A tiny wireless electronic sensor no bigger than a grain of rice can be implanted in a person's brain to monitor it following an injury, but then completely dissolve without a trace when its job is done, researchers say.

Such monitoring could save a person from having to undergo multiple rounds of surgery or be wired up to external monitors, they say.

Neurosurgeons have long desired a better way to monitor temperatures and pressures within a brain that has sustained traumatic injuries or undergone surgery, as both are crucial parameters to the health of the brain.

Current methods involve an implanted sensor that must be hard-wired to an external monitoring instrument, explains John Rogers, who headed the development of the new sensor at the University of Illinois at Urbana-Champaign.

"It works, but the wires coming out of the head limit physical movement and provide a nidus (location) for infection," he says. "You can cause additional damage when you pull them out."

A wireless device that could dissolve when no longer needed would eliminate additional surgery to remove a sensor, with its attendant risks of hemorrhage or infection, says Rogers, a professor of engineering and material science.

Rogers led a research team with colleague Wilson Ray, a professor of neurological surgery at the Washington University School of Medicine in St. Louis, to develop a wireless version, details of which have been published in the journal Nature.

The tiny device, just a millimeter long and a tenth of a millimeter wide, is made of silicon and polymer in tiny amounts that can be eventually broken down by the body without triggering any harmful side effects.

"The materials individually are safe," Rogers says. "The total amount is very small. It's about 1,000 times less than what you'd have in a vitamin tablet."

The technology could have a wide range of applications in a number of clinical practices, the researchers say, providing monitoring or therapeutic devices that can be implanted or ingested.

After performing their particular sophisticated function for a few weeks and when no longer necessary, they would be absorbed harmlessly into the body's own fluids, they say.

In testing of the wireless sensors in animal models, measurement precision obtained was just as good as conventional devices, they report.

Implanted in rats, the tiny devices transmitted measurements for about a week. After three months, they had entirely disappeared from within the rats' bodies, they say.

The researchers announced they are moving toward trials involving humans.