# 4D Printing of Multicomponent Shape-Memory Polymer Formulations
## 5 Material Jetting (MJT) 4D Printing
(**b**) An actual 3D-printed strip in its original shape and (**c**-**h**) show results of this process with differing fiber architectures. Reproduced with permission from reference [23], copyright 2013 AIP Publishing, Woodbury, NY, USA. (**i**) Active origami box and pyramid. The printed flat cross and star shapes assemble themself into the desired box and pyramid shapes after the programming steps. (**j**) Active origami airplanes. Flat triangles with three or five hinges assemble into origami airplanes with different wing arrangements. Reproduced with permission from reference [77], copyright 2014 IOP Publishing, Ltd., Bristol, UK. [PERSON] et al. utilized the MJT printing method to fabricate complex structures displaying sequential shape recovery [31]. Helical 3D objects with rigid (non-active) sections connected by active hinges on each corner with a radius of 5 mm are shown in Figure 16a. Two foldable composite strands with hinge structures were printed. The first sample was composed of nine hinges of the same SMP (\(T_{g}\) = -55 \({}^{\circ}\)C), while the second had seven hinges composed of different SMPs having \(T_{g}\) values ranging from 32 \({}^{\circ}\)C to 65 \({}^{\circ}\)C, with inner hinges having the lowest \(T_{g}\) values and outer hinges having the highest \(T_{g}\) values. After printing, the structures were deformed into a flat configuration in hot water at \(T_{H}\) = 90 \({}^{\circ}\)C, above the \(T_{g}\) of all of the trSMP sections. Then, the samples were cooled to \(T_{L}\) = 10 \({}^{\circ}\)C, at which point all the trSMP hinges were in the glassy state. During recovery by heating (\(T_{r}\) = 90 \({}^{\circ}\)C) in sample 1, all hinges were activated simultaneously, leading to incomplete folding (Figure 16b). For sample 2 the inner hinges with lower \(T_{g}\) recovered faster than the outer hinges, thus enabling sequential activation and yielding unconstrained and rapid (~7.0 s) folding to realize the targeted configuration (Figure 16b). [PERSON] et al. used MJT 3D printing to design and manufacture flat layered composites consisting of families of digital trSMP fibers with different \(T_{g}\) values embedded in a rubbery matrix [139]. After being programmed into a temporary shape by a simple thermomechanical training sequence, the printed composite was able to change into multiple shapes by stepwise increases in environmental temperature. For example, the design and shape changing capability of a two layered composite having SMP fibers with different \(T_{g}\) values (fiber 1 \(T_{g}\) \(\sim\) 57 \({}^{\circ}\)C; fiber 2 \(T_{g}\) \(\sim\) 38 \({}^{\circ}\)C) embedded in a rubbery matrix with a low \(T_{g}\) (~2 \({}^{\circ}\)C) is shown in Figure 16c. The composite strip was stretched to a prescribed strain at a programming temperature \(T_{\rm H}\) that exceeded the \(T_{g}\) of both fibers, then cooled to a fixing temperature of \(T_{L}\) = 0 \({}^{\circ}\)C, well below the \(T_{g}\) of both fiber materials. By stepwise heating the \(T_{g}\) values of the rubbery matrix and the trSMP fibers were exceeded, one after the other,  
Figure 16: Multi-shape memory effects of a printed active composite strip. (**a**) The schematic of the helical trSMP component. (**b**) A series of photographs shows its shape recovery process (1) in the case of uniformly activated hinge sections, and (2) in the case of sequentially activated hinge sections [31] (CC BY license). (**c**) The design and dimensions of the multi-material sample. The enlarged drawing represents a cross-section of the structure. (**d**) The original printed sample. The length scale at the bottom is in mm. (1–4) Shape change of the sample at different temperatures [139] (CC BY license). and a series of intermediate bending shapes was realized as a consequence (Figure 16d). Here, the amount of deformation was dependent on the thermomechanical properties of the fibers and the matrix (such as \(T_{g}\), stiffness and stress relaxation times), as well as the programming strain and the ambient temperature.