The Synergism of β‐Cyclodextrin and Fe ³⁺ Enabled Anti‐Swelling Ion‐Conductive Hydrogels for Multimodal Underwater Sensing Aided by Machine Learning Algorithms

ABSTRACT As the key sensing component of flexible sensors, conductive hydrogels are prone to mechanical property degradation and signal deterioration owing to water absorption and swelling in underwater environments. Herein, an anti‐swelling ion‐conducting hydrogels are designed by incorporating ferric chloride (FeCl ₃ ) and β‐cyclodextrin (β‐CD) into acrylamide‐acrylic acid copolymer (MA) via a one‐pot method, short for MAF _x D _y . Thanks to the synergism of β‐CD and Fe ³⁺ , the swelling ratio of MAF _x D _y is significantly reduced comparted to its counterparts, for example, 4% for MAF _0.2 D _0.3 , compared to 760% for MAF _0.2 hydrogel without β‐CD and 526% for MAD _0.3 without Fe ³⁺ after soaking in deionized water for 30 days. Notably, the multimodal underwater sensor constructed based on the MAF _0.2 D _0.3 hydrogel can not only monitor underwater human joint motion but also realizes the accurate transmission of underwater information with the help of Morse code. Moreover, aided by machine learning algorithms, this study proposes a novel shortcut key recognition strategy to achieve precise and rapid information transmission via letter recognition (with a recognition accuracy of 98.6%), dramatically shortening the time required for underwater communication. This study provides innovative solutions by the rational design of anti‐swelling ion‐conducting hydrogels for reliable and fast underwater communications.