Engineers at the University of California, Berkeley have created the very first dust-sized wireless sensors that may be implanted within the body. This is bringing technology closer to the day that technologies such as the Fitbit will be able to monitor internal nerves, muscles and organs all in real time.
These devices do not require batteries and may also be able to stimulate nerves and muscles opening up doors for electroceuticals to treat disorders including epilepsy and stimulate the immune system or lower inflammation.
The neural dust is implanted in the muscles and peripheral nerves of rats and is unique due to its use of ultrasound. It holds the ability to both power and read measurements. Ultrasound technology is already very thoroughly developed for the care of hospice patients and ultrasound vibrations are able to penetrate just about everywhere within the human body making them much more useful than radio waves.
Michel Maharbiz, associate professor of electrical engineering and computer sciences is one of the main two authors of the study. He says he believes that long term prospects for neural dust are not only within nerves and the brain but much broader. Having access to telemetry within the body has never been possible because there has been no way to put something so tiny so deep. But now he 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.
The complete findings have been published in the upcoming Neuron Journal. Sensors at this time have already been shrunken to a size of 1 millimeter cube, which is about the size of a large grain of sand. These hold a piezoelectric crystal that converts ultrasound vibrations from outside of the body into electricity that powers a tiny, on board transistor that is in direct contact with a nerve or muscle fiber. When there is a spike in voltage within the fiber, this alters the circuit and the vibration of the crystal, which then changes the echo detected by the ultrasound receiver. The same device will typically generate the same vibrations. This slight change is known as the backscatter which allows researchers to determine the exact voltage.
During their experiment, UC Berkeley’s team powered up passive sensors every 100 microseconds with six 540-nanosecond ultrasound pulses that gave off continual and real time readouts. The first generation motes were coated with surgical grade epoxy but they are currently working on building motes from biocompatible thin films that may potentially last inside the body without any signs of degradation for at least a decade.
So far the experiments have involved peripheral nervous system and muscles, but the neural dust motes could work just as well in the central nervous system and brain in order to control prosthetics according to researchers. Implantable electrodes generally degrade within a year or two and are always connected to wires that must go through holes cut directly in the skull. Wireless sensors, as many as a few dozen to a hundred could be sealed within which would limit infection as well as unwanted movement of the electrodes.
Ryan Neely, a neuroscience graduate student says the original goal of the neural dust was to help imagine the next generation of brain-machine interfaces and to make it a viable clinical technology. If a paraplegic wants to control a computer or a robotic arm, you would just implant this electrode in the brain and it would last essentially a lifetime.
In the paper that was originally published on the internet in 2013, it was estimated that researchers would be able to shrink the sensors down to a cube the size of 50 microns on a single side (or about a thousandths of an inch). At this particular size, the motes could nestle up to just a few nerve axons and continually record their electrical activity.
Carmena said the beauty is that as of now, the sensors are small enough to have a good application in the peripheral nervous system, for bladder control or appetite suppression, for example. The technology is not really there yet to get to a 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 are done.
The team is currently working on making the device even smaller, finding more biocompatible materials and improving the surface transceiver that sends and receives the ultrasounds, ideally using beam steering technology in order to focus sound waves on individual motes. They are working on building little backpacks for rats that will hold ultrasound receiver that is going to record data from notes that are implanted. They are also focusing on expanding the ability of said motes to detect non-electrical signals, such as oxygen and hormone levels.
Dongjin Seo, graduate student in electrical engineering and computer sciences says the vision is to implant these neural dust motes anywhere throughout the body and have a patch over the implanted site that sends ultrasonic waves to wake up and receive necessary information from the motes from the desired therapy you want. Eventually you would use multiple implants and one patch that would ping each implant on an individual basis or all at the exact same time.
Maharbiz and Carmena came up with the idea of neural dust five years ago but their attempts to power an implantable device and read out the data with radio waves did not work out as planned. Radio attenuates extremely fast with distance in tissue, so communicating with devices deep in the body is extremely difficult without using potentially damaging amount of radiation.
Marharbiz thought of the use of ultrasound back in 2013 when he published a paper with Carmena, Seo and their colleagues in which they described such a system and how it could potentially work. Maharbiz said their first study demonstrated that the fundamental physics of ultrasound allowed for very small implants that would not be able to record and communicate neural data. The system has now been built by him and his students.
Seo says ultrasound is far more efficient when you are targeting devices that are on the millimeter scale or smaller that are embedded deep inside of the body. You can get a lot of power into it and a lot more efficient transfer of energy and communication when using ultrasound as opposed to electromagnetic waves, which has been the go-to method for wirelessly transmitted power to miniature implants.
Carmena says now that there is a reliable and minimally invasive neural pickup in your body, the technology is able to become the driver for a whole gamut of applications, things that today don’t even exist.