When peripheral nerves are severed, the loss of function leads to atrophy of the effected muscles, a dramatic change in quality of life and, in many cases, a shorter life expectancy.
Despite decades of research, nobody has come up with an effective way to reconnect nerves that have been severed. Various techniques exist to sew the ends back together or to graft nerves into the gap that is created between severed ends.
Ultimately, the success of these techniques depends on the ability of the nerve ends to grow back and knit together. But given that nerves grow at the rate of one mm per day, it can take a significant amount of time, sometimes years, to reconnect. And during this time, the muscles can degrade beyond repair, leading to long-term disability.
So neurosurgeons have long hoped for a way to keep muscles active while the nerves regrow. One possibility is to electrically connect the severed ends so that the signals from the brain can still get through. But how to do this effectively?
Today, Jing Liu at Tsinghua University in Beijing and a few pals say they’ve reconnected severed nerves using liquid metal for the first time. And they say that in conducting electrical signals between the severed ends of a nerve, the metal dramatically outperforms the standard saline electrolyte used to preserve the electrical properties of living tissue.
Biomedical engineers have been eyeing the liquid metal alloy gallium-indium-selenium for some time (67 percent Ga, 20.5 percent In and 12.5 percent Se by volume). This material is liquid at body temperature and is thought to be entirely benign. Consequently, they have been studying various ways of using it inside the body, such as for imaging.
Now a team of Chinese biomedical engineers say the metal’s electrical properties could help preserve the function of nerves while they regenerate. And they’ve carried out the first experiments to show that the technique is viable.
Jing and co used sciatic nerves connected to a calf muscle taken from bullfrogs. They applied a pulse to one end of the nerve and measured the signal that reached the calf muscle, which contracted with each pulse.
They then cut the sciatic nerve and placed each of the severed ends in a capillary filled either with liquid metal or with Ringer’s solution, a solution of several salts designed to mimic the properties of body fluids. They then re-applied the pulses and measured how they propagated across the gap.
The results are interesting. Jing and co say the pulses that passed through the Ringer’s solution tended to degrade severely. By contrast, the pulses passed easily through the liquid metal. “The measured electroneurographic signal from the transected bullfrog’s sciatic nerve reconnected by the liquid metal after the electrical stimulation was close to that from the intact sciatic nerve,” say Jing and co.
What’s more, since liquid metal clearly shows up in x-rays, it can be easily removed from the body when it is no longer needed using a microsyringe.
That allows Jing and co to speculate about the possibility of future treatments. Their goal is to make special conduits for reconnecting severed nerves that contain liquid metal to preserve electrical conduction and therefore muscle function, but also containing growth factor to promote nerve regeneration.
That’s an exciting possibility but one that is still a long way from any kind of treatment. The questions it raises are legion. How much of the muscle function can be preserved in this way? Could the liquid metal somehow interfere with or prevent regeneration? And how safe is liquid metal inside the body, particularly if it leaks?
These are questions that Jing and others will hope to answer in the near future, with animal models at first and possibly later with humans. “This new generation nerve connecting material is expected to be important for the functional recovery during regeneration of the injured peripheral nerve and the optimization of neurosurgery in the near future,” they say.
So it’s just possible that liquid metal will become an important component in the treatment of nerve injuries in future.
Ref: http://arxiv.org/abs/1404.5931: Liquid Metal as Connecting or Functional Recovery Channel for the Transected Sciatic Nerve