Silk
is a highly sought after, gloriously soft fabric. For centuries it has made its
way into the hands of artisans, courts of kings, and closets of the rich and
famous. But where does this substance come from? For those of you who get squeamish
around entomology you probably aren’t going to like this, but you’re
technically wearing worm juice. More technically its cocoon, produced in the
salivary glands. In other words, spit.
There
are a few kinds of silk worms out there but the one that we’re going to be
talking about today isn’t one you’ll find in the wild. In fact, most silk worms
that are harvested are usually called Bombyx Mori, or domesticated silk worms,
so it’s rare you’d find those in the wild either. Although if you find one of
these guys pictured above and it has red eyes, you might want to contact
University of Wyoming, and quick. You may have a body armor builder on your
hands.
So
what’s so special about worms and silk? Well I’m glad you asked. Researchers at
University of Wyoming are currently marketing a new kind of silk. Well, it’s
not a new kind of silk, so much as it’s
a new way of spinning it. Using genetics scientists have found a way to splice
in the genes that produce Dragline silk in spiders, into the genetic structure
of worms. (We’ve talked about genetics a little bit before here at TI&IT.
You can read the past article “PhotoshoppingDNA: The Art of Molecular Editing”)
Now
this may not sound like such a big deal until you find out that harvesting this
silk in mass quantities from a spider isn’t an option. We’ll talk about why
they can’t do that today, as well as these neat little pet worms that blossom
into beautiful Silk Moths. We’ll also break down the how and why of their silk
spinning abilities, a little bit about the history of silk, the reasons they
don’t use goats to produce steel thread (Yes…you read that correctly) anymore,
and the crazy little proteins that would make Spider-Man drool.
That’s One Shiny
Loincloth
Okay,
so that’s not a loincloth, but it is really old, and at one time if you had
held it up to the light, it would have had a shimmering effect like a diamond. Back
then they probably chalked the phenomena up to the Gods…or something else along
those lines as the reasons this happens would not have been understood. (And if
they were nobody decided to share it.) But however they figured out it occurred
it certainly wasn’t divine intervention.
What
the effect actually is attributed to is very similar to gem stones referred to
as “Cat’s Eye”. It’s called Chatoyancy. While this generally refers to stones
cut in a certain way so as to make them more appealing to consumers, it works
on silk too. When light hits the surface of the fibers it’s reflected in a
triangular-prism format. That’s what gives it the shimmering effect as you move
it around in the light.
The
oldest silks can be traced back to between 3000 and 4000 B.C. Do you know where they came from? China of
course! For a few thousand years China held dominance on the silk market. That
was until the Silk Road opened up and other countries across the world got into
the game. Unfortunately though, for the rest of the world silk industry, issues
with silkworm disease and production halted the spread of the silk industry
across Europe and once again China came out on top.
But
how did they figure out that this curious cocoon could be used to clothe the
rich and fabulous? According to sources it started with a young Chinese empress
named Xi Ling Shi. (Multiple spellings abound all over the Internet) Her palace
garden was filled with these trees called Mulberry that silkworms just
absolutely adore. Legend says she touched one of the cocoons causing a strand
of silk to fall loose. Shortly after the tailors discovered the tensile
strength of this textile and decided to put it to use for the royals. Anyone
caught in those times smuggling this closely guarded imperial secret was put
swiftly to death! (Yikes!)
It
wasn’t until the Han Dynasty (206 B.C. – 220 A.D.) that the silk trade really
took off. A road was opened up (called the Silk Road by historians surprisingly…)
that led them from China to many other nations, starting with Persia and
culminating in Europe. They had a hit.
(Land
routes are in red, sea trade routes are in blue)
The
secret was out. Silk was in. For centuries it dominated the global market’s
economy, anybody who was anybody had to get their hands on this strong, soft,
pliable material. Its uses ranked from everything to clothing and blankets,
drapes and curtains, and many other luxurious items. It took an Empress to
figure out that silk was pretty; it took an industry to realize it could make
them rich. But how do you get a worm to make something created accidentally as
a byproduct of nature by innate self-preservation mechanisms?
