Building a Better Limb
Veterans are inspiring a big push to create thought-controlled prosthetics
Next steps. A direct connection into the nervous system like the BrainGate should provide clearer, more varied signals than sensors glued on skin, and thus more motion control and sense of touch. But plugging wires into humans isn't as simple as plugging an electric toothbrush into the bathroom socket. Surgery always involves risks, and the implantable sensors that have been tried so far sometimes shift and damage nerves or cause infection. They also lose their ability to pick up signals over time, for reasons still unknown. Scientists now building the DARPA arms were already experimenting with different sensor designs that might solve these problems. They include BIONs, rice-size glass-encased transmitters that could be injected into a muscle to pick up electrical signals from nerves, and electrode arrays that would be implanted at the ends of peripheral nerves, which run from the spinal cord through the body, sending signals from and to the brain. "The challenge is going to be how long those interfaces will last and the risk they pose to the patient," says Stuart Harshbarger, project manager at APL. He hopes to be testing a thought-driven arm in humans in early 2008.
Kuiken, who is involved in several aspects of the DARPA projects, likens the infusion of money to "taking what I'm doing and putting it on rocket fuel." He is now studying cadavers to see if he can split nerves and create new branches, then apply the techniques to orchestrate a wider variety of motion in an artificial arm with living nerves in patients.
"I don't think anybody really knows how far we're going to get in two years," says Dean Kamen, founder of DEKA. "But I'm confident we're going to get to something that's going to put a smile on the face of a whole lot of veterans."