Abstract
The challenge of understanding the mechanisms by which communication is achieved within the nervous system has intrigued scientists since the 18th century. It was then that Italian scientist Luigi Galvani demonstrated that muscles could be caused to twitch when stimulated using electricity. Later efforts, including the work of German biologist Emil du Bois-Reymond, gave rise to the concept of nerves being ‘wires’ that are capable of transmitting electrical signals to the brain as well as away from it. Advances in microengineering have made it possible to manufacture electrodes in the micrometer scale for studying the electrophysiological activity of nerve cells (neurons) and networks of neurons both in-vivo and in-vitro. This thesis describes the development of microelectrodes and associated hardware, software, and protocols for studying the electrical activity of in-vitro neural networks. Networks of neurons with a specific geometry were organised on top of 4 x 4 planar microelectrode arrays (pMEAs) by dielectrophoretically loading the cells inside micro-chambers (located on top of the electrodes) that were fabricated using a negative photoresist (SU-8). Each micro-chamber was connected to its neighbours via micro-trenches that served the purpose of guiding the outgrowth of neurites in order for neurons to connect. Spontaneous and evoked neural signals were successfully recorded using a 16-channel acquisition/stimulation unit. The results obtained from this work indicated good coupling between neurons and electrodes, and provided neural signals with high signal-to-noise ratios (up to 35). Unfortunately, SU-8 photoresist showed signs of toxicity, as neurons cultured on top of and adjacent to it did not grow processes and had irregular shapes. As a result neural network formation was inhibited, which necessitates the investigation of alternative materials (e. g. silicon, agarose, PDMS) for fabricating micro-chambers and micro-trenches. Nonetheless, this thesis presents a novel system that utilises the phenomenon of dielectrophoresis for loading a single neuron inside each micro-chamber of a pMEA for recording/stimulation purposes. This system provided a fast, effective and inexpensive way of assembling single-neuron-per-electrode neural grids, and could be used for creating large-scale geometrically defined networks comprised of hundreds of cells.