"Transient electronics" that dissolve in the body may eventually offer an alternative to permanent electrical medical implants, such as pacemakers.
When these permanent implants are no longer needed, surgical removal is often the only option. But implants that dissolve can offer treatment and then disappear.
"Transient electronics" are tiny, biodegradable integrated circuits that can dissolve in water or in bodily fluids.
Researchers at the University of Illinois at Urbana-Champaign and Northwestern University, in collaboration with Tufts University, are developing such electronic implants made of a mixture of silicon and magnesium encased in a silk protein.
"Imagine the environmental benefits if cell phones, for example, could just dissolve instead of languishing in landfills for years," said Fiorenzo Omenetto, lead researcher at Tufts University and a senior author of the study.
And, in the future, the devices may be able to perform life-saving diagnostic or therapeutic functions, such as monitoring a patient's condition or treating post-surgical infection, according to research the scientists published in the current issue of Science magazine.
Preliminary stage research on lab rats demonstrated the ability of the devices to operate in a way that can eliminate bacterial sources of infection in a wound through the use of heat, for example. Yet the devices inserted in the rats were almost completely dissolved three weeks later when the researchers checked on it. Remnants of the silk coating were the only thing remaining. The "silk" protein-based casings disappear more slowly than silicon and magnesium.
The protein-based silk used in the electronic devices casings is not to be confused with the material used in clothing.
The silk used in their research is entirely different and not harmful to the body; it has been approved by the Food and Drug Administration, said Yonggang Huang, a professor of civil and environmental engineering at Northwestern University and a senior author of the study.
It is protein extracted from silkworm cocoons and therefore very durable while also being completely biodegradable.
The thickness of the silk protein casing can be fine-tuned to the patient's needs and helps determine the longevity of the implant (from minutes to days to years).
The researchers were careful to choose elements that are already found in the body, they noted.
And the current size of these devices is remarkably small.
The electronic devices are roughly the size of a nickel and a mere tens of nanometers thick, which is "like less than 1 percent of your hair thickness," Huang said.
The implants are very small (due to the size of the rats), but they could be made larger for human use.
The size of the device is malleable, said John A. Rogers, University of Illinois at Urbana-Champaign professor of materials science and engineering and also one of the senior authors of the study.
"The lateral dimensions can be tailored to the size of the wound, or the surgical site," Rogers said. "The thicknesses, though on the other hand, are dictated more by circuit and electrical performance considerations, number one, and with an eye towards minimizing the amount of material that is needed for the device to minimize the potential for any adverse effect on the body."
The possibilities of transient electronics aren't limited to the medical field. The electronics could also be used as environmental monitors, as well as in consumer electronics.
Transient electronics could also be used to monitor environmental disasters, like oil spills, said Huang.
Indeed, the potential of transient electronics is wide in its scope.
The researchers indicate it's still too early to predict when transient electronics will be available for human use. Environmental and consumer product devices are likely to become available prior to their medical counterparts, which will require much more testing and approval by the FDA before being implanted in humans.
"This is a starting point I think for a new technology," said Rogers. "We've been able to demonstrate a lot in this first paper, but the book hasn't been written yet on transient electronics."