![]() The main working principle is the introduction of a rationally designed pattern of spatially varying anisotropies into the material. This approach, which has received much attention since and makes 4D printing accessible to a wide range of users, is cost-effective, highly scalable, and applicable to many materials. Recently, we demonstrated how hobbyist FDM 3D printers and widely available, inexpensive materials can be used to program complex shape-shifting behaviors 26. The simplest type of 4D printing relies on the introduction of some sort of anisotropy in the material during the printing process 23, 24, 25, 26, 27. ![]() 4D printing allows for the single-step manufacturing of complex shape-shifting structures 20, 21, 22. Examples include the swelling of hydrogels submerged in water 17 and the shrinkage of pre-strained shape-memory polymers exposed to high temperatures 18, 19. The vast majority of the existing techniques rely on the use of active materials that change their dimensions upon activation 14, 15, 16. Several strategies for the fabrication of shape-shifting structures are reported in the literature. The 3D configuration of such materials changes upon activation, thereby altering their functions and properties (e.g., stiffness or wave propagation properties 12, 13). 3D-to-3D shape-shifting, on the other hand, is particularly useful for the fabrication of reconfigurable materials 10, 11. The main advantage lies in the ability to employ planar fabrication techniques for affording an ultimately 3D object with functionalities that originate from micro-/nanoscale surface features 7, 8, 9. 2D-to-3D shape-shifting enables flat constructs to fold themselves into geometrically complex 3D objects. There are two major categories of shape-shifting: 2D-to-3D and 3D-to-3D. ![]() Other examples are origami-based metamaterials 3, 4, 5 or self-folding bio-scaffolds made from (nano-)patterned 2D sheets 6. For example, a flat mechanism can shift its shape into a fully functional robot 1, 2. Shape-shifting empowers the development of designer materials with advanced functionalities and properties. We showcase the potential of the proposed approach for the fabrication of deployable medical devices including deployable bifurcation stents that are otherwise extremely challenging to create. We demonstrate how this modified printer can be combined with various design strategies to achieve high levels of complexity and versatility in the 3D-to-3D shape-shifting behavior of our reconfigurable materials and devices. This simple modification allows the printer to print on curved surfaces. Here, we present a single-step production method for the fabrication and programming of 3D-to-3D shape-changing materials, which requires nothing more than a simple modification of widely available fused deposition modeling (FDM) printers. That is caused by the intrinsically 2D nature of the layer-by-layer manner of fabrication, which limits the possible shape-shifting modes of 4D printed reconfigurable materials. As compared with the 4D printing of 2D-to-3D shape-shifting materials, the 4D printing of reconfigurable (i.e., 3D-to-3D shape-shifting) materials remains challenging. Upon activation, not only a change in their shape but also a large shift in their material properties can be realized. Shape-shifting materials are a powerful tool for the fabrication of reconfigurable materials.
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