A tiny pacemaker like this one was placed in a rabbit and powered wirelessly from outside its body (Image: Alexander J. Yeh)

There’s electricity in the air. A rabbit’s beating heart has been regulated using a tiny pacemaker that beams in energy from outside its body. It is the first time this kind of wireless energy transfer has been demonstrated in a living animal. If such wirelessly powered medical implants can work in people too, it would reduce the seriousness of the procedures required to get them fitted.

“Our device is small, so it will be much easier to deliver into the body,” says Ada Poon of Stanford University in California, who led the team that implanted the tiny pacemaker.

Being fitted with a pacemaker currently requires surgery plus another operation when the battery eventually runs down. So Poon and her colleagues outfitted a rabbit with a pacemaker that has no battery and is just 3 millimetres long (see picture, above right). A metal plate, powered only by a cellphone battery, was then held a couple of centimetres above the rabbit’s chest.


Body boost

The plate transmitted 2000 microwatts to the pacemaker via electromagnetic waves. The pacemaker was then able to regulate the rabbit’s heartbeat, and delivered safe levels of energy to the surrounding tissue.

Such “near-field energy transmission” was previously considered too weak to power devices that are small or placed deeply in the body. To get around this problem, Poon’s team designed the plate to emit electromagnetic radiation in a directed beam towards the implant. They also used the rabbit’s own body tissue to help deliver the signal: the radiation is of a high frequency that propagates particularly well in animal tissue, allowing it to pass further into the body without losing much energy into the tissue or causing damage.

“I think that amongst the solutions that are proposed to power an implant, this is going to be the most reliable,” says Patrick Mercier at the University of California, San Diego, who works on wireless power for implants. He says that when the Stanford team first shared their unusual power scheme, many in the field were surprised. Because of the high frequencies involved, no one had thought to try this method.

Skin patch

Poon’s team also found that their device worked in tests with pig tissue, delivering energy to implants placed in samples of pig hearts and brains. The team is now launching a company, Vivonda Medical, to adapt the technology for use in humans. That will include more practical alternatives to the metal plate, perhaps delivering energy via a patch on the skin.

Robert Puers at the Catholic University of Leuven (KUL), Belgium, isn’t convinced that the technique makes sense for crucial medical devices like pacemakers. “These devices, being life-supporting, should not depend on the presence of an external powering device,” he says.

Poon’s team also plans to adapt their technology for other types of implants, such as neurostimulators which are implanted in the brain to treat conditions such as Parkinson’s disease.

Journal reference: PNAS, DOI: 10.1073/pnas.1403002111