David C. Martin, Director of the Macromolecular Science and Engineering Center at the University of Michigan, presented research on polymers that can be processed into a "fuzzy" form to enhance the compatibility of electronic implants with brain tissue.
Electrodes implanted in the brain can pick up electrical signals sent back and forth by nerve cells. The tiny devices -- about a millimeter long -- are coated with growth factors that encourage brain tissue to grow into them. The intent is for each probe to make contact with a series of neurons, allowing it to receive signals it can interpret and use to activate an external device. The technique has been called a spinal cord bypass. It could help patients with brain disorders and paralysis operate artificial limbs or control a computer mouse by simply thinking about the task.
There is, however, still a long way to go before humans will be effortlessly controlling external devices with their mind. "Our interest is in finding materials and processing schemes that can help the electrodes function better for long periods of time," Martin said.
Initial experiments in guinea pigs showed that these electrodes do not make efficient contact with the brain. "The implanted electrodes are solid, hard and smooth," Martin said, "whereas the brain is soft, wet and alive." The differences can cause the electrodes to lose contact with the brain, blocking the signal.
Martin and his team have designed rough-surfaced, fuzzy polymers with various grooves and depressions designed to mesh better with neurons. "The scheme is to have these electrodes make a connection with the neurons quickly, before the other cells get in and wall them off," Martin said.
To further encourage connection, Martin and his team have incorporated biological molecules in the polymer coating to selectively attract target neurons. In guinea pigs, the researchers found that uncoated electrodes came out clean after remaining in the brain for a period of time, while coated electrodes were covered with neural tissue. This indicates that the neurons are hanging on to the biologically doped coating, Martin said.
The team also found that the fuzzy surface of the polymer coating, in addition to improving contact with brain tissue, could be used to fine-tune its ability to conduct electrical signals.
Martin's research is being conducted in collaboration with the University of Michigan Center for Neural Communications Technology, the Kresge Hearing Research Institute, and the Keck Center for Tissue Engineering at the University of Utah. Xinyan "Tracy" Cui, Ph.D., who is now working at Unilever, did much of the work that was discussed in the presentation.