Laser-induced wet stability and adhesion of pure conducting polymer hydrogels

Conductive hydrogels can be used to make electrodes that interface with biological tissues due to their similar mechanical properties and high electrical conductivity in physiological environments. The electrical and mechanical properties of conductive hydrogels have improved in recent years, but they still suffer from poor durability and reliability, particularly in wet environments. Here we show that high-stability conductive hydrogels can be fabricated and adhered to various substrates using laser-induced phase separation and interface structures. With this approach, conducting polymers can be selectively transformed into conductive hydrogels with wet conductivities of 101.4 S cm−1 and patterned with a spatial resolution down to 5 μm. The conductive hydrogels exhibit high robustness, maintaining their electrochemical properties after 1 h of ultrasonication and 8 months of storage in water. They also exhibit peel and lap-shear strength in wet conditions of 64.4 N m−1 and 62.1 kPa, respectively. We used the conductive hydrogels to make microelectrode arrays that can stably record electrophysiological signals over 3 weeks in rat brains and hearts. The hydrogel electrodes can also be reused through intensive ultrasonication cleaning due to their durability. Robust conductive hydrogels made purely from a conducting polymer can be fabricated using a laser-induced phase separation method that also improves adhesion to a polymer substrate and allows high-resolution selective patterning.