Increasing the Conductivity and Adhesion of Polypyrrole Hydrogels with Electropolymerized Polydopamine

Abstract

Polypyrrole (Ppy) hydrogels are a promising new avenue for developing cheap wearable electronics and biotechnology. In particular, the use of conducting polymer hydrogels can impart elasticity and a high specific surface area, leading to great potential for sensors, cell growth scaffolds, and energy storage. However, their significantly low conductivity (compared to Ppy films and carbon or metallic microstructures), hydrophobicity, and low adhesiveness mean that they are currently unsuitable for most biological and wearable applications. Here, we show that by electropolymerizing a covalently bonded polydopamine (PDA) phase within polypyrrole hydrogels, we increased the conductivity by 2720% and adhesion by 2140% compared to pure polypyrrole hydrogels. Pyrrole monomers provided π-bond stabilization and prevented a π-stacked, auto-oxidized layer of PDA from forming. Instead, through potentiodynamic polarization of polypyrrole gels after dopamine incorporation, we produced covalently bonded 5,6-dihydroxyindole, producing an additional phase of conjugated polymer that interacted with the polypyrrole through noncovalent bonding. The PDA’s unoxidized catechol groups also led to increased hydrophilicity and adhesiveness of the hydrogels. These results are a further step toward the realization of fully polymer wearable electronics made with a simple, scalable technique, thereby removing the need for expensive, biologically unfriendly metals or carbon structures.

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“…Considering the three-dimensional structure of polymeric PPY-PDA-PHT-ANG nanoparticles, it is reasonable to infer the magnified improvement of electroresponsive performance. In addition, the negatively charged PDA molecules introduced free electrons in PPY main chains, increasing the conductivity ( 25 ). Upon electric stimulus, the PPY chains were reduced and then repulsed the negatively charged PHT molecules, with PDA incorporation facilitating the process.…”

Physicochemical and Electrochemical Characterization of Electropolymerized Polydopamine Films: Influence of the Deposition Process

“…Schindler and Bechtold proposed that the anodic oxidation of dopamine in a pH range of 5.8 to 7 involves formation of a semiquinone radical and subsequent deprotonation [ 18 ] leading to PDA formation. To date, the final PDA structure has not yet been fully elucidated, similar to the chemical route, although Fourier transform infrared spectroscopy (FTIR) studies indicate poly(5,6-indolequinone) with formation of C-O-C chains during the poly(indole)-like electropolymerization [ 22 ]. Single molecule force spectroscopy (SMFS) [ 23 , 24 ] measurements at pulse-deposited PDA have shown polymeric character with contour lengths in the range of 200 nm [ 17 ].…”

Multidimensional Study On The Corrosion Inhibition of Polypyrrole-Chitosan (PPy-CTS) Composites For Carbon Steel In Acid Medium

“…As a result, the polymer chains tended to form a planar structure, which improved the order of PPy molecular chains. At the same time, the π-π conjugate system, which was very important for electron migration, also became more complete, and the conductivity of PPy increased relatively 24 . Remarkably, the pattern of PPy-CTS included the diffraction peaks belonging to CTS (10° and 19°) and PPy (15° ~ 27°).…”