Pusan National University, KAIST, and Seoul National University Joint Research Team Develops "Liquid Metal Electronic Ink That Changes Shape with Temperature"

Precision Microfabrication at Room Temperature with Liquid Gallium Electronic Ink That Melts at Body Temperature
Electronic Devices with Stiffness Adjustable by Up to 1,465 Times, Switching Freely Between Rigid and Flexible States

Pusan National University (President Choi Jaewon) announced on June 4 that, in collaboration with KAIST and Seoul National University, it has developed a liquid metal electronic ink that enables microcircuit printing at room temperature and allows the shape to be freely changed depending on the temperature.

This research is regarded as an innovative achievement, as it enables the precise printing of microcircuit lines thinner than a human hair, while also allowing the completed circuits to switch freely between rigid and flexible states.

This development opens up new possibilities for various applications, including next-generation wearable and implantable devices, as well as soft robotics.

The research results were published in the internationally renowned journal 'Science Advances' on May 30. The study was jointly conducted by doctoral student Lee Simok from the Department of Electrical Engineering at KAIST and Professor Gunhee Lee from the Department of Optical Mechatronics Engineering at Pusan National University, who served as co-first authors. The research teams led by Professor Jaeung Jung (Department of Electrical Engineering, KAIST), Professor Steve Park (Department of Materials Science and Engineering, KAIST), and Professor Sungjun Park (Department of Advanced Convergence Engineering, Seoul National University) collaborated on the project.

From the left, Professor Jaeung Jung, Professor Steve Park, Professor Sungjun Park, Professor Gunhee Lee. Provided by Pusan National University

The title of the paper is "Phase-Change Metal Ink with pH-Controlled Chemical Sintering for Versatile and Scalable Fabrication of Variable Stiffness Electronics."

Evolution of 'liquid metal gallium' for the development of variable stiffness electronic devices. Conventional electronic devices have only offered either a rigid fixed form or a flexible form, which has limited their usability and technological applications.

To address this, the research team focused on 'gallium,' which melts at 29.8°C, close to body temperature. Gallium is solid and hard at room temperature but becomes extremely soft when in a liquid state, allowing the stiffness to be adjusted by up to 1,465 times.

However, the high surface tension and instability of gallium have posed significant challenges for precision printing. To overcome this, the team developed a new pH-controlled chemical sintering process, dispersing gallium particles and hydrophilic polymers in a dimethyl sulfoxide (DMSO) solvent, thereby creating an electronic ink that enables stable, high-resolution printing even at room temperature.

3D electronic devices can also be fabricated. The developed liquid metal electronic ink allows for microcircuit printing at a resolution of about 50 micrometers, with a conductivity reaching 2.27×10⁶ S/m. It is also compatible with existing manufacturing processes such as screen printing and dip coating, making it possible to fabricate electronic devices with complex three-dimensional structures.

Using this technology, the research team produced prototypes such as wearable healthcare devices that are rigid in portable form but become flexible in response to body temperature after being worn, and brain implant probes that are inserted in a rigid state during surgery but become soft inside the body, thereby demonstrating the practical potential of the technology.

Professor Gunhee Lee of Pusan National University stated, "This research newly proposes electrode technology that allows for the adjustment of stiffness based on metals with low melting points. It is a technology that can be expanded to various fields without limitations on the form of electronic devices, and it is expected to serve as a key material in the fields of flexible electronics, medical devices, and robotics in the future."