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Abstract:

3D printing technologies enable the creation of functional 3D structures with high resolution, precision, and low cost. Among these, extrusion-based Direct Ink Writing (DIW) stands out as one of the most promising methods due to its excellent compatibility with a wide range of printable materials of varying viscosities. However, traditional DIW techniques are limited by low printing speeds and typically struggle to print high-aspect-ratio, free-standing 3D structures without the need for supports. Additionally, conventional printable inks often exhibit low electrical conductivity and require post-processing to enhance their performance, which hinders their use in high-performance multifunctional electronics.

To address these limitations, we present a DIW approach that enables the direct printing of complex, free-standing structures using liquid Field’s metal. Field’s metal is a eutectic alloy with a low melting point of 62 °C and a high electrical conductivity of 2 × 10⁴ S/cm. To mitigate the beading issues caused by the high surface tension of molten metal, the DIW process is driven by shear forces for 2D planar writing and by tension for 3D out-of-plane printing. This approach achieves a high printing speed of up to 100 mm/s and demonstrates excellent compatibility with both rigid and soft substrates.

The rapid solidification of Field’s metal after printing allows for the direct creation of free-standing structures without the need for supports. Free-standing metal wires can be printed at any angle from 0° to 90°, with aspect ratios reaching up to 750. Even horizontally overhanging structures can be printed with ease. A variety of free-standing 3D architectures have been successfully printed, including vertical letters, cubic frameworks, and scalable helical structures, all exhibiting high electrical conductivity, self-healing properties, and recyclability.

To demonstrate the versatility of this technology in the fabrication of 3D electronics, a multi-layer circuit was created for battery-free temperature sensing, along with hemispherical helical antennas for contact-free vital sign monitoring. The developed DIW printing technology paves the way for the creation of high-performance, multifunctional electronics.

Biography:

Prof. Jerry Fuh is a Professor in the Department of Mechanical Engineering at the National University of Singapore (NUS) and the Founding Director and Advisor of the NUS Centre for Additive Manufacturing (AM.NUS). He is a Fellow of the Society of Manufacturing Engineers (SME) and the American Society of Mechanical Engineers (ASME), USA, and a licensed Professional Engineer (PE) in California, USA. Since 1995, Prof. Fuh has focused his research on Additive Manufacturing (AM) and 3D Printing (3DP) processes and materials.

He established NUS's cross-faculty R&D program on AM-enabled biomedical applications and played a key role in setting up advanced AM laboratories with a funding of over SGD 20 million. This was achieved through support from national agencies such as NAMIC, EDB, NRF, and A*STAR, as well as industrial collaborations.

Prof. Fuh has published extensively, with over 450 papers, five monographs, and 30 intellectual properties/patents. His work has garnered more than 21,700 citations and an h-index of 81 on Google Scholar, primarily in the fields of advanced manufacturing, materials, and design. He has also supervised more than 60 PhD graduates and serves as an Editor, Associate Editor, or Editorial Board Member for over 10 peer-reviewed journals related to design, manufacturing, materials, and AM.