SILK is a natural protein fiber , some forms of which can be woven
into textiles . The protein fiber of silk is composed mainly of
fibroin and is produced by certain insect larvae to form cocoons. The
best-known silk is obtained from the cocoons of the larvae of the
mulberry silkworm _
Bombyx mori _ reared in captivity (sericulture ).
The shimmering appearance of silk is due to the triangular prism -like
structure of the silk fibre, which allows silk cloth to refract
incoming light at different angles , thus producing different colors.
Silk is produced by several insects, but generally only the silk of
moth caterpillars has been used for textile manufacturing. There has
been some research into other types of silk, which differ at the
Silk is mainly produced by the larvae of insects
undergoing complete metamorphosis , but some insects such as
webspinners and raspy crickets produce silk throughout their lives.
Silk production also occurs in
Hymenoptera (bees , wasps , and ants ),
silverfish , mayflies , thrips , leafhoppers , beetles , lacewings ,
fleas , flies , and midges . Other types of arthropod produce silk,
most notably various arachnids such as spiders .
* 1 Etymology
* 2 History
* 2.5 Bangladesh
* 2.6 Ancient Mediterranean
* 2.8 Medieval and modern
* 2.9 North America
* 3 Production process
* 4 Properties
* 4.1 Physical properties
* 4.2 Chemical properties
* 5 Uses
* 5.1 Applications as a biomaterial
* 5.1.1 Biocompatibility
* 5.1.2 Biodegradability
* 6 Cultivation
* 7 Animal rights
* 8 See also
* 9 References
* 10 Cited sources
* 11 Further reading
* 12 External links
The word silk comes from
Old English _sioloc_, from Greek
σηρικός _serikos_, "silken", ultimately from an Asian source
(cf. Chinese _si_ "silk", Manchurian _sirghe_, Mongolian _sirkek_).
History of silk
Woven silk textile from tomb no 1. at
China , from the
Western Han Dynasty , 2nd century BC
Several kinds of wild silk , which are produced by caterpillars other
than the mulberry silkworm, have been known and used in
China , South
Asia , and
Europe since ancient times. However, the scale of
production was always far smaller than for cultivated silks. There are
several reasons for this: first, they differ from the domesticated
varieties in colour and texture and are therefore less uniform;
second, cocoons gathered in the wild have usually had the pupa emerge
from them before being discovered so the silk thread that makes up the
cocoon has been torn into shorter lengths; and third, many wild
cocoons are covered in a mineral layer that prevents attempts to reel
from them long strands of silk. Thus, the only way to obtain silk
suitable for spinning into textiles in areas where commercial silks
are not cultivated was by tedious and labor-intensive carding .
Commercial silks originate from reared silkworm pupae, which are bred
to produce a white-colored silk thread with no mineral on the surface.
The pupae are killed by either dipping them in boiling water before
the adult moths emerge or by piercing them with a needle. These
factors all contribute to the ability of the whole cocoon to be
unravelled as one continuous thread, permitting a much stronger cloth
to be woven from the silk. Wild silks also tend to be more difficult
to dye than silk from the cultivated silkworm. A technique known as
demineralizing allows the mineral layer around the cocoon of wild silk
moths to be removed, leaving only variability in color as a barrier
to creating a commercial silk industry based on wild silks in the
parts of the world where wild silk moths thrive, such as in Africa and
Genetic modification of domesticated silkworms is used to facilitate
the production of more useful types of silk.
A painting depicting women inspecting silk, early 12th century,
ink and color on silk, by
Emperor Huizong of Song . Portrait of
a silk merchant in Guangzhou,
Qing dynasty , from Peabody Essex Museum
Silk fabric was first developed in ancient China. The earliest
example of silk fabric is from 3630 BC, and it was used as wrapping
for the body of a child from a
Yangshao culture site in Qingtaicun at
Xingyang , Henan.
