Certain neurological conditions require battery-powered implants to treat them, e.g. neuron-stimulating electrodes may be surgically inserted into the brain while a separate battery-powered pacemaker-like device is implanted under the skin elsewhere in the body. These might be a hassle to replace. Scientists at Texas-based Rice University, US, led by graduate student Amanda Singer, have instead developed a deceptively tiny but magnetically-powerful neural stimulator as a means of wirelessly powering up brain implants, when needed.

This neural stimulator takes the form of a thin rectangular film – about the size of a grain of rice – and consists of two layers of material. The first of these layers is a magnetorestrictive foil made of iron, boron, silicon and carbon, which vibrates at a molecular level when subjected to a magnetic field. The second layer is a piezoelectric crystal, which converts the vibrations from the foil into electric voltage. An integrated circuit then modulates that voltage, so that neurons will respond to it.

In successful lab tests, rats received one of the implants right beneath the skin on their head. The implants were connected to an electrode that extended into the reward centre of their brain; the device was activated by a magnetic field. Interestingly, the rodents moved into areas where the magnetic field activated the device.

The scientists had earlier stated that neural stimulators with power sources such as ultrasound, radio waves and light “are either subject to interference with biological tissue, or generate harmful amounts of heat.” However, Jacob Robinson, a member of the Rice Neuroengineering Initiative and corresponding author of a paper on the alternative neural stimulator research, said: “Our results suggest that using magnetoelectric materials for wireless power delivery is more than a novel idea – these materials are excellent candidates for safe, clinical-grade, wireless bioelectronics.”