Spider silk is a strong yet flexible protein fiber produced by spiders that is used for webs, nests, and other structures. It has extraordinary mechanical properties, with high tensile strength and elasticity. This makes it tough and able to absorb energy. Spider silk is produced from liquid silk dope that is pulled through specialized glands and spinnerets and spun into fibers. The silk has a hierarchical structure at the molecular level that contributes to its properties. Researchers are working to artificially synthesize and spin spider silk by expressing spider silk proteins in organisms and using various spinning methods to replicate the native production process.

1. An over view on spider silk
Presented by:
J.ANILKUMAR
141la11001
3rd year
Textile technology
Vignan University

2. Introduction:
Spider silk is a protein fibre spun by spiders. Spiders use their silk to make webs or other
structures, which function as nets to catch other animals, or as nests or cocoons to protect
their offspring. They can also use their silk to suspend themselves. Many small spiders use
silk threads for ballooning, the popular, though technically inaccurate, scientific term for
the dynamic kitingspiderlings (mostly) use for dispersal. They extrude several threads into
the air and let themselves be carried away by winds. Although most rides will end a few
yards later, it seems to be a common way for spiders to invade islands. Many sailors have
reported that spiders have been caught in their ship's sails, even when far from land. The
extremely fine silk that spiders use for ballooning is known as gossamer. Mankind has used
spider silk as a material long before it appeared in the focus of research. In ancient Greece,
natural cobwebs were used to seal the bleeding wounds and in Australia spider silk threads
are used as fishing thread. Spider silk has potential applications in several areas including
bullet-proof materials, in the treatment of open wounds in the fabrication of textiles etc. In
some cases, spiders may even use silk as a source of food. Methods have been developed
to collect silk from a spider by force.
Biodiversity:
All spiders produce silks, and a single spider can produce up to seven different types of
silk for different uses. This is in contrast to insect silks, where an individual usually only
produces one type of silk. Spider silks may be used in many different ecological ways. As
spiders have evolved, so has their silks' complexity and diverse uses, for example from
primitive tube webs 300–400 mya to complex orb webs 110 Mya. Meeting the specification
for all these ecological uses requires different types of silk suited to different broad
properties, as either a fiber, a structure of fibers, or a silk-globule. These types include
glues and fibers. Some types of fibers are used for structural support, others for
constructing protective structures. Some can absorb energy effectively, whereas others
transmit vibration efficiently. In a spider, these silk types are produced in different glands;
so the silk from a particular gland can be linked to its use by the spider. See the later section

3. for details on the mechanical properties of silk and how the structure of silk can achieve
these different properties.
Properties:
Mechanical properties:
 Each spider and each type of silk has a set of mechanical properties optimized for
their biological function.
 Most silks, in particular dragline silk, have exceptional mechanical properties. They
exhibit a unique combination of high tensile strength and extensibility (ductility).
 This enables a silk fibre to absorb a lot of energy before breaking (toughness, the
area under a stress-strain curve).
An illustration of the differences between toughness, stiffness and strength

4. A frequent mistake made in the mainstream media is to confuse strength and toughness
when comparing silk to other materials. As shown below in detail, weight for weight, silk
is stronger than steel, but not as strong as Kevlar. Silk is, however, tougher than both.
Strength:
In detail a dragline silk's tensile strength is comparable to that of high-grade alloy steel (450
- 1970 MPa), and about half as strong as aramid filaments, such as Kevlar (3000 MPa).
Density:
Consisting of mainly protein, silks are about a sixth of the density of steel (1.31 g/cm3). As
a result, a strand long enough to circle the Earth would weigh less than 500 grams (18 oz.).
(Spider dragline silk has a tensile strength of roughly 1.3 GPA. The tensile strength listed
for steel might be slightly higher—e.g. 1.65 GPA, but spider silk is a much less dense
material, so that a given weight of spider silk is five times as strong as the same weight of
steel.)
Energy density:
The energy density of dragline spider silk is 1.2x108J/m3.
Extensibility:
Silks are also extremely ductile, with some able to stretch up to five times their relaxed
length without breaking.
Toughness:
The combination of strength and ductility gives dragline silks a very high toughness (or
work to fracture), which "equals that of commercial polyaramid (aromatic nylon)
filaments, which themselves are benchmarks of modern polymer fibre technology".
Temperature:
While unlikely to be relevant in nature, dragline silks can hold their strength below 40 °C
and up to 220 °C.
Super contraction:
When exposed to water, dragline silks undergo super contraction, shrinking up to 50% in
length and behaving like a weak rubber under tension. Many hypotheses have been
suggested as to its use in nature, with the most popular being to automatically tension webs
built in the night using the morning dew

