A Three-Dimensional Coupled Microelectrode and Microfluidic Array for Neuronal Interfacing
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The objective of this research is to develop a three-dimensional (3-D) microfluidic/ electronic interface system for sustaining and monitoring 3-D neuronal networks. This research work is divided into two parts. One is the development of a 3-D multi-electrode array (MEA) with integrated microfluidic channels. The other is a microneedle array with embedded microelectrodes and microfluidic channels. The 3-D MEA is composed of three elements that are essential for the development and monitoring of 3-D cultures of neurons. These components consist of scaffolds for cellular growth and structural stability, microfluidic channels for cell maintenance and chemical stimulation, and electrodes for electrical stimulation and recording. Two kinds of scaffold structures have been fabricated. The first scaffolding scheme employs a double exposure technique that embeds SU-8 towers into an SU-8 substrate. The second scaffolding mechanism introduces interconnects between towers for the purpose of mechanically supporting 3-D cell cultures and facilitating 3-D synaptic connections. Microfluidic channels are combined for fine control of the cellular microenvironment by means of diffusive and convective fluidic processes. Hollow towers with three-layer side ports were developed by using double exposure techniques and excimer laser ablation. The electrodes are combined into an integrated system that is capable of monitoring electrical activities and the cellular impedances of neurons which are attached to the electrodes. The second part of this research is to fabricate a microneedle array for monitoring brain slices, which will directly detect electrical signals from living brain slices. Although the microneedle array is targeting different 3-D neuronal networks, it also has three components and the fabrication steps are the same as those for the 3-D MEA. To generate the sharp tip, isotropic reactive ion etching (RIE) is performed on tapered SU-8 towers. High aspect ratio tower structures can be effectively generated with SU-8 and tapered shapes are created by backside exposure. The resulting systems will enable a new field of neurobiological research, in which the collective properties of 3-D neuronal circuits can be observed and manipulated with unprecedented detail and precision, and at a level of control not possible in living animals.