Researchers at the University of Michigan, Ann Arbor, said that the seven micron in diameter, flexible electrode they developed is ten-times smaller than the nearest competition and could make long-term measurements of neural activity practical. This kind of technology could eventually be used in brain-computer interfaces (BCIs) to send signals to prosthetic limbs, overcoming inflammation larger electrodes cause that damages both the brain and the electrodes.
An artist’s rendering of individual neurons. A new electrode developed at the University of Michigan can focus on the electrical signals of just one neuron. It may help researchers understand how electrical signals move through neural networks in the brain. Because this electrode is so small and unobtrusive, it may be able to stay in the brain for long periods without upsetting the immune system, perhaps picking up signals to send to prosthetic limbs.
Image courtesy of Takashi Kozai.
According to a paper on the research, published in the current edition of Nature Materials, the device is made of highly conductive carbon fiber and is coated in plastic, which blocks out signals from other neurons. The conductive gel pad at the end allows for a close connection so the brain-cell signals come in much clearer. Electrical impulses travel through the brain by movements of ions, or atoms with electric charges, and the signals move through the gel in the same way. On the other side, the carbon fiber responds to the ions by moving electrons, effectively translating the brain’s signal into the language of electronic devices, said Nicholas Kotov, PhD, the U-M Joseph B. and Florence V. Cejka Professor of Engineering, who led one of the three teams working on the electrode.
To demonstrate how well the electrode listens in on real neurons, the team led by Daryl Kipke, PhD, professor of biomedical engineering and director for the U-M Center for Neural Communication Technology, implanted it into the brains of rats. The electrode’s narrow profile allows it to focus on just one neuron, and the team saw this in the sharp electrical signals coming through the fiber. In addition to picking up specific signals to send to prosthesis, listening to single neurons could lead to other discoveries, such as how neurons communicate with each other and the pathways used for information processing in the brain, Kotov said.
This device also takes steps forward to realizing long-lasting implants, the researchers reported.
To listen to a neuron for long, or help prosthetic users control a prosthesis as they do a natural limb, the electrodes need to be able to survive for years in the brain without doing significant damage. During the six weeks of testing, the rat’s neurons and immune system got used to the electrodes.
“Typically, we saw a peak in immune response at two weeks, then by three weeks it subsided, and by six weeks it had already stabilized,” Kotov said. “That stabilization is the important observation.”
Although the electrode is not a clinical trial-ready device, “the results strongly suggest that creating feasible electrode arrays at these small dimensions is a viable path forward for making longer-lasting devices,” Kipke said.
Editor’s note: This story was adapted from materials provided by the University of Michigan. A third team was led by Joerg Lahann, PhD, professor in the Departments of Chemical Engineering, Materials Science and Engineering, Biomedical Engineering, and Macromolecular Science and Engineering, and director of the U-M Biointerfaces Institute.
