Hybrid hinge structure with elastic hinge on self-folding of 4D printing using a fused deposition modeling 3D printer

Recently, a new technology has come to the fore, namely four-dimensional (4D) printing. Conventional research has, however, mostly been in a glass state after a shape change such as self-folding of 4D printing, because the heat shrinkage or shape memory effect of polymers is used. Therefore, the 4D printed hinges are rigid and cannot be folded or unfolded after 4D printing below the glass transition temperature of the shape memory polymer (SMP). Hence, in this study, we proposed a hybrid hinge structure that is elastic and can be largely deformed as an origami structure even after 4D printing. On the hybrid hinge, a soft elastomer hinge was arranged beside the rigid 4D printing hinges to achieving the elastic folding deformation after self-folding. We confirmed that the samples recovered to almost their original shape without failure after 500 cycles of folding. They exhibited high durability and elasticity. Finally, the usefulness of the hybrid hinge was demonstrated by fabricating a miura-ori and an origami compliant mechanism gripper, which could be deformed as origami structure below the glass transition temperature of the SMP. We believe that our 4D printing method can be applied for developing self-folding actuators and robots, which require origami deformation.