4D printing (4DP) combines the use of additive manufacturing (AM) to produce freeform components with stimuli-responsive materials, so that the printed parts can transform over a calculated duration of time. This paper provides a collective review of the transformational behavior of 4D printed parts that can be achieved using shape-memory polymers (SMPs). Using the process of 4DP, flat-packed structures can be printed and activated by external stimuli to transform into fully deployed functional structures. The paper provides designers and engineers with an understanding of the possibilities of shape-changing behaviors that can be realized using 4DP, where examples of existing work are referenced. From this knowledge, designers and engineers are able to implement suitable design strategies using computer-aided-design (CAD) to better control the shape-change behavior. We summarize our findings using a taxonomy of shape-changing behaviors that can be categorized according to basic, complex, and combined behaviors.

Four-dimensional printing (4DP) is an approach of using Shape Memory Materials (SMMs) with additive manufacturing (AM) processes to produce printed parts that can deform over a determined amount of time. This research examines how Polylactic Acid (PLA), as a Shape Memory Polymer (SMP), can be programmed by manipulating the build parameters of material extrusion. In this research, a water bath experiment was used to show the results of the shape-recovery of bending and shape-recovery speed of the printed parts, according to the influence of the print pattern, infill density and recovery temperature (Tr). In terms of the influence of the print pattern, the ‘Quarter-cubic’ pattern with a 100% infill density showed the best recovery result; and the ‘Line’ pattern with a 20% infill density showed the worst recovery result. The ‘Cubic-subdivision’ pattern with a 20% infill density demonstrated the shortest recovery time; and the ‘Concentric’ pattern with a 100% infill density demonstrated the longest recovery time. The results also showed that a high temperature and high infill density provided better recovery, and a low temperature and low infill density resulted in poor recovery.

4D printing (4DP) is a promising technology that enables additive manufactured parts to be programmed for actuation, reducing the need for external power or electromechanical systems. As this area of research has grown exponentially, this review paper aims to define and establish fundamental concepts and terminologies used in the field of 4DP. The objective is to encourage researchers to adopt a more consistent approach and a standardized set of vocabulary associated with this emerging field. Even though the paper covers the most widely used definitions, the multidisciplinary nature may mean that certain words could be used interchangeably or have a different meaning in another context.