Fabrication and validation of flexible 3D pillar electrodes for neural electrophysiological recording

One in fifty people in the United States suffer from paralysis or another neurological disorder. In order to restore functionality and quality of life to these patients, single electrodes and microelectrode arrays (MEAs) have been implanted to record and stimulate electrical signals in the brain. These treatments have shown promise to restore mobility to stroke and amputee patients and to restore quality of life for people suffering from Parkinson's disease and severe depression. However, current silicon electrodes are 108 times stiffer than brain tissue and lead to chronic inflammation and scarring, eventually leading to the electrode becoming nonfunctional. Our lab has developed a novel MEA design with flexible 3D pillar electrodes made of polydimethylsiloxane (PDMS) and gold-coated nickel to better match the stiffness and elasticity of the brain than currently used stiff silicon electrodes. We describe the fabrication to achieve a high-aspect ratio flexible pillar electrode with a length up to ten times longer than width. As a first step, we have tested the functionality and biocompatibility of the array and pillars in vitro using cultured rat hippocampal neurons. Neurons cultured on our arrays were comparable in health to neurons grown on commercial MEAs, as demonstrated by morphology and electrophysiology during multiple weeks in culture. The pillar electrodes were sensitive enough to detect electrical signals with comparable signal-to-noise ratio, and signal activity to both custom and commercial flat electrodes. Based on this in vitro device validation, we believe this approach of making flexible, high-aspect ratio pillar electrode arrays may be translatable into an in vivo system for use as a neural prosthesis.