Using a liquid metal alloy, scientists have managed to reconnect severed nerves in bullfrogs. Their legs, at least, enjoyed a functional recovery: When electrical pulses were applied, the signals were transmitted across the gap between snipped ends of the nerve.
Peripheral nerves outside of the brain and spinal cord primarily serve organs and limbs. When severed, doctors will try to suture the ends together, but the success of this and other techniques depend on the nerve ends growing back together. This happens at a glacial rate of one millimeter a day, and in the mean time, muscles are atrophying. Ringer’s solution, a saline electrolyte that mimics fluids in our body, is conventionally used to keep the muscles active, preserving electrical properties of living tissue to buy some time as the nerve heals.
For a better functional recovery channel, a team led by Jing Liu at Tsinghua University in Beijing investigated an alloy that’s 67 percent gallium, 20.5 percent indium, and 12.5 percent tin by volume. Its favorable fluidity (liquid at room temp), super compliance, and high electrical conductivity are all good qualities for transmitting an excited nerve signal during the regeneration process in vivo. It’s also thought to be benign.
First, they took calf muscle out of bullfrogs and applied a small electrical pulse to one end of the sciatic nerve. The calf muscle contracted with each pulse, and they measured the signal that reached the muscle. Then they cut the nerve and placed the ends in a capillary filled with the liquid alloy.
When they electrically stimulated the transected nerve, they detected an “electroneurographic signal” that was close to that from an intact sciatic nerve. The pulses appeared to pass easily through the liquid metal, propagating across the gap.
Results from their control tests using Ringer’s solution were nowhere near the performance of the liquid GaInSn alloy, which was able to conduct weak electrical signals that were several orders lower than what the salty solution could do.
When set into a conduit and combined with growth factor, this next generation nerve-connecting material would help preserve electrical conduction and muscle function, as well as regenerate injured peripheral nerves, the team speculates. The material could also be convenient to use during neurosurgery; since metal shows up clearly in X-rays, it can be easily removed through a tiny syringe later.
The findings were published online in the arXiv database this month.