Liquid Metal Alloy May Repair Nerve Damage

photo credit Penn State News

There’s pain you can live with—or learn to live with—and then there’s nerve pain, and pain caused by nerve damage. Patients with pain caused by damage to the sciatic nerve often live with not being able to find a comfortable position to sit, stand, or lie down. Research into finding relief from this pain took a step forward a couple of years ago. The news hit the tech headlines for a few days, and then nothing was heard afterward. I did some digging into the story and some related information for background. Additionally, I contacted the lead researcher on that project. He provided me with some papers written on related research, and the story unfolds below. I’ll explain:

• Brief overview of nerve damage
• Current treatment for nerve damage
• Prior research into treating nerve damage
• Introduction to liquid metal used in the new research
• A very simplified explanation of the research that triggered the news blitz
• Possible future applications for liquid metal

Brief Overview of Nerve Damage

The sciatic nerve is the largest nerve in the human—and most other mammal species—body. There are five roots that combine to form this nerve. “Sciatic nerve damage” refers to damage to any of the roots or to the sciatic nerve itself (8). Because it is the largest nerve, damage to it can carry far-reaching consequences.

Damage to the nerve itself is often caused by a traumatic injury—car accidents, gunshot wounds, and other puncturing traumas. Additionally, and more commonly, damage occurs to one of the roots. This damage can be a result of a back injury, but most commonly it is an unintended side effect of back surgery. In fact, The Sciatica Authority states that “(s)urgical interventions are responsible for more spinal nerve damage than any other single cause.” (8)

Sciatic nerve damage results in pain to various locales, loss of sensitivity to extremities, and loss of muscle function and muscle atrophy. (4)

Current Treatments for Nerve Damage

There are a few current treatments for nerve damage. For a gap of 20mm or less, the severed ends of the nerve can be directly reconnected with sutures. Longer gaps in the damaged nerve require grafts, nerve transfers, or tubulization (using a cylinder of paraffin to protect the sever from surrounding tissue (2)). All of these techniques have issues that can create more problems (5). Also, the regeneration process of the nerve tissue takes time, as nerve tissue grows very slowly. During that time, the patient can suffer muscular degradation (10).

Prior Research

Recent research in regenerating nerve tissue has used stem cells to regenerate nerves or create new ones. Researchers have also experimented with growth factors, support cells, and insoluble extracellular matrices to facilitate healing of nerves. These methods have been shown to work, but not very well (5).

A team of researchers in China experimented with injecting a liquid metal material and allied packaging material into a mouse to repair a sever (6). Another team injected electrodes to stimulate muscle contractions in a frog by stimulating its sciatic nerve (6).

Angiography has also contributed to the liquid metal research. Angiography helps physicians diagnose and evaluate conditions that are related to blood vessels, using contrast agents, Typically these are solutions whose density closely resembles water—iodine or iodinated agents. However, problems can come up when higher energy imaging is used, because the efficiency of the contrast agent is significantly reduced (9).

Introduction to Liquid Metal

Liquid metal—a long way from the Termintor’s application—is an alloy of gallium, indium, and selenium. It may be truly one of the three coolest materials of all time (the others are graphene and carbon fiber). This combination is benign, and, with a melting point of 29.78 degrees celcius (close to room temperature), it is a liquid at body temperature. It is also highly conductive. Return to solid state does not occur immediately below 29.78, giving it a nice range of liquidity. The metal is stable, and it does not react with water in its liquid state. It is safe for use in humans, and its density is higher than human tissue and blood (9). It has a proven good biocompatibility to hippocampal neurons (6). It clearly shows up in x-rays and it can be easily removed with a micro-syringe when its use is completed (10). This liquid metal has no stiffness and almost infinite stretchability. The conductivity is much higher than non-metallic materials, and higher than many other metals used in electric transmission. Signals in our bioelectrical processes are very weak, so conductivity is critical to this material (5).

Here’s where it gets really awesome: Because of this liquid metal’s chemical compatibility with a whole lot of other materials, it can be directly printed on polymers, glass, and other metals (5), and the researchers are trying it on skin—more on that below.

The Research

Gallium by itself is liquid at room temperature. Researchers infused it into the heart and kidney of a pig and found that imaging was much more effective using an ordinary imaging instrument (9).

