PORTLAND, Ore. Astronauts can only endure space for about six months without irreversibly damaging their muscles, despite daily exercise.
Unfortunately, it will take at least 30 months of space travel to reach Mars, making a manned flight unfeasible today.
The National Aeronautics and Space Administration (NASA) recently reported progress toward a neural implant technology using carbon nanotubes that could enable space flights of indefinite periods.
By stimulating the neural pathways responsible for muscle atrophy, NASA hopes to fool the brain into thinking that gravity is still present even in free fall.
"We hope to let the brain feel the weight of gravity, even if it's not there," said NASA scientist Jun Li. "For a trip to Mars, we could monitor astronauts' brains, then artificially stimulate its neurons with nanofiber electrodes to fool it into thinking gravity is still
The project has been ongoing for about two and a half years at NASA's Ames Research Center in Moffett Field, Calif. Scientists are working to develop a biocompatible implant that can interface to the brain as a prosthetic device that both monitors neural activity and stimulates neural tissue as necessary. The resulting vertically aligned carbon nanofiber (VACNF) electrodes could also be helpful on Earth for biosensors, medical implants to combat Parkinson's disease, as well as an anti-atrophy stimulator for deep-space travelers, according to Li.
"We have learned a lot from others' successful cochlea implants, artificial retinas and medical prosthetics implanted into the brain to stimulate neural pathways that combat Parkinson's disease and epilepsy," said Li. "Now we think we have improved on those designs and are ready to prove it by trying out our implants in live subjects."
NASA has experimented on the brain tissue of rats and reports that their tests show a 10-fold increase in efficiency, compared with conventional electrodes. Next, they plan to test their nanofiber electrodes in the brains of live rats and measure both electrical characteristics and synaptic chemical neurotransmitters.
According to Li, the brain is just another electrical system, albeit one with incredibly sophisticated defense mechanisms designed for self-healing that defeat the electrode technologies available today. As soon
as a traditional metal electrode is placed in the brain, according to Li, the body's immune system begins attacking it for two reasons: shape and texture.
"Today's metal electrodes are degenerative for two reasons," said Li. "First, the neural networks of the brain are three-dimensional, whereas most electrodes are basically planar. Secondly, neural tissues are very
sensitive to the stiffness of metal electrodes, which are a million times stiffer than a neuron."
Consequently, the very neurons that electrodes are supposed to monitor and stimulate start moving away from metal electrodes as soon as they are implanted. To fill the void, the immune system begins surrounding
the electrode with scar tissue (glial cells), which are insulators.
Consequently, electrodes implanted in the brain continually degrade in performance until they eventually just stop working altogether.
To solve the first problem, Li grew groups of parallel nanotubes vertically from a substrate, resulting in an electrode that extends into a third dimension. Since the entire surface of the nanotube can act as a sensor or as a stimulator, their non-planar shape more easily
interfaces with the three-dimensional neural network structures of the brain.
Second, because he grows long flexible groups of very thin nanotubes, the resulting electrodes are almost as soft as the surrounding tissue into which they are implanted. The body accepts the electrodes, and the
neurons grow into the implant instead of insulating it with scar tissue, allowing the electrodes to be embedded into the brain.
"Our nanotube electrodes are vertically aligned into a structure that resembles a soft brush, so that it is not rejected by the body," said Li.
Finally, the nanofibers are coated with a polymer to prevent them from sticking to each other. In addition, the polymer carries neurotransmitter-like ions, which are released when it is electrically stimulated and replenished when the body is idle. Consequently, Li
predicts that NASA's nanofiber electrodes will eventually be able to be implanted into astronauts' brains for indefinite periods.