Gradiently Foaming Ultrasoft Hydrogel with Stop Holes for Highly Deformable, Crack‐Resistant and Sensitive Conformal Human‐Machine Interfaces

Abstract Hydrogels are considered as promising materials for human‐machine interfaces (HMIs) owing to their merits of tailorable mechanical and electrical properties; nevertheless, it remains challenging to simultaneously achieve ultrasoftness, good mechanical robustness and high sensitivity, which are the pre‐requisite requirements for wearable sensing applications. Herein, for the first time, this work proposes a universal phase‐transition‐induced bubbling strategy to fabricate ultrasoft gradient foam‐shaped hydrogels (FSHs) with stop holes for high deformability, crack‐resistance and sensitive conformal HMIs. As a typical system, the FSH based on polyacrylamide/sodium alginate system shows an ultralow Young's modulus (1.68 kPa), increased sustainable strain (1411%), enhanced fracture toughness (915.6 J m −2 ), improved tensile sensitivity (21.77), and compressive sensitivity (65.23 kPa −1 ). The FSHs are used for precisely acquiring and identifying gesture commands of the operator to remotely control a surgical robot for endoscopy and an electric ship in a first‐person perspective for cruising, feeding crabs and monitoring the environmental change in real‐time.