Science Advances
Researchers from the The KAIST and Seoul National University in South Korea has developed an electronic ink for printing of microcircuits variable stiffness at room temperature.
Variable stiffness electronics is a promising area that will allow devices to move from a rigid state to a soft state. The most a suitable material for this purpose is gallium, which changes from a solid to a liquid state relatively easily. However, this metal has a high surface tension, low viscosity and undesirable phase transitions.
The team, led by Professor Jae-Un Chong of KAIST’s School of Electrical Engineering, Professor Seongjun Park, who specializes in digital health at Seoul National University, and Professor Steve Park of KAIST’s Department of Materials Science and Engineering, decided to eliminate the restrictions on the use of gallium in the production of variable stiffness electronics.
They have developed an electronic ink that allows printing circuits with variable stiffness at room temperature. It is noted that this ink combines electrical conductivity and the necessary viscosity, which allows printing complex multilayer microcircuits high-resolution prints that are comparable to commercial printed circuit boards.
These circuits can dynamically change stiffness depending on temperature. Unlike traditional electronics, which typically have one well-defined form factor, either hard, durable devices or soft ones that are comfortable to wear, devices with variable stiffness will allow you to adapt it depending on your needs.
Temperature the melting point of gallium is 29.8 °C. In its solid state, gallium is highly rigid, while in its liquid form it is soft and fluid. Scientists have developed a printing process using liquid metal ink with pH control. By dissolving microscopic gallium particles in a hydrophilic polyurethane matrix using a neutral solvent —dimethyl sulfoxide, the researchers obtained Stable, high-viscosity ink for high-quality printing.
During post-printing heating, the dimethyl sulfoxide decomposes to form an acidic environment that removes the oxide layer from the gallium particles. This allows the gallium particles to form electrically conductive networks with customizable mechanical properties.
Dimensions of the elements printed circuit boards do not exceed 50 microns. They have high conductivity at the level of 2.27 × 10⁶ cm/m and stiffness modulation factor of up to 1465. This allows the material to move from a stiffness close to plastic to a soft state close to rubber In addition, the ink is compatible with traditional printing methods such as screen printing and dip coating.
Scientists have demonstrated the capabilities of the technology by creating a multifunctional device that normally works as a hard portable gadget, but when attached to the body, it turns into a soft medical device. They have also created a neural probe that remains rigid during surgical placement for precise positioning, but softens once it reaches the brain tissue to reduce inflammation.
«The main achievement of this research is to overcome the long-standing problems of liquid metal printing with our innovative technology. By controlling the acidity of the ink, we were able to electrically and mechanically bond the printed gallium particles, allowing us to produce large-area circuits with high resolution and adjustable stiffness at room temperature. This opens up new possibilities for future personal electronics, medical devices, and robotics», — emphasizes Prof. Jae-Un Chong.
The results of the study were published in the journal Science Advances
Source: TechXplore
