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"Investigation of surface properties of boron doped diamond for developing neuron -machine interface."

The main goal of this thesis is to study how diamond films advance the construction of the hybrid biological-solid state interfaces and to construct Micro-Electrode Arrays (MEAs) for neural recordings.  First, a literature study was carried out to review diamond applications in biology for in vitro and in  vivo and for Microelectrode arrays (MEAs). In order to develop diamond MEAs, nano crystalline  diamond (NCD) and boron-doped nano crystalline diamond (BNCD) were synthetized on fused silica  substrates, featuring the insulating and conductive properties, respectively. These diamond films were  employed for construction of neuron-device interfaces. The fabrication of the electrode arrays was  achieved by performing different microfabrication techniques such as photo lithography, metal  deposition and wet and dry etching. The resulting flat diamond MEAs on fused silica were characterized  by different techniques. Finally, cortical brain slices from rats were used to evaluate the neural signal  measurements on the diamond MEA.

The next goal was to construct flexible diamond MEAs as implantable electrodes. These flexible  diamond electrodes were to function as Electromyography (EMG) for experiments in vivo. To provide  mechanical flexibility, polyimide as a biocompatible polymer was employed, which featured also  interesting chemical and physical properties. The NCD served as the insulating part and BNCD was  integrated as the conductive electrode material. The polyimide preformed as the second insulating  layer. However, the first series of NCD-BNCD- polyimide electrodes showed mechanical problems.  Therefore, the fabrication plan was carefully investigated, adapted and finally a new plan was  introduced, to improve and advance the electrodes. The final successful flexible diamond-polyimide  MEAs consisted of BNCD-polyimide with gold interlayers. The electrodes were carefully characterized in  every step by different techniques.

In the path towards developing the neuron-machine interface, a new method was explored and  introduced, using Polyethyleneimine (PEI) monolayers. This precise coating method was developed and  applied to treat the surface of diamond to enable the neuron growth from primary neural cultures. The  PEI monolayer on diamond surface plays a key role as a neural adhesion promoter, to yield a high  density of neurons on the surface. This cationic monolayer polymer which was coated on diamond  surface, also demonstrated notably interesting electrochemical properties which was characterized  thoroughly. It was shown that the formed monolayer of PEI on diamond surface is extremely adherent  and resistant. The PEI monolayer has the benefit of non-toxicity and provides better performance for  construction of brain-machine interfaces than thicker PEI layers.