Chronic nerve recording and stimulation can be performed by means of nerve cuff electrodes in both animals and humans. These extraneural electrodes have been used not only for fundamental research but also for rehabilitation purposes as part of a neuroprosthetic device. They have therefore contributed to our knowledge of the nervous system and also allowed partial motor and sensory rehabilitation. However, the performance of existing nerve cuff electrodes remains limited and their designs must be improved. The main drawbacks of cuff electrodes are their poor selectivity and the morphological modifications they induce to surrounding tissue. Their selectivity is mainly dependant on the number of contacts which is limited by the hand-made manufacturing process. The morphological modifications are determined by the tissue-electrode interactions. A new spiral cuff nerve electrode is proposed to improve the selectivity and lessen the tissue reaction. The manufacture of this new electrode, based on photolithographic metal deposition technology, should allow for an increased number of contacts. Additionally, this electrode has self-sizing properties that potentially lowers the implant-induced tissue reaction. The present work aims to study the interactions between the electrode and implanted tissue in an attempt to better characterise the tissue reaction and to further control it. Firstly, the interactions between connective tissue and the laser-irradiated-platinum-metallised silicone rubber are assessed both with in vitro and in vivo methods. The cytocompatibility and biocompatibility of silicone is not altered by the platinum deposition process, suggesting that this new biomaterial can be used to manufacture cuff electrodes that can safely be implanted for chronic studies. The mechanical biocompatibility of spiral cuff nerve electrodes is then investigated by morphological, immunohistochemical and western-blots analyses. The peri-operative, acute and chronic events that are related to the implantation are studied. The results show that the commonly described fibrotic reaction surrounding the implant is preceded by an important early epineurial inflammation. Additionally, cytokines involved in this tissue reaction are identified and include the pro-inflammatory cytokine TNF-alpha and pro-fibrotic cytokine TGF-beta1. In continuation of the biocompatibility testing, cytokine neutralisation through monoclonal antibodies is proposed as a way to control some of the cuff electrode-induced tissue modifications. Immunohistochemistry and morphometry are used to demonstrate the feasibility of such a control. Results show that a single systemic injection of TNF-alpha neutralising antibodies is sufficient to reduce the early inflammatory reaction occurring in the epineurial compartment but not the subsequent fibrosis. The success of an implanted neuroprosthesis is fully dependant upon the interaction between the electrode and the surrounding tissue. This study suggests that, when trying to improve the design of an electrode, one should also consider the modulation of the tissue reaction as a convenient way to enhance the implanted electrode's long-term performance. / L'enregistrement et la stimulation chroniques de nerfs peuvent être réalisés au moyen d'électrodes neurales à manchon, aussi bien chez l'animal que chez l'homme. Ces électrodes extra-neurales ont été utilisées non seulement dans le cadre de recherches fondamentales mais aussi à des fins de réhabilitation au sein d'un dispositif neuro-prosthétique. Elles ont ainsi contribué à notre connaissance du système nerveux et ont parfois permis une restauration sensorielle et motrice partielle. Les performances des électrodes existantes demeurent cependant limitées et leur design doit être amélioré. Les principales faiblesses de ces électrodes à manchon sont leur sélectivité, insuffisante, et les modifications morphologiques qu'elles induisent au sein des tissus implantés. La sélectivité des électrodes dépend principalement du nombre de contacts que limite un procédé de fabrication manuel. Les modifications morphologiques sont, quant à elles, déterminées par les interactions entre les tissus et l'électrode. Une nouvelle électrode neurale, dite à manchon spiral, est proposée qui devrait accroître la sélectivité et réduire la réaction tissulaire. La fabrication de cette nouvelle électrode, basée sur la technologie de déposition photolithographique de métaux, devrait permettre d'augmenter le nombre de contacts. De plus, en raison de son aptitude à s'adapter au diamètre du nerf, cette électrode devrait potentiellement limiter la réaction tissulaire induite par l'implant. Le but de ce travail est d'étudier les interactions entre l'électrode et les tissus implantés afin de mieux caractériser la réaction tissulaire et, ultérieurement, la contrôler. Dans un premier temps, les interactions entre les tissus conjonctifs et le