경 자극기와 이미지 센서 또는 컨트롤러, 프로세서를 포함하는 외부의 주변 장치들로 구성된다. 망막 보철 장치 또는 망막 임플란트와 같이 몇몇 시각 보철 시스템은 이미 상용화 되었지만, 여전히 더 나은 시각 보철 시스템을 위하여 다뤄져야 할 많은 이슈들 (예를 들어, 이식형 장치의 기판 물질, 전극의 배열, 외부 하드웨어의 사용, 전력 공급 및 데이터 전송 방법, 설계 및 제작 방식 등)이 있다. 본 학위논문은 완전 이식형 시각 보철 시스템을 제안하며, 이를 위하여 다음과 같이 중요하다고 생각되는 총 네 가지의 이슈들과 관련된 연구 내용을 다룬다. 1) 폴리머를 기반으로 한 신경 자극기의 미세 전극 및 패키지와 같은 이식 가능한 부분을 반도체 기술 없이 간단하게 제작하는 방법과 2) 제한된 공간에서 전극 개수의 물리적인 한계를 극복하기 위하여 가상 채널을 형성하는 다극성 자극 방식, 3) 이식형 카메라를 사용하는 새로운 이미지 획득 전략, 4) 환자의 다양한 활동을 방해하지 않으면서 신경 자극기에 전력을 공급하고 데이터를 전송하는 방법. 첫째로, 금속이나 실리콘, 세라믹에 비하여 폴리머는 유연성 및 미세 제작에의 적용 가능성을 포함하는 두드러진 이점들이 있기 때문에 시각 보철 시스템을 구성하는 다양한 이식 가능한 부분들에 널리 이용되었다. 대부분의 폴리머 기반 이식형 장치들은 금속 증착과 사진 식각을 기반으로 하는 반도체 공정으로 제작되었다. 이 공정은 폴리머 기판 위에 금속을 패터닝 하는 데에 있어서 높은 정확성과 정밀도를 제공한다. 하지만 그 공정은 또한, 사진 식각에 쓰이는 마스크와 금속 증착을 위한 진공뿐만 아니라 아주 큰 공정 설비를 요구하기 때문에 시간 소모가 심하고 복잡하다. 이는 본 연구에서 낮은 수분 흡수 (<0.01 %)와 높은 빛 투과 (92 %)를 특징으로 하는 생체적합한 고리형 올레핀 폴리머 (cyclic olefin polymer, COP)가 이식형 장치를 위한 새로운 기판 물질로써 선택된 이유이다. COP를 기반으로 하여, 마스크와 진공, 큰 공정 설비가 필요 없이 이식 가능한 장치를 간단하게 제작하는 공정이 개발되었다. COP는 금과의 강한 접합과 자외선에 대한 높은 투명성을 또 다른 특징으로 한다. 이와 같은 접합 특성과 자외선 투명성 덕분에, 금박은 COP 기판에 별도의 접합층 없이 열로 접합될 수 있을 뿐만 아니라 그 기판에 손상을 주지 않으면서 자외선 레이저를 통하여 미세하게 가공될 수 있다. 개발된 COP 기반의 공정을 처음으로 사용하여 침습형 미세 프로브가 제작되었고, 그 전기화학적, 기계적 특성과 기능성이 각각 임피던스 측정과 버클링 테스트, 생체 내 신경신호 기록으로 평가되었다. 그리고 COP를 사용한 밀봉의 가능성도 알아보기 위하여, 개발된 공정을 사용하여 형성된 COP 밀봉의 장기 안정성이 생리식염수에서의 가속 노화 중 누설 전류 측정을 통하여 추정되었다. 둘째로, 자극 전극의 크기가 충분히 작아진다고 하더라도, 동시에 출력되는 자극에 의해 형성되는 전기장의 중첩인 크로스 토크 때문에 개개의 신경세포를 정밀하게 자극하기 위하여 전극을 배열하는 것은 아주 어렵다. 따라서 인접한 전극 사이에 적당한 간격이 필요하게 되고, 이는 특히 뇌 또는 망막과 같은 제한된 공간에서 전극 개수의 물리적인 한계를 야기한다. 이 한계를 극복하기 위하여, 많은 연구자들은 실제 전극 사이에서 큰 전기장 세기를 갖는 중간 영역을 나타내는 가상 채널을 이용한 자극 전략을 제안하였다. 이러한 가상 채널은 둘 이상의 전극에서 동시에 출력되는 자극 파형을 합칠 수 있는 다극성 자극에 의하여 형성이 가능하다. 본 연구에서는 가상 채널을 이용하여 더 정교한 자극 패턴을 만들기 위하여, 특히 2차원에서의 가상 채널을 생성하고자 격자형 배열의 전극과 함께 5극성 자극이 사용되었다. 이 5극성 자극은 다섯 개의 서로 다른 전류원을 갖도록 맞춤 설계된 집적회로와 개발된 COP 기반 공정으로 제작된 평면형 전극을 사용하여 구현되었다. 먼저, 5극성 자극의 효과를 확인하고자 이 자극으로 전기장을 한 곳에 더 집중된 형태로 만들 수 있음이 단극성 자극과의 비교를 통하여 검증되었다. 그리고 유한 요소 분석과 생체 외 평가 둘 모두를 통하여, 5극성 자극으로 인한 가상 채널 형성을 뜻하는 전기장 분포가 인접한 두 전극에서 나오는 자극의 진폭비와 그 전극으로부터 떨어진 거리에 따라 변화됨이 추정되었다. 셋째로, 본 연구에서는 눈에 이식된 채로 실시간 이미지를 얻음으로써 완전 이식형 시각 보철 시스템을 구성하는 이식형 카메라를 새로운 이미지 획득 방식으로써 제안한다. 이 이식형 카메라는 실명 환자들이 자연스러운 눈의 움직임을 따라서 물체를 볼 수 있으며 잠이나 샤워, 달리기와 같은 일상적인 활동들을 방해 받지 않고 수행할 수 있도록 돕는다는 점에서 독특한 장점을 갖는다. 기존의 부분 이식형 시각 보철 시스템에서 쓰이는 안경 부착형 카메라와 같은 착용 장비로는 이러한 장점들을 얻을 수 없다. 게다가, 이식형 카메라는 망막 임플란트의 미세 포토다이오드 어레이와 달리 완전한 카메라 구조를 이용하여 다양한 이미지 정보를 획득할 수 있다는 장점을 갖는다. 이러한 이점들을 달성하기 위하여, 그 이식형 카메라는 수분 침투를 막고자 생체적합한 에폭시로 코팅되었고 생체적합성과 유연성을 얻기 위하여 의료용 실리콘 엘라스토머로 밀봉된 후에 눈에 충분히 삽입될 수 있는 형태 및 크기로 제작되었다. 이 장치의 동작은 흑백으로 처리된 이미지를 표시하는 무선 이미지 획득으로 시험되었다. 그리고 몸 안에서 이식형 카메라 갖는 안정적인 통신 거리를 측정하기 위하여, 장치가 생체 내 환경을 모사하기 위한 8 mm 두께의 생체 물질로 덮인 상태에서 그 장치의 신호 대 잡음비가 측정되었다. 마지막으로, 기존의 시각 보철 시스템에서 몸에 부착된 형태의 외부 하드웨어는 이식된 장치에 전력과 데이터를 안정적으로 전달하고 이미지 신호를 수집하기 위하여 일반적으로 사용되었다. 그럼에도 불구하고, 이러한 하드웨어는 외부로부터의 손상으로 인한 기능적인 결함과 수면 및 샤워, 달리기, 수영 활동 중 이용 불가능성, 외형적인 이슈 등을 포함하는 공통적인 문제들을 야기한다. 전력 및 데이터 전송을 위한 외부 코일은 시각 보철 시스템에서 컨트롤러와 프로세서에 유선으로 연결되고, 이러한 연결은 그 코일이 앞서 언급된 문제들에 특히 취약하게 만든다. 이러한 이슈를 해결하고자, 휴대용 무선 컨트롤러로 제어되는 완전 이식형 신경 자극 시스템이 제안된다. 