Legend gives credit for developing silk to a Chinese empress, Leizu
(Hsi-Ling-Shih, Lei-Tzu). Silks were originally reserved for the
China for their own use and gifts to others, but spread
Chinese culture and trade both geographically and
socially, and then to many regions of
Asia . Because of its texture
and lustre, silk rapidly became a popular luxury fabric in the many
areas accessible to Chinese merchants.
Silk was in great demand, and
became a staple of pre-industrial international trade . In July 2007,
archaeologists discovered intricately woven and dyed silk textiles in
a tomb in
Jiangxi province, dated to the Eastern
Zhou Dynasty roughly
2,500 years ago. Although historians have suspected a long history of
a formative textile industry in ancient China, this find of silk
textiles employing "complicated techniques" of weaving and dyeing
provides direct evidence for silks dating before the Mawangdui
-discovery and other silks dating to the
Han Dynasty (202 BC-220 AD).
Silk is described in a chapter on mulberry planting by Si Shengzhi of
the Western Han (206 BC – 9 AD). There is a surviving calendar for
silk production in an Eastern Han (25–220 AD) document. The two
other known works on silk from the Han period are lost. The first
evidence of the long distance silk trade is the finding of silk in the
hair of an Egyptian mummy of the 21st dynasty, c.1070 BC. The silk
trade reached as far as the Indian subcontinent, the
Middle East ,
Europe , and
North Africa . This trade was so extensive that the major
set of trade routes between
Asia came to be known as the
Silk Road .
The Emperors of
China strove to keep knowledge of sericulture secret
to maintain the Chinese monopoly . Nonetheless sericulture reached
Korea with technological aid from
China around 200 BC the ancient
Kingdom of Khotan
Kingdom of Khotan by AD 50, and
India by AD 140.
In the ancient era, silk from
China was the most lucrative and
sought-after luxury item traded across the Eurasian continent, and
many civilizations, such as the ancient Persians, benefited
economically from trade.
* Chinese silk making process
The silkworms and mulberry leaves are placed on trays.
Twig frames for the silkworms are prepared.
The cocoons are weighed.
The cocoons are soaked and the silk is wound on spools.
The silk is woven using a loom.
Silk in the Indian subcontinent
Silk sari weaving
Silk has a long history in India. It is known as _Resham_ in eastern
and north India, and _Pattu_ in southern parts of
India . Recent
archaeological discoveries in
Chanhu-daro suggest that
sericulture , employing wild silk threads from native silkworm
species, existed in
South Asia during the time of the Indus Valley
Civilization dating between 2450 BC and 2000 BC, while "hard and fast
evidence" for silk production in
China dates back to around 2570 BC.
Shelagh Vainker, a silk expert at the
Ashmolean Museum in Oxford, who
sees evidence for silk production in
China "significantly earlier"
than 2500–2000 BC, suggests, "people of the Indus civilization
either harvested silkworm cocoons or traded with people who did, and
that they knew a considerable amount about silk."
India is the second largest producer of silk in the world after
China. About 97% of the raw silk comes from five Indian states,
Andhra Pradesh ,
Jammu and Kashmir
Jammu and Kashmir , Tamil Nadu
West Bengal . North Bangalore, the upcoming site of a $20 million
Mysore , contribute to a majority of silk
production in Karnataka. _ Antheraea assamensis_, the endemic
species in the state of Assam,
India A traditional Banarasi
sari with gold brocade
Tamil Nadu , mulberry cultivation is concentrated in the
Tiruppur , Salem and
Andhra Pradesh , and
Tamil Nadu , were
the first locations to have automated silk reeling units in India.
India is also the largest consumer of silk in the world. The
tradition of wearing silk sarees for marriages and other auspicious
ceremonies is a custom in
Assam and southern parts of India.
considered to be a symbol of royalty, and, historically, silk was used
primarily by the upper classes.
Silk garments and sarees produced in
Kanchipuram , Pochampally , Dharmavaram ,
Mysore , Arani in the south,
Banaras in the north,
Murshidabad in the east are well
recognized. In the northeastern state of
Assam , three different types
of silk are produced, collectively called
Assam silk : Muga, Eri and
Pat silk. Muga, the golden silk, and Eri are produced by silkworms
that are native only to Assam.
