4D Encryption System: Hydrophilic–Hydrophobic Polyurethane Actuators with Smart Color Switching for High‐Capacity Data Storage

Abstract Natural communication methods have influenced the creation of sophisticated artificial materials capable of coherent and abundant responses to stimuli, a crucial necessity for developing applications such as dynamic encryption systems and high‐density information storage. However, existing materials for encryption and information storage are limited by predictable, single‐stimulus responses and lack the capacity for dynamic, continuous, and programmable changes. To address this gap, a bioinspired multicolor fluorescent polyurethane actuator is developed that combines dynamic color and shape adaptability within a single material platform. This smart actuator mimics the turgor‐driven movements of Oxalis corniculata through a hydrophilic/hydrophobic network that enables water diffusion, hydrogen bonding, and dynamic bond exchange. It responds to multiple stimuli, including temperature, pH, and excitation wavelength, exhibiting reversible multi‐state deformations and programmable fluorescence across red, green, blue, and even white light. The deformation behavior is supported by finite element simulations, ensuring precise control and predictability. Additionally, the tunable trichromatic fluorescence of the actuator underpins a 3D and 4D information encoding system, demonstrating increased information storage capacity and encryption security. The employment of micro‐processing technology in the fabrication of micro‐hidden optical encryption chips has been demonstrated, thus paving the way for underwater communication encryption technologies and adaptive materials.