In 2012, he used similar tricks to make “transient electronics” that disintegrate in water after a given time. A silicon chip will do that anyway, given enough water and a few millennia. But by printing circuits thinly enough, Rogers can speed up that process to a matter of hours or days. That would be great for making medical implants that are only needed temporarily. For example, Rogers created a dissolvable heater that could burn away a bacterial infection in mice, before spontaneously vanishing once the animals were healthy.

When Murphy read about these electronics, he was enthralled. “I thought they would be perfect for what we do,” he says.

Together, the duo refined Rogers's original designs into a clinically useful pressure sensor. It consists of a membrane made from PLGA, a polymer regularly used in medical devices, suspended in a frame of silicon and magnesium. The pressure of the surrounding fluid causes the membrane to bend, which changes the electrical resistance of an adjoining silicon sensor.

John Rogers, University of Illinois

The whole device is then wrapped in a watertight polymer that gradually erodes over a few days, setting the lifetime of the sensor. (In their earlier work, Rogers’s team used silk; that’s impractical here, since silk absorbs water and would swell, pushing against the membrane in the sensor.)

When Murphy implanted the device in rats, he found that it’s as accurate as the best pressure sensors on the market. It’s also cost-effective, since it uses traditional materials with no precious metals. And most importantly, it seems to be safe. It didn’t trigger any inflammation or immune responses while it was intact, or after it had dissolved.

Nor should it. “The materials we chose include very small amounts of things like magnesium and silicon, which are recommended parts of the daily diet,” says Rogers. When they dissolve, their concentrations are so low that they are hard to track against the background of the same substances already in an animal’s body.

Next, the team will test their sensors in pigs, and carry out further studies to convince regulators that the devices are completely safe. If things go well, Murphy hopes to start clinical trials in human patients within three to five years.

In the meantime, Rogers wants to make improvements, especially around power and connectivity. Currently, the sensor is wired to a secondary implant placed under the skin in a less vulnerable part of the body. The implant then wirelessly transmits the sensor’s data to an external source, while also receiving wireless power. The sensor and its wires will disappear completely, but for now, the secondary implant is only 85 percent degradable. Rogers thinks he can reach 100 percent. “We think we can get it to 100 percent,” says Rogers.

“There is a huge unmet need to develop implantable devices that can achieve continuous monitoring of the body, to aid clinical decision making and ultimately improve patient quality of life,” says Jeff Karp from Brigham and Women's Hospital. Although Rogers, Murphy, and their colleagues have risen to that challenge, "it will be important to determine how long the system can work for and how to calibrate measurements with changes in the biological response to the implanted materials."