Materials, design, and fabrication of shape programmable polymers

Abstract

Programmable matter is a class of materials whose properties can be programmed to achieve a specific state upon a stimulus. Among them, shape programmable materials can change their shape, topographical architecture, or dimension triggered by external stimuli after material fabrication, finding broad applications in smart devices, soft robotics, actuators, reconfigurable metamaterials, and biomedical devices. Shape programmable polymers (SPPs) possess the advantages of low cost, the ability to achieve widely tunable stimuli response, and synthetic flexibility. Recent development has resulted in various new materials and fabrication techniques for SPPs. However, to better design and fabricate SPPs to satisfy specific applications, a more comprehensive understanding of SPPs is required. In this review, we provide state-of-the-art advances in materials, design methods, and fabrication techniques for SPPs. Based on different shape-shifting mechanisms, four most widely studied shape-shifting polymers, including shape-memory polymers, hydrogels, liquid crystal elastomers, and magnetoactive elastomers, are categorized. After outlining the material models of SPPs, the widely used approaches of bilayer, biomimetic, and simulation-guided design, are summarized. For the fabrication side, three main manufacturing techniques for SPPs by replica molding, electrospinning, and 3D printing are reviewed with an emphasis on 3D printing. Finally, the challenges and future perspectives for SPPs fabrication are discussed.