4D printing of shape memory polymers

Abstract The desideration to expedite sophisticated intelligence and to have an interdisciplinary accession of new forms of complexities lead to the inauguration of a modern additive manufacturing (AM) technology that adopts computer-aided design (CAD) models. 3D printing with its efficiency in material utility, surface resolution, and fine design triggered the research domain making it applicable from biomedical to electronics, and most conspicuously in biomimetics, and advanced materials for its advantages of amenity and adept fabrication of objects. However, the static and inanimate nature of the 3D printed part and the anisotropic behaviour of the technology acted as the impediment in the 3D printing technology which was annihilated by the 4D printing by adding a temporal dimension to 3D providing vitality to the design using a stimulus to trigger transfiguration in smart materials. Smart materials consisting of hydrogels, ceramics, metals, alloys, and polymers, have the propensity to origami on exposure to specific extramural stimuli, like calefaction, light, moisture, active sources, electromagnetic radiations, and pH ascribed to martensitic transformation or intrinsic elasticity. However, the high stiffness, the dominant recoverable strain (~up to 800%), the ability to trigger their shape recoverability (in bending ~ 93% and tensile ~ 87%), the facile fabrication into tailor-made products, in which some exhibit biodegradability and biocompatibility, make polymers one of the most prominent materials for 4D printing. This review discusses recent advancements in 4D printing, focusing on smart polymers and cognate stimuli response, the compatibility of the material with the 3D printer, applications, and trends of 4D printing of SMP.