How do you get an artificial leg to listen to the brain?
To design limbs that can respond to thought and send sensory info back to the brain, researchers have been looking at ways to connect electrodes to nerve endings in arms or legs.
They’d like to translate nerve signals into ‘electrical instructions’ for moving the prosthetic limb. But severed nerve cells need structural support in order to grow, and they’re notoriously fussy about the shape and size of that structure. Technology Review reports.
A team of researchers led by Ravi Bellamkonda of Georgia Tech has designed a tube-shaped scaffold with tiny grooves that fit snugly around bundles of nerve cells.
The scaffold begins as a flat sheet with tiny grooves, like corrugated cardboard. It’s then rolled to form a cylindrical spiral (pictured) with many tiny channels that are nicely suited for the healthy growth of nerve cells.
The resulting channels do double duty, not just supporting the nerve cells but picking up their electric signals – which could then be sent on to electrodes in a mechanical limb.
The ultimate goal is to enable two-way communication between the prosthetic limb and its wearer.
The scaffold would add dexterity by supporting two kinds of nerve cells: those that send orders from the brain to the limbs would travel along one channel and, along another channel, those that relay sensory information (like touch and temperature) from the limbs back to the brain.
"You need to be able to stimulate as many axons as possible for movement, and you need to be able to pick up signals from as many axons as possible," says study researcher Akhil Srinivasan. The most sophisticated of the electrodes currently used at nerve endings have about 16 channels to control movement; but the arm has 22 degrees of freedom.
The device still lacks electrodes, but the next steps will be to insert gold electrodes into the base of the scaffold. Then the new wired prototype will be tested in rats.
So far, on the scaffold, the researchers have grown non-neuronal cells that support nerve cells and dorsal root ganglion cells that carry sensory information from the limbs to the spinal cord. Both types of cells grew robustly, aligning themselves with the channels and sending projections towards them.
An abstract of the work was presented at Society for Biomaterials 2011 Annual Meeting & Exposition in Orlando earlier this month.
Via Technology Review.
Image: Ravi Bellamkonda / Georgia Tech