A review of 4D printing

Research into 4D printing has attracted unprecedented interest since 2013 when the idea was first introduced. It is based on 3D printing technology, but requires additional stimulus and stimulus-responsive materials. Based on certain interaction mechanisms between the stimulus and smart materials, as well as appropriate design of multi-material structures from mathematical modeling, 4D printed structures evolve as a function of time and exhibit intelligent behavior. Unlike 3D printing, 4D printing is time-dependent, printer-independent, predictable, and targets shape/property/functionality evolution. This allows for self-assembly, multi-functionality, and self-repair. This paper presents a comprehensive review of the 4D printing process and summarizes the practical concepts and related tools that have a prominent role in this field. Unsought aspects of 4D printing are also studied and organized for future research.