Directed Motility of Hygroresponsive Biomimetic Actuators

The capability of cellulose microfibrils to elicit directionality by anisotropically restricting the deformation of amorphous biogenic matrices is central to the motility of many plants as motoric and shape-restoring elements. Herein, an approach is described to control directionality of artificial composite actuators that mimic the hygroinduced motion of composite plant tissues such as the opening of seed pods, winding of plant tendrils, and burial of seed awns. The actuators are designed as bilayer structures where single or double networks of buried parallel glass fibers reinforce the composite. By anisotropically restricting the expansion along certain directions they also effectively direct the mechanical reconfiguration, thereby determining the mechanical effect. A mathematical model is developed to quantify the kinematic response of fiber-reinforced actuators. Within a broader context, the results of this study provide means for control over mechanical deformation of artificial dynamic elements that mimic the oriented fibrous architectures in biogenic motoric elements. A simple, yet universal approach to the design of composite thermoresponsive and hygroresponsive actuators with directional motion that mimics the motility of bilayer architectures in plants is reported. An overarching mathematical model is also developed to quantify the kinematic response of fiber-reinforced actuators in artificial dynamic elements.