Wet-Adhesive Multifunctional Hydrogel with Anti-swelling and a Skin-Seamless Interface for Underwater Electrophysiological Monitoring and Communication

Abstract

A stable and seamless adhesion between the human skin and the hydrogel-based electronic skin is necessary for accurate sensing and human health monitoring in aquatic environments. Despite achieving significant progress in this field, it remains a great challenge to design skin-interfaced conductive hydrogels with high electrical conductivity, stablility, and seamless underwater adhesion to skin. Herein, a skin-inspired conductive multifunctional hydrogel is proposed, which has a wet-adhesive/hydrophilic and a non-adhesive/hydrophobic bilayer structure. The hydrogel shows high stretchability (∼2400%) and an ultra-low modulus (4.5 kPa), which facilitate the conformal and seamless attachment of the hydrogel to the skin with reduced motion artifacts. Owing to synergistic physical and chemical interactions, this hydrogel can achieve reliable underwater adhesion and display remarkable underwater adhesion strength (388.1 kPa) to porcine skin. In addition, MXene has been employed to obtain high electrical conductivity, create a route for stable electron transport, and reinforce mechanical properties. The hydrogel also possesses self-healing ability, a low swelling ratio (∼3.8%), biocompatibility, and specific adhesion to biological tissues in water. Facilitated with these advantages, the hydrogel-based electrodes achieve reliable electrophysiological signal detection in both air and wet conditions and demonstrate a higher signal-to-noise ratio (28.3 dB) than that of commercial Ag/AgCl gel electrodes (18.5 dB). Also, the hydrogel can be utilized as a strain sensor with high sensitivity for underwater communication. This multifunctional hydrogel improves the stability of the skin–hydrogel interface in aquatic environments and is expected to be promising for the next-generation bio-integrated electronics.

Ultrastretchable, Highly Conductive, Rapid Self-Recovery, and Antiswelling Hydrogels as Multifunctional Wearable Electronic Devices

“…Further, the tensile strain and stress of the reported conductive hydrogels and CPAL hydrogels are compared in Figure i. The CPAL hydrogels possessed an advantage at the tensile strain and stress levels. − …”

“…(d–h) Mechanical properties of CPAL hydrogels adjusted by changing AlCl 3 content. (i) Ashby plots of tensile stress and tensile strain values of reported hydrogels and the CPAL hydrogel. − …”

Functional adhesive hydrogels for biological interfaces

“…In addition, there were already many wet environment adhesive hydrogels that could replace existing solutions. For example, hydrogel Janus Tough Adhesive firmly adhered to the bloody tendon and contributed to rapid wound healing, 13 hydrogel gelatin‐polydopamine‐nano‐clay (GPC) promoted the healing of oral ulcers, 92 double‐layered structure hydrogel was used as an underwater sensor 93 …”

Stretchable Multi‐Channel Ionotronic Electrodes for In Situ Dual‐Modal Monitoring of Muscle–Vascular Activity

“…This is attributed to perspiration improving the conformal adherence between the electrode and the skin. [47,49] Subsequently, we assessed the EP signals before and after sweating. For EMG signal monitoring (Figure S14b, Supporting Information), ionogel exhibits consistent signal tracking pre-and post-sweating, with a slightly higher SNR observed in post-sweating EMG signals.…”