Liquid Crystalline Network Microstructures for Stimuli Responsive Labels with Multi‐Level Encryption

Abstract Two‐photon direct laser writing enables the fabrication of shape‐changing microstructures that can be exploited in stimuli responsive micro‐robotics and photonics. The use of Liquid Crystalline Networks (LCN) allows to realize 3D micrometric objects that can contract along a specific direction in response to stimuli, such as temperature or light. In this paper, the fabrication of free‐standing LCN microstructures is demonstrated as graphical units of a smart tag for simple physical and optical encryption. Using an array of identical pixels, information can be hidden to the observer and revealed only upon application of a specific stimulus. The reading mechanism is based on the shape‐change of each pixel under stimuli and their color that combine together in a two‐level encryption label. Once the stimulus is removed, the pixels recover their original shape and the message remains completely hidden. Therefore, an opto‐mechanical equivalent of an “invisible ink” is realized. This new concept paves the way for introducing enhanced functionalities in smart micro‐systems within a single lithography step, spanning from storage devices with physical encryption to complex motion actuators.