Transparent, Adhesive, and Conductive Hydrogel for Soft Bioelectronics Based on Light-Transmitting Polydopamine-Doped Polypyrrole Nanofibrils

Conductive hydrogels are promising materials for soft electronic devices. To satisfy the diverse requirement of bioelectronic devices, especially those for human–machine interfaces, hydrogels are required to be transparent, conductive, highly stretchable, and skin-adhesive. However, fabrication of a conductive-polymer-incorporated hydrogel with high performance is a challenge because of the hydrophobic nature of conductive polymers making processing difficult. Here, we report a transparent, conductive, stretchable, and self-adhesive hydrogel by in situ formation of polydopamine (PDA)-doped polypyrrole (PPy) nanofibrils in the polymer network. The in situ formed nanofibrils with good hydrophilicity were well-integrated with the hydrophilic polymer phase and interwoven into a nanomesh, which created a complete conductive path and allowed visible light to pass through for transparency. Catechol groups from the PDA–PPy nanofibrils imparted the hydrogel with self-adhesiveness. Reinforcement by the nanofibrils made the hydrogel tough and stretchable. The proposed simple and smart strategy of in situ formation of conductive nanofillers opens a new route to incorporate hydrophobic and undissolvable conductive polymers into hydrogels. The fabricated multifunctional hydrogel shows promise in a range of applications, such as transparent electronic skins, wound dressings, and bioelectrodes for see-through body-adhered signal detection.