Selective Transformation of PEDOT:PSS into Highly Conductive Hydrogels by Laser-Induced Phase Separation

Engineering conductive hydrogels with high electrical conductivity and mechanical stability in aqueous environments are important in research fields such as bioelectronics, e-skin, and energy devices. Especially, bioelectronics has actively adopted conductive hydrogels as bio-interfacing electronic material owing to similar natures to biological tissues. The softness and high water contents of hydrogels can minimize mechanical mismatch with biological tissues that can potentially realize long-term medical diagnosis or treatment such as neural signal recording and nerve stimulation.<br/><br/>The most commercialized conducting polymer, Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is a promising candidate for the fabrication of conductive hydrogels based on its electrical conductivity and electrochemical properties. However, fabricating PEDOT:PSS hydrogels still has critical issues in aqueous instability and poor electrical conductivity. “Phase separation method” that redesigns the arrangement and crystallinity of PEDOT:PSS binary system has been rapidly studied to achieve high conductivity with aqueous stability. Ironically, most of the phase separation additives are cytotoxic and require a long detoxification process. Moreover, high-resolution patterning techniques of PEDOT:PSS hydrogels are required for bioelectronics, but conventional processes are limited by low resolution or process complexity such as inkjet printing and photolithography.<br/><br/>We introduce a novel biocompatible manufacturing process that overcomes such limitations explained above. Through the laser-induced phase separation of PEDOT:PSS, the phase distribution of binary PEDOT and PSS was dramatically reconstructed. The micro-patterned PEDOT:PSS hydrogels achieved high electrical conductivity and aqueous stability with 6-μm spatial resolution. We further demonstrated stable neural signal recording and stimulation with PEDOT:PSS hydrogels electrodes fabricated by laser.