Make Checks Payable
To Wormy, 302 Mulberry Ln.
Left
in the wild, silk worms will do their thing. They’ll eat their Mulberry leaves,
spin their cocoon, hibernate inside, and through metamorphosis become a flying
silk moth. But somewhere along the lines their plans were changed. People began
cutting the cocoon’s open, removing the worms, and spinning the delicate fibers
into clothing using various machines. Don’t worry about the worm either, they
aren’t just thrown away. In fact, most places where silk is harvested, the
worms are cooked into various delicacies after de-cocooning them.
If
the worms are allowed to enter their moth phase they destroy the silky cocoon
on their way out. Proteolytic Enzymes are the reason this happens. It can cause
the silk to fall away in strands of random length instead of the cocoon being
unraveled as one continuous piece. As you can probably imagine this won’t do
for clothing makers. Not only does it shorten the length of the silk strands,
it compromises the integrity as well. That’s not good for an industry looking
to market silk as some of the most durable stuff around.
Once
the cocoon is boiled, de-wormed, and unraveled it’s sent to a machine called a
Doubler. This machine does just as the name implies, it doubles the thickness
of silk by weaving strands of it together thereby increasing its tensile
strength. While silk is strong, it still can break. The Doubler just increases
its longevity.
Some
of you may be wondering what Tensile strength. Tensile strength just refers to
the amount of stress a material can handle before it breaks or snaps. Think in
terms of a fishing line, different lines come with different strengths and
thicknesses. You wouldn’t go shark fishing with a line rated for Smallmouth
Bass. Any kind of material capable of stretching has a tensile strength and, as
you can imagine, some are much higher than others.
After
the Doubler comes dying the silk. Various Acetic Acid mixtures (found in vinegar)
are used to help the dyes bond better to the silk. From there it’s sent to a
weaving loom, where it can be spun by a craftsman into a new dress, a soft bed
sheet, or even a flowing pair of curtains for your new office room.
(Models wearing dresses spun from fine silks)
But
there are other silks out there with higher tensile strengths than that
produced by Bombyx mori, (The
domesticated silkworm) that are much more highly sought after. Silks produced
by the webs of spiders. Yet, it isn’t the clothing industry looking to
capitalize on the strong, durable, luxury good. It’s actually the military, and
no, not because they want Versace to make uniforms that “pop” and “shimmer”.
Peter Parker’s Haberdashery
Silkworms
may have been the first species we commercialized the silk trade through, but
Spiders have been doing it better for eons. Spiders produce several kinds of
webs. Some are for their internal nests, some are used to catch themselves
should they fall, others are used to make the intricate lattices that form
their deadly nets, and some are even used to protect their young inside an egg
sack. But whatever kind of web the spider spins there is one thing that remains
constant. It’s a form of silk.
The
strongest silk that a spider is capable of producing is known as Dragline silk.
This fiber is so strong that scaled up, it makes Spider-Man seem plausible.
(Aside from the radioactive bite to create the acquisition of his powers.) If
humans could produce the proteins capable of spinning this material however, and
if adjusted for ratios, it would be strong enough to support them. (Think Nylon
on steroids)
Dragline
silk is used to make the outer connection points for a spider’s web. Because it’s
so strong it’s capable of withstanding bombardment from the elements, large
prey snags, and constant traversal by our eight-legged arachnids. Some species,
such as the orb weaver, have very large abdomens that are relatively weak. They
will die if they were to fall from a great height. To avoid this scenario, they
use Dragline silk to keep them suspended in the air. Ever seen a spider just
dangling there? The fibrous tendril he’s hanging from is what we’re talking
about here.
So if it’s
so strong, why use silkworms at all? Why not just switch over to using spiders
as the main method of harvesting silk? In theory it sounds like a good one but
in practice it doesn’t really work so well. See, spiders are extremely
territorial, so when one wanders into their neighborhood it becomes a
cannibalistic version of the Bloods vs. the Crips. Not a pretty sight. Darn
those gangster spiders…
So that
rules out spider farms.
As a
result scientists turned to splicing the genes into bacteria. This met with
failure. So they tried putting it into Tobacco plants. That didn’t work either.
