Review of 4D printing materials and reinforced composites: Behaviors, applications and challenges

The introduction of 4D printing has revolutionized the manufacturing industry. Current research indicates that 4D printing, although at a nascent stage, is a promising technology that brings immense benefits that will soon outweigh high initial costs. 4D technology is considered an upgrade of 3D printing technology by the introduction of the fourth dimension: time. It has been shown that printed 4D materials can adapt to different stimuli such as temperature, water, pH, and light. These stimuli allow for self-assembly, self-repair, and multiple functionalities in these materials, which yield enormous potential for critical applications of 4D printed materials in the medical and aerospace fields. This paper reviews the current state of 4D printing and includes the technologies, materials, shifting/deformation behaviors, applications, and challenges surrounding this innovative approach to manufacturing. Advantages of 4D over 3D are also highlighted and the novel 4D printing technology via automated fiber placement is discussed. This review offers an analysis of composite materials used in this technology and describes how transformations of these materials elevate 3D printing technology. By highlighting opportunities for further improvement of 4D printing and contributing its fundamental understanding, this review article concludes that 4D printing is a revolutionary technology that is here to stay.