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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,
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