sponsored links
TED2010

Cheryl Hayashi: The magnificence of spider silk

February 21, 2010

Cheryl Hayashi studies spider silk, one of nature's most high-performance materials. Each species of spider can make up to 7 very different kinds of silk. How do they do it? Hayashi explains at the DNA level -- then shows us how this super-strong, super-flexible material can inspire.

Cheryl Hayashi - Spider silk scientist
Cheryl Hayashi studies the delicate but terrifically strong silk threads that make up a spider's web, finding startling applications for human use. Full bio

sponsored links
Double-click the English subtitles below to play the video.
I'm here to spread the word about the
00:16
magnificence of spiders
00:18
and how much we can learn from them.
00:20
Spiders are truly global citizens.
00:23
You can find spiders in nearly
00:25
every terrestrial habitat.
00:27
This red dot marks
00:29
the Great Basin of North America,
00:31
and I'm involved with an alpine biodiversity
00:33
project there with some collaborators.
00:35
Here's one of our field sites,
00:37
and just to give you a sense of perspective,
00:39
this little blue smudge here,
00:41
that's one of my collaborators.
00:43
This is a rugged and barren landscape,
00:45
yet there are quite a few spiders here.
00:48
Turning rocks over revealed this crab spider
00:50
grappling with a beetle.
00:54
Spiders are not just everywhere,
00:56
but they're extremely diverse.
00:59
There are over 40,000 described species
01:01
of spiders.
01:04
To put that number into perspective,
01:05
here's a graph comparing the 40,000
01:07
species of spiders
01:09
to the 400 species of primates.
01:11
There are two orders of magnitude more
01:13
spiders than primates.
01:15
Spiders are also extremely old.
01:17
On the bottom here,
01:21
this is the geologic timescale,
01:23
and the numbers on it indicate millions
01:25
of years from the present, so the zero here,
01:27
that would be today.
01:29
So what this figure shows is that spiders
01:31
date back to almost 380 million years.
01:34
To put that into perspective, this red
01:38
vertical bar here marks the divergence time
01:40
of humans from chimpanzees,
01:43
a mere seven million years ago.
01:46
All spiders make silk
01:49
at some point in their life.
01:51
Most spiders use copious amounts of silk,
01:53
and silk is essential to their survival
01:56
and reproduction.
01:58
Even fossil spiders can make silk,
02:00
as we can see from this impression of
02:02
a spinneret on this fossil spider.
02:04
So this means that both spiders
02:07
and spider silk have been around
02:09
for 380 million years.
02:11
It doesn't take long from working with spiders
02:16
to start noticing how essential silk is
02:19
to just about every aspect of their life.
02:22
Spiders use silk for many purposes, including
02:25
the trailing safety dragline,
02:28
wrapping eggs for reproduction,
02:30
protective retreats
02:33
and catching prey.
02:35
There are many kinds of spider silk.
02:37
For example, this garden spider can make
02:39
seven different kinds of silks.
02:42
When you look at this orb web, you're actually
02:44
seeing many types of silk fibers.
02:46
The frame and radii of this web
02:49
is made up of one type of silk,
02:51
while the capture spiral is a composite
02:54
of two different silks:
02:56
the filament and the sticky droplet.
02:58
How does an individual spider
03:01
make so many kinds of silk?
03:04
To answer that, you have to look a lot closer
03:07
at the spinneret region of a spider.
03:09
So silk comes out of the spinnerets, and for
03:11
those of us spider silk biologists, this is what
03:13
we call the "business end" of the spider. (Laughter)
03:15
We spend long days ...
03:17
Hey! Don't laugh. That's my life.
03:19
(Laughter)
03:21
We spend long days and nights
03:23
staring at this part of the spider.
03:25
And this is what we see.
03:28
You can see multiple fibers
03:30
coming out of the spinnerets, because
03:32
each spinneret has many spigots on it.
03:35
Each of these silk fibers exits from the spigot,
03:38
and if you were to trace the fiber back
03:41
into the spider, what you would find is that
03:43
each spigot connects to its own individual
03:46
silk gland. A silk gland kind of looks like a sac
03:48
with a lot of silk proteins stuck inside.
03:51
So if you ever have the opportunity to dissect
03:54
an orb-web-weaving spider,
03:56
and I hope you do,
03:58
what you would find is a bounty
04:00
of beautiful, translucent silk glands.
04:03
Inside each spider, there are hundreds
04:06
of silk glands, sometimes thousands.
04:08
These can be grouped into seven categories.
04:11
They differ by size, shape,
04:14
and sometimes even color.
04:16
In an orb-web-weaving spider,
04:18
you can find seven types of silk glands,
04:20
and what I have depicted here in this picture,
04:22
let's start at the one o'clock position,
04:24
there's tubuliform silk glands, which are used
04:27
to make the outer silk of an egg sac.
04:29
There's the aggregate and flagelliform silk
04:31
