A miniature, wireless, and magnetically powered neural stimulator may be the future of deep brain stimulation for Parkinson’s disease, and disorders like epilepsy and chronic pain, a study reported.
The study, “Magnetoelectric Materials for Miniature, Wireless Neural Stimulation at Therapeutic Frequencies,” was published in the journal Neuron.
Neurostimulation through surgically placed, battery-powered implants is often used to help reduce tremors in people with Parkinson’s disease. However, the devices are often large and batteries may need to be charged or replaced through surgery. Their wires can also facilitate infections.
Neuroengineers at Rice University have developed a tiny (about the size of a grain of rice) wireless surgical implant that uses “magnetoelectric” technology to electrically stimulate the brain and nervous system.
The implant is made up of two layers of two very different materials, joined in a single film, that converts magnetic energy directly into an electrical voltage.
The first layer is a magnetostrictive foil of iron, boron, silicon, and carbon that vibrates at a molecular level and generates acoustic waves when placed in a magnetic field. (Magnetostrictive is a property of magnetic materials that causes them to change their shape or dimensions in response to a magnetic field.)
“The magnetic field generates stress in the magnetostrictive material,” Amanda Singer, the study’s lead author, said in a press release.
“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,” Singer added.
Acoustic resonance in magnetostrictive materials is what causes an audible hum in large electrical transformers.
The implant’s second layer is a piezoelectric crystal, which converts the acoustic waves created by the first layer directly into an electric voltage.
Using this method, the implant is reported to harvest plenty of power but operates at a frequency too high to affect brain cells. This is the same kind of high-frequency signals as used by clinically approved, battery-powered implants.
“A major piece of engineering … was creating the circuitry to modulate that activity at a lower frequency that the cells would respond to,” said Jacob Robinson, associate professor of electrical and computer engineering and of bioengineering at Rice.
“It’s similar to the way AM radio works. You have these very high-frequency waves, but they’re modulated at a low frequency that you can hear,” Robinson added.
Having established that the technology worked, the team spent about a year creating a miniature version of the implant.
The end result was a battery-free, wireless device, small enough to be implanted without major surgery — important for making neural stimulation therapy more widely available.
This device could be implanted almost anywhere in the body with a minimally invasive procedure, similar to the one used to place stents in blocked arteries, Robinson said.
To demonstrate the viability of the technology, the team implanted the device beneath the skin of the skull in a rat model of Parkinson’s disease.
“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,” said Caleb Kemere, an associate professor of electrical and computer engineering and of bioengineering at Rice.
Scientists observed that the animals preferred to be in areas of their enclosures where a magnetic field activated the stimulator, and provided a small voltage to the reward center of their brains.
“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,” Robinson said.