Dissolvable chips offer brain monitoring

Researchers from the Washington University School of Medicine have revealed an implantable wireless chip that can be used to remotely monitor pressure, temperature, pH, motion, and blood flow within the brain, before dissolving when its batteries deplete. So far, the device has been successfully tested in the brains of rats, but researchers believe that it should be used in the organs and tissues of human subjects, with the test articles showing no harm to the test rats.

From the folds and crinkles of a living brain, a fleeting fleck of electronics smaller than a grain of rice can wirelessly relay critical health information and then gently fade away.

The transient sensors, which can measure pressure, temperature, pH, motion, flow, and potentially specific biomolecules, stand to permanently improve patient care, researchers said. With a wireless, dissolving sensor, doctors could ditch the old versions that require tethering patients to medical equipment and performing invasive surgery to remove, which adds risks of infections and complications to already vulnerable patients.

Though the first version, reported in Nature, was designed for the brain and tested in the noggins of living rats, the authors think the sensors could be used in many tissues and organs for a variety of patients—from car crash victims with brain injuries to people with diabetes. “Sensors are incredibly important,” chief resident of neurosurgery and study co-author Rory Murphy of Washington University School of Medicine told Ars. But they’ve been a hassle, too.

To develop the wireless, dissolving model, Murphy and colleagues teamed up with John Rogers’ group at the University of Illinois at Urbana-Champaign, which specializes in wearable and implantable electronics. The wee gadgets they came up with generally contain biodegradable silicon-based piezoresistive sensors, which change their electrical resistance with slight bending, surrounded by more silicon, magnesium, and a dissolvable copolymer, poly(lactic-co-glycolic acid) (PLGA), which is already used in medical devices.

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Essentially, the sensors are made of elements and minerals that we already eat and drink, Murphy said.

The devices can also be customized with different types of sensors and coatings. The thicker the coating, the longer they take to dissolve, Murphy explained. The current versions can last for a few days in biofluids, including cerebrospinal fluid, at physiological temperature. But, Murphy said, the researchers are hoping to make versions that can last for weeks.

To make the sensors wirelessly transmit information, they ran dissolvable molybdenum wires, from the implantable sensor to a miniature, wireless data transmission device that can sit on the outside of the body, just on top of the skin

In rats, the researchers successfully implanted devices that measured temperature and pressure from inside the rat’s brain and transmitted the information wirelessly. Such information is critical for monitoring inflammation and swelling as patients recover from a brain injury, Murphy said.

The team also closely tracked the sensor’s demise, carefully noting whether it caused any immune response or inflammation—it didn’t.

“We’ve shown that the concept is possible,” Murphy said. Now, the team will move to more animal tests, optimization, and eventually clinical trials. With any luck, Murphy hopes that the sensors will be in early human tests in three to four years.

Nature, 2015. DOI: 10.1038/nature16492 (About DOIs).