Bioinspired hydrogel with both outstanding actuation and conductive properties still remains challenging. Here, we use a simple and universal method to fabricate an octopus-tentacle inspired multifunctional gradient hydrogel with both...
A hydrogel strain sensor can successfully transform its deformation into resistance changes, offering novel options for the Internet of Things (IoT) and artificial intelligence (AI). However, it remains challenging to prepare hydrogel sensors with superior performance (e.g., high conductivity). Here, we produced a conductive hydrogel (named PPC hydrogel) utilizing only three components, PVA (poly(vinyl alcohol)), PAAS (polyacrylate sodium), and CaCl 2 , through freezing cross-linking and ion chelation. The PPC hydrogel is endowed with high electrical conductivity of approximately 5.2 S/m without the addition of highly conductive materials due to the unique ionic cluster mesh structure, thus enabling an outstanding performance of strain sensing. The PPC hydrogel also maintains electrical conductivity in frozen and underwater conditions and resists swelling in underwater environments, allowing it to be used under water for extended periods of time (more than 15 days). The PPC hydrogel-based strain sensor can be used as a flexible electrode for electrocardiogram (ECG) and electromyogram (EMG) examinations and sensitively monitor human activity as well as recognize handwriting. Moreover, we designed a python-based visualization program combined with a PPC hydrogel array to implement pressure-sensing digital image mapping for remote IoT monitoring. As a flexible sensor for biosafety, the PPC hydrogel has potential applications in the field of intelligent sensing, the IoT, and even Internet of Body systems.
Recent developments in hydrogel functional materials have created opportunities for building flexible sensors with multiple kinetic properties. Despite this, the research of multifunctional hydrogels for sensor applications is still a challenge. Herein, we present a recyclable multifunctional hydrogel synthesized from polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC), glycerin, and borax with three different states (named PHG, PHG‐F, and PHG‐S, respectively). Among them, PHG hydrogels have unique transparency, plasticity, self‐healing, injectability, electrical conductivity and thermal sensitivity, and can be used to detect temperature changes with high accuracy and fast response. PHG‐F hydrogels are obtained by cryogenic freezing of PHG hydrogels, which have strong mechanical properties and toughness (up to 0.66 MPa) and can provide excellent performance for human motion monitoring applications. PHG‐S hydrogels, obtained by swelling of dried PHG hydrogels, have stronger mechanical properties and toughness (up to 1.31 MPa), and high conductivity (up to 2.3 S m−1) obtained by immersion in ionic salt solutions, making them very suitable for strain sensing. The tri‐state and recyclable multifunctional hydrogels we developed might even prove useful for practical/smart materials, wearable devices, soft machines, and biomedical uses.
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