Sequential Self-Folding Structures by 3D Printed Digital Shape Memory Polymers

Abstract

Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices, and self-assembling robots and airbags. Here we demonstrate sequential self-folding structures realized by thermal activation of spatially-variable patterns that are 3D printed with digital shape memory polymers, which are digital materials with different shape memory behaviors. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. This is demonstrated via a series of 3D printed structures that respond rapidly to a thermal stimulus, and self-fold to specified shapes in controlled shape changing sequences. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations. A simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. An important aspect of self-folding is the management of self-collisions, where different portions of the folding structure contact and then block further folding. A metric is developed to predict collisions and is used together with the reduced-order model to design self-folding structures that lock themselves into stable desired configurations.

Ultrafast Digital Printing toward 4D Shape Changing Materials

“…[17][18][19] Upon triggering (e.g., heating), the stress is released and the structure further evolves with time (the fourth dimension) into 3D. [17][18][19] Such processes overcome the typical layer-by-layer printing limitation.…”

Graphene‐Based Polymer Bilayers with Superior Light‐Driven Properties for Remote Construction of 3D Structures

“…Folding is actually localized bending, so these terms are sometimes used interchangeably 8. So far, many stimuli‐responsive polymers have been investigated and employed to fabricate 3D structures including hydrogels,9 shape memory polymers,10 thermoresponsive polymers,11 and gradient polymeric composites 12. Moreover, the frequently used external stimuli to trigger a shape change in stimuli‐responsive polymers include solvents,13 electricity,14 pneumatic stimulus,15 mechanical stimulus,16 heat,17 and light 18.…”

“…However, the delamination and fracture from the defects in the fabrication process may appear during the assembly. Temperature‐responsive composites (e.g., poly( N ‐isopropylacrylamide)[[qv: 17c]] and hydrogels11) have been widely used as precursor materials in 3D structures. However, these deformation processes require extra solvent media and are generally slow owing to the reliance on the diffusion of the solvent into the polymer 13.…”

A Rewritable, Reprogrammable, Dual Light‐Responsive Polymer Actuator

“…Among these, folding, often related to origami art, has attracted considerable interest 4, 5, 6, 7, 8. An appealing feature of folding is the ability to deform a 2D object into a chosen 3D structure in response to a stimulus.…”