silicone après son irradiation au laser et sa métallisation sont testées au moyen de méthodes in vitro et in vivo. La cyto-compatibilité et la biocompatibilité du silicone ne sont pas altérées pas le procédé de dépôt du platine. Ceci suggère que ce nouveau biomatériau convient à la manufacture d'électrodes à manchon qui pourront être implantées chroniquement de façon sûre. Dans un second temps, la biocompatibilité mécanique des électrodes à manchon spiral est examinée au moyen d'analyses morphologiques, immunohistochimiques et de western-blots. Les événements péri-opératoires, aigus et chroniques liés à l'implantation sont étudiés. Les résultats montrent qu'une importante réaction inflammatoire précoce précède la réaction fibrotique autour de l'électrode, classiquement décrite après une implantation. De plus, une partie des cytokines impliquée dans la réaction tissulaire est identifiée: la cytokine pro-inflammatoire TNF-alpha et la cytokine pro-fibrotique TGF-beta1. Dans la continuité des études de biocompatibilité, la neutralisation de cytokine au moyen d'anticorps monoclonaux est proposé comme moyen de contrôle de modifications tissulaires induite par l'électrode à manchon. L'immunohistochimie et la morphométrie sont utilisées pour démontrer la possibilité d'un tel contrôle. Le résultats montrent qu'une seule injection systémique d'anticorps anti-TNF-alpha est suffisante pour réduire la réaction inflammatoire précoce dans le compartiment épineurial mais pas la fibrose subséquente. Le succès d'une neuroprothèse implantable dépend entièrement des interactions entre l'électrode et les tissus environnants. Cette étude suggère que, lors des tentatives d'amélioration du design des électrodes, la modulation de la réaction tissulaire devrait être considérée comme un moyen aisé d'augmenter les performances à long terme des électrodes implantées.

Within the field of neuroprosthetics the possibility to use implanted electrodes for communication with the nervous system is explored. Much effort is put into the material aspects of the electrode implant to increase charge injection capacity, suppress foreign body response and build micro sized electrode arrays allowing close contact with neurons. Conducting polymers, in particular poly(3,4-ethylene dioxythiophene) (PEDOT), have been suggested as materials highly interesting for such neural communication electrodes. The possibility to tailor the material both mechanically and biochemically to suit specific applications, is a substantial benefit with polymers when compared to metals. PEDOT also have hybrid charge transfer properties, including both electronic and ionic conduction, which allow for highly efficient charge injection.   Part of this thesis describes a method of tailoring PEDOT through exchanging the counter ion used in electropolymerisation process. Commonly used surfactants can thereby be excluded and instead, different biomolecules can be incorporated into the polymer. The electrochemical characteristics of the polymer film depend on the ion. PEDOT electropolymerised with heparin was here determined to have the most advantageous properties. In vitro methods were applied to confirm non-cytotoxicity of the formed PEDOT:biomolecular composites. In addition, biocompatibility was affirmed for PEDOT:heparin by evaluation of inflammatory response and neuron density when implanted in rodent cortex.   One advantage with PEDOT often stated, is its high stability compared to other conducting polymers. A battery of tests simulating the biological environment was therefore applied to investigate this stability, and especially the influence of the incorporated heparin. These tests showed that there was a decline in the electroactivity of PEDOT over time. This also applied in phosphate buffered saline at body temperature and in the absence of other stressors. The time course of degradation also differed depending on whether the counter ion was the surfactant polystyrene sulphonate or heparin, with a slightly better stability for the former.   One possibility with PEDOT, often overlooked for biological applications, is the use of its semi conducting properties in order to include logic functions in the implant. This thesis presents the concept of using PEDOT electrochemical transistors to construct textile electrode arrays with in-built multiplexing. Using the electrolyte mediated interaction between adjacent PEDOT coated fibres to switch the polymer coat between conducting and non conducting states, then transistor function can be included in the conducting textile. Analogue circuit simulations based on experimentally found transistor characteristics proved the feasibility of these textile arrays. Developments of better polymer coatings, electrolytes and encapsulation techniques for this technology, were also identified to be essential steps in order to make these devices truly useful.   In summary, this work shows the potential of PEDOT to improve neural interfaces in several ways. Some weaknesses of the polymer and the polymer electronics are presented and this, together with the epidemiological data, should point in the direction for future studies within this field. / QC 20100623

