Programmable and reconfigurable hygro-thermo morphing materials with multifunctional shape transformation

Humidity responsive materials are increasingly attracting significant interest for soft robotics and deployable structures. Their shape-changing behavior is based on differential hygroscopic characteristics of the single components of their microscopic architecture. Although existing moisture-induced materials achieve morphing in various humidity conditions, practical operational environments involve the presence of uncontrolled humidity regimes, which restrict those materials to reach broad ranges of shapes. Here we describe programmable and reconfigurable composite materials based on natural fibres and shape memory polymers that extend the current one-to-one relation between external humidity and final actuated shape. The heating of flexible polymer networks permits to program the architecture of the natural fibres flax reinforcements and their spatial distribution within the composite, when a moisture gradient is present. Once cooled, the programmed materials create new sets of different shapes, even when exposed to the same humidity conditions. These multifunctional biobased materials also show large stiffness (>13 GPa) that make them suitable for structural load-bearing applications. New multifunctional shape transformations capabilities of these bio-based hygro-thermo composites are demonstrated in a bio-robotic grasping hand and a bio-frame for electro-adhesive gripping. These examples show the full functionality, structural integrity, programmability and remarkable mechanical properties of our multifunctional hygromorph biocomposites. (C) 2022 Elsevier Ltd. All rights reserved.