Sustainable 4D Printed Meta Biocomposite Materials for Programmable Structural Shape Changing

Biological structures provide inspiration for developing advanced materials from sustainable resources, enabling passive structural morphing. Despite an increasing interest for parsimony-oriented innovation, sustainable shape-changing materials based on renewable resources remain underexplored. In this work, the architecture of a single plant fiber cell wall (S₂, for instance) is simplified to design novel concepts of 4D printed tubular moisture-driven structural actuators, using the hygromorphic properties of continuous flax fiber (cFF) reinforced materials. This new class of bioinspired active materials is referred to as metabiocomposites. Before bioinspired design, the materials are produced with a customized rotary 3D printer, qualified, and tested for sorption behavior. A parametric experimental, analytical, and FEA analysis highlights the programmability of the material through the effects of mesostructural parameters (printing inclination α) and geometric factors (operational length L, inner diameter D, and thickness h) on the actuation authority. The overall performance is a trade-off between rotation and torque, with energy density comparable to that of the source of inspiration: natural fibers cell wall. The potential applications are illustrated through a proof of concept for a meteosensitive rotative structure that transmits motion to an external device, such as a solar tracker.