A tiny, injectable magnetoelectric antenna implanted deep in the brain can receive power from low-frequency external magnetic fields. [Image courtesy of MIT/Baju Joy]
The antennas measure at about the size of a fine grain of sand, the researchers say. They believe they can inject the devices into the body to wirelessly power devices like pacemakers in cardiac patients and neuromodulators in people with epilepsy or Parkinson’s disease.
“This is the next major step in miniaturizing deep-tissue implants,” said Baju Joy, a PhD student in the MIT Media Lab’s Nano-Cybernetic Biotrek research group. “It enables battery-free implants that can be placed with a needle, instead of major surgery.”
The researchers published their findings in the October issue of IEEE Transactions on Antennas and Propagation. Joy was joined on the paper by lead author Yubin Cai, PhD student at the Media Lab, Benoît Desbiolles and Viktor Schell, former MIT postdocs, Shubham Yadav, an MIT PhD student in media arts and sciences, David Bono, an instructor in the MIT Department of Materials Science and Engineering and senior author Deblina Sarkar, the AT&T Career Development Associate Professor at the Media Lab and head of the Nano-Cybernetic Biotrek group.
Currently, deep-tissue implants receive power either from a surgically implanted battery in the body that requires periodic replacement, or with a surgically placed magnetic coil that can harvest power wirelessly. The coil only functions at high frequencies, the researchers say, which can cause tissue heating and limit the amount of power that’s delivered safely when miniaturized to sub-millimeter size.
To combat the size issue with these current options and the safety issue as well, the team sought to develop their antenna at ultra-small dimensions. At just 200 micrometers, the device operates at low frequencies (109 kHz). The researchers attribute this to a novel technology in which a magnetostrictive film, which deforms when a magnetic field is applied, is laminated with a piezoelectric film. This converts deformation to electric charge.
With alternating magnetic field application, magnetic domains within the magnetostrictive film contort it in the same way that a piece of fabric interwoven with pieces of metal would contort if subjected to. a strong magnet. The mechanical strain in the magnetostrictive layer causes the piezoelectric layer to generate electric charges across electrodes placed above and below. Joy says the team found a way to use the mechanical vibration to convert magnetic fields to electric fields.
According to Sarkar, the antenna delivers 4-5 times more power than implantable antennas of similar size that rely on metallic coils and operate in the GHz frequency range.
“Our technology has the potential to introduce a new avenue for minimally invasive bioelectric devices that can operate wirelessly deep within the human body,” Sarkar said.
Min-Vasive Medtech: Read more about minimally invasive devices and systems
The researchers liken the activation device to a rechargeable wireless cell phone charger. It’s small enough to be applied on the skin as a stick-on patch or slipped into a pocket close to the skin surface and still produce the magnetic field that activates the antenna. The team fabricated the antenna with the same technology as a microchip, so it can easily integrate with existing microelectronics.
Altogether, the system can be placed with a simple needle injection.
The researchers say they could easily scale antenna manufacturing and multiple offerings could be injected to treat large areas of the body. In addition to pacemakers and neuromodulation devices, they may look to apply their technology to glucose sensing.
“That’s just one example,” Joy said. “We can leverage all these other techniques that are also developed using the same fabrication methods, and then just integrate them easily to the antenna.”
