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Updated: January 23, 2014 13:02 IST

Wearable electronics for inside-the-body use developed

Vasudevan Mukunth
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Thin, flexible mechanical energy harvester, with rectifier and microbattery, mounted on the bovine heart.
Credit: University of Illinois and University of Arizona Thin, flexible mechanical energy harvester, with rectifier and microbattery, mounted on the bovine heart.

Researchers from universities in the U.S. and China have developed a microscopic device capable of producing power from the body’s organs. They say such devices could in turn be used to power other implanted biomedical devices, like pacemakers, heart-rate monitors and neural stimulators, eliminating the need for invasive surgeries to replace their batteries.

“This device mounts onto the surface of the organ of interest, to produce and store power associated with mechanical motions,” wrote Dr. John Rogers, Director of the Frederick Seitz Materials Research Laboratory at the University of Illinois, Urbana-Champaign, in an email. He was a part of this research which involved scientists from four universities.

The device relies on the piezoelectric effect, where electricity is generated when some pressure is applied on a specific crystal. In the researchers’ system, they are lead zirconate titanate (PZT) crystals, which are one of the highest-performance piezoelectric crystals known.

The PZT is mounted on a thin sheet of plastic, with a chip for a rectifier and a small chip-scale battery. The pacemaker, or other implantable device, connects to the device through the battery component. “Our harvester provides about enough power, on average, to operate a pacemaker,” Dr. Rogers added. The battery acts as a buffer between the PZT harvester and the pacemaker, evenly spacing out the power to be fed.

The researchers tested their device with both experiments and computer simulations. During experiments, they implanted the device on the hearts of cows and sheep, the size of whose hearts, lungs and diaphragm are close to those of humans. They found that the device operated at an efficiency of 2 per cent.

Implanted devices like cardiac pacemakers need about 1 microwatt to function, and last for some 10 years. Currently, such devices come with a built-in cell that produces this power, and requires replacement after the lifetime period. Dr. Rogers’s team observed that stacking five of the PZT harvesters on an organ resulted in a power-density of 1.2 microwatt/cm, sufficient to operate a pacemaker.

Conversely, although computer simulations have shown that the device can survive over 20 million bending-unbending cycles in a moist environment, Dr. Rogers wrote that “longer term survivability tests are needed in animal models.”

“This direction represents an area of current work,” he wrote, adding that it will be at least two more years until they can progress to human tests.

Simulations proved that the silicone encasement of the crystal protects it from deformation when implanted on an organ’s surface. The team also notes in their paper, published in the Proceedings of the National Academy of Sciences on January 20, that silicone’s pliant mechanical properties meant their device could be used to measure other bodily functions by attaching on the skin or around fingers.

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