glands which combine to make the sticky
04:33
capture spiral of an orb web.
04:35
Pyriform silk glands make the attachment
04:38
cement -- that's the silk that's used to adhere
04:40
silk lines to a substrate.
04:43
There's also aciniform silk,
04:46
which is used to wrap prey.
04:48
Minor ampullate silk is used in web construction.
04:50
And the most studied silk line
04:52
of them all: major ampullate silk.
04:54
This is the silk that's used to make the frame
04:56
and radii of an orb web, and also
04:58
the safety trailing dragline.
05:01
But what, exactly, is spider silk?
05:04
Spider silk is almost entirely protein.
05:08
Nearly all of these proteins can be explained
05:11
by a single gene family,
05:13
so this means that the diversity of silk types
05:16
we see today is encoded by one gene family,
05:18
so presumably the original spider ancestor
05:23
made one kind of silk,
05:26
and over the last 380 million years,
05:28
that one silk gene has duplicated
05:31
and then diverged, specialized,
05:34
over and over and over again, to get
05:37
the large variety of flavors of spider silks
05:40
that we have today.
05:42
There are several features that all these silks
05:45
have in common. They all have a common
05:47
design, such as they're all very long --
05:49
they're sort of outlandishly long
05:51
compared to other proteins.
05:54
They're very repetitive, and they're very rich
05:56
in the amino acids glycine and alanine.
05:59
To give you an idea of what
06:02
a spider silk protein looks like,
06:04
this is a dragline silk protein,
06:06
it's just a portion of it,
06:08
from the black widow spider.
06:10
This is the kind of sequence that I love
06:12
looking at day and night. (Laughter)
06:14
So what you're seeing here is the one letter
06:17
abbreviation for amino acids, and I've colored
06:19
in the glycines with green,
06:21
and the alanines in red, and so
06:23
you can see it's just a lot of G's and A's.
06:25
You can also see that there's a lot of short
06:28
sequence motifs that repeat over and over
06:31
and over again, so for example there's a lot of
06:34
what we call polyalanines, or iterated A's,
06:36
AAAAA. There's GGQ. There's GGY.
06:39
You can think of these short motifs
06:43
that repeat over and over again as words,
06:45
and these words occur in sentences.
06:48
So for example this would be one sentence,
06:51
and you would get this sort of green region
06:54
and the red polyalanine, that repeats
06:56
over and over and over again,
06:58
and you can have that hundreds and
07:00
hundreds and hundreds of times within
07:02
an individual silk molecule.
07:04
Silks made by the same spider can have
07:06
dramatically different repeat sequences.
07:08
At the top of the screen, you're seeing
07:11
the repeat unit from the dragline silk
07:14
of a garden argiope spider.
07:17
It's short. And on the bottom,
07:20
this is the repeat sequence for the
07:22
egg case, or tubuliform silk protein,
07:24
for the exact same spider. And you can see
07:26
how dramatically different
07:29
these silk proteins are -- so this is
07:31
sort of the beauty of the diversification
07:34
of the spider silk gene family.
07:36
You can see that the repeat units differ
07:38
in length. They also differ in sequence.
07:40
So I've colored in the glycines again
07:42
in green, alanine in red, and the serines,
07:44
the letter S, in purple. And you can see
07:47
that the top repeat unit can be explained
07:50
almost entirely by green and red,
07:52
and the bottom repeat unit has
07:55
a substantial amount of purple.
07:57
What silk biologists do is we try to relate
07:59
these sequences, these amino acid
08:02
sequences, to the mechanical properties
08:04
of the silk fibers.
08:06
Now, it's really convenient that spiders use their silk
08:08
completely outside their body.
08:11
This makes testing spider silk really, really
08:13
easy to do in the laboratory, because
08:15
we're actually, you know, testing it in air
08:17
that's exactly the environment that
08:20
spiders are using their silk proteins.
08:22
So this makes quantifying silk properties by
08:24
methods such as tensile testing, which is
08:26
basically, you know, tugging on one end
08:28
of the fiber, very amenable.
08:30
Here are stress-strain curves
08:33
generated by tensile testing
08:36
five fibers made by the same spider.
08:38
So what you can see here is that
08:41
the five fibers have different behaviors.
08:44
Specifically, if you look on the vertical axis,
08:47
that's stress. If you look at the maximum
08:49
stress value for each of these fibers,
08:52
you can see that there's a lot of variation,
08:54
and in fact dragline, or major ampullate silk,
08:57
is the strongest of these fibers.
09:00
We think that's because the dragline silk,
09:02
which is used to make the frame and radii
09:05
for a web, needs to be very strong.
09:08
On the other hand, if you were to look at
09:10
strain -- this is how much a fiber can be
09:12
extended -- if you look at the maximum value
09:14
here, again, there's a lot of variation
