Radio-powered optogenetic brain implant
A fingernail-sized wireless brain implant that is powered only by radio waves and can control nerve cells using pulses of light has been developed by researchers in the US. The device makes use of a phenomenon called "optogenetics" where scientists first make nerve cells light-responsive by turning on a gene that produces a light-sensitive chemical. The implant communicates with these cells by producing light from an embedded LED. It is controlled and picks up energy using a tiny grid of wires that work like an antenna. It's the brain-child of Robert Gereau from Washington University, in St Louis and he was kind enough to talk Chris Smith through it.
Robert - Essentially what opto-genetics is, is a technology that allows scientists to control the activity of neurons, the cells that mediate transmission in the brain using light. Typically the way this is done is something like a fibre-optic cable carries light from a laser to allow you to shine light into the brain, and so for that to happen you have to insert the fibre-optic cable into the particular part of the brain. This has a couple of problems, one is that the fibre-optic insert itself is rigid and can damage when there is relative motion of the implant, and of course the tethering to the laser, to the light source restricts your ability to implement this in, say, complex behavioural experiments that have been the standard of behavioural neuroscience for decades. So it's hard to apply this technology to the standard approaches in the field that would really enable great insight into complex behaviours.
Chris - So what was your approach instead?
Robert - So the approach that we've been taking is to take small electrical circuits that are flexible and bio-compatible and couple them with tiny light sources, something we call micro LEDs, that can be integrated into these small flexible circuits. That technology has been advancing, there have been a couple of papers in the last couple of years of implanting micro LEDs into the brain, injecting them into the brain, and sort of integrating those LEDs with the circuit but the remaining problem was powering them, and so there have been wired cables that power the LEDs, which gets you back the same tethering problem we have before or you can envision tiny batteries, or in the case of what we've been working on here is wireless energy harvesting from an RF antennae.
Chris - They are basically just a grid of wires that can pick up fields aren't they? So if you can beam in radio waves and they'll be sensitive, they'll pick those radio waves up and can turn it into some electricity that the devise can use.
Robert - Yes, exactly. You design a small circuit so that it kind of matches the frequency of that energy, and harvest that energy to power this tiny little LED, and we have been able to incorporate them into materials that are stretchy and flexible and tiny, and that means that they can be completely implanted under the skin in the animal. You can put these micro-LED devices with their antennas anywhere in the body and because they are stretchy and soft, they move with the body, so they kind of match the properties of the biological tissue.
Chris - If I had one in front of me, a) how big is it and b) what would it look like?
Robert - If you imagine sort of holding out your pinkie finger and looking at the nail on your pinkie finger, the basic prototype device would fit on the nail with a bit of room to spare. They are sort of clear, looking like a gelatinous substance. They are made of a substance called PDMS. Medical devices are made of this, it's stretchy and soft and bio-compatible. Imbedded in that are little gold traces, which are the metallic components of energy harvesting antennae and then some tiny electronic component that basically amplify that energy and power the LED, which is small to the point of not being visible to the naked eye.
Chris - And you could lay one of these devices alongside say, a nerve, along the spinal cord or onto the brain.
Robert - Yes, precisely.
Chris - The idea being you'd send the energy in with the radio waves it would make the LED light up and put light of the right colour into the brain and stimulate those nerve cells.
Robert - Yes, that's exactly right.
Chris - How do you know this is going to work? What tests have you done to show, a) it's safe and b) that you actually can control nerve tissue with this?
Robert - Well we have done long term bio-compatibility studies in our animal models, thus far. Implanting them and leaving the animals for weeks and months, and then looking at the tissue to look for any signs of damage, and signs of inflammation and we have no indication that there's any kind of adverse effects of implanting these devices over a proliferal nerve, or in the space above the spinal cord, for example to manipulate those circuits. And in terms of knowing whether it will work, we've done some proof on concept studies to demonstrate that by implanting these over a proliferal nerve or above the spinal cord, we can very clearly manipulate the circuits that are involved in pain and pain relief, and are able to very robustly affect those behaviours in these animal models.
Chris - Could you use this therapeutically? If you had a patient with a certain condition, could you apply this and use this to control their brain?
Robert - Well, that's certainly been my goal as we have been developing these, not only as research tools to enable us to understand the cells and circuits that mediate pain, and how to relieve that, but ultimately, down the road, we hope to be able to develop these in the direction of medical devices where we can use them to very precisely control cells that are involved in aberrant communication in the nervous system that mediate pathological conditions, and in my case, chronic pain is at the forefront.