Could Pacemakers Use Energy Harvesters? This Professor Thinks So

Amin Karami at the University of Buffalo found a materials solution to overcome a design challenge related to energy harvesting from the heart.

Chris Newmarker

The dream of pacemakers that make their own power still seems years if not more than a decade away, but a University of Buffalo professor's work may be bringing it closer to reality.

As a postdoc research fellow at the University of Michigan and now as a professor at Buffalo since 2013, Amin Karami has found more effective ways to utilize the piezoelectric properties of a crystalline, ceramic compound called lead zirconate titanate (PZT).

Karami is in the process of securing a patent and forming a company to commercialize his inventions. (See Karami discuss energy harvesting at MD&M East, June 9-11 in New York City.)

PZT has already proved useful when it comes to converting vibrations to electricity to self-power sensors on bridges or airplanes, according to Karami. But using it to harvest energy off the heart is trickier because heart beat frequency varies a great deal, making it hard to even squeeze out the few microwatts needed for a pacemaker.

"We have a very meaningful amount of motion, which is heart motion. ... It's a very small amount of power, but it's enough to power a pacemaker," Karami says.

The PZT might not be able to always be layered in a flat surface, either, since the latest generation of tiny leadless pacemakers such as Medtronic's Micra and St. Jude Medical's Nanostim require a lot of electronics packed into a tiny horse pill-sized shape. With the Micra, for example, the pacemakers canister is actually it's battery, too.

Karami started out four years ago by testing heart beat vibrations all over the inside of pigs.

He then figured out that two strategically placed magnets on a brass strip covered with PZT created nonlinear behaviors in the PZT that boosted power production a hundredfold, to up to 20 microwatts, and allowed it to take place anywhere from seven to 700 beats per minute. It could utilize heart vibrations that could be found all over a torso.

While an improvement, there was still a major challenge because magnets are not MRI-compatible, which would post challenges for heart disease patients.

Karami found a materials solution to create similar nonlinear behavior without the magnets.

"We are achieving the same thing without the magnets by placing the PZTs on a composite structure. Before it was a thin sheet of brass. Now it is a thin sheet of carbon fiber composite manufactured in a way to be unstable, to have these natural properties we want," Karami said.

The composite is made up of two layers of carbon fiber, fused together with an epoxy at high temperatures.

"There will always be internal forces. The composite, the substrate has two shapes. In either shape, one of the two materials will be under internal stress, because one of them would be pulled and the other would be in a comfortable situation. This internal type of structure makes it nonlinear," Karami said.

"The arrangements of the two layers of fibers is very key here."

Karami has also been able to shrink the energy harvester down to a cubic centimeter.

When it comes to incorporating the energy harvester, there will be more regular engineering challenges, such as making sure voltage matches a pacemaker or integrating the PZT harvester into a pacemaker's design. "All of these can be done. I don't see a significant challenge down the road," Karami said.

Researchers elsewhere have been experimenting with using PZT-based energy harvesting for pacemakers and other devices. For example, a team led by flexible electronics pioneer John Rogers, PhD, of the University of Illinois-Champaign, has created a super-thin silicone-encased, bendable energy harvester that can be affixed to a beating heart.

Karami sees an important advantage with his technology: "It doesn't have to be attached to the heart."

Related Article: Find out five things you need to know about energy harvesting.

Chris Newmarker is senior editor of Qmed and MPMN. Follow him on Twitter at @newmarker.

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