Electrically Induced Wire-Forming 3D Printing Technology of Gallium-Based Low Melting Point Metals

Low-melting point metals and alloys, as emerging 3D printing ink, have attracted more and more attention especially for flexible or intelligent conductors and electronics. However, achieving 3D continuity of liquid metal structures or patterns using a common method is still challenging and worth pursuing. In this study, a generalized method is proposed for 3D printing structures made of low melting gallium-based alloys with diverse melting points, which should greatly expand their applications. The mechanism for shaping liquid metal inks relies on the combination actions between electrocapillarity and oxidation, which significantly reduces the high surface tension as well provides solid frame for the inner liquid metals. Taken galinstan as an example, the printing conditions, including the viscosity of hydrogel, positive voltage (0–15 V), calcium chloride concentration, and velocity (the movement speed of the printing head) are explored to optimize the process. The printed galinstan is characterized to observe the morphology and elemental analysis of the surface oxide layer. During the process, the chemical reagents are all safe and non-toxic, which is in line with the green product requirements. This printing method shall have broad application prospect in flexible electronics, biosensors, biomedical engineering, contrast agent in vivo, and other fields.