5. Highest-performance:
The toughest known spider silk is produced by the species Darwin's bark spider (Caerostris
Darwin): "The toughness of forcibly silked fibers averages 350 MJ/m3, with some samples
reaching 520 MJ/m3. Thus, C. Darwin silk is more than twice as tough as any previously
described silk, and over 10 times tougher than Kevlar".
Types of silk:
Many species of spider have different glands to produce silk with different properties for
different purposes, including housing, web construction, defense, capturing and detaining
prey, egg protection, and mobility (gossamer for ballooning, or for a strand allowing the
spider to drop down as silk is extruded). Different specialized silks have evolved with
properties suitable for different uses. For example, Argiope argentata has five different
types of silk, each used for a different purpose:
Silk Use
major-ampullate
(dragline) silk
Used for the web's outer rim and spokes and the lifeline. Can be as
strong per unit weight as steel, but much tougher.
capture-spiral
(flabelliform) silk
Used for the capturing lines of the web. Sticky, extremely stretchy and
tough. The capture spiral is sticky due to droplets of aggregate (a spider
glue) that is placed on the spiral. The elasticity of flabelliform allows
for enough time for the aggregate to adhere to the aerial prey flying into
the web.
tubiliform (a.k.a.
cylindriform) silk
Used for protective egg sacs. Stiffest silk.
acini form silk
Used to wrap and secure freshly captured prey. Two to three times as
tough as the other silks, including dragline.
minor-ampullate silk Used for temporary scaffolding during web construction.

6. Piriform (pyriform)
Piriform serves as the attachment disk to dragline silk. Piriform is used
in attaching spider silks together to construct a stable web.
Structural
Macroscopic structure down to protein hierarchy
Structure of spider silk.
Inside a typical fiber there are crystalline regions separated by amorphous linkages. The
crystals are beta-sheets that have assembled together.
Silks, as well as many other biomaterials, have a hierarchical structure
(e.g., cellulose, hair). The primary structure is its amino acid sequence, mainly consisting
of highly repetitive glycine and alanine blocks, which is why silks are often referred to as
a block co-polymer. On a secondary structure level, the short side chained alanine is mainly
found in the crystalline domains (beta sheets) of the Nano fibril, glycine is mostly found in
the so-called amorphous matrix consisting of helical and beta turn structures. It is the

7. interplay between the hard crystalline segments, and the strained elastic semi-amorphous
regions that gives spider silk its extraordinary properties. Various compounds other than
protein are used to enhance the fiber's properties. Pyrrolidine has hygroscopic properties
which keeps the silk moist furthermore the additive wards off ant invasion. It occurs in
especially high concentration in glue threads. Potassium hydrogen
phosphate releases protons in aqueous solution, resulting in a pH of about 4, making the
silk acidic and thus protecting it from fungi and bacteria that would otherwise digest the
protein. Potassium nitrate is believed to prevent the protein from denaturing in the acidic
milieu.
This first very basic model of silk was introduced by Term onia in 1994 suggested
crystallites embedded in an amorphous matrix interlinked with hydrogen bonds. This
model has refined over the years: Semi-crystalline regions were found as well as a fibrillar
skin core model suggested for spider silk, later visualized by AFM and TEM. Sizes of the
nanofibrillar structure and the crystalline and semi-crystalline regions were revealed by
neutron scattering.
Non-protein composition:
Various compounds other than protein are found in spider silks, such as sugars, lipids, ions,
and pigments that might affect the aggregation behavior and act as a protection layer in the
final fiber.
Biosynthesis:
The production of silks, including spider silk, differs in an important respect from the
production of most other fibrous biological materials: rather than being continuously grown
as keratin in hair, cellulose in the cell walls of plants, or even the fibers formed from the
compacted faecal matter of beetles, it is "spun" on demand from liquid silk precursor
sometimes referred to as unspun silk dope, out of specialized glands.