이 휴대용 무선 컨트롤러는 저전력이지만 비교적 장거리 통신이 가능한 직비 (ZigBee) 무선 통신을 통하여 재충전 가능한 배터리로 동작하는 완전 이식형 자극기를 제어할 수 있다. 이 외에도, 이 휴대용 컨트롤러를 사용하면 폭넓은 응용을 위한 두 가지 기능을 추가로 수행할 수 있다. 하나는 유선 경피 자극이며, 다른 하나는 재충전 가능한 배터리의 유도 충전 기능이다. 또한, 이 휴대용 컨트롤러의 간단한 스위치를 사용하면 사용자는 게임패드와 같이 자극 파라미터를 쉽게 조절할 수 있다. 이러한 휴대 가능하고 사용자 친화적인 인터페이스를 통해 다양한 상황에서 그 컨트롤러를 쉽게 사용할 수 있다. 그 컨트롤러의 기능은 생체 외 평가뿐만 아니라 조류의 움직임 제어를 위한 유선 경피 자극 및 원격 제어를 통해 생체 내에서도 평가되었다. 또한, 그 컨트롤러를 사용한 원격 신경 자극 제어의 수행 가능성을 검증하기 위하여 두 생체 내 실험의 결과가 서로 비교되었다. 결론적으로, COP 기반의 간단한 제작 공정과 5극성 자극, 이식형 카메라, 휴대용 다기능 무선 컨트롤러를 포함하는 연구 결과에 대한 여러 논의가 이루어진다. 그리고 이러한 결과와 고찰에 기초하여, 본 학위논문의 연구가 완전 이식형 시각 보철 시스템의 구현에 어떻게 적용될 수 있는 지가 이 논문의 끝에서 상세히 설명된다.Abstract ------------------------------------------------------------------ i Contents ---------------------------------------------------------------- vi List of Figures ---------------------------------------------------------- xi List of Tables ----------------------------------------------------------- xx List of Abbreviations ------------------------------------------------ xxii Chapter 1. Introduction --------------------------------------------- 1 1.1. Visual Prosthetic System --------------------------------------- 2 1.1.1. Current Issues ------------------------------------------------- 2 1.1.1.1. Substrate Materials ---------------------------------------- 3 1.1.1.2. Electrode Configurations --------------------------------- 5 1.1.1.3. External Hardware ----------------------------------------- 6 1.1.1.4. Other Issues ------------------------------------------------- 7 1.2. Suggested Visual Prosthetic System ------------------------ 8 1.3. Four Motivations ---------------------------------------------- 10 1.4. Proposed Approaches ---------------------------------------- 11 1.4.1. Cyclic Olefin Polymer (COP) ------------------------------ 11 1.4.2. Penta-Polar Stimulation ----------------------------------- 13 1.4.3. Implantable Camera --------------------------------------- 16 1.4.4. Handheld Remote Controller ---------------------------- 18 1.5. Objectives of this Dissertation ------------------------------ 20 Chapter 2. Materials and Methods ----------------------------- 23 2.1. COP-Based Fabrication and Encapsulation -------------- 24 2.1.1. Overview ----------------------------------------------------- 24 2.1.2. Simple Fabrication Process ------------------------------- 24 2.1.3. Depth-Type Microprobe ---------------------------------- 26 2.1.3.1. Design ----------------------------------------------------- 26 2.1.3.2. Characterization ----------------------------------------- 27 2.1.3.3. In Vivo Neural Signal Recording ---------------------- 30 2.1.4. COP Encapsulation ---------------------------------------- 31 2.1.4.1. In Vitro Reliability Test ---------------------------------- 33 2.2. Penta-Polar Stimulation ------------------------------------- 34 2.2.1. Overview ---------------------------------------------------- 34 2.2.2. Design and Fabrication ----------------------------------- 35 2.2.2.1. Integrated Circuit (IC) Design ------------------------- 35 2.2.2.2. Surface-Type Electrode Fabrication ------------------ 38 2.2.3. Evaluations -------------------------------------------------- 39 2.2.3.1. Focused Electric Field Measurement ---------------- 42 2.2.3.2. Steered Electric Field Measurement ----------------- 42 2.3. Implantable Camera ----------------------------------------- 43 2.3.1. Overview ---------------------------------------------------- 43 2.3.2. Design and Fabrication ----------------------------------- 43 2.3.2.1. Circuit Design -------------------------------------------- 43 2.3.2.2. Wireless Communication Program ------------------ 46 2.3.2.3. Epoxy Coating and Elastomer Sealing -------------- 47 2.3.3. Evaluations ------------------------------------------------- 50 2.3.3.1. Wireless Image Acquisition --------------------------- 50 2.3.3.2. Signal-to-Noise Ratio (SNR) Measurement -------- 52 2.4. Multi-Functional Handheld Remote Controller --------- 53 2.4.1. Overview ---------------------------------------------------- 53 2.4.2. Design and Fabrication ----------------------------------- 53 2.4.2.1. Hardware Description ---------------------------------- 53 2.4.2.2. Software Description ----------------------------------- 57 2.4.3. Evaluations -------------------------------------------------- 57 2.4.3.1. In Vitro Evaluation -------------------------------------- 57 2.4.3.2. In Vivo Evaluation --------------------------------------- 59 Chapter 3. Results ------------------------------------------------- 61 3.1. COP-Based Fabrication and Encapsulation ------------- 62 3.1.1. Fabricated Depth-Type Microprobe ------------------- 62 3.1.1.1. Electrochemical Impedance -------------------------- 63 3.1.1.2. Mechanical Characteristics --------------------------- 64 3.1.1.3. In Vivo Neural Signal Recording --------------------- 66 3.1.2. COP Encapsulation --------------------------------------- 68 3.1.2.1. In Vitro Reliability Test --------------------------------- 68 3.2. Penta-Polar Stimulation ------------------------------------ 70 3.2.1. Fabricated IC and Surface-Type Electrodes ---------- 70 3.2.2. Evaluations ------------------------------------------------- 73 3.2.2.1. Focused Electric Field Measurement --------------- 73 3.2.2.2. Steered Electric Field Measurement ---------------- 75 3.3. Implantable Camera ---------------------------------------- 76 3.3.1. Fabricated Implantable Camera ----------------------- 76 3.3.2. Evaluations ------------------------------------------------ 77 3.3.2.1. Wireless Image Acquisition -------------------------- 77 3.3.2.2. SNR Measurement ------------------------------------ 78 3.4. Multi-Functional Handheld Remote Controller ------- 80 3.4.1. Fabricated Remote Controller ------------------------- 80 3.4.2. Evaluations ------------------------------------------------ 81 3.4.2.1. In Vitro Evaluation ------------------------------------ 81 3.4.2.2. In Vivo Evaluation ------------------------------------- 83 Chapter 4. Discussions ------------------------------------------ 86 4.1. COP-Based Fabrication and Encapsulation ------------ 87 4.1.1. Fabrication Process and Fabricated Devices -------- 87 4.1.2. Encapsulation and Optical Transparency ------------ 89 4.2. Penta-Polar