Tiny Disks, Big Impact: Wireless Brain Therapy with Magnetic Nanodiscs
Injected magnetoelectric nanodiscs offer a less invasive method of neuron stimulation for biomedical research ― and potential clinical use.
Photo courtesy of Anikeeva Lab
Your brain is a massive game of well-choreographed pinball. At every instant, a hundred billion neurons fire through a hundred trillion synaptic connections. It’s an incredibly complicated system ― and things can go wrong. In Parkinson’s disease, misfiring neurons cause tremors and uncontrollable movements. One possible treatment is Deep Brain Stimulation (DBS): using implanted electrodes that send electrical impulses to specific brain areas responsible for motor control, DBS essentially resets parts of the pinball board. By hijacking neural signals, it’s been shown to reduce symptoms and improve motor function. However, DBS’s applicability is limited by its invasiveness. The surgery can cause hemorrhages and infection, and the target, commonly a region called the subthalamic nucleus, is buried deep inside the folds of the brain.
A new study published last October in Nature Nanotechnology offers an alternative: tiny magnetic nanodisks, five hundred times smaller than a human hair, that can be easily injected into specific locations in the brain. “Under magnetic fields, these particles are generating electrical signals, and those electrical signals can activate the neurons,” explained Ye Ji Kim, a graduate student in the Department of Materials Science and Engineering and the first author on the paper.
Kim got the idea from one of the core classes in the Material Science graduate program on quantum physics. “I just saw the section about magnetostriction effects,” she said. “And then I kept thinking, how can we exploit these in real life?”
Magnetostriction is an effect that causes some materials to undergo mechanical strain (that is, they squish) in the presence of a magnetic field. The researchers coupled a magnetostrictive substance with a piezoelectric material, which responds to the strain by generating electric currents. The result is a nanodisc that generates electrical stimulations when exposed to magnets, like a tiny rubber duck that squeaks when it’s squeezed.
The team previously used different techniques for stimulating neurons, such as heat or light. These signals aren’t directly detectable by human neurons, so the researchers needed to use genetically modified neurons for their experiments. But electricity is a common language. The electrical signal generated by the nanodiscs is “naturally perceivable by the neurons,” Kim said.
To show that the nanodiscs work in live animals, the researchers injected the nanodiscs into the reward center of mice brains. “When this circuit gets activated, animals feel happiness,” Kim explained. Mice injected with the nanodiscs wanted to stay inside a magnetic stimulation chamber, whereas normal mice were scared by it.
The research team also demonstrated the ability for the nanodiscs to affect motor control. Kim said that when only one side of the subthalamic nucleus is activated, the mice start to rotate in one direction. The new nanodiscs enable wireless control of reward and motor behaviors in mice at concentrations 100 times lower than prior studies with nanodiscs, allowing for safer and more powerful electric stimulation.
“I definitely think there is a lot of promise for it,” said Ciarra Ortiz, a graduate student who studies biomedical engineering and was not involved with the study. Compared to DBS surgery, Ortiz explained that “being able to control [the stimulation] remotely is something that is way more appealing.” She noted that the relatively non-invasive nature of the nanodiscs, combined with their ability to be precisely controlled by external magnetic fields, represents a significant step forward in the field of neuromodulation. However, there’s still work to be done. “It probably needs to go through more iterations to make sure that it can be translated to larger animals,” Ortiz said. According to the researchers, the nanodiscs have other more immediate applications in biomedical research, potentially as a tool to noninvasively stimulate specific regions.
In your brain, a hundred billion neurons fire through a hundred trillion synaptic connections. It’s an incredibly complicated game of pinball ― and if things go wrong, perhaps these magnetic nanodiscs could help kick your neurons back into action.