A Mussel-Inspired Conductive, Self-Adhesive, and Self-Healable Tough Hydrogel as Cell Stimulators and Implantable Bioelectronics

A conductive, stretchable, self-adhesive, and self-healable hydrogel was designed by partially converting graphene oxide (GO) to conductive graphene through PDA reduction. A facile three-step synthesis process was developed to form the hydrogel. First, dopamine was prepolymerized to form PDA chains under oxidative and alkaline condition. Second, graphene oxide (GO) was added to the PDA solution, and reduced by PDA partially to pGO or fully to reduced GO (rGO) by controlling the reaction time. Finally, the PDA�pGO�PAM hydrogel was developed with the polymerization of acrylamide (AM) monomers at the presence of initiator and crosslinker. PDA entangled rGO was well dispersed in the network and interweaved to form electronic pathway, resulting in good conductivity. The remained unreduced GO together with PDA chains interacted with the polyacrymide (PAM) network via noncovalent interaction, including the hydrogen bonds and π�πstacking between catechol groups of PDA chains and the electrostatic interactions between GO and PAM. The synergistic contribution of covalent bonds in PAM network, and the noncovalent interaction between GO, PDA, and PAM, led to high stretchability and toughness. SEM images demonstrated that PDA microfibrils were entangled with GO nanosheets and intertwined with nanonetworks in the PDA�pGO�PAM hydrogel. Moreover, the free catechol groups on PDA chains formed noncovalent bonds which imparted self-healability and selfadhesiveness to the hydrogel.