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

Abstract

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.

Advanced Soft Materials, Sensor Integrations, and Applications of Wearable Flexible Hybrid Electronics in Healthcare, Energy, and Environment

“…Han et al demonstrated that programmable changes in the adhesion strength of hydrogel, which are synthesized by in situ formation of polydopamine (PDA)-doped polypyrrole nanofibrils, interwoven in an elastic and transparent polyacrylamide network, resulted in controllable values up to 30 kPa in maximum. [211] Moreover, Oh et al recently demonstrated a resistor-type temperature sensor exhibiting high thermal sensitivity of 2.6% °C −1 (25-40 °C), enabled by the integration of the use of functional hydrogel and the aforementioned hierarchical layout of the surface (Figure 8g). [212] They designed PDMS surfaces according to bioinspired octopus sucker-like microstructures that have a cavity (7.5 µm) and rim (4 µm).…”

Physical sensors for skin‐inspired electronics

“…Furthermore, electrophysiological sensors can record important information about health by visualizing human body electrical signals into diagrams, such as the electrocardiogram (ECG), electromyogram (EMG), and electroencephalogram (EEG) . Various flexible and conformable electrophysiological sensors have been developed for long‐term monitoring electrophysiological signals.…”

Tough Adhesion of Nucleobase‐Tackifed Gels in Diverse Solvents

“…Adhesive materials play a significant role in industrial and biomedical fields, which have been widely applied into various applications, including soft robots, [1] wound dressing, [2,3] wearable devices, [4][5][6] and 3D printing [7,8] in water or oil. Up to now, intense endeavor has been devoted to revolutionizing adhesion science and technology for developing more promising applications.…”