Silk is produced year-round in
Thailand by two types of silkworms,
the cultured Bombycidae and wild Saturniidae. Most production is after
the rice harvest in the southern and northeastern parts of the
country. Women traditionally weave silk on hand looms and pass the
skill on to their daughters, as weaving is considered to be a sign of
maturity and eligibility for marriage.
Thai silk textiles often use
complicated patterns in various colours and styles. Most regions of
Thailand have their own typical silks. A single thread filament is too
thin to use on its own so women combine many threads to produce a
thicker, usable fiber. They do this by hand-reeling the threads onto a
wooden spindle to produce a uniform strand of raw silk. The process
takes around 40 hours to produce a half kilogram of silk. Many local
operations use a reeling machine for this task, but some silk threads
are still hand-reeled. The difference is that hand-reeled threads
produce three grades of silk: two fine grades that are ideal for
lightweight fabrics, and a thick grade for heavier material.
The silk fabric is soaked in extremely cold water and bleached before
dyeing to remove the natural yellow coloring of
Thai silk yarn. To do
this, skeins of silk thread are immersed in large tubs of hydrogen
peroxide . Once washed and dried, the silk is woven on a traditional
Rajshahi Division of northern Bangladesh is the hub of the
country's silk industry. There are three types of silk produced in the
region: mulberry, endi and tassar. Bengali silk was a major item of
international trade for centuries. It was known as Ganges silk in
Bengal was the leading exporter of silk between the
16th and 19th centuries.
Gunthertuch _, an 11th-century silk celebrating a Byzantine
emperor 's triumph
In the _
Odyssey _, 19.233, when Odysseus, while pretending to be
someone else, is questioned by Penelope about her husband's clothing,
he says that he wore a shirt "gleaming like the skin of a dried onion"
(varies with translations, literal translation here) which could
refer to the lustrous quality of silk fabric.
Aristotle wrote of _Coa
vestis _, a wild silk textile from
Sea silk from certain large
sea shells was also valued. The
Roman Empire knew of and traded in
silk, and Chinese silk was the most highly priced luxury good imported
by them. During the reign of emperor
Tiberius , sumptuary laws were
passed that forbade men from wearing silk garments, but these proved
ineffectual. Despite the popularity of silk, the secret of
silk-making only reached
Europe around AD 550, via the Byzantine
Empire . Legend has it that monks working for the emperor Justinian I
smuggled silkworm eggs to
Constantinople in hollow canes from China.
All top-quality looms and weavers were located inside the Great Palace
complex in Constantinople, and the cloth produced was used in imperial
robes or in diplomacy, as gifts to foreign dignitaries. The remainder
was sold at very high prices.
Torah , a scarlet cloth item called in Hebrew "sheni tola'at"
שני תולעת – literally "crimson of the worm" – is described
as being used in purification ceremonies, such as those following a
leprosy outbreak (Leviticus 14), alongside cedar wood and hyssop
(za\'atar ). Eminent scholar and leading medieval translator of Jewish
sources and books of the
Arabic , Rabbi
Saadia Gaon ,
translates this phrase explicitly as "crimson silk" – חריר
קרמז حرير قرمز.
Islamic teachings, Muslim men are forbidden to wear silk. Many
religious jurists believe the reasoning behind the prohibition lies in
avoiding clothing for men that can be considered feminine or
extravagant. There are disputes regarding the amount of silk a fabric
can consist of (e.g., whether a small decorative silk piece on a
cotton caftan is permissible or not) for it to be lawful for men to
wear, but the dominant opinion of most Muslim scholars is that the
wearing of silk by men is forbidden. Modern attire has raised a number
of issues, including, for instance, the permissibility of wearing silk
neckties , which are masculine articles of clothing.
Despite injunctions against silk for men, silk has retained its
popularity in the
Islamic world because of its permissibility for
women, and due to the presence of non-Muslim communities. The Muslim
Moors brought silk with them to Spain during their conquest of the
Iberian Peninsula .
