Abstract
Hydrogels of conducting polymers, particularly poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), provide a promising electrical interface with biological tissues for sensing and stimulation, owing to their favorable electrical and mechanical properties. While existing methods mostly blend PEDOT:PSS with other compositions such as non-conductive polymers, the blending can compromise resultant hydrogels’ mechanical and/or electrical properties. Here, we show that designing interconnected networks of PEDOT:PSS nanofibrils via a simple method can yield high-performance pure PEDOT:PSS hydrogels. The method involves mixing volatile additive dimethyl sulfoxide (DMSO) into aqueous PEDOT:PSS solutions followed by controlled dry-annealing and rehydration. The resultant hydrogels exhibit a set of properties highly desirable for bioelectronic applications, including high electrical conductivity (~20 S cm−1 in PBS, ~40 S cm−1 in deionized water), high stretchability (> 35% strain), low Young’s modulus (~2 MPa), superior mechanical, electrical and electrochemical stability, and tunable isotropic/anisotropic swelling in wet physiological environments.
Highlights
Hydrogels of conducting polymers, poly(3,4-ethylenedioxythiophene):poly (PEDOT:poly(styrene sulfonic acid) (PSS)), provide a promising electrical interface with biological tissues for sensing and stimulation, owing to their favorable electrical and mechanical properties
We show that adding volatile additive dimethyl sulfoxide (DMSO) into aqueous PEDOT:PSS solutions followed by controlled dry-annealing, and subsequent rehydration can yield pure PEDOT:PSS hydrogels, of which electrical, mechanical, and swelling properties can be systematically tuned by the amount of added DMSO and the way of dry-annealing
We find that the electrical conductivity of pure PEDOT:PSS hydrogels in phosphate buffered saline (PBS) adjusted to pH 1 recovers high electrical conductivity measured in deionized water (~40 S cm−1) (Supplementary Fig. 9), which is consistent with the previous reports[39,52]
Summary
Poly(3,4-ethylenedioxythiophene):poly (styrene sulfonate) (PEDOT:PSS), provide a promising electrical interface with biological tissues for sensing and stimulation, owing to their favorable electrical and mechanical properties. While conductive nanofillers, such as metal nanoparticles/wires, carbon nanotubes, and graphene, have been added into IPN-based PEDOT:PSS hydrogels to enhance electrical conductivity[15,24,25], the dispersion of nano-fillers within polymer chains of hydrogel networks (typically sub-nm scale) can invite potential issues such as inhomogeneity in mechanical and electrical properties, as well as instability and cytotoxicity in contact with wet biological tissues[15,24,25,26,27] In light of these challenges, pure PEDOT:PSS hydrogels have been developed by avoiding the use of other compositions such as non-conducting hydrogel template and/or nano-fillers[28,29,30,31,32], but they still face numerous technical challenges including low electrical conductivity (
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