Pat Anson, PNN Editor

Engineers at Rice University have created a tiny implant – about the size of a grain of rice -- that can electrically stimulate the brain and central nervous system without using a battery or wired power supply.

The magnetically powered implant generates the same kind of high-frequency signals as much larger battery-powered stimulators used to treat chronic pain, epilepsy, Parkinson's disease and other medical conditions. It could be implanted almost anywhere in the body in a minimally invasive procedure.

Researchers demonstrated the viability of the implants by placing them beneath the skin of laboratory rodents that were fully awake and free to roam about their enclosures. The rodents preferred to be in portions of the enclosures where a magnetic field activated the stimulator, which provided a small voltage to the reward center of their brains.

"Doing that proof-of-principle demonstration is really important, because it's a huge technological leap to go from a benchtop demonstration to something that might be actually useful for treating people," said Jacob Robinson, PhD, a member of the Rice Neuroengineering Initiative and corresponding author of a study published in the journal Neuron.

"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."

The implant has a thin film of magnetoelectric material that converts magnetic energy into electricity. Lead author Amanda Singer created the film by joining together two layers of very different materials.

The first layer, a magnetostrictive foil of iron, boron, silicon and carbon, vibrates at a molecular level when it's placed in a magnetic field. The second layer, a piezoelectric crystal, converts mechanical stress directly into an electric voltage.

This method avoids the drawbacks of radio waves, ultrasound, light and other wireless methods to power stimulators, which can interfere with living tissue or produce harmful amounts of heat.

"The magnetic field generates stress in the magnetostrictive material," Singer explained. "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."

Acoustic resonance in magnetostrictive materials is what causes large electrical transformers to audibly hum.

"A major piece of engineering that Amanda solved was creating the circuitry to modulate that activity at a lower frequency that the cells would respond to," Robinson said. "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."

Tiny implants capable of modulating the brain and central nervous system could have wide-ranging implications. They could replace battery-powered implants used to treat epilepsy and reduce tremors in patients with Parkinson's disease. Neural stimulation could also be useful for treating depression, obsessive-compulsive disorders and chronic intractable pain.

Singer said creating a 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. "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.’

"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."

In all, the study took more than five years to complete, largely because Singer had to make virtually everything from scratch.