09:16
and the clear winner is flagelliform,
09:19
or the capture spiral filament.
09:21
In fact, this flagelliform fiber can
09:23
actually stretch over twice its original length.
09:25
So silk fibers vary in their strength
09:29
and also their extensibility.
09:32
In the case of the capture spiral,
09:34
it needs to be so stretchy to absorb
09:36
the impact of flying prey.
09:38
If it wasn't able to stretch so much, then
09:40
basically when an insect hit the web,
09:42
it would just trampoline right off of it.
09:44
So if the web was made entirely out of
09:46
dragline silk, an insect is very likely to just
09:48
bounce right off. But by having really, really
09:51
stretchy capture spiral silk, the web is actually
09:53
able to absorb the impact
09:55
of that intercepted prey.
09:57
There's quite a bit of variation within
10:00
the fibers that an individual spider can make.
10:02
We call that the tool kit of a spider.
10:05
That's what the spider has
10:08
to interact with their environment.
10:10
But how about variation among spider
10:12
species, so looking at one type of silk
10:14
and looking at different species of spiders?
10:16
This is an area that's largely unexplored
10:19
but here's a little bit of data I can show you.
10:21
This is the comparison of the toughness
10:25
of the dragline spilk spun
10:27
by 21 species of spiders.
10:29
Some of them are orb-weaving spiders and
10:31
some of them are non-orb-weaving spiders.
10:33
It's been hypothesized that
10:36
orb-weaving spiders, like this argiope here,
10:38
should have the toughest dragline silks
10:41
because they must intercept flying prey.
10:43
What you see here on this toughness graph
10:46
is the higher the black dot is on the graph,
10:49
the higher the toughness.
10:51
The 21 species are indicated here by this
10:53
phylogeny, this evolutionary tree, that shows
10:56
their genetic relationships, and I've colored
10:59
in yellow the orb-web-weaving spiders.
11:01
If you look right here at the two red arrows,
11:04
they point to the toughness values
11:07
for the draglines of nephila clavipes and
11:10
araneus diadematus.
11:12
These are the two species of spiders
11:14
for which the vast majority of time and money
11:16
on synthetic spider silk research has been
11:19
to replicate their dragline silk proteins.
11:22
Yet, their draglines are not the toughest.
11:25
In fact, the toughest dragline in this survey
11:29
is this one right here in this white region,
11:32
a non orb-web-weaving spider.
11:35
This is the dragline spun by scytodes,
11:37
the spitting spider.
11:39
Scytodes doesn't use a web at all
11:41
to catch prey. Instead, scytodes
11:44
sort of lurks around and waits for prey
11:46
to get close to it, and then immobilizes prey
11:49
by spraying a silk-like venom onto that insect.
11:52
Think of hunting with silly string.
11:56
That's how scytodes forages.
11:59
We don't really know why scytodes
12:02
needs such a tough dragline,
12:04
but it's unexpected results like this that make
12:07
bio-prospecting so exciting and worthwhile.
12:10
It frees us from the constraints
12:14
of our imagination.
12:16
Now I'm going to mark on
12:18
the toughness values for nylon fiber,
12:20
bombyx -- or domesticated silkworm silk --
12:23
wool, Kevlar, and carbon fibers.
12:26
And what you can see is that nearly
12:29
all the spider draglines surpass them.
12:31
It's the combination of strength, extensibility
12:33
and toughness that makes spider silk so
12:37
special, and that has attracted the attention
12:40
of biomimeticists, so people that turn
12:43
to nature to try to find new solutions.
12:46
And the strength, extensibility and toughness
12:49
of spider silks combined with the fact that
12:52
silks do not elicit an immune response,
12:55
have attracted a lot of interest in the use
12:58
of spider silks in biomedical applications,
13:01
for example, as a component of
13:03
artificial tendons, for serving as
13:05
guides to regrow nerves, and for
13:08
scaffolds for tissue growth.
13:12
Spider silks also have a lot of potential
13:15
for their anti-ballistic capabilities.
13:18
Silks could be incorporated into body
13:20
and equipment armor that would be more
13:22
lightweight and flexible
13:25
than any armor available today.
13:27
In addition to these biomimetic
13:30
applications of spider silks,
13:33
personally, I find studying spider silks
13:35
just fascinating in and of itself.
13:39
I love when I'm in the laboratory,
13:42
a new spider silk sequence comes in.
13:46
That's just the best. (Laughter)
13:49
It's like the spiders are sharing
13:52
an ancient secret with me, and that's why
13:55
I'm going to spend the rest of my life
13:57
studying spider silk.
13:59
The next time you see a spider web,
14:01
please, pause and look a little closer.
14:04
You'll be seeing one of the most
14:07
high-performance materials known to man.
14:09
To borrow from the writings
14:12
of a spider named Charlotte,
14:14
silk is terrific.
14:17
Thank you. (Applause)
14:19
(Applause)
14:22

