Knitting Severed Spinal Cords With Graphene Ribbons

A new material made of graphene nanoribbons and a common polymer might help knit damaged or even severed spinal cords.

The nanoribbons are highly soluble in polyethylene glycol (PEG), a biocompatible polymer gel used in surgeries, pharmaceutical products, and in other biological applications. When the nanoribbons have their edges functionalized with PEG chains and are then further mixed with PEG, they form an electrically active network that helps the severed ends of a spinal cord reconnect.

Earlier experiments have suggested that neurons will grow along graphene, explains James Tour, a chemist at Rice University:

“Neurons grow nicely on graphene because it’s a conductive surface and it stimulates neuronal growth. We’re not the only lab that has demonstrated neurons growing on graphene in a petri dish,” he says. “The difference is other labs are commonly experimenting with water-soluble graphene oxide, which is far less conductive than graphene, or nonribbonized structures of graphene.

We’ve developed a way to add water-solubilizing polymer chains to the edges of our nanoribbons that preserves their conductivity while rendering them soluble, and we’re just now starting to see the potential for this in biomedical applications.”

Ribbonized graphene structures allow for much smaller amounts to be used while preserving a conductive pathway that bridges the damaged spinal cords. Tour says only 1 percent of the material, dubbed Texas-PEG, consists of nanoribbons, but that’s enough to form a conductive scaffold through which the spinal cord can reconnect.

Successful Spinal Cord Repair

Texas-PEG succeeded in restoring function in a rodent with a severed spinal cord in a procedure performed at Konkuk University in South Korea by coauthors Bae Hwan Lee and C-Yoon Kim.

Tour says the material reliably allowed motor and sensory neuronal signals to cross the gap 24 hours after complete transection of the spinal cord and almost perfect motor control recovery after two weeks.

“This is a major advance over previous work with PEG alone, which gave no recovery of sensory neuronal signals over the same period of time and only 10 percent motor control over four weeks,” Tour says.

The Tour lab has spent a decade working with graphene nanoribbons, starting with the discovery of a chemical process to “unzip” them from multiwalled carbon nanotubes, as revealed in a Nature paper in 2009. Since then, the researchers have used them to enhance materials for the likes of deicers for airplane wings, better batteries and less-permeable containers for natural gas storage.

Kim C, Sikkema WKA, Hwang I, Oh H, Kim UJ, Lee BH, Tour JM
Spinal cord fusion with PEG-GNRs (TexasPEG): Neurophysiological recovery in 24 hours in rats
Surg Neurol Int 13-Sep-2016;7

Image: Tour Group/Rice