Self-assembly origami structures by 4D-printed programmable hinges with bilayer actuators

Four-dimensional (4D) printing of self-assembly origami structures has received increased attention in recent years, which allows the structure to change its configuration under certain stimulating conditions during calculated times. It holds substantial potential for applications such as space structures for packaging, biomedical devices for drug delivery, and self-assembling robots. However, the creation of 4D-printed self-assembly origami structures that alter their shapes in a controllable manner in response to environmental stimuli is a grand challenge. One of the main reasons is that such complex final configuration of a self-folding origami structure depends on the sequence of folding of the individual pieces, which generally leads to design difficulties from collision issues during deforming. In this paper, we design 4D-printed programmable hinges with bilayer actuators for self-assembly origami structures, which realize the sequential self-folding based on the thermal-response control mechanism of bilayer actuators. Time-dependent behaviors of a hinge with bilayer actuators and effects of its configurations on time-dependent behaviors are investigated. A mathematical model of hinge configuration problem of 4D-printed self-assembly origami structures is established, which minimizes the complexity of the folding sequence. The grouping genetic algorithm (GGA) is employed to find the optimal configuration of hinges that enables the successful sequential shape transformation of the 2D origami layout into desired 3D structures without interruption by collisions. Two illustrative cases are introduced to demonstrate the proposed method, where a programmable gesture structure is choreographed to accurately achieve a sequential self-folding, and a self-assembly origami structure requires a folding sequence in order to assemble a stable and fully packed structure from a 2D origami layout without collision.