Stimulation------------------------------------ 99 4.2.1. Designed IC and Electrode Configurations --------- 99 4.2.2. Virtual Channels in Two Dimensions ---------------- 101 4.3. Implantable Camera -------------------------------------- 102 4.3.1. Enhanced Reliability by Epoxy Coating ------------- 106 4.4. Multi-Functional Handheld Remote Controller ------ 107 4.4.1. Brief Discussions of the Two Extra Functions ------ 108 4.5. Totally Implantable Visual Prosthetic System --------- 113 Chapter 5. Conclusion ------------------------------------------ 117 References -------------------------------------------------------- 121 Supplements ------------------------------------------------------ 133 국문 초록 ----------------------------------------------------------- 143Docto

Functional Electrical Stimulation of Peripheral Nerve Tissue Via Regenerative Sieve Microelectrodes

Functional electrical stimulation (FES) of peripheral nervous tissue offers a promising method for restoring motor function in patients suffering from complex neurological injuries. However, existing microelectrodes designed to stimulate peripheral nerve are unable to provide the type of stable, selective interface required to achieve near-physiologic control of peripheral motor axons and distal musculature. Regenerative sieve electrodes offer a unique alternative to such devices, achieving a highly stable, selective electrical interface with independent groups of regenerated nerve fibers integrated into the electrode. Yet, the capability of sieve electrodes to functionally recruit regenerated motor axons for the purpose of muscle activation remains largely unexplored. The present dissertation aims to examine the potential role of regenerative electrodes in FES applications by testing the unifying hypothesis that sieve electrodes of various design and geometry are capable of selectively stimulating regenerated motor axons for the purpose of controlling muscle activation. This hypothesis was systematically tested through a series of experiments examining the ability of both micro-sieve electrodes and macro-sieve electrodes to achieve a stable interface with peripheral nerve tissue, electrically activate small groups of regenerated motor axons, and selectively recruit motor units present in multiple distal muscles. Custom sieve electrodes were fabricated via sacrificial photolithography. In vivo testing in rat sciatic nerve validated the ability of chronically-implanted regenerative sieve electrodes to support motor axon regeneration and integrate into peripheral nerve tissue. Sieve electrode geometry was shown to strongly modulate axonal regeneration, muscle reinnervation, and device functionality, as high-transparency macro-sieve electrodes facilitated superior neural integration and functional recovery compared to low-transparency micro-sieve electrodes. Inclusion of neurotrophic factors into sieve electrode assemblies increased axonal regeneration through implanted electrodes and improved the quality of the sieve/nerve interface in low-transparency devices. In vivo testing in rat sciatic nerve further validated the ability of chronically-implanted regenerative sieve