Jellyfish-Inspired Ultrastretchable, Adhesive, Self-Healing, and Photoswitchable Fluorescent Ionic Skin Enabled by a Supramolecular Zwitterionic Network

Ionic hydrogels suit ionic skins, but advanced hydrogels are challenging. Inspired by jellyfish, we developed an ionic hydrogel with ultrastretchability, conductivity, adhesion, self-healing, and photoswitchable fluorescence via a supramolecular zwitterionic network. This hydrogel consists of silk fibroin, zwitterionic betaine analogue, biomineral calcium salts, and spiropyran in a dynamically cross-linked macromolecular network. Calcium ions facilitate electrical signal transmission and ionic interactions, while spiropyran enables photoswitchable color and fluorescence. Density functional theory and Fourier transform infrared analysis reveal abundant hydrogen bonding, ionic associations, and van der Waals forces, contributing to stretchability, adhesion, and self-healing, making them ideal for epidermal electrodes. The hydrogel also shows potential in optical printing and anti-counterfeiting applications due to spiropyran's reversible photochromic and photoluminescent behaviors. Moreover, a jellyfish-like robot capable of electric-driven movement is created by using these features. This study enhances understanding of dynamic noncovalent interactions in zwitterionic networks, enriching hydrogel design principles and advancing intelligent ionic skins.