Grayscale stereolithography 3D printing of shape memory polymers for dual information encryption based on reconfigurable geometry and tunable optics

Dual information encryption such as geometry and transparency switching is highly desirable for preventing the leakage of confidential information and constructing a secure environment which has wide range of applications in privacy protection, anti-counterfeiting, and information security. However, it is still a challenge to develop a novel encrypted strategy and smart material to achieve credible protective capacity for stored information by a facile and programmed manner. Herein, integrating with arbitrary grayscale stereolithography, the hydrophilic ultraviolet (UV) curable shape memory polymers (HU-SMPs) with superior mechanical properties (the tensile strength of 29.39 MPa, elongation of 46.32 %, and the toughness of 1021.98 kJ.m−3) were prepared, which can be used for multifunctional information encryption. During the encrypted process, the HU-SMPs with the performances of high deformable and excellent shape memory behaviors can provide the preprogrammed morphological information and inevitable encryption, while the humidity-responsive of HU-SMPs capable of generating revisable transparency switching that can be encoded as the secondary information encryption. In this way, the dual encrypted information in the HU-SMPs is readable only after sequential shape recovery and fast hydration under heat-stimuli and humidity-stimuli. In addition, with the aid of digitally grayscale drawing, the secondary encrypted information is cyclically displayed and erasable due to the reversible hydration and dehydration process of HU-SMPs. Finally, the encrypted information is also can be permanently storage or decryption by the versatile post-processing methods of UV irradiation after and before decryption, respectively. In short, the design of HU-SMPs that compatible with grayscale digital light process (g-DLP)-based 3D printing, will motivates the future development of smart materials and provides a new insight into the information encrypt fields.