Direct 4D printing of gradient structure of ceramics

Shape-morphing ceramics with complex geometries can be applied in several scenarios; however, the fabrication of such structures remains challenging owing to the brittleness and stiffness of ceramics. This paper proposes a direct four-dimensional (4D) printing technology for achieving and precisely controlling complex ceramic architectures that may be transformed, in a free-standing manner, from a pre-programmed gradient structure after sintering without intervention of a manual physical force and stimuli. The proposed method involves three steps: printing, curing, and sintering. The designability and flexibility of the proposed approach were demonstrated by preparing different topologies, such as fingers in a palm (multi-curvature), leaves (anisotropic morphing), a dragonfly (high-precision localised deformation), and an intricate structure (self-locking). The obtained ceramics exhibited excellent mechanical properties. This study can help establish a novel paradigm for designing ceramics with complex structures, with potential for application in various fields such as aerospace and biomedical engineering.