The nerve research with this liquid metal involved a frog. The research team applied an electric pulse so that the calf muscle contracted. They then severed the sciatic nerve, then reconnected the ends of the nerve with either the liquid metal or a Ringers solution. (Ringers is a solution of electrolytes that mimics body fluids.) The Ringers carried the charge only so far. The nerve connected by the liquid metal worked pretty much like it did before it was severed (1). The metal’s electrical properties were able to preserve nerve function during the healing process (10).

What else do we need to know?

Further research looks to find how much muscle function can be preserved using this liquid metal to facilitate regeneration. Also unknown at this time is whether the metal may somehow interfere with or prevent regeneration altogether. The metal is known to be safe in the applications previously using it, but if it leaks from the intended location, what happens? (10)

The body doesn’t always like intrusions into it, and often fights against newcomers; some researchers have raised concerns about using metal in the body; however, we’ve been using metal plates for skull protection for quite some time (7).

Possible Future Application

As an alternative to the usual methods of nerve repair, this material shows a lot of promise, as well as a tool for even more complex nerve transplants (4). Researchers are considering the possibility of using the liquid metal along with growth factors to encourage regeneration (4).

Now consider this–if it isn’t fascinating enough to be using a little sliver of liquid metal to help repair a severed nerve—a research team has experimented with spraying it onto pig skin in electrical circuitry. This material can potentially be used for spray-on bioelectronics—sensors, actuators, and complex electrical circuits. It can flex, bend, and stretch with the skin without losing structural integrity, and still maintain skin contact (3).

Far from a terminator, this liquid metal has life-saving—and life changing—potential. I’ll be watching for further developments on this.

What are some other applications you would like to see for liquid metal?

Sources:

1. Estes, Adam Clark. “Scientists Have Reconnected Severed Nerves with Liquid Metal.” Gizmodo. 28 Apr. 2014. Web. 12 Feb. 2016. <http://gizmodo.com/scientists-have-reconnected-severed-nerves-with-liquid-1568766259>.
2. “Tubulization.” Farlex Partner Medical Dictionary. 2012. Print.
3. Guo, Cangran, Jing Liu, and Yang Yu. “Rapidly Patterning Conductive Components on Skin Substrates as Physiological Testing Devices via Liquid Metal Spraying and Pre-designed Mask.” Journal of Materials Chemistry B 2014: 5739. Print
4. Hsu, Jeremy. “Liquid Metal Reconnects Severed Nerves in Frogs.” IEEE Spectrum. 29 Apr. 2014. Web. 16 Feb. 2016. <http://spectrum.ieee.org/tech-talk/biomedical/bionics/liquid-metal-reconnects-severed-nerves-in-frogs>.
5. Jin, Chao, Jing Liu, Lei Sheng, and Jie Zhang. Liquid Metal as Connecting or Functional Recovery Channel for the Transected Sciatic Nerve. Rep. Print.
6. Jin, Chao, Jingjing Li, Xiaokang Li, and Jing Liu. “Injectable 3-D Fabrication of Medical Electronics at the Target Biological Tissues.” Nature.com. Nature Publishing Group, 6 Dec. 2013. Web. 16 Feb. 2016. <http://www.nature.com/srep/2013/131206/srep03442/full/srep03442.html>.
7. Mack, Eric. “Healing, ‘Terminator’-style: Liquid Metal Could Fix Severed Nerves.” CNET. 28 Apr. 2014. Web. 16 Feb. 2016. <http://www.cnet.com/news/healing-terminator-style-liquid-metal-fixes-severed-nerves/#!>.
8. “Sciatic Nerve Damage.” Sciatica-Pain.Org. Web. 19 Feb. 2016.
9. Wang, Qian, Yang Yu, Keqin Pan, and Jing Liu. “Liquid Metal Angiography for Mega Contrast X-Ray Visualization of Vascular Network in Reconstructing In-Vitro Organ Anatomy.” IEEE Transactions on Biomedical Engineering IEEE Trans. Biomed. Eng. 61.7 (2014): 2161-166. Web.
10. Owano, Nancy. “Beijing Researchers Explore Liquid Metal to Reconnect Nerves.” Beijing Researchers Explore Liquid Metal to Reconnect Nerves. 29 Apr. 2014. Web. 16 Feb. 2016.