Most electronics are built to withstand deterioration, but a team of scientists have used silk and ultra-thin slices of silicon to create an electronic circuit that is intentionally impermanent and will dissolve in water.
Biodegradable electronics could enable a dramatic rethinking of how circuits can be used safely and conveniently. Sensors could monitor the status of an environmental cleanup site, then dissolve harmlessly. Doctors could implant a medical device to kill bacteria in a wound, without the need for follow-up surgery to remove it. Biodegradable circuits could even help curb the growing problem of “e-waste,” a result of consumer appetite for the latest gadgets, which regularly turns cellphones and laptops into electronic detritus.
“What they’ve done is created a whole kind of manufacturing procedure and a way of setting up degradable electronic implants that is very nice,” said Robert Langer, a biomedical engineer from the Massachusetts Institute of Technology who was not involved in the work. “I expect there will be things like new kinds of sensors” enabled by such technology.
The idea emerged from a collaboration between scientists with very different expertise: Tufts University bioengineers who have for years been finding nontraditional uses for silk and researchers from the University of Illinois Urbana-Champaign who specialize in building thin, flexible electronics.
“We started working on silk a long time ago and specifically the transformation of silk into a technological material,” said Fiorenzo Omenetto, a professor of biomedical engineering at Tufts and one of the leaders of the study, published last week in the journal Science. “Then we started thinking about dissolvable [electronics]; we can control the degradation of silk in many ways.”
The researchers realized they could use silk as a laminating material, carefully controlling its properties so it would disintegrate on a predetermined time scale, ranging from under a minute to months.
First, they had to get the silk. Researchers removed the worms from silkworm cocoons. Then, Omenetto said, “You make pasta basically. You put them in a beaker; boil them with salt.” That breaks down the “glue” that holds the cocoon together. The Tufts researchers then made sheets of transparent silk material on which their collaborators could build a circuit.
Because the researchers wanted the whole circuit to be biodegradable, they needed to make unconventional substitutions and engineering decisions when designing the elements. They used slices of silicon thinner than a human hair and substituted other materials found in the body, including magnesium, to take the place of other circuit elements.
As an initial demonstration, the team built a device enveloped in silk that could heat up, killing bacteria at the site where it was implanted. They also built electronic devices and tested whether they biodegraded in the bodies of mice. After three weeks, they reported in the paper, they found only “faint residues” of the electronic chips.
“We try to do a lot of research in close collaboration and consultation with clinicians,” said John Rogers, a professor of materials science and engineering at the University of Illinois Urbana-Champaign whose laboratory specializes in engineering flexible circuits. “Surgical site infection is a leading cause for the risk for readmission to the hospital — put a therapeutic device in there, and it’s a perfect example of a kind of function where transient” electronics would be useful.
Many steps remain before such devices could be used in the human body, including conducting safety tests and making decisions about what would be the most useful application. The work was supported by the Defense Advanced Research Projects Agency, and outside scientists said military applications were possible.
Jeffrey Borenstein, a biomedical engineer at Draper Laboratory, said the techniques could potentially be used to design sensors that would be implanted in soldiers to monitor their health remotely, allowing medical care to be deployed more rapidly on the battlefield.
The disposable circuits could also be employed to control the delivery of drugs to specific spots in the body at designated times.
Other teams, such as Borenstein’s, are working on a rival approach: developing an implantable device that could deliver, on demand, a drug to the inner ear of a patient with tinnitus, using degradable circuits made of polymers that conduct electricity instead of silicon.
Because the researchers can take advantage of traditional silicon technologies and design devices to decay over a set period of time, the potential applications are diverse — including implants that could monitor blood sugar or release hormones; sensors that could be dropped onto a polluted area to track the progress of a cleanup; and components in consumer electronics that could degrade over years instead of building up in landfills.
Omenetto said many things are possible with this new technology, but a lot of testing remains to be done. Each application will come with its own engineering challenges.
“It is a bit early to speculate,” he said. “You don’t want to be on a phone call and have your phone melt. There are going to be a lot of practical requirements that require different amounts of material control.”