What’s the News: Engineers and patients dream of mechanical prosthetic limbs that can talk and listen to the brain, moving in response to thought and sending back sensory information. For that dream to become reality, electrodes from the prosthetic have to connect with nearby nerve cells—a tricky proposition, given that nerve cells in an amputated limb won’t grow without proper structural support. A new tubular scaffold, described in detail by Technology Review, has tiny grooves that fit bundles of nerve cells, which could provide the support nerves need to interface with a mechanical limb better than current designs.
What’s the News: Scientists have discovered a new technique for linking semiconducting tubes with mouse nerve cell tendrils: They let the cells do the work for them. After creating biologically friendly semiconductor tubes, they found that nerve cells’ tendril-like axons didn’t shy away. “They seem to like the tubes,” University of Wisconsin-Madison biomedical engineer Justin Williams told Science News. This represents a step toward new technology involving computer-brain networks.
How the Heck: The trick was to create tubes of layered germanium and silicone (which insulate the nerve’s electrical signals) that were big enough for the nerve cell’s threadlike projections to enter but too small for the cell body: When seeded with live mouse nerve cells, the only way the cells could interact with the tubes was be sending tendrils into it—which is just what they did.
What’s the Context:
Not So Fast: The researchers don’t yet know whether the connected nerves are actually talking with each other.
Next Up: Now they want to hook the tubes to voltage sensors that can “listen” to the cells communicating with each other. If successful, this could lead to new drug tests where doctors can actually measure how nerve cells respond to certain types of drugs, leading to further innovations in the battle against neurological diseases like Parkinson’s.
Image: Minrui Yu, University of Wisconsin–Madison
Reference: “Semiconductor Nanomembrane Tubes: Three-Dimensional Confinement for Controlled Neurite Outgrowth” Minrui Yu et al. DOI: 10.1021/nn103618d
For DARPA, the secretive military research agency, it’s not enough for a prosthetic limb to simply resemble a normal one, or for a patient to be able to move it through some remote control. DARPA-backed engineers are attempting to build a system in which peripheral nerves would be reattached to artificial limbs, which could send signals to a brain sensor that could reply. This would be a vast improvement over prosthetics that require conscious directives, and could turn a prosthetic into something that responds the way an ordinary limb would.
Darpa’s after a prosthetic that can record motor-sensory signals right from peripheral nerves (those that are severed when a limb is lost) and then transmit responding feedback signals from the brain. That means an incredibly sensitive platform, “capable of detecting sufficiently strong motor-control signals and distinguishing them from sensory signals and other confounding signals,” in a region packed tightly with nerves. Once signals are detected, they’ll be decoded by algorithms and transmitted to the brain, where a user’s intended movements would be recoded and transmitted back to the prosthetic. [Wired.com]
According to the team behind the system at Johns Hopkins University’s Applied Physics Laboratory, tests on monkeys have shown that the primates have remarkable success controlling a prosthesis through a cortical chip implanted in their brains, and researchers have undertaken some human tests. What remains to be seen, though, is how much dexterity people can get through this process.
If a young tadpole loses its tail, no problem—it can grow a new one. Biologist Michael Levin and his team experimented with this amphibian talent, and they say they found the signal that triggers the regeneration: sodium. If scientists can find the trigger in tadpoles, perhaps someday they could find triggers for other species. Maybe even humans.
By using drugs to prompt a flood of sodium ions into injured nerve cells, biologists from Tufts University were able to regenerate severed tadpole tails — complex appendages containing spinal cord, muscle and other tissue. [LiveScience]