Hydrogel-based wearable electronic devices have received increasing attention. However, the construction of underwater strain sensors remains a significant challenge because of the swelling of hydrogels in an aquatic environment. This work presents the fabrication of an antiswellable hydrogel composed of polyvinyl alcohol (PVA), a copolymer of [2-(methacryloyloxy) ethyl]dimethyl-(3-sulfopropyl) ammonium hydroxide (SBMA) and 2-hydroxyethyl methacrylate. Interestingly, facile switch of the SBMA moiety from neutral to positively charged status at a low pH value leads to reduced osmotic pressure of the hydrogel for electrostatic repulsion-driven elimination of water molecules and anti-swelling. The resulting anti-swellable hydrogel exhibits high toughness (518 kJ m −3 ) and compressive modulus (8.12 Mpa), ionic conductivity (up to 4.58 S m −1 ), and anti-swelling behavior (equilibrium swelling ratio of 9% in water for 30 days). An underwater strain sensor based on this anti-swellable hydrogel is further developed to monitor the movements of underwater sports. High sensitivity is achieved to identify multidirectional motions, including raising the head, swinging the arm, bending the elbow, knee and finger. Therefore, this study offers a facile strategy to generate hydrogel-based sensors that can be adopted in an underwater environment as well as expands the potential applications of wearable electronic devices.

Ionic gel-based electronic devices are essential in future healthcare/biomedical applications, such as advanced diagnostics, therapeutics, physiotherapy, etc. However, considerable efforts have been devoted to integrating ultrahigh stretchability, transparency, self-adhesion, and a low-cost manufacturing process in one material for dealing with a variety of application scenarios in the real world. Here, we describe an ionically conductive hydrogel-based electronic technology by introducing charge-rich polyzwitterions into a natural polysaccharide network. The proposed hydrogel possesses ultrahigh stretchability (975%), unique optical transmittance (96.2%), and universal conformal adhesion. The bionic hydrogel electronic devices possess superior dual force/temperature sensation with high sensitivity. Moreover, we develop dedicated sensor arrays via an additive manufacturing route and demonstrate the feasibility of monitoring physical activity or analyzing the mental state of a human body based on the multichannel signal acquisition of joint bending, pulse, vocal-cord vibration, electroencephalogram, eye movement, body temperature, etc. This all-in-one strategy based on a versatile ionic hydrogel electronic platform is anticipated to open up new tactical sensing applications in smart robotics, human−machine interfaces, and wearable monitoring systems.

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