Harnessing the Intrinsic Asymmetry of Wheat Straw for Multimodal Humidity‐Driven Actuation

ABSTRACT

Humidity‐responsive actuators are widely used for their non‐contact operation and environmental compatibility, and cellulose with abundant hydrophilic groups is an ideal material. However, most cellulose‐based actuators exhibit poor mechanical properties, disordered deformation (uncontrollable), and limited actuation modes (bending). Wheat straw has high cellulose content, aligned cellulose chains, and natural thickness‐direction asymmetry. A natural structure‐retaining strategy combining delignification, programming, and densification is developed to fabricate robust (>450 MPa), programmable (controllable), and multimodal (bending, twisting, jumping) wheat straw‐based films. Through directional programming of wheat straw units, the orthogonally laid film (DWSF‐90°) can rapidly achieve structural transformation under mechanical or moisture stimulation, generating a large stroke force, with a maximum jumping height of 10.2 cm and jumping under loads below 203.32% of its weight. Meanwhile, the parallel‐laid film (DWSF‐0°) can reach a maximum bending angle of 202° in 9.78 s after moisture absorption, and the bending direction is precisely controllable. Both films exhibit good stability over 100 cycles. Applications such as jumping robots and humidity indicators are demonstrated, achieving sustainable and high‐value utilization of agricultural residues in intelligent monitoring, agriculture, and packaging by manufacturing high‐performance smart actuators through leveraging the natural structure of biomass materials.