MEDIEVAL AND MODERN EUROPE
Silk satin leaf, wood sticks and guards, c. 1890
Italy was the most important producer of silk during the Medieval
age. The first center to introduce silk production to Italy was the
Catanzaro during the 11th century in the region of
The silk of
Catanzaro supplied almost all of
Europe and was sold in a
large market fair in the port of Reggio
Calabria , to Spanish,
Venetian, Genovese and Dutch merchants.
Catanzaro became the lace
capital of the world with a large silkworm breeding facility that
produced all the laces and linens used in the Vatican. The city was
world-famous for its fine fabrication of silks, velvets, damasks and
Another notable center was the Italian city-state of Lucca which
largely financed itself through silk-production and silk-trading,
beginning in the 12th century. Other Italian cities involved in silk
Silk Exchange in Valencia from the 15th century—where
previously in 1348 also _perxal_ (percale ) was traded as some kind of
silk—illustrates the power and wealth of one of the great
Mediterranean mercantile cities.
Silk was produced in and exported from the province of
Spain, especially the
Alpujarras region, until the Moriscos , whose
industry it was, were expelled from
Granada in 1571.
Since the 15th century, silk production in France has been centered
around the city of Lyon where many mechanic tools for mass production
were first introduced in the 17th century. "La charmante
rencontre", rare 18th century embroidery in silk of Lyon (private
James I attempted to establish silk production in England, purchasing
and planting 100,000 mulberry trees, some on land adjacent to Hampton
Court Palace , but they were of a species unsuited to the silk worms,
and the attempt failed. In 1732 John Guardivaglio set up a silk
throwing enterprise at Logwood mill in Stockport ; in 1744, Burton
Mill was erected in
Macclesfield ; and in 1753 Old Mill was built in
Congleton . These three towns remained the centre of the English silk
throwing industry until silk throwing was replaced by silk waste
spinning . British enterprise also established silk filature in Cyprus
in 1928. In England in the mid-20th century, raw silk was produced at
Lullingstone Castle in Kent. Silkworms were raised and reeled under
the direction of Zoe Lady Hart Dyke, later moving to Ayot St Lawrence
in Hertfordshire in 1956.
* Medieval and modern Europe
Dress made from silk.
Bed covered with silk
A hundred year old pattern of silk called "Almgrensrosen"
The necktie originates from the cravat , a neckband made from silk
Yếm – the traditional silken bra in
King James I introduced silk-growing to the American colonies around
1619, ostensibly to discourage tobacco planting. The
Kentucky adopted the practice. In the 19th century a new attempt at a
silk industry began with European-born workers in Paterson, New Jersey
, and the city became a silk center in the United States. Manchester,
Connecticut emerged as center of the silk industry in America from the
late 19th through the mid-20th century. The Cheney Brothers Historic
District showcases mills refurbished as apartments and includes nearby
World War II
World War II interrupted the silk trade from Asia, and silk prices
increased dramatically. U.S. industry began to look for substitutes,
which led to the use of synthetics such as nylon . Synthetic silks
have also been made from lyocell , a type of cellulose fiber, and are
often difficult to distinguish from real silk (see spider silk for
more on synthetic silks).
Terengganu , which is now part of
Malaysia , a second generation
of silkworm was being imported as early as 1764 for the country's silk
textile industry, especially songket . However, since the 1980s,
Malaysia is no longer engaged in sericulture but does plant mulberry
In Vietnamese legend, silk appeared in the sixth dynasty of Hùng
The process of silk production is known as sericulture . The entire
production process of silk can be divided into several steps which are
typically handled by different entities. Extracting raw silk starts by
cultivating the silkworms on mulberry leaves. Once the worms start
pupating in their cocoons, these are dissolved in boiling water in
order for individual long fibres to be extracted and fed into the
To produce 1 kg of silk, 104 kg of mulberry leaves must be eaten by
3000 silkworms. It takes about 5000 silkworms to make a pure silk
kimono . :104 The major silk producers are
China (54%) and India
(14%). Other statistics:
TOP TEN COCOONS (REELABLE) PRODUCERS — 2005
PRODUCTION (INT $1000)
PRODUCTION (1000 KG)
People\'s Republic of
Democratic People\'s Republic of
No symbol = official figure, F = FAO estimate,*= Unofficial figure, C
= Calculated figure;
Production in Int $1000 have been calculated based on 1999–2001
Source: Food And Agricultural Organization of United Nations:
Economic And Social Department: The Statistical Division
The environmental impact of silk production is potentially large when
compared with other natural fibers. A life cycle assessment of Indian
silk production shows that the production process has a large carbon
and water footprint, mainly due to the fact that it is an
animal-derived fiber and more inputs such as fertilizer and water are
needed per unit of fiber produced.
