4D Printing of Liquid Metals

Room temperature liquid metals, as a unique intelligent material in the form of liquids, have demonstrated significant research value and immense application prospects in the realm of 4D printing. The structure of 4D-printed liquid metals can be effectively regulated and controlled through multiple external fields, endowing them with exceptional reconfigurable characteristics and diverse functionalities. Moreover, compared to conventional metals, liquid metals appear much easier to achieve additive manufacturing at room temperature due to their low melting point. Herein, we provide a comprehensive summary of the state-of-the-art research on 4D printing of liquid metals from various aspects including additive manufacturing technologies for liquid metals, structural response to multi-external field stimulation, potential application scenarios, and challenges. Firstly, the appropriate additive manufacturing technologies for liquid metals are meticulously chosen and comprehensively elucidated, including powder bed fusion, directed energy deposition, material extrusion techniques, as well as hybrid 4D printing techniques. Then, the different mechanisms and methods for driving as-printed liquid metals are outlined, such as thermo-responsive, electro-responsive, photo-responsive, and magneto-responsive 4D printing with liquid metals. Following that, the potential applications and significance of 4D-printed liquid metals are clarified. Finally, a perspective interpretation is given regarding the potentials and challenges of 4D printing of liquid metals.