electrodes to facilitate FES of regenerated motor axons and selective recruitment of distal musculature. Selective stimulation of regenerated motor axons using implanted micro- and macro-sieve electrodes enabled effective, external control of muscle activation within anterior and posterior compartments of the lower leg (e.g. ankle plantarflexion / dorsiflexion). Selective activation of distal musculature was achieved through modulation of stimulus amplitude, channel activation, and field steering. In summary, the present body of work provides initial evidence of the utility of regenerative electrodes as a means of selectively interfacing peripheral nerve tissue for the purpose of restoring muscle activation and motor control. These findings further highlight the clinical potential of implantable microelectrodes capable of intimately integrating into host neural tissue

Numerical modeling of dielectrophoretic effect for manipulation of bio-particles

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.This text describes different aspects of the design of a Doctor-on-a-Chip device. Doctor-on-a-Chip is a DNA analysis system integrated on a single chip, which should provide all of the advantages that stem from the system integration, such as small sample volume, fast and accurate analysis, and low cost. The text describes all of the steps of the on-chip sample analysis, including DNA extraction from the sample, purification, PCR amplification, novel dielectrophoretic sorting of the DNA molecules, and finally detection. The overview is given of the technologies which are available to make the integration on a single chip possible. The microfluidic technologies that are used to manipulate the sample and other chemical reagents are already known and in this text they are analyzed in terms of their feasibility in the on-chip system integration. These microfluidic technologies include, but are not limited to, microvalves, micromixers, micropumps, and chambers for PCR amplification. The novelty in the DNA analysis brought by Doctor-on-a-Chip is the way in which the different DNA molecules in the sample (for example, human and virus DNA) are sorted into different populations. This is done by means of dielectrophoresis – the force experienced by dielectric particles (such as DNA molecules) when subject to a non-uniform electric field. Different DNA molecules within a sample experience different dielectrophoretic forces within the same electric field, which makes their separation, and therefore detection, possible. In this text, the emphasis is put on numerical modelling of the dielectrophoretic effect on biological particles. The importance of numerical modelling lies in the fact that with the accurate model it is easier to design systems of microelectrodes for dielectrophoretic separation, and tune their sub-micrometre features to achieve the maximum separation efficacy. The numerical model described in this text is also experimentally verified with the novel microelectrodes design for dielectrophoretic separation, which is successfully used to separate the mixture of different particles in the micron and sub-micron range