Growing Neural Implants

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Animal tests of cortical implants in rodents and cochlear implants--in which an electrode array is implanted into the auditory portion of the inner ear--in guinea pigs suggest that coated electrodes perform better than bare metal versions, particularly in the short term. However, it's not yet clear how they'll fare in the long term, which is one of the biggest problems facing chronic implants--especially devices that record neural activity. "Recording quality deteriorates over time with all existing electrodes," says Andrew Schwartz, a neuroscientist at the University of Pittsburgh.

Martin's most ambitious goal is to get the electrodes to fully integrate with tissue by growing the coating after the electrode is implanted. The idea is that the polymer's hairlike fingers would reach into the tissue, extending beyond the dead zone surrounding the metal electrodes. "Imagine the cells are like M&Ms suspended in Jell-O," says Martin. "We're growing the polymer around the M&Ms and through the Jell-O." So far, the scientists have succeeded in growing the polymer in a piece of muscle tissue and a piece of mouse cortex.

Scientists developing new implants are excited about the possibility. But they also see serious hurdles. "It's a very interesting concept," says Ravi Bellamkonda, a biomedical engineer at the Georgia Institute of Technology, in Atlanta. "But the challenge is, will they actually penetrate the scar tissue and grow through or not?" McCreery, whose work has centered on acoustic prostheses, says that such an approach would be useful for cochlear implants. However, he warns that "you'd need to make sure it doesn't grow into a frizzy mess that shorts everything out."

Along with former lab members, Martin founded a company, Massachusetts-based Biotectix, to commercialize the materials developed in his lab. He says that he is already in talks with a cochlear-implant technology company about using his lab's materials in their devices.