Encoding and Encryption via Dual‐Wavelength 3D Digital Light Processing

Abstract

ABSTRACT Additive manufacturing of multi‐responsive materials is opening new opportunities in a wide range of applications, including information storage, security, and sensing. Herein, complex structures enabling both the encoding and encryption of information in three dimensions (3D) are achieved by combining photo‐ and pH‐responsive chromophores, spiropyran and phenolphthalein derivatives, respectively, within a single ink formulation. To this end, a multi‐wavelength digital light processing (DLP) system is employed to fabricate initially colorless structures using a 405 nm wavelength LED to trigger the photopolymerization process. In parallel, a 365 nm wavelength LED integrated into the same system can induce locally controlled isomerization of spiropyran to the colored merocyanine, enabling information encoding in 3D in a layer‐by‐layer fashion. The stored information can be reversibly encrypted on demand via pH variation. The pH‐responsive chromophore, phenolphthalein, enables modulation of optical contrast, rendering the encoded patterns temporarily unreadable. This work opens new pathways toward engineering multi‐responsive functionality in complex 3D architectures.