A team of neuroengineers at Rice University have created a tiny surgical implant that can electrically stimulate the brain and nervous system without using a battery or wired power supply.
The device about the size of a grain of rice could be implanted almost anywhere in the body with a minimally invasive procedure similar to the one used to place stents in blocked arteries.
It is the first magnetically powered neural stimulator that produces the same kind of high-frequency signals as clinically approved, battery-powered implants that are used to treat epilepsy, Parkinson's disease, chronic pain and other conditions.
The study, published in the journal Neuron, has wide-ranging implications. Tiny implants capable of modulating activity of the brain and nervous system could be useful for treating depression, obsessive-compulsive disorders and more than a third of those who suffer from chronic, intractable pain that often leads to anxiety, depression and opioid addiction.
The implant's key ingredient is a thin film of "magnetoelectric" material that converts magnetic energy directly into an electrical voltage. The method avoids the drawbacks of radio waves, ultrasound, light and even magnetic coils, all of which have been proposed for powering tiny wireless implants and have been shown to suffer from interference with living tissue or produce harmful amounts of heat.
The researchers demonstrated the viability of magnetoelectric technology in rodents that were fully awake and free to roam about their enclosures.
"Our results suggest that using magnetoelectric materials for wireless power delivery is more than a novel idea. These materials are excellent candidates for clinical-grade, wireless bioelectronics," said Jacob Robinson, corresponding author, and a member of the Rice Neuroengineering Initiative.
"The magnetic field generates stress in the magnetostrictive material," said Amanda Singer, an applied physics student in Robinson's lab. "It doesn't make the material get visibly bigger and smaller, but it generates acoustic waves and some of those are at a resonant frequency that creates a particular mode we use called an acoustic resonant mode."
Study co-author and neuroengineering initiative member Caleb Kemere said, "When you have to develop something that can be implanted subcutaneously on the skull of small animals, your design constraints change significantly. Getting this to work on a rodent in a constraint-free environment really forced Amanda to push down the size and volume to the minimum possible scale."
Robinson said the magnetoelectric films harvest plenty of power but operate at a frequency that's too high to affect brain cells.
Singer said creating a modulated biphasic signal that could stimulate neurons without harming them was a challenge, as was miniaturization.
"When we first submitted this paper, we didn't have the miniature implanted version," she said. "Up to that point, the biggest thing was figuring out how to actually get that biphasic signal that we stimulate with, what circuit elements we needed to do that.
"When we got the reviews back after that first submission, the comments were like, 'OK, you say you can make it small. So, make it small,'" Singer said. "So, we spent another a year or so making it small and showing that it really works. That was probably the biggest hurdle. Making small devices that worked was difficult, at first."
“The study took more than five years, largely because Singer had to make virtually everything from scratch,” Robinson said.
"There is no infrastructure for this power-transfer technology," he said. "If you're using radio frequency (RF), you can buy RF antennas and RF signal generators. If you're using ultrasound, it's not like somebody says, 'Oh, by the way, first you have to build the ultrasound machine.'