Models in silk dresses at the MoMo Falana fashion show
Silk fibers from the _Bombyx mori_ silkworm have a triangular cross
section with rounded corners, 5–10 μm wide. The fibroin-heavy chain
is composed mostly of beta-sheets , due to a 59-mer amino acid repeat
sequence with some variations. The flat surfaces of the fibrils
reflect light at many angles, giving silk a natural sheen. The
cross-section from other silkworms can vary in shape and diameter:
crescent-like for _Anaphe_ and elongated wedge for _tussah_. Silkworm
fibers are naturally extruded from two silkworm glands as a pair of
primary filaments (brin), which are stuck together, with sericin
proteins that act like glue , to form a bave . Bave diameters for
tussah silk can reach 65 μm. See cited reference for cross-sectional
SEM photographs. Raw silk of domesticated silk worms, showing
its natural shine.
Silk has a smooth, soft texture that is not slippery, unlike many
synthetic fibers .
Silk is one of the strongest natural fibers, but it loses up to 20%
of its strength when wet. It has a good moisture regain of 11%. Its
elasticity is moderate to poor: if elongated even a small amount, it
remains stretched. It can be weakened if exposed to too much sunlight.
It may also be attacked by insects, especially if left dirty.
One example of the durable nature of silk over other fabrics is
demonstrated by the recovery in 1840 of silk garments from a wreck of
1782 : 'The most durable article found has been silk; for besides
pieces of cloaks and lace, a pair of black satin breeches, and a large
satin waistcoat with flaps, were got up, of which the silk was
perfect, but the lining entirely gone ... from the thread giving way
... No articles of dress of woollen cloth have yet been found.'
Silk is a poor conductor of electricity and thus susceptible to
static cling .
Unwashed silk chiffon may shrink up to 8% due to a relaxation of the
fiber macrostructure, so silk should either be washed prior to garment
construction, or dry cleaned .
Dry cleaning may still shrink the
chiffon up to 4%. Occasionally, this shrinkage can be reversed by a
gentle steaming with a press cloth. There is almost no gradual
shrinkage nor shrinkage due to molecular-level deformation.
Natural and synthetic silk is known to manifest piezoelectric
properties in proteins, probably due to its molecular structure.
Silkworm silk was used as the standard for the denier , a measurement
of linear density in fibers.
Silkworm silk therefore has a linear
density of approximately 1 den, or 1.1 dtex .
COMPARISON OF SILK FIBERS
LINEAR DENSITY (DTEX)
Moth : _
Bombyx mori _
Spider : _Argiope aurentia _
Silk emitted by the silkworm consists of two main proteins, sericin
and fibroin , fibroin being the structural center of the silk, and
serecin being the sticky material surrounding it.
Fibroin is made up
of the amino acids Gly -Ser -Gly-Ala -Gly-Ala and forms beta pleated
sheets . Hydrogen bonds form between chains, and side chains form
above and below the plane of the hydrogen bond network.
The high proportion (50%) of glycine allows tight packing. This is
because glycine's R group is only a hydrogen and so is not as
sterically constrained. The addition of alanine and serine makes the
fibres strong and resistant to breaking. This tensile strength is due
to the many interceded hydrogen bonds, and when stretched the force is
applied to these numerous bonds and they do not break.
Silk is resistant to most mineral acids , except for sulfuric acid ,
which dissolves it. It is yellowed by perspiration. Chlorine bleach
will also destroy silk fabrics.
