"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.