Wireless Tiny Medical Implants Could Change Health Care

Medical Implants

Popular Mechanics is not usually a source for a health article, but it is appropriate to write about a new mechanical breakthrough that could revolutionize medical technology. A Stanford University Engineering team developed a tiny medical implant that could change health care delivery for all future implants – it is wireless.

Right now, medical implants, such as pacemakers and ones used for epilepsy, are successful but have a serious drawback. They use batteries, which means they cannot be too microscopic. Also, if the battery runs out, the device or battery has to be replaced. There have been ideas floated about harvesting energy from the body’s heat, motion or other sources, but none has product the electricity needed to ensure that people can rely on the devices.

The wireless solution developed by Ada Poon, a Stanford electrical engineer, and her colleagues offers a promising advance in implant technology. Their work was published today in the Proceedings of the National Academy of Sciences. Their mechanism for wirelessly transferring power deep in the body to power electronic medical gadgets could eliminate bulky batteries and recharging systems.

As a Stanford University press release noted, the “technology could provide a path toward a new type of medicine that allows physicians to treat diseases with electronics,” much like pacemakers, nerve stimulators or medical implants devices not yet invented.

The device they developed is smaller than a grain of rice recognizing the “need to make these devices as small as possible to more easily implant them deep in the body,” noted Poon. Their device is charged wirelessly by holding the power source, which is about the size of a credit card, outside the body area where the device is located.

The central discovery creates a new type of wireless power transfer – roughly using comparable power to a cell phone. The development team did have an independent laboratory that tests cell phones verify that the levels they were using fell well below the danger exposure levels for human safety.

The idea of using wireless power for tiny implanted healthy care devices is well established for cochlear implants that help people hear. However, those devices required “near-field wireless power transfer,” which meant they have a small range and the devices cannot be implanted deep in the body. Poon’s team sought to use far-field electromagnetic communications, similar to radio towers, along with near-field power-transfer. The result was the creation of a new midfield power transfer system that can transmit deeper into living tissue.

The Stanford scientists came up with a power-harvesting coil that is a mere 2 millimeters wide. They paired the coil with a power-transmitting metal plate that is 36 square centimeters. The team tested their medical implants-charging device using pig tissue. They found that the metal plate could deliver up to 2,000 microwatts of power through 2 inches of tissue, which is deep enough for the heart or brain. The power level far exceeds current uses, such as conventional pacemakers, which require 8 microwatts of power, or 0.4 percent of what the new metal plate can generate.

The team conducted another experiment using a rabbit to show their system’s ability to power a pacemaker that was implanted nearly 2 inches deep on the animal’s heart. The implant was 2 mm wide and considerably smaller than conventional human pacemakers. The test showed the power was successfully transmitted at levels well below the established safety thresholds.

Noting that they imagine people needing to charge their wireless medical implants for about 10 minutes a month, Poon acknowledged that it will take years to satisfy the safety and efficacy requirements before this wireless charging system could be used in commercial health care devices. She added, “but I hope this provides us a first step.”

By Dyanne Weiss

Stanford University
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