Implantable bioelectronics utilizes ionic communication system

STEPHEN RIFFLE: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Stephen Riffle.  When we can’t reach something ourselves, we build devices to help. Want to measure the seismic activity of Martian volcanoes? Send in a rover. Want to stop a seizure before it begins? Build an implantable electronic device. 

JENNIFER GELINAS:  A lot of diseases and disorders are starting to be treated with implantable devices, whether that's a pacemaker or if it's a neural implant to treat epilepsy or a spinal cord stimulator, more and more devices are being innovated and are being found to be very useful for a wide range of clinical conditions.

STEPHEN RIFFLE: That’s Jennifer Gelinas, an assistant professor in the Department of Neurology and Institute for Genomic Medicine at Columbia University Irving Medical Center. She and her colleagues at Columbia University have been working to develop and improve implantable electronic devices for a myriad of clinical and research applications. Implanted electronic devices are exactly what they sound like - electrical devices that can be inserted into a living organism for any number of purposes. Sometimes the device is intended to deliver an electrical pulse to the surrounding tissue, as in the case of a pacemaker. Other times the device may be observing and relaying information about its environment for diagnostic or research purposes. Whatever its use, maintaining a communication link with the device can be useful in the event that you need to change parameters, harvest data, or simply check to see that it’s actually working. The mechanics of communicating with the device can be tricky, though. Most devices rely on wires that transect tissue, and you can imagine that that’s not ideal to have a wire running through muscle all the way up to the skin. A lot of devices also rely on radio frequency or RF communications. In many cases RF has served its purpose, but according to Dion Khodagholy, in the department of electrical engineering at Columbia University, RF also has several important limitations. 

DION KHODAGHOLY: RF, because of the way waves propagate and the way they radiate, it consumes a lot of energy. And that means you have to have bigger battery packs. It also requires rigid electronic components. So we don't have yet any flexible approaches for essentially RF systems. All of them are made out of rigid components, which means you have a large mechanical mismatch between your implant and the body. So as a result, the immune response or the inflammation and so on is even higher.

JENNIFER GELINAS:  So for the devices right now that are used for epilepsy, in order to implant them, they actually have to hollow out an area of the skull centimeters by centimeters in order to be able to implant this rigid box that houses all of the components for the device and its transmission. 

STEPHEN RIFFLE:  Together, Khodagholy and Gelinas are hoping to improve implantable devices by tapping into a different form of communication, one that is more familiar in biological systems.

DION KHODAGHOLY: So the body is basically composed of water ions and biomolecules, like lots of charge atoms. We were thinking we have this ionic medium, instead of relying on electromagnetic waves, can we utilize this ionic, nicely, highly conducting ionic medium to turn it into our benefit and establish a communication based on the ionic physical parameters.

STEPHEN RIFFLE:  What he’s describing is ionic communication, or IC for short. The basic idea is that the body is comprised of many highly charged ions, which can be used to transmit and store energy. If you place two conducting electrodes in the body and introduce an alternating current, the tissue between the electrode will act as an electrolyte medium. Together, these two electrodes and their electrolyte medium form a capacitor that’s capable of generating a detectable electrical field. The idea for this capacitor came from a postdoc in Khodagholy’s lab, Zifang Zhao, who prefers to go by the name Frank. 

DION KHODAGHOLY:  So Frank hypothesized that if we establish this capacitor in the body, that means that there's a constant charging and discharging of this medium, and we would be able to look at this capacitor activity from outside.

STEPHEN RIFFLE: The IC capacitor polarizes the tissue around it, leading to fluctuations in the energy field that can be detected by geometrically similar electrodes outside of the body. These fluctuations can then be used to code information. Though it’s simple to say, it took Frank and his colleagues years of hard work to generate a robust communication device. Working with miniature electronics is its own kind of hurdle, but more so was figuring out how air, ions, double layer capacitance, and capacitive coupling all influenced the device’s function. 

DION KHODAGHOLY: The hard part of this was we needed to understand how these capacitors work and there's a specific window of frequency ranges that IC becomes highly effective. So the nice thing is the window that this essentially works for is well in the megahertz. And so it's very high speed in terms of data communication, you can establish quite a fast data rate so that most bioelectronic devices will be able to have it.

STEPHEN RIFFLE: Gelinas, Khodagholy, and Frank approached this work with the idea that any device they make must be able to enter a clinical setting within five years. This means working with safe, biocompatible materials. To that end, the ionic communication device is fabricated with materials that have already been shown to be safe in the body, such as gold and P.PSS - a semiconducting plastic. To cap it off, the team showed that this device can successfully gather and transmit high resolution data from living rats over several weeks. Ultimately, this means a new type of implantable device can be developed, one where the communication is carried out through small, flexible, biocompatible electrodes. 

According to Gelinas: 

JENNIFER GELINAS: We're also very excited to actually use the devices for different experiments. So there are several situations where it's essentially impossible to use the currently available technologies for data transmission. So for instance, we work with developing animals—so very, very small fragile animals. And this helps us to understand pediatric diseases. But you can imagine a huge RF transmitter does not really work well with an animal that still needs to be cared for by its mother in a nest. And so we're really excited about being able to use these sorts of minimally invasive technologies to open up new experimental avenues, to be able to obtain data that we weren't able to obtain before.

STEPHEN RIFFLE: This work was published in a recent issue of Science Advances. My name is Stephen Riffle from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.