DLP 4D Printing of Programmable Molecularly-Engineered Liquid Crystal Elastomer Actuators.

Liquid crystal elastomers (LCE) are highly attractive for 4D printing due to their ability to undergo large, rapid, and reversible shape changes in response to external stimuli. While direct ink writing (DIW) enables mesogen alignment during extrusion, it remains limited in resolution and geometric complexity. In contrast, digital light processing (DLP) offers fast, high-resolution fabrication of complex architectures but lacks an intrinsic mechanism for aligning mesogens, which prevents reversible actuation. Here, we present a scalable and versatile strategy for DLP 4D printing of LCEs, based on partially cured printed structures subjected to mechanical programming followed by photo-crosslinking to fix mesogen alignment. This two-stage photo-crosslinking approach enables the fabrication of monodomain nematic LCEs with tunable thermo-mechanical properties and programmable, multimodal, and large actuation strains up to 45%. The strategy is demonstrated through complex LCE architectures, including an octopus model that undergoes consistent, reversible actuation over 100 thermal cycles. Additionally, sports-themed stickman models based on these LCEs show how a single printed object can be programmed with different actuation modes, such as bending, twisting, or contraction, and their combinations, by selecting the ink best suited to the targeted actuation. These results highlight the design and programming flexibility of the method, establishing DLP as a compelling alternative to DIW for fabricating functional soft actuators.