While 3D printing electronics is still a pipe-dream, you can be sure that researchers and engineers are going to push, stretch and hack current 3D printing technology step-by-step until the light at the end of the tunnel is at least detectable.
There is some new research from Purdue University that shows how liquid metal alloys and inkjet-printing technology can be used to mass-produce electronic circuits for"soft robots" and flexible electronics.
Elastic technologies offer a lot of possibilities for creating whole new classes of bendable robots and flexible "smart fabrics" that people could wear for a wide variety of reasons, including interfacing and interacting with computers, or wearing as a patient-specific therapeutic device. Of course before soft machines become commercially viable or feasible, a lot of sustained effort must come to pass.
Rebecca Kramer, an assistant professor of mechanical engineering at Purdue University said that the first step is to develop new manufacturing techniques.
In her words, "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. Conductors made from liquid metal can stretch and deform without breaking."
One potential manufacturing approach being considered at Purdue 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," Kramer said.
The method will be fully described in an upcoming research paper due out on April 18th in the journal Advanced Materials. Currently, we know that the method introduced in the paper is called "mechanically sintered gallium-indium nanoparticles", and describes research and the project itself. The authors are postdoctoral researcher John William Boley and graduate students Edward L. White and Kramer.
The paper describes the paper in the following way: "A printable ink is made by dispersing the liquid metal in a non-metallic solvent using ultrasound, which breaks up the bulk liquid metal into nanoparticles. This nanoparticle-filled ink is compatible with inkjet printing."
"Liquid metal in its native form is not inkjet-able," according to Kramer. "So what we do is create liquid metal nanoparticles that are small enough to pass through an inkjet nozzle. Sonicating liquid metal in a carrier solvent, such as ethanol, both creates the nanoparticles and disperses them in the solvent. Then we can print the ink onto any substrate. The ethanol evaporates away so we are just left with liquid metal nanoparticles on a surface."
After they are created and dispersed in the solvent, the nanoparticles have to be rejoined by applying light pressure. This also makes the material conductive. This step is crucial because the liquid-metal nanoparticles are initially coated with oxidized gallium, which acts as a conductivity blocking skin.
"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."
An interesting characteristic which this approach presents is the possibility for researchers to select which portions to activate depending on particular designs, suggesting that a blank film might be eventually be manufactured for a multitude of potential applications.
"We selectively activate what electronics we want to turn on by applying pressure to just those areas," according to Kramer, who was awarded an Early Career Development award in support of researching the development of inkjet printing metal alloys from the National Science Foundation this year.
The process described in the upcoming paper could make it possible to eventually mass-produce large quantities of the film quickly and efficiently.
On the horizon for the researchers is an explorative study of how the ink and the surface it's being printed on might be conducive to the producing specific types of devices.
"For example, how do the nanoparticles orient themselves on hydrophobic versus hydrophilic surfaces? How can we formulate the ink and exploit its interaction with a surface to enable self-assembly of the particles?” Kramer asked.
It will be interesting to see how researchers will study and model how individual particles break apart when pressure is applied, which could provide the right information to liberate the possibility of manufacturing ultrathin traces and new kinds of sensors.