University of Illinois and University of Arizona

Pacemakers supply electrical pulses so hearts can keep a steady beat -- and maybe now it's time for hearts to return the favor.

As electronics spread to smaller and smaller devices, a new technology called energy harvesting can in some cases solve the problem of supplying electrical power. Researchers at the University of Illinois-Champaign have shown they can harvest energy from the movement of internal organs to power pacemakers and other medical devices that today depend on hard-to-change batteries.

The researchers attached small flexible strips they call piezoelectric nanoribbons to organs like the hearts of cows, sheep, and pigs.

The research offers a new option for power pacemakers -- surgically embedded devices that issue electric pulses to keep hearts ticking rhythmically -- as well as heart rate monitors and other medical devices embedded in the human bodies.

They're not the first to try the idea, but their approach -- using flexible strips and a piezoelectric made from lead zirconate titanate -- generates three to five times more current, the researchers said in a Tuesday paper in the Proceedings of the National Academies of Science. In addition, an encapsulation technique protects it from the body's immune system, and it's been tested to maintain its flexibility throughout 20 million flexes. The flexible strips are better suited to real-world bodies than typically rigid electronic devices, they argue in the paper.

"Heart rate monitors, pacemakers, cardioverter-defibrillators, and neural stimulators ... rely on battery power for operation. Means for harvesting power directly from natural processes of the body represent attractive alternatives for these and future types of biomedical devices," the researchers said in the paper. "Here we demonstrate a complete, flexible, and integrated system that is capable of harvesting and storing energy from the natural contractile and relaxation motions of the heart, lung, and diaphragm at levels that meet requirements for practical applications."

Piezoelectric materials already are widely used in everything from sensors to tiny loudspeakers because of a handy property: they produce voltage when compressed, or alternatively compress when a voltage is applied to them. That means piezo electrics can be used as physical sensors since they can convert pressure into an electrical signal that can be measured.

The technique could work on the outside of the body, too. That could be helpful for the hotly active wearable computer field, though the mechanical energy of human movement is more likely to power sensors than something as power-hungry as a mobile phone processor.

Energy harvesting, also called scavenging, is an area of active research relevant to people designing sensors and other small electronic devices. Other energy sources include heat, shock waves, vibrations, and chemical reactions.

One example of energy harvesing: the Holst Centre R&D lab in the Netherlands is developing an energy harvesting system that powers a car tire pressure sensor, including a wireless network to transmit data to the car's control computer.