8. The spinning process occurs when a fiber is pulled away from the body of a spider, be that
by the spider’s legs, by the spider's falling and using its own weight, or by any other method
including being pulled by humans. The name "spinning" is misleading as no rotation of
any component occurs, but the name comes from when it was thought that spiders produced
their thread in a similar manner to the spinning wheels of old. In fact the process is a
pultrusion—similar to extrusion, with the subtlety that the force is induced by pulling at
the finished fiber rather than being squeezed out of a reservoir of some kind.
The unspun silk dope is pulled through silk glands, of which there may be both numerous
duplicates and also different types on any one spider species.
Silk gland:
The gland's visible, or external, part is termed the spinneret. Depending on the complexity
of the species, spiders will have two to eight sets of spinnerets, usually in pairs. There exist
highly different specialized glands in different spiders, ranging from simply a sac with an
opening at one end, to the complex, multiple-section Major Ampullate glands of the
Nephilim golden orb weaving spiders.
Behind each spinneret visible on the surface of the spider lies a gland, a generalized form
of which is shown in the figure to the right, "Schematic of a generalized gland".
Schematic of a generalized gland of a Golden silk orb-weaver. Each differently
colored section highlights a discrete section of the gland
The gland described here will be based upon the major ampullate gland from a golden orb
weaving spiders as they are the most-studied and presumed to be the most complex.
The first section of the gland labelled 1 on Figure 1 is the secretory or tail section of the
gland. The walls of this section are lined with cells that secrete proteins Spidroin I and
Spidroin II, the main components of this spider’s dragline. These proteins are found in the
form of droplets that gradually elongate to form long channels along the length of the final
fiber, hypothesized to assist in preventing crack formation or even self-healing of the fiber.

9. The second section is the storage sac. This stores and maintains the gel-like unspun silk
dope until it is required by the spider. In addition to storing the unspun silk gel, it secretes
proteins that coat the surface of the final fiber.
The funnel rapidly reduces the large diameter of the storage sac to the small diameter of
the tapering duct.
The final length is the tapering duct, the site of most of the fiber formation. This consists
of a tapering tube with several tight about turns, a valve almost at the ending in a spigot
from which the silk fiber emerges. The tube here tapers hyperbolically, therefore the
unspun silk is under constant shear stress, which is an important factor in fiber formation.
This section of the duct is lined with cells that exchange ions and remove water from the
fiber. The spigot at the end has lips that clamp around the fiber, controlling fiber diameter
and further retaining water.
Almost at the end of the tapering duct is a valve, approximate position marked "5" on figure
1. Though discovered some time ago, the precise purpose of this valve is still under
discussion. It is believed to assist in restarting and rejoining broken fibers acting much in
the way of a helical pump, regulating the thickness of the fiber, and/ or clamping the fiber
as a spider falls upon it. There is some discussion on the similarity of the silk worm’s silk
press and the roles each of these valves play in the production of silk in these two
organisms.
Throughout the process the unspun silk appears to have a nematic texture, in a similar
manner to a liquid crystal. This allows the unspun silk to flow through the duct as a liquid
but maintain a molecular order.
As an example of a complex spinning field, the spinneret apparatus of an adult Araneus
diadematus (garden cross spider) consists of the following glands:
 500 Glandule piriformis for attachment points
 4 Glandular ampullaceal for the web frame
 About 300 Glandular acini forms for the outer lining of egg sacs, and for ensnaring
prey
 4 Glandular tubuli forms for egg sac silk
 4 Glandular aggregate for glue
 2 Glandular coronate for the thread of glue lines.
Artificial synthesis:
In order to artificially synthesize spider silk into fibers, there are two broad areas that must
be covered. These are synthesis of the feedstock (the unspun silk dope in spiders), and
synthesis of the spinning conditions (the funnel, valve, tapering duct, and spigot). There
have been a number of different approaches discussed below.

10. Single strand of artificial spider silk produced under laboratory conditions.
Feedstock:
As discussed in the Structural section of the article, the molecular structure of unspun silk
is both complex and extremely long. Though this endows the silk fibers with their desirable
properties, it also makes replication of the fiber somewhat of a challenge. Various
organisms have been used as a basis for attempts to replicate some components or all of
some or all of the proteins involved. These proteins must then be extracted, purified and
then spun before their properties can be tested. The table below shows the results including
the true gold standard- actual stress and strain of the fibers as compared to the best spider
dragline.

11. Organism Details
Average
Maximum
breaking
stress (MPa)
Average
Strain (%)
Gold Standard: Darwin’s
bark spider (Caerostris
Darwin)
Malagasy spider famed for
making webs with strands up
to 25 m long across rivers.
"...C. Darwin silk is more than
twice as tough as any
previously described silk"
1850 ±350 33 ±0.08
Gold Standard:Nephila
clavipes
Typical golden orb weaving
spider
710–1200 18–27
Bombyx mori Silkworms
Silkworms were genetically
altered to express spider
proteins and fibers measured.
660 18.5
E. coli
Synthesizing such a large and
repetitive molecule (250–320
kDa) is complex. Yet, if this is
not achieved, the properties
will not match those of actual
spiders. Here a 285 kDa
protein was produced and
spun.
508 ±108 15 ±5

