In Wagner’s electrode arrays, thin gold electrical contacts printed using standard lithography techniques play the same role as Ziaie’s liquid alloy contacts. These electrodes do experience a spike in resistance when stretched, but this lasts less than a second, says Morrison. The stretchiness of the electrodes allows the Columbia team to inflict TBI-like mechanical stress on neurons grown in culture, and monitor their electrical activity over the long term.
“One of the big issues right now in TBI is that we aren’t sure of the thresholds of injury,” says Kevin Kit Parker, a U.S. Army Reserve captain and a biomedical-engineering professor at Harvard University. Electrodes like those being developed by Ziaie and Morrison “would allow us to precisely determine what kind of blast forces are required to acutely disrupt the electrical activity in the brain,” Parker says.
Morrison says that his studies have shown that TBI-like damage can be initiated in cells grow in the lab by a 10 percent strain inflicted over 50 milliseconds. In a forthcoming paper to be published in the Journal of Neurotrauma, he and Wagner describe the effects of simulated trauma on cells from different regions of the brain. “We’ve shown that, depending on the brain region, cell death is responsive to the rate and magnitude of stretch,” says Morrison.
Over the long term, the researchers hope that stretchable electrode arrays will prove suitable for more than just studying cells, and can be used to make implantable devices for studying and treating disease. Morrison says that stretchable electrodes may prove friendlier interfaces for neural prosthetics that connect to the brain, such as implants that allow quadriplegics to control their wheelchair or use a cursor on a computer screen just by thinking about it. Because these implants are flexible, they ought to cause less scarring than a rigid silicon chip. Scarring interferes with the performance of an implant.
Stretchable electrode arrays also show promise as an electrical interface to other kinds of muscle. A compliant electrode array wrapped around the smooth muscles of the bladder might be used to send electrical signals that allow the muscle to move again, helping to treat patients suffering from incontinence.