4D printing has attracted academic interest in the recent years because it endows static printed structures with dynamic properties with the change of time. The shapes, functionalities, or properties of the 4D printed objects could alter under various stimuli such as heat, light, electric, and magnetic field. Briefly, 4D printing is the development of 3D printing with the fourth dimension of time. Among the fabrication techniques that have been employed for 4D printing, the direct ink writing technique shows superiority due to its open source for various types of materials. Herein, the state‐of‐the‐art achievements about the topic of 4D printing through direct ink writing are summarized. The types of materials, printing strategies, actuated methods, and their potential applications are discussed in detail. To date, most efforts have been devoted to shape‐shifting materials, including shape memory polymers, hydrogels, and liquid crystal elastomers, showing great prospects in areas ranging from the biomedical field to robotics. Finally, the current challenges and outlook toward 4D printing based on direct ink writing are also pointed out to leave open a significant space for future innovation.

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Four‐dimensional (4D) printing of shape memory materials has attracted increasing interests for personalized structures. In this study, a biocompatible poly(d,l‐lactide‐co‐trimethylene carbonate) (PLMC) is utilized to fabricate 4D shape‐changing structures with customized geometries through direct ink writing. The printed objects show shape transformations at different dimensions under thermal programming. The influence of the printing parameters on the properties including rheological, solvent evaporation, and static mechanical behavior are systematically investigated. A printing map is further depicted to achieve high‐quality printing with high viscous ink flowed from micronozzle to construct various structures. The printed structures in one‐dimensional, two‐dimensional, and three‐dimensional (3D) exhibit shape‐changing behavior with fast response around body temperature. The fast responsive time shows potential in the field of surgical suture (4 s), nonwoven fabric (3 s), and self‐expandable stent (35 s). The feasibility of 3D printing of PLMC opens the way for applications in shape‐changing devices with small diameter. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 48177.

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