Self-powered pacemaker works on a heartbeat

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A thin, flexible mechanical energy harvester, with rectifier and microbattery, mounted on a bovine heart. – University of Illinois and University of Arizona

Pacemakers keep millions of hearts on the beat, protecting their owners from potentially fatal arrhythmias. But there’s a problem. The batteries give out after five to 10 years and replacing them requires surgery, not a thing to be taken lightly. 

Now John Rogers and his team at the University of Illinois are trialling a solution reminiscent of a perpetual motion machine: a battery powered by the heart’s own power. 

Robbing the heart of energy is a bad idea, especially for someone with a heart problem. The pacemaker works because its battery requires so little of it – a mere one to 10 microwatts. The powerful contractions of the heart produces around a million times more than that with each beat.

Rogers described the stamp-sized gizmo at the conference of The American Association for the Advancement of Science in Chicago this month. It relies on a crystalline material called lead zirconate titanate (PZT) that has piezoelectric qualities, meaning it releases a small electric current every time it is bent. Nanometre-thin ribbons of PZT are hooked up to a rechargeable battery and the whole thing is encased in a biocompatible plastic called polyimide. 

In initial studies in cows, pigs and sheep, the pacemaker was sewn on to the right ventricle wall, where it seemed to interfere least with the heart’s motion. The results were published in January in the Proceedings of the National Academy of Sciences. The idea is not entirely new. Others have, for instance, used zinc oxide wires to harvest body power. But this project is “taking what has been done on a small scale and integrating it up to a much more significant scale,” Michael McAlpine, a professor of mechanical engineering at Princeton University told The Scientist.    

The heart itself can manage five billion beats in a lifetime. So far
the PZT device has performed only a million.

There’s still some way to go before we might see self-charging pacemakers in people, though. Rogers says the device needs to last at least 15 years to give it an edge over battery-powered pacemakers. And it has to withstand the wear and tear of perpetual bending and stretching. The heart itself can manage five billion beats in a lifetime. So far the PZT device has performed only a million. It’s “baby steps”, admits Rogers.

But the pacemaker is just one of the potentially game-changing devices emerging from the award-winning lab of the clean-cut, 46 year-old Rogers, the recipient of a MacArthur “genius” grant.  The devices make for a dazzling array: skin patches that relay information about temperature and moisture to monitor wound healing;  helmets developed in collaboration with Reebok that relay how much head damage footballers have sustained; soluble hair-thin circuits inserted into wounds to heat-sterilise them and then melt away; brain implants that stimulate or record from clusters of neurons, and now the self-charging pacemaker. What all have in common is a central intent: to meld human flesh with silicon circuitry – long the standard fare of science fiction but no longer fantasy. And Rogers' lab is helping pave the way.

While silicon chips are traditionally rigid and hard, flesh bends and stretches. Rogers’ work is all about making silicon more flesh-like, more bendy and stretchy – all the better to mesh with our bodies. The flexible, stamp-sized pacemaker, for instance, integrates seamlessly with the heart surface through its ability to contour with the nooks and crannies and pass electrical signals. 

Everyone is eager to get on board with these fleshy devices. Rogers' collaborators include the US Defense Advanced Research Projects Agency (DARPA),  medical device makers and pharmaceutical giant GlaxoSmithKline, which is eager to deliver “electroceuticals” that might one day be implanted at nerve endings to replace drugs as painkillers.

The flex in Rogers’ gizmos comes from the materials science wizardry applied to the basic components: silicon inlaid with gleaming golden circuits of magnesium, magnesium oxide and molybdenum, and interspersed with rubber to allow the Band Aid-sized patches to bend and stretch.  And some are not just bendy, but fully biocompatible. “You can eat it,” says Rogers. At a past lecture he did eat one device, although he declined to repeat the demonstration in Chicago.

For now, the devices are relatively banal circuit-laden patches that contour to the skin, brain or heart. But the android  peering out from Rogers' final PowerPoint slide suggests where all this is heading. As Rogers put it. “Terminator?  We’re a long way from something like that, but I do think that, over time, existing regulatory bodies will need to adapt to the fast-changing technology landscape.”

Related story: Melt-in-your-mouth silicon

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