12. Goats
Goats were genetically
modified to secrete silk
proteins in their milk, which
could then be purified.
285–250 30–40
Tobacco & potato plants
Spider proteins were inserted
into tobacco and potato plants,
the rationale being that should
this be successful, scaled-up
harvesting would be much
facilitated. Patents have been
granted in this area, but no
fibers have yet been described
in the literature.
n/a n/a
Syringe and needle:
Feedstock is simply forced through a hollow needle using a syringe. This method has been
shown to make fibers successfully on multiple occasions.
Although very cheap and easy to assemble, the shape and conditions of the gland are very
loosely approximated. Fibers created using this method may need encouragement to
change from liquid to solid by removing the water from the fiber with such chemicals as
the environmentally undesirable methanol or acetone, and also may require post-stretching
of the fiber to attain fibers with desirable properties.
Microfluidics:
As the field of microfluidics matures, it is likely that more attempts to spin fibers will be
made using microfluidics. These have the advantage of being very controllable and able to
test spin very small volumes of unspun fiber but setup and development costs are likely to
be high. A patent has been granted in this area for spinning fibers in a method mimicking
the process found in nature, and fibers are successfully being continuously spun by a
commercial company.
Electrospinning:
Electrospinning is a very old technique whereby a fluid is held in a container in a manner
such that it is able to flow out through capillary action. A conducting substrate is positioned
below, and a large difference in electrical potential is applied between the fluid and the
substrate. The fluid is attracted to the substrate, and tiny fibers jump almost instantly from

13. their point of emission, the Taylor cone, to the substrate, drying as they travel. This method
has been shown to create Nano-scale fibers from both silk dissected from organisms
and regenerated silk fibroin.
Other artificial shapes formed from silk
Silk can be formed into other shapes and sizes such as spherical capsules for drug delivery,
cell scaffolds and wound healing, textiles, cosmetics, coatings, and many others.
Research milestones:
Due to spider silk being a scientific research field with a long and rich history, there can
be unfortunate occurrences of researchers independently rediscovering previously
published findings. What follows is a table of the discoveries made in each of the
constituent areas, acknowledged by the scientific community as being relevant and
significant by using the metric of scientific acceptance, citations. Thus, only papers with
50 or more citations are included.
Human uses:

14. A cape made from Madagascar golden silk.
 Peasants in the southern Carpathian Mountains used to cut up tubes built
by Atypus and cover wounds with the inner lining. It reportedly facilitated healing,
and even connected with the skin. This is believed to be due to antiseptic properties
of spider silk and because the silk is rich in vitamin K, which can be effective in
clotting blood. Silk of Nephilim clavipes has recently been used to help
in mammalian neuronal regeneration.
 At one time, it was common to use spider silk as a thread for crosshairs in optical
instruments such as telescopes, microscopes, and telescopic. Due to the difficulties
in extracting and processing substantial amounts of spider silk, the largest known
piece of cloth made of spider silk is an 11-by-4-foot (3.4 by 1.2 m) textile with
a golden tint made in Madagascar in 2009. Eighty-two people worked for four years
to collect over one million golden orb spiders and extract silk from them

15.  In 2011, spider silk fibers were used in the field of optics to generate very fine
diffraction patterns over N-slit interferometric signals utilized in optical
communications.
 In 2012, spider silk fibers were used to create a set of violin strings.
 Spider silk is used to suspend inertial confinement fusion targets during laser
ignition, as it remains considerably elastic and has a high energy to break at
temperatures as low as 10-20K. In addition, it is made from "light" atomic number
elements that won't emit x-rays during irradiation that could preheat the target so
that the pressure differential required for fusion is not achieved.
Attempts at producing synthetic spider silk:
 Replicating the complex conditions required to produce fibers that are comparable
to spider silk has proven difficult to accomplish in a laboratory environment. What
follows is a miscellaneous list of attempts on this problem. However, in the absence
of hard data accepted by the relevant scientific community, it is difficult to judge
whether these attempts have been successful or constructive.
 In 2000, Canadian biotechnology company Nexia successfully produced spider
silk protein in transgenic goats that carried the gene for it; the milk produced by the
goats contained significant quantities of the protein, 1–2 grams of silk proteins per
liter of milk. Attempts to spin the protein into a fiber similar to natural spider silk
resulted in fibers with tenacities of 2–3 grams per denier (see Bio Steel). Nexia used
wet spinning and squeezed the silk protein solution through small extrusion holes
in order to simulate the behavior of the spinneret, but this procedure has so far not
been sufficient to replicate the properties of native spider silk.
 Extrusion of protein fibers in an aqueous environment is known as "wet-spinning".
This process has so far produced silk fibers of diameters ranging from 10 to 60 μm,
compared to diameters of 2.5–4 μm for natural spider silk.
 In March 2010, researchers from the Korea Advanced Institute of Science &
Technology (KAIST) succeeded in making spider silk directly using the
bacteria E.coli, modified with certain genes of the spider Nephila clavipes. This
Approach eliminates the need to milk spiders and allows the manufacture the spider
silk in a more cost-effective manner.
 The company Kraig Bio craft Laboratories has used research from the Universities
of Wyoming and Notre Dame in a collaborative effort to create a silkworm that has
been genetically altered to produce spider silk. In September 2010 it was announced

