A wireless pacemaker that dissolves
A new, dissolving, implantable pacemaker has been developed by scientists in the US. The idea is that, like dissolving stitches, in situations where a permanent pacemaker is not needed, with this device, once its job is done after a couple of months, it disappears without the need for an operation to remove it. It actually works in the same way as traditional pacemakers, which send electrical impulses along fine wires into the heart to control heart rhythm. Power is beamed into the new device from outside, so no batteries are needed. Charlotte Birkmanis had her finger on the pulse and called up the device’s creator, John Rogers, to hear how it works...
John - Well the function is equivalent - the kind of stimulation is functionally identical. The key differences are that it's wireless and it's resorbable. We were able to demonstrate that on actual human hearts, not in human patients, but hearts from organ donors. So we were able to demonstrate that the devices work well in small and large animal model studies; and most importantly that it's applicable to the human cardiac system, which is ultimately the goal in this type of context.
Charlotte - How does it work?
John - The device itself includes several subsystems. One is designed to harvest power wirelessly. Another is designed to take that radio frequency power and smooth it out; that component involves a radio frequency silicon-based diode and a smoothing capacitor. And the third kind of element of the device is set of interconnected traces that terminate in leads that interface to the surface of the heart. Those three components are all integrated into a thin, flexible, lightweight device that gently adheres to the surface of the beating heart.
Charlotte - It doesn't need to be removed - how does it get eliminated from the body?
John - The electronics, the stimulator leads, wireless control interface, and so on are all water-soluble. They react with surrounding biofluids and just dissolve over time, and disappear completely at a molecular level, to biocompatible end products that are just naturally excreted from the body via usual processes of kidney filtration, urination, for example.
Charlotte - What are they actually made from?
John - We use primarily polymer based materials, either biomaterials like silk fibroin... that's a protein that can be extracted from silkworm cocoons as a substrate for building our electronics. Of course, you also need conducting materials; there we choose metals that are naturally occurring in the body, such as iron, magnesium, these types of materials. They're also water-soluble and biocompatible. And then the third class of materials: silicon itself is water soluble. If you use silicon in very, very thin film forms, then it will dissolve completely. When you put those different materials together then you can begin to build wide ranging classes of water-soluble electronics.
Charlotte - Because you don't remove it, how do you control the amount of time that it functions for?
John - Yeah, so the way that we control the operating life is we use a capping layer, a thin layer of a polymer that protects the underlying electronic materials from interaction with surrounding biofluids. And then once that capping layer has dissolved and disappeared, the electronic materials start to dissolve and the performance drifts. So we assume that the device is no longer operating in a stable fashion from that point on.
Charlotte - And what else could you make out of these materials?
John - We have wireless nerve stimulators that can accelerate rates of neuro-regeneration in damaged peripheral nerves. The other thing that you can do is you can build wirelessly programmable drug release vehicles; so these are platforms that contain an array of reservoirs, each one of which is filled with a drug, and we can wirelessly trigger the opening of valves to allow programmed release of those drugs at specific time intervals. Once all of the drugs have been released the platform itself can just naturally resorb and disappear in the body.
Charlotte - Is it ready to be used in human surgery?
John - Not quite yet. Ultimately we hope to use this device with humans, but it's a process and it's a very rigorous process, so the timescale for that is typically a year or two to get the first human tests completed. And we're just starting down that path now.