For ideal physical rehab, it might be necessary to go a little “cyborg”. That’s the reasoning a Chinese biomedical firm used to develop a new method of repairing damaged nerve endings. Borrowing a page from Terminator 2, their new treatment calls for the use of liquid metal to transmit nerve signals across the gap created in severed nerves. The work, they say, raises the prospect of new treatment methods for nerve damage and injuries.
Granted, it’s not quite on par with the liquid-metal-skinned cyborgs from the future, but it is a futuristic way of improving on current methods of nerve rehab that could prevent long-term disabilities. 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 them yet.
Various techniques exist to sew the ends back together or to graft nerves into the gap that is created between severed ends. And 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 and lead to long-term disability.
As a result, 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 up until now, an effective means of making this happen has remained elusive. For some time, biomedical engineers have been eyeing the liquid metal alloy gallium-indium-selenium for some time as a possible solution – a material that is liquid at body temperature and thought to be entirely benign.
But now, a biomedical research team led by Jing Liu of Tsinghua University in Beijing claims they’ve reconnected severed nerves using liquid metal for the first time. They claim that the metal’s electrical properties could help preserve the function of nerves while they regenerate. Using sciatic nerves connected to a calf muscle, which were taken from bullfrogs, they’ve managed to carry out a series of experiments that prove that the technique is viable.
Using these bullfrog nerves, they applied a pulse to one end 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, and Jing’s team claim that the pulses that passed through the Ringer’s solution tended to degrade severely. By contrast, the pulses passed easily through the liquid metal. As they put it in their research report:
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.
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. All of this has allowed Jing and colleagues 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.
Naturally, there are still many challenges and unresolved questions which must be resolved before this can become a viable treatment option. For example, how much of the muscle function can be preserved? Can the liquid metal somehow interfere with or prevent regeneration? And how safe is liquid metal inside the body – especially if it leaks? These are questions that Jing and others will hope to answer in the near future, starting with animal models and possibly later with humans..