However, engineers at the University of California, Berkeley have developed ‘neural dust’, a dust-sized implant, which promises to take things a few steps further.
1mm3 wireless and battery-free 'neural dust'
These neural dust implants have been reduced to sizes approximating one millimetre cube. The device consists of an external transceiver and the implant, containing a piezoelectric crystal that converts ultrasonic pulses from the transceiver, to electricity for power. Hence, it manages to be both wireless and battery-less.
Electrodes in the implant record electrical signals from the body, which are then used to alter the vibration of the crystal, which are reflected to the transceiver, which records it in a technique known as backscattering.
“This is the first time someone has used ultrasound as a method of powering and communicating with extremely small implantable systems,” says one of the study’s authors, Dongjin Seo.
“This opens up a host of applications in terms of embodied telemetry: being able to put something super-tiny, super-deep in the body, which you can park next to a nerve, organ, muscle or gastrointestinal tract, and read data out wirelessly.”
Led by neuroscientist Jose Carmena and electrical and computer engineer Michel Maharbiz, the team demonstrated the use of the mote in monitoring neural activity in a live animal. The device recorded activity in the sciatic nerve and a leg muscle of an anaesthetised rat in response to electrical stimulation that had been applied to its foot.
Potential beyond monitoring health towards treating conditions
The potential uses of the implant may be stretched. The team projects that they could modify the implants to not only monitor nerves, but also stimulate them. This would allow closed-loop control of nervous system activity.
Furthermore, the results of animal studies already suggest the possibility of the technology being used to treat type 2 diabetes. According to Seo, they are also looking into treating bladder control problems and bowel disease.
“The idea that you could use these to take data about pH, oxygen, chemicals, tumors, all sorts of things, deep in your body, and communicate robustly, is extremely exciting,” adds Maharbiz.
Usually, the body rejects foreign objects that are larger than a couple of cells. In 2013, the team had already published a theoretical analysis proving that the use of the implants would be effective even were it shrunk to a size comparable to a neuron.
If indeed this can be achieved, then why stop at one implant when you can have many? The team is planning to increase the number of transceivers used, which would track the implants in the body in case they move, as well as allow multiple implants in one body.
“The vision is to implant a bunch of these motes anywhere in the body and have a patch that sends ultrasonic waves to wake up the sensors and receive information for any desired therapy,” says Seo. “Everything would be sealed in, with one patch over the site that can talk to the implants individually or simultaneously.”
In fact, the original aim of the project was to develop viable brain-machine interfaces. Some of the issues traditionally faced include the tendency of implants to irritate tissue in the body and degrade too quickly to be feasible. If sufficiently small implants can indeed be developed, it could pave the way for the treatment of neurological disorders, such as epilepsy.
Several improvements to be made
The next steps in harnessing the potential of the device are to test how long the implants last in biological systems without degradation, and to conduct the same experiments in non-tranquilised and freely-moving animals.
Following that, the team plans to make several improvements to the implants. “As we validate these platforms are stable for chronic use, we'll be making them smaller, adding additional functionality like stimulation, and other types of sensors,” Maharbiz says.
Currently, the implants are coated in surgical-grade epoxy. To enhance the chances of the implants lasting in the body for longer - such as, at least a decade - the team is looking into making implants from biocompatible thin films.
Moreover, the aim is to shrink the size of the implant down to just 50 microns wide (roughly half the average width of a human hair), so that "the body should tolerate them much longer," stated Maharbiz.
“The Berkeley group is on the exciting path towards developing a completely novel type of sensors that would have widespread uses in bioelectronic medicines,” says Victor Pikov, head of research platforms at GSK Bioelectronics, who was not involved in the Berkeley team’s research. MIMS
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