These kinds of electronics could have applications in medicine, pharmaceuticals, environmental monitors and the military, among other uses. Transient electronics physically vanish over time in a well-controlled manner and at a prescribed time, dissolving when they react with water. A magnesium oxide encapsulation layer and silk overcoat envelops the electronics, and the thickness determines how long the system will take to disappear into its environment.
"These electronics are there when you need them, and after they've served their purpose they disappear," said Yonggang Huang, who led the Northwestern portion of the research focused on theory, design and modeling. "This is a completely new concept."
The novel technology opens up important possibilities. Transient electronics could be useful as medical devices implanted inside the human body to monitor such things as temperature or brain, heart and muscle tissue activity, to apply thermal therapy or to deliver drugs. When no longer needed, the electronics would be fully absorbed by the body with no adverse effects. (Implantable electronics are not commonly used in medicine because of concern about the long-term effects.)
Such a system also could be used as environmental monitors placed on buildings, roadways or military equipment to detect temperature change or structural deformation. The device would dissolve when exposed to water, eliminating the need for it to be recovered at a future date.
"We selected materials familiar to the human body, such as magnesium," said Huang, a senior author of the paper and the Joseph Cummings Professor of Civil and Environmental Engineering and Mechanical Engineering at Northwestern's McCormick School of Engineering and Applied Science. "We didn't want to use a material the body has no experience with."
While the researchers studied a number of different biocompatible materials, including zinc and iron, they focused on silicon-based electronics with conductors made of magnesium. The key question they needed to answer was: How long will it take the entire electronic device to dissolve?