Microfabrication technologies for a coupled three-dimensional microelectrode, microfluidic array

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Abstract
Planar or two-dimensional (2D) microelectrode arrays (MEAs), which are used forin vitroculturing of neurons and tissue slices, have been in existence for over 30 years. However, in order to study complex network morphologies and tissue slices which contain substantial 3D neuronal structures, 3D MEAs with microfluidic ports are required. Integrated fabrication of 3D MEAs with embedded microfluidic ports for nutrient perfusion through these relatively thick tissues typically requires non-planar lithography, which is not easily accomplished. This paper reports a laser-scribing technique coupled with electroplating to fabricate 3D MEAs coupled with microfluidic ports. An excimer laser has been used to define patterns in a polymer mold layer that is conformally vapor-deposited on a 3D microfluidic SU-8 substrate. Metal is electroplated through this mold to fabricate electrodes at multiple heights. To demonstrate 3D MEAs, a standard design was chosen consisting of an array of three-dimensional protrusions (‘towers’) optionally with microfluidic functionality on which electrodes can be formed extending to the top of each tower. Additional electrodes are formed on the substrate resulting in a multi-level electrode structure. Since microfluidics can exist both in the substrate as well as along the towers, a coupled three-dimensional electrical and microfluidic functionality is achieved. The resulting 3D MEAs have been analyzed electrically using impedance spectroscopy and baseline noise measurements. They have further been evaluated fluidically using micro-particle image velocimetry measurements.

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