Brain Implants on Dissolvable Silk

David Kaplan, Tufts University, explains the work he is conducting with Dr. Brian Litt, associate professor of bioengineering and neurology, University of Pennsylvania, in placing brain implants on dissolvable silk.

Could you explain the work you’re doing with Dr. Litt with dissolvable silk?

The basic goals of the studies are to improve ways to record brain signals with compatible substrates that would enhance both sensitivity to recording, as well as the resolution, meaning how fine you can go to target certain areas. The basic approach has been to utilize our silk protein substrates as thin film carriers that provide a way to pattern electrodes on the surface because of the robust nature of the silk protein, and by that I mean both thermally stable as well as chemically stable. So, it’s a really nice substrate to then tailor the mechanical properties based on how it’s processed, so it will be flexible enough so when it’s laid on the brain of an animal, it will conform to the hills and valleys, if you will, of the brain in this particular study. Because of the biocompatibility of silk, it will dissolve away in the brain and not cause any adverse effects but allow the electrodes to do their job. This is an example of implantable, degradable electronic systems that we’re trying to pursue, in this case with Brian Litt’s lab.

In this particular study, the silk was only a temporary carrier and then designed to dissolve away. In other systems, we’re targeting for longer-term utility. And we can regulate or control that based on how we process the silk protein, so we can make it dissolve away quickly or it could last more than a year if we need that to happen. For example, in other studies we’ve published on silk-based implants in the brain for control of epilepsy, we have those last for weeks and months to deliver drugs until it fades away. So, it just depends on the goal of the particular study.

What types of devices are you able to put on the silk?

In the case of the work we’re doing with Dr. Litt’s lab, we’re mainly patterning fine electrodes on the surface, and they can be really of any metal that is compatible in the human body, and those patterned electrodes can transfer onto silk because silk is stable up 200 degrees centigrade, and also the metals stick very well, so the interface is very favorable. So, this allows us to carry out that kind of work.

How did you arrive at silk—how was it determined that it would be a good vehicle for brain implants?

For metal electrode printing, we had done some work last year in collaboration with John Rogers at UI—and John’s involved in the project with Brian Litt as well—where we prepared a series of silk substrates that we’ve studied the material properties of for many years in terms of thermal stability, mechanical stability, all these things. And with John’s lab, we looked at how to sort of optimize the patterning of electrodes on the surface—what conditions for the films, what solvents, what temperatures. Out of that work, which was published earlier last year, we sort or identified what would make the most sense. And then in the work with Dr. Litt’s lab, we could then maximize the mechanics and processing protocol to meet what we needed for the brain work.

Aside from the temperatures it can withstand and it’s ability to dissolve, what benefits does silk provide over other materials?

There are many, and I don’t want to overdo it, so I’ll give you a couple of quick ones. Silk can be processed from beginning to end in only water, at room temperature, and this opens up opportunities to, we call it, “doping the silk,” so you can add in things like drugs or other factors that might be useful, and I mentioned one already, add in drugs for treatment of epilepsy in the brain, and that derives from the very non-invasive process and conditions based on water. You can also make films out of silk that are absolutely clear to visible light, and so we’ve been able to use that in a direction to control light propagations through films as a diagnostic redoubt. These are important sort of extras you can use with the silk to go along with what I said before, the ability to design to degrade away quickly or slowly and the ability for the body to handle this as a biocompatible substrate.

Is the silk expensive?No, it’s actually relatively inexpensive as a biomaterial. There are a few other degradable, implantable, polymeric biomaterials, things like collagens, polylactic acids, and so on, and silk really is very cost-competitive with any of those, and it’s available in large quantities because of the textile world. So, it’s a real advantage.

How long are we from the silk implants being used in surgeries and medical procedures?

I hate to speculate too much. I always probably say the wrong thing, but some of the technology has be licensed, not so much the brain work yet with the implants, but other avenues for medical devices from silk. Some have been to the FDA already, by the companies that have licensed that technology, and so we anticipate we’ll see a steady stream of new medical devices based on this protein over the next few years