Tiny implant monitors brain injury, then melts away

It's one of those early stage animal studies that's just too cool not to talk about.

Researchers have implanted chips holding tiny electronic sensors and wires in the brains of rats that will melt away once they are no longer needed. The hope is that someday the use of these dissolving sensors could eliminate the need for large, bulky externally hardwired systems that leave human patients open to infection, bleeding and allergic reactions.

"The ultimate strategy is to have a device that is entirely implanted, intimately connected with the organ you want to monitor and can transmit signals wirelessly, allowing doctors to intervene if necessary to prevent bigger problems," said Washington University neurosurgeon Dr. Rory Murphy in a statement. "After the critical period that you actually want to monitor, it will dissolve away and disappear."

About the size of a grain of rice, the implant in the study was placed under the skin but on top of the rat's skull. Information on temperature and intracranial pressure was fed wirelessly to computers, and accurately matched the readings on conventional monitors, said the researchers.

"Our devices eliminate the wired interface and the need for surgical extraction," said study co-author John Rogers, an engineering and materials science professor at the University of Illinois at Urbana-Champaign. "The outcome greatly reduces the risk for the patient, without any sacrifices in the accuracy or precision of the monitoring data."

In this initial study, the implants were designed to keep track of intracranial pressure and temperature after traumatic brain injury or brain surgery. That's important, because the skull keeps the brain from expanding, so an increase of temperature or pressure can lead to permanent brain or spinal damage.

The concept of absorbable medical supplies is not new; dissolvable stitches have revolutionized surgery. Usually made from a collagen material, such as silk, hair or processed animal intestines, the stitches are seen by the body as foreign materials. Therefore, they are attacked and broken down by the immune system in about the same period as healing occurs. The implant used in the rats is similar in nature.

"The devices consist of a multilayer stack of materials," said Rogers, and "each of these materials dissolves in biofluids to yield biocompatible end products. Some of these materials are already used in existing, non-electronic bioresorbable implants sutures; others are naturally occurring in the body, and are recommended parts of a daily diet (silicon and magnesium)."

But the idea of creating "smart chips" that can feed doctors information and then waste away takes the concept to a new level, say the researchers.

"This is a new class of electronic biomedical implants," said Rogers. "The devices can be adapted to sense fluid flow, motion, pH or thermal characteristics, in formats that are compatible with the body's abdomen and extremities, as well as the deep brain."

"These kinds of systems have potential across a range of clinical practices, where therapeutic or monitoring devices are implanted or ingested," said Rogers.

Of course, there's no guarantee that what works in rats will work in people. But the researchers are optimistic, and plan to take their implant to human trials.

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