Carbon Fibre Electrodes Allow Unprecedented Neural Recording
A tiny, implantable carbon fibre electrode has the potential to provide a long-term brain-computer interface which can record electrical signals over lengthy periods of time.
The carbon fibre electrodes were developed at the University of Michigan and demonstrated in rats. The new research shows the promise of carbon fibre electrodes in recording electrical signals from the brain without damaging brain tissue. Directly implanting carbon fiber electrodes into the brain allows the capturing of bigger and more specific signals than current technologies.
This technology could lead to advances that could give amputees and those with spinal injuries control of advanced prosthetics, stimulate the sacral nerve to restore bladder control, stimulate the cervical vagus nerve to treat epilepsy and provide deep brain stimulation as a possible treatment for Parkinson’s.
“There are interfaces out there that can be implanted directly into the brain but, for a variety of reasons, they only last from months to a few years,” said Elissa Welle, a recent PhD graduate from the U-M Department of Biomedical Engineering. “Any time you’re opening up the skull for a procedure involving the brain, it’s a big deal.”
Brain implants are typically made from silicon due to its ability to conduct electricity and its historic use in cleanroom technology. But silicon is not very biocompatible and leads to the formulation of scar tissue over long periods. Such electodes will eventually degrade and no longer capture brain signals, requiring removal.
Carbon fibres may be the answer to getting high-quality signals with an interface that lasts years, not months. And by laser cutting and sharpening carbon fibers into tiny, subcellular electrodes in the lab with the help of a small blowtorch, U-M engineers have harnessed the potential for excellent signal capture in a form the body is more likely to accept.
“After implantation, it sits inside the brain in a way that does not interfere with the surrounding blood vessels, because it’s smaller than those blood vessels,” Welle said. “They’ll move around and adjust to an object that small, rather than get torn as they would when encountering larger implants.”
Part of the electrode’s compatibility in brain tissue is down to smaller size, but its needle-like shape may also minimise compacting of any surrounding tissue. Larger carbon-based electrodes have been shown to actually encourage neural tissue to grow instead of degrading. The team is hopeful that similar potential for their carbon fibre electrodes will be revealed by further testing.
Carbon fibre electrodes in a previous study dramatically outperformed conventional silicon electrodes with 34% of electrodes recording a neuron signal compared to 3%. Laser cutting then improved this number to 71% at 9 weeks after implantation. Flame sharpening has now enabled these high performance probes to be implanted directly into the cerebral cortex, negating the need for a temporary insertion aid, or shuttle, as well as into the rat’s cervical vagus nerve.
It is relatively easy to insert electrodes into the brain. But the researchers have also taken on the more difficult task of inserting the sharpened carbon fibre electrodes into nerves, with micrometre diameters.
Those findings show that potential for these electrodes goes beyond prosthetic manipulation, according to Cindy Chestek, a U-M associate professor of biomedical engineering, and principal investigator of the The Cortical Neural Prosthetics Lab.
“Someone who is paralysed may have no control over things like their bladder, for example,” Prof Chestek said. “We may be able to utilise these smaller electrodes to stimulate and record signals from areas that can’t be reached by larger ones, maybe the neck or spinal cord, to help give patients some level of control.”
Source: University of Michigan