Spatially selective adhesion enabled transfer printing of liquid metal for 3D electronic circuits

3D printing, well known by the public, is regarded as an important symbol of entering the next industrial revolution that is well suited for the development of 3D electronics. However, reducing the manufacturing cost and time of 3D electronics is still one of the biggest challenges for its wide application. With low melting point, high conductivity, and reversible stiffness, gallium-based liquid metals are of great importance in developing multifunctional 3D electronic circuits. While, most research only use liquid metal as filler in 3D channels, which greatly weakened the interface function of liquid metal. Here, we report a straightforward, practical, and rapid fabrication strategy for multifunctional 3D electronic circuits based on 3D printing and a spatially selective adhesion mechanism of liquid metal inks. This method is applicable to diverse 3D structures with various mechanical properties and material types. A series of electronic circuits were printed out, and conceptual experiments were performed to demonstrate and justify the working of the new approach. Because of the phase transition and contact welding, the liquid metal based 3D electronic circuits show excellent stiffness variation and assemblability, which are promising to fabricate complex flexible 3D electronic systems, reconfigurable 4D electronics, and variable stiffness robots.