New flexible, electronically conductive material developed by Assistant Professor Qiming Wang. Photo courtesy of Qiming Wang
A world with flexible electronics—screens you can roll up or cellphones that can bend—may not be so far away. Researchers and electronics companies have been working on developments in this field for years, using 3-D printing to provide low-cost manufacturing of flexible devices that are rugged, lightweight and portable.
The advancement of thin-film has led to a handful of pliant items, such as bendable transistors and stretchable circuits that make building electronics easier. However, without an entire array of flexible components, a completely flexible device cannot be produced.
Using his novel 3-D printing technique, Qiming Wang, assistant professor in the Sonny Astani Department of Civil and Environmental Engineering, has developed a material that could create some of these components. “Scientific Reports” published in late September an article detailing his findings.
“Plastic 3-D printing is traditional; lots of 3D printers can print these kinds of structures. However, this kind of soft materials 3-D printing in this kind of complex geometry, I would say this is a first,” Wang said. “Potentially, we can imagine this can really facilitate the design of flexible electronics by the design of very complex conductors.”
Using a typical rubber material, called an elastomer, Wang manufactured a 3-D lattice structure with incredible stretchability and shock-absorption qualities. Wang believes it could be used for a number of applications, including robotics, joint rehabilitation, cushioning and, you guessed it, flexible electronics.
Traditional 3-D printing is typically associated with rigid, plastic structures made of PLA (polylactic acid) or ABS (acrylonitrile butadiene styrene), created one thin layer at a time. While a small selection of rubber-like materials has been developed for 3-D printers, they do not provide the substantial flexibility or motion needed to build flexible electronics. Additonally, printing flexible materials consisting of a highly intricate 3-D lattice is extremely challenging.
Wang has addressed this by using a new fabrication method. He begins by printing a 3-D scaffold of plastic material but, instead of solid beams, he creates hollow channels that are then filled with liquid elastomer. Over a period of several hours, sitting at room temperature, the liquid solidifies. Finally, the plastic, which is water dissolvable, is removed, leaving a freestanding, complexly structured, 3-D printed rubber.
When comparing the novel design to similar materials, such as other 3-D printed materials, Wang found his could stretch nearly twice as much as the competitions’. In fields like robotics that are turning to 3-D printing for low-cost part manufacturing, designs are limited by what materials are available. In their case, Wang’s new development may literally be the missing link.
“In robotics you have lots of joints, so you need a lot of flexibility to rotate or bend,” Wang said. “We can imagine our soft material 3-D printing can do that here. We can bridge rigid structures and do large angle rotation, large angle bending and stretching.” Good quote
His material also has superb shock absorption qualities, outperforming conventional elastomer foams used in cushioning during impact loading tests. Additionally, offering a customizable rigidity, his material could be used in joint rehabilitation, replacing existing brace designs.
Photo courtesy of Qiming Wang
But what Wang believes is the most interesting application is flexible electronics.
“Say people want to design a flexible screen they can bend or twist. Right now, the design is constrained to flexible, conductive thin-film,” Wang said. “However, if you want to design this kind of screen, you also need some bulk material to be flexible and conductive.”
With his new material already having the necessary flexibility, Wang just needed to make it electronically conductive as well. To do this, he used his hollow channel method, this time filling elastomer channels with a conductive liquid. The result: a soft, flexible structure indistinguishable from the original, but now a conductor with a complex geometry.
Wang and his team are currently hard at work making improvements to the novel material. He wants to be able to control the deformation of the material without having to touch it.
“Right now, we can control the deformation of this structure by an external magnetic field,” Wang said. “You don’t need to manually push it or deform it, we just apply a magnetic field outside, and the structure can deform as we want.”
They are also working to optimize the elasticity of the structure by fine-tuning the geometry. Once all their developments are complete, they will be one step closer to ultra-stretchable, externally controlled, flexible electronics.
“This would be a revolution beyond the traditional thin-film flexible electronics,” Wang said. “This will be 3-D flexible electronics.”