Silk filaments being unravelled from silk cocoons,
Turkey , 2007.
Silk's absorbency makes it comfortable to wear in warm weather and
while active. Its low conductivity keeps warm air close to the skin
during cold weather. It is often used for clothing such as shirts ,
ties , blouses , formal dresses , high fashion clothes, lining ,
lingerie , pajamas , robes , dress suits , sun dresses and Eastern
folk costumes . For practical use, silk is excellent as clothing that
protects from many biting insects that would ordinarily pierce
clothing, such as mosquitoes and horseflies . Silk's attractive lustre
and drape makes it suitable for many furnishing applications. It is
used for upholstery , wall coverings, window treatments (if blended
with another fiber), rugs , bedding and wall hangings. While on the
decline now, due to artificial fibers, silk has had many industrial
and commercial uses, such as in parachutes , bicycle tires , comforter
filling and artillery gunpowder bags.
Fabrics that are often made from silk include charmeuse , habutai ,
chiffon , taffeta , crepe de chine , dupioni , noil , tussah , and
shantung , among others.
A special manufacturing process removes the outer sericin coating of
the silk, which makes it suitable as non-absorbable surgical sutures .
This process has also recently led to the introduction of specialist
silk underclothing, which has been used for skin conditions including
eczema . New uses and manufacturing techniques have been found for
silk for making everything from disposable cups to drug delivery
systems and holograms.
APPLICATIONS AS A BIOMATERIAL
Silk has been considered as a luxurious textile since 3630 BC.
However, it started to serve also as a biomedical material for suture
in surgeries decades ago. In the past 30 years, it has been widely
studied and used as a biomaterial, which refers to materials used for
medical applications in organisms, due to its excellent properties,
including remarkable mechanical properties, comparative
biocompatibility, tunable degradation rates _in vitro_ and _in vivo_,
the ease to load cellular growth factors (for example, BMP-2), and the
ability to be processed into several other formats such as films,
gels, particles, and scaffolds. Silks from _Bombyx mori_, a kind of
cultivated silkworm, are the most widely investigated silks.
Silks derived from _Bombyx mori_ are generally made of two parts: the
silk fibroin fiber which contains a light chain of 25kDa and a heavy
chain of 350kDa (or 390kDa ) linked by a single disulfide bond and a
glue-like protein, sericin , comprising 25 to 30 percentage by weight.
Silk fibroin contains hydrophobic
Beta sheet blocks, interrupted by
small hydrophilic groups. And the beta-sheets contribute much to the
high mechanical strength of silk fibers, which achieves 740 MPa, tens
of times that of poly(lactic acid) and hundreds of times that of
collagen . This impressive mechanical strength has made silk fibroin
very competitive for applications in biomaterials. Indeed, silk fibers
have found their way into tendon tissue engineering, where mechanical
properties matter greatly. In addition, mechanical properties of silks
from various kinds of silkworms vary widely, which provides more
choices for their use in tissue engineering.
Most products fabricated from regenerated silk are weak and brittle,
with only ~1–2% of the mechanical strength of native silk fibers due
to the absence of appropriate secondary and hierarchical structure,
(g/den) Tensile modulus
_Philosamia cynthia ricini_
5 ± 1
87 ± 17
12 ± 5
2.7 ± 0.9
59 ± 18
11 ± 6
3.3 ± 0.8
71 ± 16
10 ± 4
2.8 ± 0.7
58 ± 18
12 ± 6
3.1 ± 0.8
54 ± 14
16 ± 7
3.1 ± 0.8
57 ± 15
15 ± 7
2.8 ± 0.4
48 ± 13
19 ± 7
0.9 ± 0.2
39 ± 6
4 ± 3
Biocompatibility, i.e., the ability to what level the silk will cause
an immune response, is definitely a critical issue for biomaterials.
The biocompatibility of silk arose during its increasing clinical use.
