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Liquid Metal Reconnects Severed Nerves in Frogs

A liquid metal alloy can provide an electrical conduit to help reconnect severed nerves

2 min read
Liquid Metal Reconnects Severed Nerves in Frogs
Photo: Getty Images

Severed nerves in the body can lead to the loss of muscle function and muscle atrophy, unless the severed nerve endings get reconnected. One possible new solution devised by Chinese researchers uses liquid metal to create an electrical conduit capable of transmitting  signals between the severed nerve ends.

The liquid metal solution consists of a gallium-indium-tin (GaInSn) alloy that has successfully bridged severed sciatic nerves taken from the calf muscles of bullfrogs, according to Technology Review. A team at Tsinghua University in Beijing showed that the metal alloy—capable of remaining liquid at body temperature and thought to be benign—could transmit nerve signals much more effectively than the commonly-used Ringer's solution meant to mimic the salt mixture in body fluids.

Such a solution could keep the affected muscles active by continuing to transmit nerve signals and prevent muscle loss. That would buy plenty of time for the severed nerve endings to slowly grew back together at the snail's pace of one millimeter per day. The liquid metal idea also presents an alternative to usual methods of suturing together the cut nerve endings if they're close enough together, or as a tool for even more complex nerve transplants.

Caption: Photographs of x-ray images showing a bullfrog's lower body both with the injected liquid metal and without. Images: Tsinghua University

The Chinese team ran its experiments by snipping the sciatic nerve and the connected muscles from bullfrogs, placing the severed nerve ends and their respective muscles in separate petri dishes, and then testing connecting conduits consisting of either the liquid metal or Ringer's solution. In the liquid metal case, the electroneurographic signal was "virtually similar" to the signal transmitted by an intact sciatic nerve, according to the paper published on 7 April in the arXiv database.

As a bonus, the Chinese researchers found that the liquid metal injected into a bullfrog's calf muscles shows up clearly under x-rays. That would make it easy to locate and remove the liquid metal using a micro-syringe if it no longer became necessary.

A future step might involve using the liquid metal alongside growth factors that encourage nerve regeneration. Tiny microchannels or concentric tubes could contain the liquid metal and growth factors in a complete package for helping to repair severed nerves. But many questions remain about whether the liquid metal solution really does help preserve muscle function in the long term, as well as whether it's truly safe to use inside human bodies. 

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Restoring Hearing With Beams of Light

Gene therapy and optoelectronics could radically upgrade hearing for millions of people

13 min read
A computer graphic shows a gray structure that’s curled like a snail’s shell. A big purple line runs through it. Many clusters of smaller red lines are scattered throughout the curled structure.

Human hearing depends on the cochlea, a snail-shaped structure in the inner ear. A new kind of cochlear implant for people with disabling hearing loss would use beams of light to stimulate the cochlear nerve.

Lakshay Khurana and Daniel Keppeler

There’s a popular misconception that cochlear implants restore natural hearing. In fact, these marvels of engineering give people a new kind of “electric hearing” that they must learn how to use.

Natural hearing results from vibrations hitting tiny structures called hair cells within the cochlea in the inner ear. A cochlear implant bypasses the damaged or dysfunctional parts of the ear and uses electrodes to directly stimulate the cochlear nerve, which sends signals to the brain. When my hearing-impaired patients have their cochlear implants turned on for the first time, they often report that voices sound flat and robotic and that background noises blur together and drown out voices. Although users can have many sessions with technicians to “tune” and adjust their implants’ settings to make sounds more pleasant and helpful, there’s a limit to what can be achieved with today’s technology.

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