Thank you to Climeworks for  sponsoring today’s video.

Climeworks removes carbon  dioxide from the atmosphere, helping fight the climate crisis. Go to gift.climeworks.com/SciShow  to give the sustainable gift of CO2 removal this holiday season. [♪ INTRO] Science is always fun, but it’s not every  day that researchers get to go out into the parking lot and run their  experiment over with their car.

On purpose! For science reasons! But, researchers publishing online last week in the journal Nature Materials did just that.

It was one way to demonstrate the  awesomeness of their newly developed “super jelly,” a soft material that regains  its shape surprisingly well under pressure. Their new material is a type of hydrogel, a material made from a network  of molecules that hold onto water. In fact, this hydrogel is  made up of 80 percent water, which the researchers say makes  it even more surprising that it doesn’t, like, pop like a water  balloon would under pressure.

Most of the time, it’s soft and  flexible, kind of like squishy jelly. But put some pressure on it, and this material’s properties change to become more like a glass. And we’re talking a lot of pressure.

In this case, approximately the weight of an elephant,  or, ya know I did mention a car earlier. Even when compression does  cause it to change shape, the hydrogel can spring back into its  original shape in about two minutes. So what makes this wacky combination  of material properties possible?

The hydrogel is part of a  class of materials known as supramolecular polymer networks, or SPNs. These are materials made of  polymers, or chains of molecules, that are assembled together  using non-covalent bonds. In a conventional polymer, long  chains of molecules are held together by relatively stable covalent bonds.

Individual polymers may also  be crosslinked together, which means that various points on different  polymers are attached to each other. And that makes everything  hold together a bit more. Those crosslinks are generally  also formed from covalent bonds, which are interactions where  atoms share electrons and generally require a chemical  reaction to make or break.

SPNs do often contain conventional polymers that are held together by covalent bonds. But polymers within the  SPN are crosslinked by more transient intermolecular forces,  such as hydrogen bonding. These crosslinks form and dissolve  and form again in an equilibrium.

That temporariness gives SPNs  all kinds of special properties. Because their molecules can shift  their crosslinks around on the fly, the materials are stretchy,  can repair themselves quickly, can dissipate excess energy, and are usually soft. But while researchers have tried  optimizing those temporary bonds for those properties, the researchers behind this  study wondered what would happen if the temporary bonds actually  stuck around a little longer.

The hypothesis was that longer-lasting  bonds would nudge the SPN towards a state that is more  resistant to any forces applied to it. So, the researchers developed a library  of slightly-tweaked possible molecules that might be slower to  dissolve a crosslinked bond. They tested out lots of different options, and observed that some behaved  in a more rigid manner.

And ultimately, the one whose  bonds dissolved the slowest was the strongest when compressed.  And that is our super jelly! In addition to running it over repeatedly  with their car, the researchers also developed a pressure sensor  from the material that they used to measure people walking,  and standing, and jumping. You know, just to show that  it does have applications for things like soft robotics and bioelectronics.

But honestly, even if it’s not useful yet, the super jelly’s squishy-yet-shatterproof  combination? Pretty darn cool. Speaking of supramolecular polymer  networks, and no, I’m not kidding.

This time, they acted as scaffolding  to help heal spinal injuries. In a study published last  month in the journal Science, researchers injected paralyzed  mice with nanofibers that triggered injured spinal cord cells to regenerate. Within 3 to 4 weeks, the mice could walk again.

Now it’s super important to note that  this study was only done in mice. This technique has not been used to  treat spinal injuries in humans, yet. But for the mice, the results  were definitely promising.

The damaged neurons regrew their  long signaling tails, called axons. The mice also developed less scar  tissue and more new blood vessels in the region in question, which are  important for successful healing. As a neat bonus, the molecules  all broke down within 12 weeks, leaving nothing behind but  nutrients for the cells to use.

The nanofibers were injected in liquid form. But once they made contact with living tissue, the fibers bonded to each other  to form a gel-like SPN that mimicked the normal scaffolding  around the cells of the spinal cord. Importantly, the fibers also  contained components that would encourage the spinal neurons to regenerate.

Some of them were attached  to a molecule that signals neural stem cells to turn into  neurons, while others were attached to a molecule that encourages  cells to reproduce and survive. The researchers expected  that a more stable scaffold structure would help ensure that  receptors on neurons and other cells would encounter the signaling  molecules attached to the fibers. The signaling molecule could then bind to the cells and instruct them  to begin repairing themselves.

But the weak bonds of the fibers’ SPN  meant that even once they were assembled into their extracellular  scaffolding, the fibers continued to move slightly, sometimes  even escaping the network. And to the researchers’ surprise,  that movement seemed to be important. They found that the versions  of their fibers that moved more within their structure also correlated  with better healing and regeneration.

While they can’t say for sure  that the movement caused this better result, they think it likely did. The target cells and their  receptors also move around, so the researchers think  the fibers’ movement could increase the chance that  they’ll collide with a receptor. The researchers say the  finding could even help explain why biological systems so often have  proteins that seem messy and disordered.

It’s possible that the chaos could  help with cellular signaling. Now that’s all we know about this for now,  but the results are so promising that the researchers say they want to adapt the  technique for use in humans very soon. But also this more basic principle that  motion is important to cell signaling?

They say that could someday have even  broader applications, from countering neurodegenerative diseases to  better targeting all kinds of drugs. Thanks for watching this episode of SciShow News, which was supported by Climeworks. The climate crisis is the most  important issue facing us right now.

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