Neuroengineers 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 draws its power from magnetic energy and is about the size of a grain of rice. 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 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.
Tiny implants capable of modulating activity of the brain and nervous system could have wide-ranging implications. While battery-powered implants are frequently used to treat epilepsy and reduce tremors in patients with Parkinson’s disease, research has shown that neural stimulation could be useful for treating depression, obsessive-compulsive disorders, and more than a third of those who suffer from chronic pain that often leads to anxiety, depression, and opioid addiction.
The miniaturization is important because the key to making neural stimulation therapy more widely available is creating battery-free, wireless devices that are small enough to be implanted without major surgery. Devices 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.
To make the device wireless, the researchers used layers of two very different materials in a single film. 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, a piezoelectric crystal, converts mechanical stress directly into an electric voltage. The acoustic reverberations activate the piezoelectric half of the film.