4D printing of shape-memory fluorescent liquid crystal hydrogels

Liquid crystal hydrogels (LCHs) hold promise for smart applications due to the combination of highly ordered, anisotropic and stimuli-responsive properties, yet their fabrication into complex architectures remains challenging due to limitations in conventional manufacturing techniques. While 3D printing offers a promising alternative, progress has been hindered by poor compatibility between hydrophobic liquid crystal (LC) monomers and hydrogel monomers in photo-curing resins, as well as a narrow selection of 3D-printable functional LC materials. This work reports a successful 3D printing of LCHs via digital light processing (DLP), addressing monomer incompatibility through solvent exchange. The molecular ordering and mechanical performance of LCHs were also further improved by solvent exchange and subsequent formation of hydrogen bonding. The printed LCHs exhibit exceptional shape-memory behaviour (100 % fixation, >95 % recovery at approximately 80 °C and above) driven by temperature-controlled LC domain alignment and intrinsic UV fluorescence derived from the design of carbazole-biphenyl conjugated liquid crystal monomer. Demonstrations include reprogrammable soft grippers capable of lifting objects and intricate hollow 3D structures, highlighting the LCH's printability, multifunctionality and structural stability. The study provides critical insights for designing multifunctional LCH systems via additive manufacturing and broadens the scope of 3D-printable LC materials.