4D direct laser writing of photo-triggered liquid crystal elastomer microactuators with large actuation strain

4D printed photo-triggered liquid crystal elastomers (LCEs) microactuators by direct laser writing via two-photon polymerization (DLW-TPP) have attracted increasing attention due to their manipulation flexibility, reversible and rapid actuation capabilities. However, their development is hampered by the lack of room-temperature printable liquid crystal (LC) photoresists. Here, we developed new light-responsive LC photoresists by incorporating novel conjugated polymers (CPs) as photothermal agents for the DLW-TPP technology. The CPs displayed a remarkable photothermal effect and effectively avoided the aggregation problems that always happened for inorganic nanoparticles in photoresists. Moreover, the CPs incorporation lowered the nematic-to-isotropic temperature of the LC photoresists which is beneficial for room-temperature DLW-TPP. The printing parameters, including laser power and scanning speed, were investigated using the developed LC photoresists. It was found the range of printing parameters decreased with the increase of the CPs loading fraction from 0.1 to 0.5 wt%, which was attributed to the high photothermal conversion efficiency (52.7%). A well-defined CPs/LCEs microactuator with CPs as low as 0.3 wt% was printed, which could achieve a large 25.0% actuation strain in 5 s upon near-infrared (NIR) light stimulation. It could be used for thriving soft micro-robotics and micro-membranes with controllable separation capabilities.