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Researchers have been able to engineer super-strong fibers made of muscle proteins with the help of protein-assembling microbes. And some other research might eliminate the need to temper chocolate, a part of the chocolate production process that is the bane of amateur bakers everywhere.

Hosted by: Hank Green

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Sources:
Muscles
http://dx.doi.org/10.1038/s41467-021-25360-6
https://www.eurekalert.org/news-releases/926667
https://www.embl-hamburg.de/~wilmanns/titin/lit/tskhovrebova03.pdf
https://www.washingtonpost.com/news/wonk/wp/2012/12/13/how-to-pronounce-the-longest-word-in-the-world/

Chocolate
https://www.nature.com/articles/s41467-021-25206-1
https://altonbrown.com/how-and-why-to-temper-chocolate/
https://www.researchgate.net/profile/Nuria-Acevedo/publication/289728067_Nanostructure_and_Microstructure_of_Fats/links/5a4ba9fd0f7e9b8284c2d3c9/Nanostructure-and-Microstructure-of-Fats.pdf
https://www.sciencedirect.com/science/article/pii/S221479931500079X
https://www.chemistryworld.com/features/well-tempered-chocolate/9200.article
https://www.compoundchem.com/2014/04/19/the-polymorphs-of-chocolate/
https://www.chemistryviews.org/details/ezine/808827/Chocolate__The_Noblest_Polymorphism_II.html

Images:
https://www.istockphoto.com/vector/skeletal-muscle-gm1256975161-368215673
https://www.istockphoto.com/photo/neuromuscular-junction-gm1272322355-374628894
https://www.nature.com/articles/s41467-021-25360-6
https://commons.wikimedia.org/wiki/File:Titin_IG_Domains.jpg
https://www.eurekalert.org/multimedia/797897
https://www.istockphoto.com/vector/3-types-of-muscle-tissue-and-cell-gm1256972678-368214716
https://commons.wikimedia.org/wiki/File:Chocolate_tempering_(3).JPG
https://commons.wikimedia.org/wiki/File:Couverture_chocolate_samples,_tempered_and_untempered.jpg
https://www.istockphoto.com/photo/chocolate-spread-gm157403716-7661008
https://www.istockphoto.com/photo/chocolate-assortment-background-top-view-of-different-kinds-of-chocolate-gm1276645382-376096164
https://www.nature.com/articles/s41467-021-25206-1
https://www.istockphoto.com/vector/muscle-tissue-seamless-pattern-gm902384584-248913613
https://www.istockphoto.com/photo/education-anatomy-and-histological-sample-striated-muscle-tissue-under-the-microscope-gm1174812814-326873138
[♪ INTRO].

What’s stronger than silk, nylon, or Kevlar? Well… muscle, apparently.

And no, this isn’t a corny message about how nature is the best engineer. In a new paper published in the journal Nature Communications, researchers produced super-strong fibers made of muscle proteins. And the cool part?

They engineered them with the help of protein-assembling microbes, no animal products required. Scientists have long known that muscle is, appropriately, both strong and tough. That means it can withstand a lot of force before it changes shape, and once it changes shape, it doesn’t easily break.

And we’ve been trying to replicate its impressive properties to create new materials. But the researchers behind this study thought it might be more straightforward to just make muscle proteins. The protein they were interested in was titin.

And titin is one of three key proteins in our cardiac and skeletal muscle. It’s responsible for much of those muscles’ elasticity and structural integrity. It also happens to be one of the biggest proteins found in nature.

Like many of nature’s strongest materials, it’s made up of a massive series of repeating and interlocking units. That allows it to both withstand passive tension, and to dissipate energy associated with strain. Now, bacteria don’t usually produce proteins anywhere near the size of titin.

Repetitive proteins like this are prone to mistakes, and cost a lot of energy. But the researchers were able to engineer titin’s genetic sequence so that it was a little more bacteria-friendly. The bacteria created short snippets of the repeating amino acid sequence, then strung them together to create a close approximation of the titin protein.

Once the proteins were produced, the researchers spun them into fibers. Only one-tenth the width of a human hair, the fibers were both stronger and tougher than actual muscle fibers. They were also tougher than most natural and synthetic fibers.

And these fibers actually got better at dealing with strain as the amount of strain on them increased, and as the fibers elongated. This was expected, since it’s similar to how natural titin works, but the synthetic fibers actually did it better than natural titin. These fibers could be strong enough to be used for protective clothing like bulletproof vests.

But their most interesting potential uses are the biomedical ones. Since they’re literally made of muscle, they could potentially be used for surgical stitches or for tissue engineering. The researchers say these fibers could be a sustainable alternative to conventional petroleum-produced ones.

And this research may open the door for using microbes to produce all kinds of large-scale materials. And now, it’s time to talk about something tastier. Or at least we assume that this is tastier than the muscle fiber clothing...

We’re going to talk about chocolate. And to be at its best, chocolate needs to be tempered. That’s the tricky process by which chocolate is heated, and then cooled, and then heated again before solidifying to form a smooth, shiny product that snaps cleanly and melts in your mouth.

Tempering is the bane of amateur bakers everywhere. And while we probably can’t get microbes to do it for us, it turns out that small molecules found in our own cells might be able to help. More new research from Nature Communications presents a method of adding small fat molecules to chocolate that might someday render tempering totally unnecessary.

The fats in foods are mostly composed of molecules called triacylglycerols, which crystallize when they solidify to form complex structures. Cocoa butter, the fat found in chocolate, is particularly complicated. It actually has six different crystalline structures it can take on when it melts and then solidifies.

All of them have different melting points, and all of them affect the final texture of the chocolate. That’s why tempering is so temperamental. You’re looking for just one of those crystal structures, called Form V.

In tempering, the chocolate reaches a temperature high enough to melt all the crystals. Then it’s cooled slowly at room temperature, which allows Form V crystals to form, alongside a few pesky Form IV crystals. These early crystals are what’s known as seed crystals, and they act as templates to encourage the formation of more crystals just like them as the cocoa butter continues to solidify.

To keep the Form IV crystals from egging on additional Form IV crystals, the chocolate is heated just a bit again. And because Form IV has a lower melting point than Form V, the unwanted crystals melt again. And the resulting chocolate is Form V perfect: shiny and melt-in-your-mouth, with a long shelf life.

I bet you didn’t realize all of this was so complicated! But there are more than just triacylglycerols in food fats. There’s also a whole smorgasbord of smaller molecules, called minor components.

Previous studies had hypothesized that minor components could either help or hinder the crystallization process, by creating or blocking sites for crystal growth. But the researchers in this study wanted to see if adding particular minor components in the right amounts could promote Form V crystal production. They were particularly interested in molecules called phospholipids.

These molecules are actually found in cell membranes, and are great at assembling into structures that keep our cells’ outsides separate from their insides. And the researchers thought the molecular properties that let them do that might also let them aid chocolate crystal formation. They found that cocoa butter containing certain phospholipids crystallized more quickly and tended towards everyone’s favorite Form V.

And when the phospholipids were added to commercial chocolate, they produced chocolate with ideal shine, snap, and melt, all without the fussy tempering that would usually have been necessary. The researchers say that their study highlights just how complicated the quest for perfect chocolate can be. But they do think that, with some more tweaking, their new method could pave the way for self-tempering chocolate!

And who isn’t a fan of easier, better chocolate? Thanks for watching this episode of SciShow, and thanks to this month’s. President of Science, Emily Z.!

Happy birthday, Emily, and thank you for your support. If you want to become President of Science yourself, or maybe hook somebody up with a fun birthday surprise, you can get started at patreon.com/scishow. [♪ OUTRO].