Indeed, wax or silicone is usually used as a coating to avoid fraying
and potential immune responses when silk fibers serve as suture
materials. Although the lack of detailed characterization of silk
fibers, such as the extent of the removal of sericin, the surface
chemical properties of coating material, and the process used, make it
difficult to determine the real immune response of silk fibers in
literature, it is generally believed that sericin is the major cause
of immune response. Thus, the removal of sericin is an essential step
to assure biocompatibility in biomaterial applications of silk.
However, further research fails to prove clearly the contribution of
sericin to inflammatory responses based on isolated sericin and
sericin based biomaterials. In addition, silk fibroin exhibits an
inflammatory response similar to that of tissue culture plastic in
vitro when assessed with human mesenchymal stem cell s (hMSCs) or
lower than collagen and PLA when implant rat MSCs with silk fibroin
films in vivo. Thus, appropriate degumming and sterilization will
assure the biocompatibility of silk fibroin, which is further
validated by in vivo experiments on rats and pigs. There are still
concerns about the long-term safety of silk-based biomaterials in the
human body in contrast to these promising results. Even though silk
sutures serve well, they exist and interact within a limited period
depending on the recovery of wounds (several weeks), much shorter than
that in tissue engineering. Another concern arises from biodegradation
because the biocompatibility of silk fibroin does not necessarily
assure the biocompatibility of the decomposed products. In fact,
different levels of immune responses and diseases have been
triggered by the degraded products of silk fibroin.
Biodegradability (also known as biodegradation )--the ability to be
disintegrated by biological approaches, including bacteria, fungi, and
cells—is another significant property of biomaterials today.
Biodegradable materials can minimize the pain of patients from
surgeries, especially in tissue engineering, there is no need of
surgery in order to remove the scaffold implanted. Wang et al. showed
the in vivo degradation of silk via aqueous 3-D scaffolds implanted
into Lewis rats.
Enzyme s are the means used to achieve degradation of
silk in vitro. Protease XIV from Streptomyces griseus and
α-chymotrypsin from bovine pancreases are the two popular enzymes for
silk degradation. In addition, gamma-radiation , as well as cell
metabolism , can also regulate the degradation of silk.
Compared with synthetic biomaterials such as polyglycolides and
polylactides , silk is obviously advantageous in some aspects in
biodegradation. The acidic degraded products of polyglycolides and
polylactides will decrease the pH of the ambient environment and thus
adversely influence the metabolism of cells, which is not an issue for
silk. In addition, silk materials can retain strength over a desired
period from weeks to months as needed by mediating the content of beta
Thai man spools silk Cocoon
Silk moths lay eggs on specially prepared paper. The eggs hatch and
the caterpillars (silkworms) are fed fresh mulberry leaves. After
about 35 days and 4 moltings, the caterpillars are 10,000 times
heavier than when hatched and are ready to begin spinning a cocoon. A
straw frame is placed over the tray of caterpillars, and each
caterpillar begins spinning a cocoon by moving its head in a pattern.
Two glands produce liquid silk and force it through openings in the
head called spinnerets. Liquid silk is coated in sericin, a
water-soluble protective gum, and solidifies on contact with the air.
Within 2–3 days, the caterpillar spins about 1 mile of filament and
is completely encased in a cocoon. The silk farmers then heat the
cocoons to kill them, leaving some to metamorphose into moths to breed
the next generation of caterpillars. Harvested cocoons are then soaked
in boiling water to soften the sericin holding the silk fibers
together in a cocoon shape. The fibers are then unwound to produce a
continuous thread. Since a single thread is too fine and fragile for
commercial use, anywhere from three to ten strands are spun together
to form a single thread of silk.
As the process of harvesting the silk from the cocoon kills the
larvae by boiling them, sericulture has been criticized by animal
welfare and rights activists. Mohandas Gandhi was critical of silk
production based on the
Ahimsa philosophy which led to promotion of
Ahimsa silk, a type of wild silk made from the cocoons of
wild and semi-wild silk moths. Since silk cultivation kills
silkworms, possibly painfully, People for the Ethical Treatment of
Animals (PETA) urges people not to buy silk items.
International Year of Natural Fibres
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