Wearable technology devices like activity trackers feed us data on our personal metrics. Steps walked or climbed, heart rate, quality of sleep, cycling speed, elevation, the list of activity preferences seems endless.
Typically, the devices are designed as wrist bands, but other types of activity trackers include clip-ons that attach to articles of clothing (shoes, shirts, pockets), or as elements placed inside a strap worn around the leg.
Did you hear about the trackers that you wear not outside, but inside, your body?
They're wireless, batteryless implantable sensors the size of dust particles, actually, and designed by a team of engineers from the University of California, Berkeley.
Called "motes," the wireless micro-sensors can be implanted in the body, bringing closer the day when a Fitbit-like device could monitor internal nerves, muscles or organs in real time. The sensors use ultrasound to both power and read the measurements. Ultrasound technology is already well-developed for hospital use, and ultrasound vibrations can penetrate nearly anywhere in the body, unlike radio waves, the researchers say.
Dubbed "neural dust," the sensors could be used to stimulate nerves and muscles, the technology also opens the door to “electroceuticals” to treat disorders such as epilepsy or to stimulate the immune system or tamp down inflammation.
“I think the long-term prospects for neural dust are not only within nerves and the brain, but much broader,“ says Michel Maharbiz, associate professor and co-author of the study.
“Having access to in-body telemetry has never been possible because there has been no way to put something supertiny superdeep. 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.“
Each sensor mote contains a piezoelectric crystal (silver cube) plus a simple electronic circuit that responds to the voltage across two electrodes to alter the backscatter from ultrasound pulses produced by a transducer outside the body. The voltage across the electrodes can be determined by analyzing the ultrasound backscatter.
While the researcher's 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 prosthetics, the researchers say.
Today’s implantable electrodes degrade within one to two years, and all connect to wires that pass through holes in the skull. Wireless sensors—dozens to a hundred—could be sealed in, avoiding infection and unwanted movement of the electrodes.
“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,” said Dongjin Seo, a UC graduate student. “Eventually you would use multiple implants and one patch that would ping each implant individually, or all simultaneously.”
The researchers estimated they could shrink the sensors to a cube 50 microns on a side—about 2 thousandths of an inch, or half the width of a human hair. At that size, the motes could nestle up to just a few nerve axons and continually record their electrical activity.
“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. “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.“
The study was published in the August issue of the journal Neuron.