Stability of thin-film PEDOT:PSS electrodes for neuromodulation

Abstract

Implantable electrodes that can reliably measure brain activity and deliver an electrical stimulus to a target tissue are increasingly employed to treat various neurological diseases and neuropsychiatric disorders. However, their long-term stability has yet to be proven in neuromodulation applications where electrical stimulation over months to years is desired. This thesis addresses this critical challenge. An accelerated aging platform enabled high-throughput screening of various electrode configurations. Metal-free PEDOT:PSS electrodes exhibited the best stability, with a failure rate of only 4.3% after 800 days. They significantly outperformed pristine and PEDOT:PSS-coated gold electrodes, which failed at rates of 89.7% and 82.1%, respectively. Delamination and gold corrosion were identified as key degradation mechanisms. Further aging revealed limitations with traditional polymeric encapsulation materials during stimulation. Introducing a PDMS elastomeric substrate significantly reduced device failure rates (<1%) and prolonged the device lifetime twenty-fold. This device architecture, consisting of stretchable PDMS/PEDOT:PSS electrodes fabricated using lithographic techniques, conformed to dynamic tissues like the gastrointestinal tract and simultaneously recorded electrical activity and mechanical strain. This holds immense potential for studying and treating complex gastrointestinal disorders. Beyond the gastrointestinal system, the long-term stability of metal-free PEDOT:PSS electrodes opens doors for chronic disease monitoring and treatment, eliminating the need for repeated surgeries. These electrodes represent advancements in both the nanofabrication, and bioelectronics fields. This expands prospects for long-term neuroscience studies such as mapping neuromodulatory pathways, improving our understanding of neural communication and treatment of neurological disorders.