Domestic researchers have developed a "liquid metal-based electronic ink" that can freely switch between hardness and softness depending on the temperature.
The research team led by Professor Jeong Jae-woong of the Korea Advanced Institute of Science and Technology (KAIST) collaborated with Professor Park Seong-jun of Seoul National University and Professor Steve Park of KAIST's Department of Materials Science and Engineering to announce on the 4th that they have developed a liquid metal electronic ink that allows for the printing of micro-width circuits measuring ㎛ (micrometers, one-millionth of a meter) at room temperature and can freely adjust its hardness and softness depending on the temperature.
The research team focused on "gallium," a liquid metal that melts at around 29.8 degrees Celsius, near body temperature. Gallium is very hard in its solid state, but when melted, it becomes a soft liquid that allows for a significant change in rigidity. However, conventional gallium tends to cluster like droplets and has instability in its liquid state, making precise circuit fabrication challenging and leading to unwanted phase changes during the manufacturing process.
To overcome these limitations of gallium, they developed a pH-controlled liquid metal electronic ink printing technology. First, gallium particles of ㎛ size were mixed with a neutral solvent called dimethyl sulfoxide (DMSO) and hydrophilic polyurethane polymer to create the electronic ink. Thanks to the neutral state of the DMSO solvent, a stable high-viscosity ink is formed with gallium particles evenly dispersed in the polymer, enabling high-resolution circuit printing at room temperature.
After printing, during the heating process, the DMSO solvent decomposes to produce acidic substances, and in this acidic environment, the oxide layer on the surface of the gallium particles is removed, allowing the particles to physically connect, forming a circuit that can conduct electricity and adjust rigidity. This two-step process allowed for stable printing at room temperature while implementing electronic devices with excellent electrical conductivity and adjustable rigidity characteristics after completion.
The developed electronic ink can print precise circuits with a micro-width equal to half the thickness of a strand of hair (about 50㎛) and can transform freely from a hard state like plastic to a soft state like rubber. It is also compatible with existing printing methods such as screen printing and deep coating, allowing for the production of high-resolution, large-area circuits as well as a variety of complex three-dimensional electronic devices.
The research team developed a versatile multi-purpose device that uses this technology, which is hard for portable electronic devices in everyday use but transforms into a soft wearable healthcare device when worn on the body. It has proved its potential as an implantable component by being capable of brain insertion in a hard state during surgery while becoming soft within brain tissue to minimize inflammatory responses.
Professor Jeong Jae-woong noted, "By controlling the acidity of the electronic ink solvent to electrically and mechanically consolidate the gallium particles, we have addressed the persistent issues of liquid metal printing and enabled ultra-precise high-resolution circuit fabrication at room temperature, which is the core of this research," and he added, "A single device can transform freely into hard and soft states depending on the situation, making it applicable in various fields such as multipurpose electronic devices, medical technology, and robotics."
This study was published in the international journal "Science Advances" on the 30th.
References
Science Advances (2025), DOI: https://doi.org/10.1126/sciadv.adv4921