Schematic drawing of the structure of the CNT-interfaced PGF scaffold and outgrowing axons with Schwann cells (upper left), and a photo showing an implanted CNT-PGF scaffold between the transected sciatic nerve in a rat and immunohistochemical findings of regenerating axons (green) and Schwann cells (red) within the scaffold (lower right).Carbon nanotubes could spark new life into damaged nerves, say researchers, thanks to their unique combination of length, strength, and electrical conductivity.
Severely damaged peripheral nerves cannot regenerate themselves and the options for repair are limited. Current treatments rely on nerve grafts from elsewhere in the patient’s body or from a donor, but do not restore function completely. Hollow tubes can be implanted to guide nerve regrowth, but these artificial conduits cannot help repair long defects. So researchers from Dankook University in Korea and University College London have tried using carbon nanotubes (CNTs) to repair damaged nerves instead [Ahn, H.-S., et al., Acta Biomaterialia (2014), http://dx.doi.org/10.1016/j.actbio.2014.11.026].
Led by Hae-Won Kim and Jung Keun Hyun, the researchers made bundles of aligned phosphate glass fibers (PGF) with tethered on carboxylated CNTs. To create a more nerve-like structure, the CNT-PGF fibers are aligned inside a porous biopolymer cylinder. Moreover, by fixing the CNTs to the PGF, potential toxicity arising from cellular internalization of free CNTs is minimized.
“We want to give an attractive cue for outgrowing axons using CNTs, which are interfaced onto a physical guidance structure of phosphate glass microfibers,” explain Jung Keun Hyun and Hae-Won Kim. “While the PGFs act as physical guidance, CNTs provide electrical/nanotopological cues and the polymer sheet allows permeability for blood circulation and nutrition supply.”
The team implanted the CNT-PGF scaffold into the severed sciatic nerve in the hip of test rats and compared the results to a PGF control scaffold without CNTs. After 16 weeks, the researchers found more axons – the thread-like part of nerve cells that conducts electrical impulses – crossing the CNT-PGF scaffold than in the control sample and more nerve (or Schwann) cells. The CNT-PGF scaffold was also more effective in restoring motor function to the damaged nerve and did not appear to induce a toxic response in vivo.
Long, fibrous PGF implants have already been shown to act as a guide to the regrowth of neurites, but the addition of CNTs appears to boost cell adhesion and neurite growth. The researchers don’t know why, but suggest that the conductivity of CNTs could be a factor in stimulating neuron cell regrowth. Whatever the details, CNTs appear to play a dual role with growing nerve tissue – providing physical guidance while stimulating cell adhesion and growth at the same time.
Now the researchers plan to incorporate more channels, instead of fibers, into the scaffold to give outgrowing axons more space and add in active agents or drugs to enhance nerve regeneration even further.