#Sequential structures series

Shape memory polymers (SMPs) are smart materials that can recover their permanent shapes from one (or sometimes multiple) programmed temporary shape(s) when an appropriate stimulus is applied, such as temperature 26, 27, 28, 29, 30, magnetic fields 31, 32, 33 and light 34, 35, 36, 37. These works demonstrated structures and machines that are modular, self-assembled, self-reconfigurable and capable of adapting to their environments. More recently, 3D printing technology is used to print active structures, leading to the emergence of 4D printing 21, 22, 23, 24, 25. Several self-folding mechanisms have been developed, such as using residual stress 15, 16, 17, shape memory alloy actuation 18, DNA 19 and hydrogels 20. Self-folding is more attractive in many applications as it saves the expensive infrastructure investment, such as robotic arms, to automate the folding 10. Complimentary theoretical work shows that the controlled folding and unfolding are complicated due to the independent folding motions of individual folds. A contemporary example is origami 5, the ancient art of paper folding that has found increasing engineering applications ranging from space exploration 6, foldable photovoltaics 7 and batteries 8, to shopping bags 9, 10, biomedical devices 11, 12, 13 and metamaterials 14. In recent years, folding has attracted increasing interest for technological applications. 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.įolding and unfolding are one of the most important mechanisms for generating large deformation and motions in nature, with a plethora of examples such as the winged insects 1 and tree leaves 2, 3, 4. 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 simplified reduced-order model is also developed to rapidly and accurately describe the self-folding physics. Measurements of the spatial and temporal nature of self-folding structures are in good agreement with the companion finite element simulations.

#Sequential structures series

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. The time-dependent behavior of each polymer allows the temporal sequencing of activation when the structure is subjected to a uniform temperature. 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. It finds technological applications including packaging of solar cells and space structures, deployable biomedical devices and self-assembling robots and airbags. Folding is ubiquitous in nature with examples ranging from the formation of cellular components to winged insects.