Introduction to<scp>4D</scp>Printing: Concepts and Material Systems

Abstract

Four-dimensional (4D) printing has emerged and witnessed tremendous progress since 2013. The advances in critical fields such as three-dimensional (3D) printing techniques, programmable smart materials, and design/modeling tools have promoted the development of 4D printing. The 4D printing techniques enable 3D-printed structures to change their shapes, properties, and functions with time (the fourth dimension) in response to external stimuli after printing. The stimuli-triggered shape change of 3D-printed objects offers some advantages in manufacturing and end-use functions by 4D printing, finding applications in diverse fields, including actuators, soft robots, smart electronics, active metamaterials, and biomedical devices. This chapter provides the advances in 4D printing, focusing on programmable polymeric materials and structural design. After briefly introducing the history and basic elements of 4D printing, we overview the 3D printing techniques. Then, we cover the recent progress in using four major types of smart polymers (i.e., shape-memory polymers, hydrogel composites, liquid crystal elastomers, and magnetoactive materials) for 4D printing. State-of-the-art progress in using single-material-based material design and multi-materials-based structural design for 4D printing is presented. In addition, we summarize the advances in modeling-based design approaches. To close, we discuss the trend, perspectives, and potential applications of 4D printing.