Stiff, steel microwires can damage tissue when implanted deep into patients' brains. Engineers at MIT have found a way around this problem with a flexible brain-implant technology.
Photo Credit: Bill Brooks | CC BY-SA 2.0
Brain implants have come a long way in the past few decades: surgeons routinely wire up the brains of patients with movement disorders, like Parkinson's disease, using brain pacemakers (similar to heart pacemakers) that effectively reduce tremors and other motor symptoms. But the stiff, steel microwires that are lowered deep into the brain aren't particularly friendly to brain tissue, sometimes causing complications like inflammation and scarring that can lead to stroke.
Now, a team led by MIT professor Polina Anikeeva has harnessed insights from the materials sciences to develop a better wire for deep-brain stimulation. They managed to fabricate flexible wires capable of not only stimulating brain tissue, but delivering drugs and recording brain activity simultaneously, while drastically reducing the side-effects one would expect from a traditional metal implant.
The key to the technology is making a larger-scale version, called a preform, of the desired arrangement of channels within the fiber: optical waveguides to carry light, hollow tubes to carry drugs, and conductive electrodes to carry electrical signals. These polymer templates, which can have dimensions on the scale of inches, are then heated until they become soft, and drawn into a thin fiber, while retaining the exact arrangement of features within them.
A single draw of the fiber reduces the cross-section of the material 200-fold, and the process can be repeated, making the fibers thinner each time and approaching nanometer scale. During this process, Anikeeva says, "Features that used to be inches across are now microns."
Combining the different channels in a single fiber, she adds, could enable precision mapping of neural activity, and ultimately treatment of neurological disorders, that would not be possible with single-function neural probes. For example, light could be transmitted through the optical channels to enable optogenetic neural stimulation, the effects of which could then be monitored with embedded electrodes. At the same time, one or more drugs could be injected into the brain through the hollow channels, while electrical signals in the neurons are recorded to determine, in real time, exactly what effect the drugs are having.
While the new electrodes are currently being tested in animal models, they hold promise for neural prosthetics of the future. A single electrode, capable of multiple functions, would enable doctors to finely tune their treatments for particular patients, and monitor the outcome in real-time. Further ahead, these electrodes might even lead to non-therapeutic brain/machine interfaces in the population at large.
Read the full study at Nature Biotechnology.