Researchers at Oregon State University (OSU)’s College of Engineering, Corvallis, Oregon, USA, report that they developed a modified, highly conductive gallium alloy which can be additively manufactured to produce flexible and stretchable structures. The development of the alloy, undertaken by a team within the college’s Collaborative Robotics and Intelligent Systems Institute, is potentially a first step toward the Additive Manufacturing of tall, complicated structures with a highly conductive gallium alloy.
The team developed the alloy by adding nickel nanoparticles into galistan, the liquid metal, in order to thicken it into a paste with a consistency suitable for Additive Manufacturing. Gallium alloys are already being used as the conductive material in some flexible electronics, thanks to their low toxicity and good conductivity. They are also inexpensive and ‘self-healing’ – having the ability to attach back together at break points. However, prior to development of the modified gallium alloy at OSU, galistan’s wetness meant that it could only be used to produce two-dimensional designs.
“The runny alloy was impossible to layer into tall structures,” explained Yiğit Mengüç, assistant professor of mechanical engineering and co-corresponding author on the study. “With the paste-like texture [after the addition of nickel], it can be layered while maintaining its capacity to flow, and to stretch inside of rubber tubes. We demonstrated the potential of our discovery by 3D printing a very stretchy two-layered circuit, whose layers weave in and out of each other without touching.”
The researchers at OSU used sonication – sound energy – to mix the nickel partcles and oxidised gallium into the liquid metal paste. The result was a paste thick enough to produce three dimensional, layered structures. For the purpose of the study, the alloy was used in the manufacture of structures up to 10 mm x 20 mm.
“Liquid metal printing is integral to the flexible electronics field,” added co-author Doğan Yirmibeşoğlu, a robotics Ph.D. student at OSU. “Additive Manufacturing enables fast fabrication of intricate designs and circuitry.”
The potential field of applications features a range of products including electrically conductive textiles; bendable displays; sensors for torque, pressure and other types of strain; wearable sensor suits, such as those used in the development of video games; antennae; and biomedical sensors. There is even potential for the production of robots from the new alloy. “It’s easy to imagine making soft robots that are ready for operation, that will just walk out of the printer,” stated Yirmibeşoğlu.
According to another of the co-corresponding authors, Uranbileg Daalkhaijav, Ph.D. candidate in chemical engineering, the gallium alloy paste demonstrates several features new to the field of flexible electronics. “It can be made easily and quickly,” he explained. “The structural change is permanent, the electrical properties of the paste are comparable to pure liquid metal, and the paste retains self-healing characteristics.”
This research project was supported by The Office of Naval Research Young Investigator Program. The team’s findings have since been published in Advanced Materials Technologies. The team stated that future work will explore the exact structure of the paste, how the nickel particles are stabilised and how the structure changes as the paste ages.