LONDON – Imagine recovering from an operation without fear of a post-op infection from a drug-resistant superbug. Imagine that this is because of a tiny electronic device left behind when they sewed you back up, which monitors the wound, picks up signs of infection, administers a specific amount of heat to the right area and then, job done, disappears into your bodily fluids.
Imagine, too, an oil spill cleanup being monitored by 100,000 sensors dropped from a plane that would dissolve into the water when it was all over. Or a no-longer-loved smartphone that could actually dissolve down the sink rather than clog up your desk drawer.
Then imagine what the military could do with these so-called born-to-die devices. How about electronic eyes and ears that could be deployed for black ops in a war zone and then be triggered to dissolve when their mission was over or when they were about to be discovered? And finally, realize that this isn’t science fiction from Orson Scott Card, the writer of “Ender’s Game,” but rather current technology funded by DARPA, the Pentagon’s Defense Advanced Research Project Agency, who are the nice people working hard to make autonomous killer robots a living nightmare.
In one video of this born-to-die technology, when water drops hit the fingernail-size integrated circuit, its see-through silk substrate quickly starts to curl up, causing the strands of silicon and magnesium that make up its circuits to peel away. After just a minute, what had been a fully functioning board, with transistors, diodes and capacitors, is now just a long, thin, dirty strand of gunk.
In another video, it takes just two hours for the integrated circuit to dissolve in a glass of water.
In 2012 a transient device was implanted in the body of a mouse and powered wirelessly. The device was able to produce enough heat to kill off the bacteria that cause post-surgery infections. It lasted two weeks and then dissolved into the mouse’s bodily fluids with no obvious side effects for the mouse.
Now, professor John Rogers believes that we may be only “a year or two away” from testing biodegradable electronics in humans, albeit in surface wounds (for which the regulations are lighter). Rogers is head of the John Rogers Research Group at the University of Illinois, Urbana-Champaign, and one of the leading researchers into the development of these born-to-die electronic devices. It is his and his colleagues’ work that is featured in the videos.
While Rogers is “not allowed to say anything” about his work for DARPA, which began funding his research in 2008, other than that “we have done some amazing demonstrations” for them, he does confess that “I did eat one device, and I didn’t feel a thing. It just dissolved in my mouth.” For Rogers, “today’s electronics are remarkable feats of engineering” as they are “designed to last forever” with no loss of performance. “However,” he says, “when we looked to the future we realized that there was an opportunity for a new electronics — transient electronics — that might function properly for a finite amount of time and then disappear.”
However, there are a number of significant challenges that Rogers has to overcome, including trying to work out whether having a piece of electronics that dissolves in our bodies harms our health. There is even the tricky issue of how a water-soluble piece of technology can be mass-produced in a production process that conventionally uses a lot of water. Beyond that, there is the power problem: wireless power transmission is good for devices near, or on, the body surface but not so useful when they have to be implanted deep in the body. Further ahead lies another thorny problem, and one that is vital for the widespread use of the technology: how to get these devices to die on demand — and in substances other than water, so that the Pentagon doesn’t have to wait for rain before the evidence of its covert work disappears.
Rogers has tried to get round many of the problems that hold up innovative new technologies by trying to reuse “as much as possible of the stuff that is already out there for semiconductor manufacture” for the mass production of his transient electronics devices. He has also tried to use materials that already have approval by the U.S. Food and Drug Administration to cut out more potential holdups.
For example, the integrated circuit shown in the videos uses slices of silicon (silicon nano-membranes) so thin that they will dissolve in water; magnesium rather than copper as the conductor (since magnesium is nontoxic in small quantities and, indeed, an essential nutrient in the human body); and layers of silk to encase the whole device. Its life span is determined by the thickness of this silk substrate. The device is wirelessly coupled with an external power source, but in the future it might be powered by the movement of the body, and even have its transience activated remotely. Other materials, including zinc oxide and bio-resorbable polymers already FDA-approved, can work in transient technology as well, giving Rogers “a wide palette of materials to work from.”
“Our first attempt at transience was a bit of a hack,” he says, “in the sense that the devices we built were small and thin, but only partially transient. We then found ourselves being forced to think about things like the minimum lethal dose of transistors.” “The actual eureka moment came,” he adds, “when we had full transience in everything.” Now he is pretty confident that he has materials that can make transient electronics do “meaningful things.”
While Rogers has had “some amazing first demonstrations,” says Michael McAlpine, assistant professor of aerospace engineering at Princeton, the challenge is, he believes, to build a transient device “where there aren’t just, say, 10 transistors but the billion that you find on a real chip.” Then, for McAlpine, there is also the small matter of how well you can control exactly when the sensors will live or die, which “is critical for the applications” envisaged for the technology. This is called tunability: the ability to decide when the device will dissolve “so you can keep it for as long as you want.”
Professor Michael Dickey, of the faculty of engineering at North Carolina State University, says Rogers’ achievement is “pretty remarkable.” One of the “most elegant things” is trying to use conventional materials in an unconventional way so that transient devices can be made in a bog-standard electronics factory. “Then manufacture them very thin so they are easier to make go away. When you work on very thin substrates you can do all sorts of neat things that have been impossible to do with a silicon chip.” For Dickey, the ability to apply this born-to-die technology to more complex tasks isn’t too much of an issue as “they are not competing with Intel in terms of sophistication of the electronics.” Yet, says Dickey, “the devil could be in the detail. Every time you go into a new area there is no road map for you to follow.” In particular, “they didn’t demonstrate in their original work” that there could be triggers other than water for the device to dissolve in. Triggers such as a remote signal are particularly important for its wider application, whether monitoring an oil spill or movements on a battlefield.
“This concept is incredibly novel and a big deal,” says Teri Odom, professor of chemistry and of materials science and engineering at Northwestern University in Illinois. However, she thinks that “there are many design constraints” that have to be overcome before they can breathe life into the technology, such as “the dissolution rates of the layers, the types of materials used to conduct electricity, and the types of materials that can be used in the transistors. One limitation could be whether it would be possible to build in a power source on the electronics themselves instead of relying on external sources.”
Like Dickey, Odom feels that worries over the complexity of these born-to-die devices are “a straw man” as “the real sweet spot” for the technology are low-powered devices that are built to perform a specific function. However, she does warn that “anything in the biomedical arena takes time — in the order of 10 years for a device. Other applications like sensors to detect temperatures of structures like bridges might take less time.” While Rogers accepts that significant challenges remain, they are trying to adapt production lines “that have been designed to manufacture technology that lasts forever” to make something that might die after two weeks. He argues that as yet unpublished research will demonstrate that transience in dry conditions is possible and that he “can even trigger dissolution remotely, using a radio link.” As well as remote control, other triggers Rogers says are possible are “mechanical shocks, temperature change, light exposure and chemical-biological,” all of which are more suitable for battlefield conditions or a pollution incident than water. Quietly confident, he states: “It is still very early stages, but we are very optimistic that transient electronics will represent a big breakthrough.”
For Dickey, the wider success of this born-to-die technology beyond the “bio-resorbable stuff, which is a big deal” may well come down to the men in uniform. “The military are very interested in it and if they embrace it then it might become a much bigger deal, as it is an enabling idea whose wider significance just depends on how creative people are at using it.”