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%0 Thesis
%A Brusius, Janis Sebastian
%T 3-dimensionale penetrierende Multielektrodenarrays zur Stimulation und Ableitung in der Retina
%I RWTH Aachen University
%V Dissertation
%C Aachen
%M RWTH-2015-01074
%P VII, 147 Bl. : Ill., graph. Darst.
%D 2015
%Z Aachen, Techn. Hochsch., Diss., 2015
%X A variety of retinal degenerating diseases leads to the loss of photoreceptor cells, causing the retina to lose its light-sensitivity. Several million people worldwide are suffering from those degenerative diseases.Retinal prostheses try to replace the functionality of photoreceptor cells by electrically stimulating the remaining neurons of the retinal network.Previous retinal implants use planar multi-electrode arrays (MEAs), covering the retinal network in a 2–dimensional manner. Those MEAs usually contact only single layers within the retina and are not capable of recording the neuronal response and stimulate electrically through the same device. Relief could derive from penetrating, bidirectional MEAs, which penetrate the retina in the vertical direction and are able to both, record neuronal activity and perform electrical stimulation.The main aim of this thesis was the development of a penetrating, bidirectional MEA, with which multiple layers of the retinal network can be recorded and stimulated simultaneously. The MEA presented in this thesis consists of four shanks penetrating the retina in vertical direction. Every single shank carries four linearly aligned electrodes. The dimensions of the MEA and the arrangement of the electrodes were chosen in a way they could serve as the basis of a retinal implant.Different materials were used for coating the microelectrodes: iridium, iridiumoxide and the conductive polymer poly-3,4-ethylendioxythiphene. Their appropriateness to act as coatings on stimulation and recording electrodes was tested. Iridiumoxide proved to have the best mechanical and chemical stability. The lowest impedances were achieved with PEDOT coatings. Only with PEDOT-coated electrodes, it was possible to transfer sufficient charge to elicit neuronal responses. However, PEDOT coatings were easily degraded by mechanical and chemical influences during the experiments as shown by impedance spectroscopy and electron microscopy imaging.In the second part of this thesis the new penetrating MEAs were used for the first time to perform experiments in the extracted retina of rats. A method was established to reliably position the MEAs, monitoring the electrical activity of retinal ganglion cells.Different stimulation parameters were used to successfully stimulate close to the retinal bipolar cells. The ganglion cells’ reaction to the electrical stimulation of the network was recorded extracellularly. The success of electrical stimulation mainly depended on the absolute amount of charge transferred to the tissue and the frequency of stimulation patterns. By pharmacologically blocking the synaptic transmission within the retina, it could be shown that the stimulation affected the deeper retinal layers – presumably the bipolar cells.By means of penetrating MEAs, characteristic low-frequency oscillations could be measured in the degenerated retina of rd10 mice. By reversibly blocking the synaptic transmission, it could be shown that the chosen MEA-architecture is feasible for the use in a future bidirectional retinal implant.
%F PUB:(DE-HGF)11
%9 Dissertation / PhD Thesis
%U https://publications.rwth-aachen.de/record/463850