4D Printing of Supramolecular Liquid Crystal Elastomer Actuators Fueled by Light

Recent years have seen major advances in the additive manufacturing of stimuli-responsive materials, also known as 4D printing, among which liquid crystal elastomers (LCEs) play an important role. However, during fabrication photo-crosslinking of the LCEs is required, but this step is time-consuming and efficient polymerization is challenging, especially in the case of light-responsive materials. In this work, the first light-fueled supramolecular LCEs suitable for the direct ink writing (DIW) of soft actuators are synthesized in which a photopolymerization step is not needed. With the responsive supramolecular material, 3D-printed objects are fabricated by exploiting the thermoreversible interplay of the hydrogen-bonding physical cross-links. After printing, the supramolecular LCE shows reversible shape changes in response to light and is capable of bending and lifting a load. Through the combined photothermal and photochemical contributions of the incorporated azobenzene, the actuators can be triggered both in air and water. The freedom provided by DIW allows for the printing of complex responsive objects, as demonstrated by fabricating re-entrant honeycomb and spiral director structures. This approach of printing light-responsive supramolecular soft actuators opens avenues toward the application of smart and sustainable materials for additive manufacturing without the requirement of photo-crosslinking.

Automated summary

In recent years, there have been significant advances in the additive manufacturing of stimuli-responsive materials, also known as 4D printing, with liquid crystal elastomers (LCEs) playing a crucial role. However, the time-consuming nature and challenging polymerization process of photo-crosslinking in LCE fabrication is a hurdle, particularly for light-responsive materials. This research introduces the first light-fueled supramolecular LCEs suitable for direct ink writing (DIW) of soft actuators, eliminating the need for photopolymerization. These responsive supramolecular materials enable the fabrication of 3D-printed objects through the thermoreversible interplay of hydrogen-bonding physical cross-links. The printed supramolecular LCE exhibits reversible shape changes in response to light and can bend and lift a load. By incorporating azobenzene, the actuators can be triggered by both photothermal and photochemical stimuli in air and water. The DIW process allows for the printing of complex responsive objects, as exemplified by re-entrant honeycomb and spiral director structures. This approach of printing light-responsive supramolecular soft actuators paves the way for the application of smart and sustainable materials in additive manufacturing without the requirement of photo-crosslinking.