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 electrode is inserted in the brain without stiffening it by coating with foreign material or by attaching a rigid support and hence the method is less invasive. Based on two new mechanisms, namely spinning and guided insertion, it is possible to insert ultra-thin micro-wire flexible electrodes in rodent brains without buckling. I have demonstrated successful insertion of 25 µm platinum micro-wire electrodes about 10 mm deep in rat brain. A novel micro-motion compensated ultra-thin flexible platinum microelectrode has been presented for chronic single unit recording. Since manual insertion of the proposed microelectrode is not possible, I have developed a microelectrode insertion device based on the proposed method. A low power low noise 16 channel programmable neural amplifier ASIC has been designed and used to record the neural spikes. The ability to record neural activity during insertion is a unique feature of the developed inserter. In vivo implantation process of the microelectrode has been demonstrated. Microelectrodes were inserted in the Botzinger complex of rat and long term respiratory related neural activity was recorded from live rats. The developed microelectrode has also been used to study brain activity during seizures. In-vivo experimental results show that the proposed method and the prototype insertion system can be used to implant flexible microelectrode in deep brain structures of rodent for brain studies.

<div>The present thesis was completed to satisfy two functions in our laboratory: (1) explore carbon-black (CB) as an additive for electrodeposited intrinsically conductive polymers (ICPs) to improve electrical properties across the electrode-electrolyte interface for use in neuromodulation; and (2) design a histology protocol that will analyze peripheral nerve system (PNS) tissue following implantation of conventional metal and modified conventional metal electrodes with the ICP poly(3,4-ethylenedioxythiophere):poly(styrenesulfonate)/carbon-black (PEDOT:PSS/CB). It would appear that the functions explored may seem unrelated, however, these two topics play a crucial role in designing a viable electrode for use in acute and chronic neuromodulation and the subsequent analysis required to determine the mechanical properties and overall biocompatibility of design.</div><div><br></div><div><div>A series of experiments with different PEDOT:PSS solutions containing varying amounts of suspended CB (n=19; 0 mg/mL to 2 mg/mL) were explored. Solutions were characterized using cyclic voltammetry (CV) using the intended electrode for deposition, composed of stainless steel (SS), as the working electrode (WE) to determine respective redox potentials. SS was chosen because of its inherently bad electrochemical properties, meaning that improved functionality post electrodeposition would be easy to identify. Immediately following CV, stainless-steel electrodes were electrodeposited using one of two techniques: (1) potentiostat, allowing the cell to rest at the redox potential required for bipolaron formation (0.9 V); or (2) galvanostat, where the electrode was submitted to a constant current of 200 mA and allowed to coat. Rapid electrochemical impedance spectroscopy was performed prior to and immediately following coating to determine the pre-electrochemical and post-electrochemical impedance characteristics. Results indicate that there was a positive relationship between the amount of CB additive and the relative impedance drop between the uncoated and coated counterparts. Furthermore, the modified electrochemical interfaces are substantially improved for use in frequency ranges of 10 Hz to 50 kHz, which encompass the ranges of our labs recently discovered low frequency alternating current (LFAC) for use in neuromodulation; thus indicating that PEDOT:PSS/CB modification may be used to improve impedance characteristics during our future LFAC experiments. This protocol, the one that contains the ideal concentration of carbon-black, was then recorded and will be used in our lab.</div></div><div><br></div><div><div>Histology protocols were developed to improve our labs capabilities of post-mortem analysis of PNS tissue. Processing and embedding preparations that explored included paraffin, acrylic, and frozen. Subsequently, staining protocols were developed; however, they varied as a function of the embedding media used; staining protocols developed incorporated progressive and regressive hematoxylin and eosin (H&E) staining as well as toluidine blue (TB). Tissue was sectioned and observed using light microscopy.</div></div>