16. at a press conference at the University of Notre Dame that the effort had been
successful.
 The company AM Silk has succeeded in making spidroin using bacteria, and
making it into spider silk. They are now focusing on increasing production rate of
the spider silk.
Applications of Spider Silk:
 Humans have been making use of spider silk for thousands of years.
 The ancient Greeks used cobwebs to stop wounds from bleeding and the Aborigines
used silk as fishing lines for small fish.
 More recently, silk was used as the crosshairs in optical targeting devices such as
guns and telescopes until World War II and people of the Solomon Islands still use
silk as fish nets.
 The interest in spider silk is mainly due to a combination of its mechanical
properties and the non-polluting way in which it is made.
 The production of modern man-made super-fibres such as Kevlar involves
petrochemical processing which contributes to pollution.
 Kevlar is also drawn from concentrated sulphuric acid. In contrast, the production
of spider silk is completely environmentally friendly.
 It is made by spiders at ambient temperature and pressure and is drawn from
water. In addition, silk is completely biodegradable.
 If the production of spider silk ever becomes industrially viable, it could replace
Kevlar and be used to make a diverse range of items such as:
 Bullet-proof clothing.
 Wear-resistant lightweight clothing.
 Ropes, nets, seat belts, parachutes.
 Rust-free panels on motor vehicles or boats.
 Biodegradable bottles.
 Bandages, surgical thread.

17.  Artificial tendons or ligaments, supports for weak blood vessels.
However the production of spider silk is not simple and there are inherent problems. Firstly
spiders cannot be farmed like silkworms since they are cannibals and will simply eat each
other if in close proximity. The silk produced is very fine so 400 spiders would be needed
to produce only one square yard of cloth. The silk also hardens when exposed to air which
makes it difficult to work with.

18. There are still problems with developing synthetic spider silk production. An artificial
method of spinning silk remains a mystery. Spider spinning dope is approximately 50%
protein but this is too high a concentration to use industrially since the fluid would be too
viscous to allow efficient spinning. The silk is also insoluble in water but this can be
overcome by attaching soluble amino acids such as histidine or arginine to the ends of the
protein molecules. In addition, the silk coagulates if the fluid is stirred so it would have to
be redissolved. Current research focuses around these problems and a possible solution
would be to adapt the composition of silk proteins to alter its properties. Research is still
in its early stages but unravelling the secrets of spider silk is underway.
References:
 Work, Robert W.; Emerson, Paul D. (1982). "An Apparatus and Technique for the
Forcible Silking of Spiders". Journal of Arachnology 10 (1): 1–
10. JSTOR 3705113.
 Nentwig, W. & Heimer, S. (1987). Wolfgang Nentwig, ed. Ecological aspects of
spider webs. Springer-Verlag. p. 211
 "Overview of materials for AISI 4000 Series Steel". www.matweb.com.
Retrieved18 August 2010.
 "DuPont Kevlar 49 Aramid Fiber". Www.matweb.com. Retrieved 18
August 2010.
 Porter, D.; Vollrath, F.; Shao, Z. (2005). "Predicting the mechanical properties of
spider silk as a model nanostructured polymer". European Physical Journal
E 16 (2): 199.Bibcode: 2005EPJE...16...199P. Doi: 10.1140/epje/e2005-00021-2.
 "Spider Silk". Www.chm.bris.ac.uk. Retrieved 18 August 2010.
 Seidel A, liivak O, jelnski L W,(1998),artificial spinning of spider silk,
macromolecules, 31: 6733-6736.
 Seidel A et al, (2000), regenerated spider silk ; processing, properties, and
structure , macromolecules, 31 ; 775-780
 Asian textile journal, February 2015, spider silk: A potential high performance
fibre.