Invention powers wireless medical implants deep inside the body

Devices the size of a grain of rice that can be implanted deep inside the body herald a new wave of miniature medical electronics to treat illness and alleviate pain. Now thanks to an engineer at Stanford University, CA, there is a way to transmit power to them safely from outside the body - without wires.

Ada Poon, assistant professor of electrical engineering at Stanford has been working for years to find a way to eliminate bulky batteries and clumsy recharging systems - the biggest drawback in the use of implantable medical devices.

Writing in Proceedings of the National Academy of Sciences, she and her colleagues report how they developed and tested a way to safely and wirelessly transfer power to tiny gadgets lodged deep inside the body.

They hope the technology will lead to a new type of medicine that allows patients to be treated with electronics instead of drugs. This could include tiny pacemakers, nerve stimulators to treat pain, and devices yet to be invented.

Prof. Poon says, "We need to make these devices as small as possible to more easily implant them deep in the body and create new ways to treat illness and alleviate pain."

To test their new wireless recharging system, the team developed a tiny pacemaker that is smaller than a grain of rice and can be powered wirelessly from a charger about the size of a credit card that is held above the implant, outside the body.

The achievement is significant because no suitable method for powering tiny devices deep inside the body has been demonstrated before.

"Existing methods for energy storage, harvesting, or transfer require large components that do not scale to millimeter dimensions," write the authors.

Breakthrough blends safety of near-field with reach of far-field waves

At the heart of the invention is an engineering breakthrough that enables a new type of wireless transfer of power - using about the same power as a cell phone. The method can reach deep inside the body, and independent tests similar to those carried out on cell phones show the system falls well below the exposure levels considered harmful to humans.

The engineering breakthrough came when Prof. Poon found a way to blend two existing methods - near-field and far-field electromagnetic waves - to create what she terms "mid-field waves."

Prof. Poon describes her work in the video below:

Near-field waves are already safely used in wireless power systems like hearing implants. But as their name implies, they can only transfer power over short distances, and so are unsuitable for powering deep implants.

Far-field waves, such as those broadcast by radio towers, can travel over long distances, but when they meet living tissue they either bounce off it or get absorbed and generate heat.

Prof. Poon blended the safety of near-field waves with the reach of far-field waves and achieved this by taking advantage of the fact that when waves hit a different material they travel differently.

She made a power source that generated a special type of near-field wave that when it moved from air to skin, changed the way it traveled so it could keep moving. This is not dissimilar to what happens when you put your ear to the railroad track and you can feel the vibration of an approaching train before you can hear it in the air.

First author John Ho, a doctoral candidate in Prof. Poon's lab, notes:

"With this method, we can safely transmit power to tiny implants in organs like the heart or brain, well beyond the range of current near-field systems."

Prof. Poon and colleagues have tested the wireless charger in a pig and used it to power a tiny pacemaker in a rabbit. They are now planning to test it in humans. However, even if human tests are successful it could be years before the technology is commercially available, because of the time it takes to prove safety and effectiveness of new medical devices.

Nevertheless, the discovery is likely to spur a new generation of programmable microimplants, says Prof. Poon. These could take the form of sensors that monitor vital functions deep in the body, nerve stimulators that change signals in the brain, and even tiny dispensers that deliver drugs directly to affected tissue. Such alternatives to drug therapy are called "electroceutical" treatments.

Meanwhile, Medical News Today recently learned about the first fully implantable device to treat central sleep apnea in heart failure patients. Prof. William T. Abraham of Ohio State University, who tested the device in a pilot study, presented the first year of results to the annual meeting of the Heart Failure Association of the European Society of Cardiology.

Written by Catharine Paddock PhD

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