Implantable sand-sized sensors to monitor internal goings on in real time

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In their current form, the researchers say the sensors could be used not just for monitoring, but also stimulating nerves and muscles to treat things like epilepsy(Credit: Ryan Neely)

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Health and fitness monitors may have come along in leaps and bounds, but there's still a whole lot they don't know about us. Placing miniaturized sensors deep inside our bodies would be one way to change that, and now it seems such a technology mightn't be so far away. Scientists have developed tiny wireless sensors they call "neural dust", which track nerve signals and muscles in real time, opening up a wide array of potential applications that range from checking internal organs to wirelessly controlling prosthetics with your mind.

Neural dust is more than just a catchy name. The researchers, from the University of California, Berkeley, have managed to squish the sensors into 1 mm cubes around the size of a large grain of sand, and implanted them into the muscles and peripheral nerves of rats. These cubes house piezoelectric crystals that turn ultrasound vibrations (applied from outside the body) into electricity. This provides a power source for a miniature on-board transistor that rests in contact with the nerve to measure electrical activity.

When there is a voltage spike in the adjacent nerve, it modifies the circuit and in turn the vibrations of the piezoelectric crystals. When the vibrations are bounced back to an ultrasound device on the outside of the skin, the change in echo can be analyzed to reveal the voltage of the nerve.

"Having access to in-body telemetry has never been possible because there has been no way to put something supertiny superdeep," says Michel Maharbiz, one of the study's co-authors. "But now I can take a speck of nothing and park it next to a nerve or organ, your GI tract or a muscle, and read out the data."

In their current form, the researchers say the sensors could be used outside the brain not just for monitoring, but also stimulating nerves and muscles to treat things like epilepsy, inflammation or fire up the immune system. Eventually, they hope to develop tinier versions that can be packed into the brain, an advance that could mean big, big things.

"The beauty is that now, the sensors are small enough to have a good application in the peripheral nervous system, for bladder control or appetite suppression, for example," says neuroscientist Jose Carmena, a member of the research team. "The technology is not really there yet to get to the 50 micron target size, which we would need for the brain and central nervous system. Once it's clinically proven, however, neural dust will just replace wire electrodes. This time, once you close up the brain, you're done."

A 50-micron sensor would measure about half the width of a human hair, and planted in the brain it could represent a game-changing development in the way our minds communicate with machines.

Our ever-improving ability to track the electrical signals coming from the brain has already opened up some exciting possibilities, from mind-controlled drones to mind-controlled colleagues, but these involve immobile, specialized caps or implanting electrodes into the brain, which then degrade within a couple of years.

If working with the neural dust instead, scientists could implant them in the brain by the hundreds, seal up the wound and be done with it. This would avoid infection and undesired movement of the electrodes and could potentially last for decades, where they could perform the role of relaying brain signals to be turned into control inputs for prosthetics.

There's still a lot of work to do before this happens. Not only are the researchers working to make the device smaller, but the sensors are currently coated in surgical grade epoxy. They are looking to improve on this by using biocompatible thin films instead, which they say could last for decades. They are also working towards improving the ultrasound transmitter and even expanding the sensors' capacity to pick up on non-electrical signals, like oxygen and hormone levels.

"The vision is to implant these neural dust motes anywhere in the body, and have a patch over the implanted site send ultrasonic waves to wake up and receive necessary information from the motes for the desired therapy you want," says Dongjin Seo, a graduate student in electrical engineering and computer sciences at UC Berkeley. "Eventually you would use multiple implants and one patch that would ping each implant individually, or all simultaneously."

The research was published in the journal Neuron, and the video below provides an overview of how the sensor works.

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