Paper-like foldable shape memory wood actuator with consecutive gesture programming by water and thermal dual stimuli for soft robots

In recent years, smart shape memory materials have garnered significant attention for their potential applications in flexible electronics. However, the exploration of wood, a natural polymer with shape memory capabilities, has been limited, particularly concerning its editable and controllable memory shapes and moveable functions. This study presents a shape memory wood actuator (SMWA) with dual activation capabilities through water and heat. The SMWA is developed by connecting the treated wood with PDMS and LCE for consecutive gesture programming. The controlled contraction of LCE upon thermal activation, combined with strength changes due to reversible hydrogen bonding in the cellulose amorphous region during water activation, enables the SMWA to exhibit continuous shape memory capabilities and programmability. Additionally, the SMWA demonstrates satisfactory mechanical performance (tensile strength of 17.3 MPa when dry and 4.4 MPa when wet) and shape recovery capabilities (over 80 % shape recovery). Notably, the rigidity/flexibility change of SMWA under water-activated conditions, coupled with heat-activated posture control and memory through built-in circuits, allows for practical applications such as object grasping. Such efficient strategy offers a guideline for developing high- performance smart wooden shape memory materials, with promising prospects for applications in soft robotics, flexible sensors and oil–water separation.