Direct Ink Printing of Liquid Crystalline Elastomers Towards Photoresponsive Artificial Muscles

Smart materials enable the preparation of 3D structures capable of reversible shape changes in response to external stimuli. Among them, liquid crystalline elastomers (LCE) combine the rubber-like mechanical properties of elastomers with the ordered molecular arrangement and sensitivity to external stimuli that are typical of liquid crystals. In this study, a thiol-acrylate Michael addition reaction was used to synthesize a 3D printable nematic photoresponsive LCE ink. Through direct ink writing, LCE strips were 3D printed with a molecular orientation along the direction of printing. The strips displayed tunable photoactuation properties, with ability to generate active stresses up to 13.5 kPa in response to an illumination with blue light at 470 nm and at an optical power density of ~4 mW/mm2 for 2 s. This makes them usable for applications that require remotely controlled artificial muscles that should operate small loads, such as light-activated soft robots.