Prestrain Programmable 4D Printing of Nanoceramic Composites with Bioinspired Microstructure

Four-dimensional (4D) printing enables programmable, predictable, and precise shape changes of responsive materials to achieve desirable behaviors beyond conventional three-dimensional (3D) printing. However, applying 4D printing to ceramics remains challenging due to their intrinsic brittleness and inadequate stimuli-responsive ability. One can draw inspiration from Nature. Concentric cylinder structure is common in biological systems such as scallion, the tracheid of wood, the spicule of Euplectella aspergillum, and the bone Haversian system due to their unique growth organism. Such kind of structure plays a significant role in improving their strength and toughness by increasing the fracture path and energy absorption. Here, this work proposes a conceptional combination of bioinspired microstructure design and a programmable prestrain approach for 4D printing of nanoceramics. To overcome the flexibility limitation, the bioinspired concentric cylinder structure in the struts of 3D printed lattices is replicated to develop origami nanoceramic composites with high inorganic content (95 wt%). Furthermore, 4D printing is achieved by applying a programmed prestrain to the printed lattices, enabling the desired deformation when the prestrain is released. Due to the bioinspired concentric cylinder microstructures, the printed flexible nanoceramic composites exhibit superior mechanical performance and anisotropic thermal management capability. Further, by introducing oxygen vacancies to the ceramic nanosheets, conductive nanoceramic composites are prepared with a unique sensing capability for various sensing applications. Hence, this research introduces a type of high-performance shape-morphing materials for applications under extreme conditions, such as space exploration and high-temperature systems.