They're called "biocompatible electronics" - tiny medical implants designed to dissolve into the body's tissues after they have done their work. Such devices may some day be used for fighting post-surgical infections, speeding bone development and a host of other medical applications.
Unlike conventional medical implants such as heart valves or hip replacements that are designed to last a lifetime, “transient electronics” are made with tiny, ultra-thin silicon chips, containing magnesium electrodes, that completely melt away when they have served their function. They're now being developed by a team of researchers at the University of Illinois, Northwestern University in Illinois and Tufts University in Massachusetts.
John Rogers is a University of Illinois engineering professor who leads the development team. Rogers envisions a number of medical applications for the new devices, which combine microchips with so-called nano-membranes that slowly melt when exposed to water or biofluids.
“One example of that kind of device is in an applique, a thin film device that goes into the body at the site of a surgical incision to provide thermal therapy that can eliminate bacteria that would otherwise cause infection," said Rogers.
Rogers says the chip, which can be controlled wirelessly, is packaged in silk gathered from silkworm cocoons. Researchers can alter the structure of the silk, Rogers says, to pre-set how long the silicon chips last - from minutes to days, weeks or even longer.
Rogers and colleagues conducted experiments in which they slipped the silicon wafers into surgical incisions on mice. Rogers says the dissolvable chips, only a few tens of nanometers thick, heated the animals’ wounds for two weeks - just long enough to prevent infection and for healing to begin.
“And in that type of time regime, it’s advantageous for the device to simply disappear," he said.
Scientists examining the mice a few weeks later saw little sign of infection and only a faint residue of the silicon wafer at the wound sites.
Rogers says the device's electrodes are made of magnesium, a naturally fluid-soluble material. The amount of magnesium on a single chip is less than most people consume every day through their diets or in a multi-vitamin.
The biodegradable technology might some day have a wide range of applications - from environmental monitoring to creating disposable and non-polluting consumer electronic products. But for now, researchers are focusing on the medical possibilities, including heart, brain and muscle activity monitors, as well as targeted drug delivery devices.
An article by John Rogers and colleagues on the development of a transient electronic medical device is published in the journal Science.