Solvent‐Free and Skin‐Like Supramolecular Ion‐Conductive Elastomers with Versatile Processability for Multifunctional Ionic Tattoos and On‐Skin Bioelectronics

Abstract

The development of stable and biocompatible soft ionic conductors, alternatives to hydrogels and ionogels, will open up new avenues for the construction of stretchable electronics. Here, a brand‐new design, encapsulating a naturally occurring ionizable compound by a biocompatible polymer via high‐density hydrogen bonds, resulting in a solvent‐free supramolecular ion‐conductive elastomer (SF‐supra‐ICE) that eliminates the dehydration problem of hydrogels and possesses excellent biocompatibility, is reported. The SF‐supra‐ICE with high ionic conductivity (>3.3 × 10−2 S m−1) exhibits skin‐like softness and strain‐stiffening behaviors, excellent elasticity, breathability, and self‐adhesiveness. Importantly, the SF‐supra‐ICE can be obtained by a simple water evaporation step to solidify the aqueous precursor into a solvent‐free nature. Therefore, the aqueous precursor can act as inks to be painted and printed into customized ionic tattoos (I‐tattoos) for the construction of multifunctional on‐skin bioelectronics. The painted I‐tattoos exhibit ultraconformal and seamless contact with human skin, enabling long‐term and high‐fidelity recording of various electrophysiological signals with extraordinary immunity to motion artifacts. Human–machine interactions are achieved by exploiting the painted I‐tattoos to transmit the electrophysiological signals of human beings. Stretchable I‐tattoo electrode arrays, manufactured by the printing method, are demonstrated for multichannel digital diagnosis of the health condition of human back muscles and spine.

Force-Induced Single-Ion Transport in Porous Polyelectrolyte Hydrogels for Dual-Mode Output Sensing

“…The hydrogel is initially soft and then hardens during large deformations, which suggests that it has good resistance to damage. Young’s modulus of the hydrogel ( E = 0.09–0.22 MPa) matches the elastic modulus of human skin ( E = 0.14–0.6 MPa) . In addition, the CPAM-IP6 30 hydrogel underwent 100 loading–unloading stress cycles at 100% high strain (Figure c).…”

Solid-state, liquid-free ion-conducting elastomers: rising-star platforms for flexible intelligent devices

“…Beyond DES-based ion-conducting elastomers, a solvent-free and biocompatible supramolecular ion-conductive elastomer consisting of polyvinyl alcohol and inositol hexakisphosphate was designed as dry skin electrodes with better adhesion than commercial electrodes. 150 This supramolecular ion-conductive elastomer could be facilely painted into I-tattoos as ultra-conformal skin electrodes to harvest long-term and high-fidelity acquisition of various electrophysiological signals for human–machine interactions and multichannel digital diagnosis (Fig. 13a).…”

E-Tattoos: Toward Functional but Imperceptible Interfacing with Human Skin

“…Another approach to preserving the mechanical and electrical properties of hydrogels over time involves reducing their water content. In a recent work, Niu et al developed a poly­(vinyl alcohol) (PVA) encapsulated inositol hexakisphosphate (IP6) ionic-conductive elastomer, known as an ionic-tattoo (i-tattoo), which contains only 2.6 wt % water content at a room humidity of 30% . This elastomer maintains its conductivity and stretchability for up to 150 days.…”