Thiol-Isocyanate Photoprinting of Liquid Crystal Elastomers Toward High Toughness and Reprintability

Photoprinting of liquid crystal elastomers (LCEs) is blooming for creating soft actuators with complex geometries, reversible large and anisotropic deformations. However, they exhibit poor toughness below 10 MJ m^-3 due to the limited chemical design under the necessary constraint of photoreactive groups (complete reliance on acrylate-based polymerization); the introduction of toughening units along the chain backbone often reduces the mesogen content and compromises liquid crystallinity. The resulting permanent photocuring sites fundamentally hinder reprintability, which is critical for recyclability in photoprinted LCEs. Here, a thiol-isocyanate photoprinting strategy is introduced in LCEs. The in situ formation of thiourethane bonds during crosslinking not only provides greater design freedom with higher hydrogen bond density, but also serves as dynamic photocuring sites. The resulting SU-xLCE achieves high toughness and large elongation at break (85.3 ± 2.5 MJ m^-3 and 1498.1 ± 32.5%, respectively), exhibiting actuation load 10 000 times its own weight and self-healing ability, along with remarkable tear and puncture resistance, while sustaining over 10 000 fatigue and actuation cycles. It can also achieve chemical recycling of LC oligomer (accounting for 90.0 wt% of resin, 98.3% of cost) and the reprintability of the actuator without large performance loss. This work establishes a photoprinting platform toward next-generation high-performance soft robotics.