External Reflection From Two-Photon Laser-Printed Micromirrors Enables Photomechanical Actuation at a 90° Incident Angle

Abstract

Optically driven robotic actuators are synthetic materials capable of reversible shape-morphing under the control of incident light. Conventional approaches typically require a favorable illumination condition, that is small incidence angle excitement covering large sample area, which poses challenges for optical integration and applicability in optically restricted environments. Here, we present a method that utilizes two-photon polymerization laser-printing of micromirrors on the surface of a soft actuator to redirect parallel incident light into the material. This mirror reflection enables photomechanical actuation at 90° incidence angle. To validate the concept, we employ a liquid crystalline elastomer thin film as the soft actuator operated under photothermal mechanism. The actuator exhibits only moderate deformation at oblique incidence and no deformation at grazing incidence (90°) without micro mirror assistance. Integrating the micro mirrors manifests the photomechanical deformation at oblique angles. The merits of this micro mirror deflection strategy are illustrated by two demonstrations: a walking robot driven by an optical beam that is confined to the locomotive 2D plane, and an optical fiber tip integrated gripper can manipulate objects. These results provide the facts that the photomechanical deformation can be elevated significantly by microscopically constructed pattern on the actuator surfaces, providing new designs for micro robots.