Printed circuits can stretch the wearable boundaries
Electronic circuit boards that are stretchable may soon be used in robots and wearable smart clothing, say researchers at a US-based university.
The aim of research at Purdue University is to inkjet-print liquid-metal alloys to create a new type of flexible electronic circuit.
Elastic technologies could make possible a new class of pliable robots and stretchable garments that people might wear to interact with computers or for therapeutic purposes. However, new manufacturing techniques must be developed before soft machines become commercially feasible, said Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University.
“We want to create stretchable electronics that might be compatible with soft machines, such as robots that need to squeeze through small spaces, or wearable technologies that aren’t restrictive of motion,” said Kramer. “Conductors made from liquid metal can stretch and deform without breaking.”
Liquid metal in its native form is not inkjet-able so the research team has created liquid metal nanoparticles that are small enough to pass through an inkjet nozzle.
The nanoparticles are dispersed in a solvent, such as ethanol, for printing. The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface.
After printing, the nanoparticles must be rejoined by applying light pressure, which renders the material conductive. This step is necessary because the liquid-metal nanoparticles are initially coated with oxidized gallium, which acts as a skin that prevents electrical conductivity.
“But it’s a fragile skin, so when you apply pressure it breaks the skin and everything coalesces into one uniform film,” said Kramer. “We can do this either by stamping or by dragging something across the surface, such as the sharp edge of a silicon tip.”
The process could make it possible to rapidly mass-produce large quantities of the film.
A new potential manufacturing approach focuses on harnessing inkjet printing to create devices made of liquid alloys.
“This process now allows us to print flexible and stretchable conductors onto anything, including elastic materials and fabrics,” said Kramer.
A research paper about the method will appear on April 18 in the journal Advanced Materials. The paper generally introduces the method, called mechanically sintered gallium-indium nanoparticles, and describes research leading up to the project.
Future research will explore how the interaction between the ink and the surface being printed on might be conducive to the production of specific types of devices.