Using a newly-developed technique called mid-field wireless transfer through a thin metal plate placed over the skin, Stanford engineers successfully and safely powered an embedded device the size of a grain of rice to regulate the cardiac rhythm of a rabbit’s heart.
Increased miniaturization of electronic parts has made it possible for manufacturers to build smaller medical devices. That has made implantable devices such as pacemakers much less bulky compared to the earliest models. We want them to shrink further, but the technology for batteries that power these devices have lagged behind.
Batteries still make up the bulk of today’s medical devices. In the case of pacemakers, manufacturers encase batteries with the electronic parts in a single unit for implantation. If the battery runs out, patients need to undergo another surgery to replace the whole unit.
Not having to implant a battery would make these devices much smaller. It would also lessen the need for repeated surgeries just to replace devices that run out of juice. But first, researchers have to make alternative methods of powering these devices.
Stanford engineers came up with the idea of using what they call mid-field wireless transfer as an alternative to traditional wired energy transmission from a battery that comes packaged with a device. The method uses electromagnetic waves to power a device instead.
In an experiment described in the May 19 issue of Proceedings of the National Academy of Sciences, they implanted a rabbit’s heart with a tiny, 3-mm-long pacemaker with no battery source. They then used a thin electromagnetic plate placed over the skin in the area directly above the heart. The plate delivered up to 2,000 microwatts of power to the pacemaker device 5 cm deep beneath the skin.
Power-harvesting coils inside the pacemaker received the electromagnetic waves and converted them into energy. The device functioned properly and regulated the rabbit’s cardiac rhythm as expected.
The researchers noted that similar techniques using near-field energy transmission have been tested before, but they were either too weak to charge devices or pose a risk of soft tissue damage. They claimed no such damage occurred in the experiment on rabbits, as well as later trials involving a pig’s hearts and brains. The scientists said a direct beam of high-frequency waves to the implant delivered the required energy without harming the body.
“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,” Ada Poon, assistant professor of electrical engineering, Stanford University, said in a statement.
The device could be implanted not just in the heart and brain, but also along nerves to lessen pain signals, or for spinal cord stimulation. These tiny devices could be used as “electroceuticals” - devices that deliver treatment, a viable alternative to ingesting pills with potentially less side effects.
In an interview, Poon hopes their work would pave the way for a “new type of medicine where diseases can be treated by electronics rather than drugs.”
During prospective human trials, the researchers hope that the method can prove its potential to treat abnormal heart rhythms, heart failure, Parkinson’s disease, epilepsy, depression, urinary incontinence, and chronic pain.
“I think that amongst the solutions that are proposed to power an implant, this is going to be the most reliable,” Patrick Mercier at the University of California, San Diego, who studies wireless power methods for implantable devices, told New Scientist.