sponsored links

Cheryl Hayashi - Spider silk scientist
Cheryl Hayashi studies the delicate but terrifically strong silk threads that make up a spider's web, finding startling applications for human use.

Why you should listen

Biologist Cheryl Hayashi is fascinated with spiders and their silks, and for good reason. Made of a mix of proteins, spider silks come in thousands of variations; there are over 40,000 species of spiders, with many spiders capable of producing half a dozen types. Some silks have the tensile strength of steel -- and often are much tougher -- while remaining light as air and extremely supple. And spiders use their silk in diverse ways: to make their homes and trap their food, to travel, to court and to protect their eggs.
 
In her lab at UC Riverside, Hayashi explores spider silk’s genetic makeup, evolution and unique biomechanics (winning a MacArthur “genius" grant for it in 2007). Her work blurs the boundary between biology and materials science, looking for the molecular basis of this wondrous material and exploring how humans might learn from it. Hayashi's work may inspire new biomimetic materials for a huge variety of uses, from biodegradable fishing lines and sutures to superstrong ropes and armor cloth.

The original video is available on TED.com
sponsored links

If you need translations, you can install "Google Translate" extension into your Chrome Browser.
Furthermore, you can change playback rate by installing "Video Speed Controller" extension.

Data provided by TED.

This website is owned and operated by Tokyo English Network.
The developer's blog is here.