4D Printing Using Multifunctional Polymeric Materials: A Review

The use of 4D printing is, without any doubt, one of the current challenges and also an exciting opportunity to create customized and perfectly defined 3D structures capable of changing their shape according to a particular external stimulus. This article aims to provide a basic and general overview of 4D printing, providing the characteristics and requirements of this technology in comparison with the well-established 3D printing. The most extensively employed materials that include shape memory polymers and hydrogels are also discussed in detail. The last part of this article illustrates, with selected examples, the vast myriad of applications in which 4D printing offers unique opportunities. These include the preparation of origami structures, sensors, and actuators, or particularly in the biomedical area, to prepare fully customized implants capable of adapting to a particular patient׳s needs.