Tunable deformation behavior of 4D printed shape memory polymers with embedded pre-stretched elastomers

Four-dimensional (4D) printing has attracted considerable attention for its diverse capabilities. However, there has been limited discussion regarding the direct programming of a 3D shape during the 4D printing process to enable active deformation under external stimuli. Therefore, we have developed a novel 4D printing method that imparts active deformation capabilities to shape memory polymers (SMPs) by embedding pre-stretched elastomers using UV-curing bonding. Comprehensive studies have been conducted on elastomer modifications, the bonding performance between pre-stretched elastomers with SMPs, as well as the thermally and electrically responsive deformation behaviors of active deformation SMPs samples. The bending curvature of thermally responsive active deformation SMPs samples exhibited a clear linear relationship with the stretch ratio and the offset position of the pre-stretched elastomers. By adjusting the inclination angle and embedding position of pre-stretched elastomers, the SMPs samples successfully achieved various forms of active deformation, including torsional, segmented, and wave-shaped deformations. Moreover, the integration of an embedded silver nanowire (AgNW) electrothermal layer (ETL) in SMPs samples facilitated electrically responsive deformations. The deformation speed and force of SMPs samples can be regulated by controlling the applied current. Thermally responsive flowers, electrically responsive cross-shaped grippers, as well as reverse deformation grippers were designed and printed. These application examples effectively exemplified the immense potential of active deformation SMPs in the fields of soft robotics, flexible electronic devices, and aerospace equipment.