A team of neuroengineers at Rice University have created a small surgical implant capable of electrically stimulating the nervous system and brain without a need for wired power supply or battery, according to a study recently published in the journal Neuron.

Magnetically powered neural stimulator

Generating power from magnetic energy and roughly the size of a grain of rice, the neural stimulator is the first magnetically powered neural stimulator capable of functioning at high-frequency signals – much like clinically approved, battery-powered implants typically used as a treatment for epilepsy, chronic pain, Parkinson's disease, and other conditions, according to a blog post on the Rice University website.

The key ingredient of the implant is a thin strip of 'magnetoelectric' material that converts magnetic energy directly into an electrical voltage.

This new method avoids common pitfalls of using radio waves, light, ultrasound, and even magnetic coils – all of which have been proposed before as possible power sources for tiny wireless implants – that each suffer from interference with living tissue, or even produce dangerous amounts of heat within the body.

To prove the concept of the miniature, magnetoelectric-powered neural stimulator, engineers outfitted the device under the skin of rodents, who preferred areas with active magnetic fields over those without. Source: J. Robinson / Rice University

Proof-of-concept for neural stimulator without batteries

To prove the viability of magnetoelectric technology, researchers tested the implants in rodents who were totally awake and free to roam around their enclosed spaces.

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

"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."

Future applications of tiny neural stimulants

Tiny brain- and nervous-system stimulants might have applications across  a wide spectrum of future technology. Battery-powered implants are typically used for epilepsy and tremor reduction in patients suffering from Parkinson's disease, but new research shows neural stimulation might be a useful way to treat depression, obsessive-compulsive disorders, and more than a third of patients suffering from chronic intractable pain associated with depression, anxiety, and opioid addiction.

Robinson adds that the miniaturisation study's lead author and graduate student Amanda Singer is significant because it opens the door to neural stimulation therapy without using external or batter-provided power – and, notably, without need for major surgery.

Surgeons could install a device the size of a grain of rice almost anywhere in the body with a minimally invasive procedure, akin to the one used to put stents in blocked arteries.

Graduate student solves wireless power problem

Singer solved the wireless power problem by placing layers of two disparate materials together in a single film. The first layer was a magnetostrictive foil of iron, silicon, carbon, and boron – and vibrates at a molecular level when placed within a magnetic field. The second layer is a piezoelectric crystal that converts mechanical stress directly into electric voltage.

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

As advances like Elon Musk's Neuralink work to augment brain function in patients with chronic neurological illnesses, this latest research from Rice University gives us a glimpse into a future where neuroengineering might stimulate a brain with no power source – except for a nearby magnetic field.

This article was written by Brad Bergan and first appeared in Interesting Engineering.