4D printing through vat photopolymerization of two-stage UV-curable liquid crystal elastomers.

Liquid crystal elastomers (LCEs) offer significant promise as soft actuator materials, but their potential has not yet been fully explored for 4D printing applications. Most existing studies rely on extrusion-based printing methods, which offer limited resolution and impose constraints on fabricating intricate, free-standing structures. Moreover, it remains a significant challenge to design and spatially control liquid crystal orientation within complex 3D structures to achieve desired shape transformations. To address these challenges, this study introduces a 4D printing strategy that combines two-stage UV-curable LCEs with vat photopolymerization-based 3D printing, such as digital light processing (DLP). The LCE can be initially printed into complex geometries with high precision, followed by a post-printing programming step in which mechanical deformation is applied to the printed structure to define the desired shape. A subsequent thermal treatment forms covalent linkages to lock the programmed configuration. The resulting structures can reversibly transition between the printed and programmed configurations upon temperature change. This 4D printing strategy is shown to overcome key limitations of current approaches and significantly broaden the design space and functional potential of programmable shape-changing structures for various applications, including mechanically active metamaterials, morphing architecture, and soft robotics.