Finally they thought maybe we can put the gene into goats and cows! …I’m
sure you can guess that went over like a turd in a punch bowl as well…
Part of the reason it’s so hard to generate spider
silk in the lab is that it starts out as a liquid protein that’s produced by a
special gland in the spider’s abdomen. Using their spinnerets, spiders apply a
physical force to rearrange the protein’s molecular structure and turn it into
solid silk. Goats, Tobacco plants, and single-celled organisms can’t do this;
they don’t have the biological structure capabilities.
(Spider-Silk “milking”
harness)
In 2009, textile expert Simon Peers used 70 people
and four years of his life to milk spiders to produce a golden tapestry in
Madagascar. While the final result is absolutely gorgeous, (you can read the
full article and see what the tapestry looks like here on Wired.) it
wasn’t very practical. Nobody wants to wait four years for a rug. It seemed
scientists were at an impasse because no other animal had the necessary
equipment.
But silkworms do. Silkworms use silk all the time. So
if scientists could isolate the right gene for the silk they wanted, maybe they
could put it into the body of a worm and it could produce it for them. That was
exactly the kind of thinking that led Donald Jarvis, a researcher at University
of Wyoming, to this brand new kind of super silk.
Silky Smooth Troops
Because silk is so strong for it’s incredibly
miniscule diameters the textile industry wasn’t the only one who wanted to use
it. In fact, the military, medical professionals, and architects had their eye
on this remarkable material. But before it could be used for these various
applications, there first had to be a way to produce it abundantly.
That’s where Jarvis comes in. Using genetics (gotta
love genetics) he was able to piggyback the DNA sequence of spiders responsible
for creating silk proteins into the makeup of silkworms. Through trial and
error they managed to come up with some worms capable of producing various new
kinds of silk with even more variable tensile strengths. Just last year this
went into production.
But the gene didn’t transfer over to all worms. If
there is one thing we know about genes it’s that they are hereditary, which
means they are passed on. But not all genes are passed down at once; it seems
some of them are selective. (Morgan’s fruit flies anyone?) So how did the scientists
determine which worms carried the spider DNA and which ones didn’t?
By using fluorescent dyes they created a mutant
worm with glowing red eyes, (that’s a terrifying feature) and used these as an
indicator for which ones the gene was present in. After separating the red eyes
from the black eyes and breeding them they finally ended up with a stable
colony of steel spinning silkworms.
This technology is useful in biodegradable sutures.
If you need internal surgery, chances are something inside the body cavity is
going to get stitched up. Manufactured sutures, while they can be made
biodegradable, still aren’t natural, so harmful chemicals (even though they
aren’t deadly ones) get transmuted back into the body. With spider sutures, the
proteins will break down naturally and be transformed into other substances the
body can either use or safely discard through waste. (Spider poo)
Another particularly interesting use would be for
ligament repair. Currently production methods of artificial ligaments are
costly, require multiple painful surgeries throughout the patient’s life, and lack
the tensile abilities of the real thing. Spider silk on the other hand is
extremely pliable, and if woven together into the thickness of a ligament,
could require only one surgery to install and last the rest of a patient’s
life. Another use they’re looking into is for gauze that can aide in wound
healing, (although to be totally honest I’m not sure how that one works.)
While all of these uses will better mankind in the
long run, perhaps the shortest-term technological use for this stretchy super
string is in body armor.
Currently body armor is bulky, cumbersome, and
while it has advanced since the early days of Vietnam, it has a long way to go
before it creates perfect protection. Silk is flexible, lightweight, it
breathes rather easily and when combined with Dragline Spider-Silk DNA, it’s
virtually indestructible. You can see the implications here.
While all these technologies are still in the
R&D phase, silk has inadvertently redefined itself and once again is at the
top of the pile. Time will tell if we’ll see Spider-men running around the
deserts with Orb-Weaver tendons but there is one thing I’m certain of. Science
has shown us that silk is much more than just a pretty face.
- Ryan
Sanders
Thanks
for reading! If you would like to know more about anything we talked about
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happy learning!
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