Shrinkage-induced alignment in multiphoton 3D printed liquid crystal elastomers enables direct-write, arbitrary axis microactuators

Abstract Multi-photon lithography (MPL) is a nano-scale additive manufacturing technique capable of creating extremely detailed structures with sub-micron 3D resolution, providing a leading platform for innovation in the field of microrobotics. Liquid crystalline elastomers (LCEs) are a class of soft, stimuli-responsive materials that undergo large, reversible shape changes, motivating their extensive study as artificial muscles for soft microrobotic systems. Actuation in LCEs relies on the alignment of their polymer backbone, yet achieving spatially programmable alignment at sub-micrometer scales remains a challenge. In this work, we report a straightforward method for introducing controlled alignment in LCEs 3D printed using MPL. LCE inks containing a non-reactive solvent are printed between fixed constraints and, upon solvent removal, a shrinkage-induced volume change generates internal stresses, leading to alignment of the printed LCE network. Importantly, the direction of alignment and resulting actuation can be programmed along arbitrary axes in a 3D printing coordinate system without substrate pretreatment or external fields. These MPL printed LCE microactuators demonstrate actuation in functional micromechanical systems including a micro-mirror array and gear system, achieving specific work values of up to 212 J/kg. This approach enables simultaneous 3D printing and alignment of LCEs at the microscale, providing a pathway for creating efficient, stimuli-responsive actuators for microrobotic systems.