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Neural Dust May Power Prosthetic Limbs

Wireless, battery-less implantable sensors could improve brain control of prosthetics, avoiding wires that go through the skull. The sensor is pictured attached to a nerve fiber in a rat. Photograph by Ryan Neely, courtesy of UC Berkeley.

University of California, Berkeley (UC Berkeley), engineers said they have built the first dust-sized, wireless sensors that can be implanted in the body. The so-called neural dust, which the team implanted in the muscles and peripheral nerves of rats, uses ultrasound both to power and read out the measurements; ultrasound vibrations can penetrate nearly anywhere in the body, unlike radio waves, the researchers said. Because these battery-less sensors could also be used to stimulate nerves and muscles, the technology also opens the door to “electroceuticals” to treat disorders such as epilepsy, to stimulate the immune system, or tamp down inflammation. They could also improve brain control of prostheses, avoiding wires that go through the skull. The study findings were reported in the August 3 issue of the journal Neuron.

The sensors, which the researchers have already shrunk to a 1mm cube-about the size of a large grain of sand-contain a piezoelectric crystal that converts ultrasound vibrations from outside the body into electricity to power a tiny, on-board transistor that is in contact with a nerve or muscle fiber. A voltage spike in the fiber alters the circuit and the vibration of the crystal, which changes the echo detected by the ultrasound receiver, typically the same device that generates the vibrations. The slight change, called backscatter, allows them to determine the voltage.

While the experiments so far have involved the peripheral nervous system and muscles, the neural dust motes could work equally well in the central nervous system and brain to control prostheses, the researchers said. Wireless sensors-dozens to a hundred-could be sealed in the skull, avoiding infection and unwanted movement of the electrodes.

“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,” said Jose Carmena, PhD, a professor of electrical engineering and computer sciences and a member of the Helen Wills Neuroscience Institute at UC Berkeley. “Once it’s clinically proven, however, neural dust will just replace wire electrodes. This time, once you close up the brain, you’re done.”

The team is working now to miniaturize the device further, find more biocompatible materials, and improve the surface transceiver that sends and receives the ultrasounds, ideally using beam-steering technology to focus the sounds waves on individual motes. They are now building little backpacks for rats to hold the ultrasound transceiver that will record data from implanted motes. They’re also working to expand the motes’ ability to detect nonelectrical signals, such as oxygen or hormone levels.

Editor’s note: This story was adapted from materials provided by UC Berkeley.