The Macro Side of Spider Silk

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The Macro Side of Spider Silk
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• Spider Silk is a fibrous protein secreted as a
  fluid which hardens as it oozes out of the
  spiders abdomen.
• As the fluid oozes out, the protein molecules are
  aligned in such a way that they form a solid.

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• The spider hauls out the silk with its legs,
  stretching, fluffing it up or changing it in
  other ways to suit the purpose at hand.
• Spiders use this silk to build webs to capture
  insects for their food.
• Spider webs need to be strong and pliable to be
  able to capture these insects.

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• Spider Silk is 5x stronger than steel of the same
  diameter.
• A section of silk can be stretched 2-4 times its
  length.
• It is these properties of strength and
  elasticity, that gives spider silk the ability to
  withstand the impact of insects.

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• Seven types of silk glands
• For wrapping prey
• For wrapping eggs
• Non-sticky for draglines and for the frames of a
  web
• For attachment of the web at certain points
• For the sticky fibers the cover the web
• A second type of wrapping prey
• A second type of sticky fibers that are very
  elastic (used for capturing flying insects)

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• The extraordinary abilities of spider silk makes
  it incredibly useful to spiders and humans as
  well.
• It is these properties that have scientists
  interested in spider silk. Maybe spider silks
  makeup can be used in other areas.

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Molecular Structure of Spider Silk
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What makes Spider Silk so Special?

• One of the toughest known fibers (MJ/m3)
• Produced Biologically
• Made of Protein
• Can stretch
• more than
• many other
• fibers

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General Structure A rubber supported by crystals
Taken from J. M. Gosline 1999
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Amino Acid Sequences Create Spider Silk
G- Glycine A- Alanine S- Serine P- Proline Q-
Glutamine Y- Tyrosine L- Leucine V- Valine R-
Arginine X- either Alanine, Serine, Valine,
or Tyrosine
Yellow highlighted Sequences show the
patterns responsible for forming beta sheets
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Diagram of the proposed model for the molecular
arrangement of alanine residues in a fiber of
spider dragline silk. Highly oriented
alanine-rich crystals of -sheets (rectangles) and
weakly oriented yet crystalline unaggregated
sheets (canted sheet-like structures) are
depicted in an amorphous glycine-rich matrix
(curved lines). In reality, the glycine-rich
matrix composes about 70 percent of the fiber in
this drawing it has been largely suppressed for
clarity.
Picture and quote from http//www.nap.edu/readingr
oom/books/bmm/
Beta Sheet Structure From http//www.xs4all.nl/7e
ednieuw/Spiders /Info/spindraad.htm
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Spider Silk Fiber Being Stretched
Spider Silk shown being stretched at 1x, 5x, and
20x its normal length From http//www.xs4all.nl/
7eednieuw/Spiders/Info/spindraad.htm
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Spider Silk Model
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Goals of Model

• Visually represent combination and attachments of
  beta sheets and connections
• Visually portray randomness of structure
• Examine combinations of two different parts to
  create final improved structure
• Functionally demonstrate durability and strength
• Functionally show elastic and inelastic expanding
  of spider web

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Beta Sheets and Connections

• Model uses strong but inflexible beta sheets
  connected with weak but flexible and multiple
  connections

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Testing

• Each individual part must be tested before the
  whole (rubber bands and beta sheets)
• Test for mass compared to weight and stress can
  withstand and hold
• Test for elasticity and displacement related to
  weight
• Hung from ceiling and stressed with weights
  attached to bottom, measuring distance displaced

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Testing in Action
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Results Notes

• Had to split into two separate graphs due to beta
  sheet expansion
• Graphed displacement as a function of force
  because force was independent variable
• K constant (elasticity) is the inverse of the
  slope
• Beta sheet had no elasticity, thus could not be
  graphed, only numerically analyzed.

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Beta Sheet Results

• Mass of 4.0g
• Can hold 6.37 N before expanding, which is about
  1000X own weight
• Initially 8cm and expands to 23cm inelastically
  without breaking, 3X its length
• After expanding, beta sheet seemed unbreakable
  though experiment was limited to 42 N
• Model contained 13 beta sheets

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Results of Rubber Band

• Mass of 0.1g
• Can hold 10.29 N before breaking, which is about
  10,000X its own weight
• Initial length of 4cm and can expand to about
  48cm
• Can expand to about 12X its initial length
• K constant is about 5000 /- 600 N/m
• Model contains about 32 rubber bands/connections

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Observations

• The rubber band is both stronger and more elastic
  than the beta sheet before expansion
• The beta sheet after expansion can withstand much
  more weight than the rubber band
• There exists an average of about 2.5 connections
  per beta sheet
• The connections are not spread evenly throughout

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Model Testing

• Mass of 60.5g
• Initially 42cm and expanded to 109cm
• Two beta sheets expanded at approximately 10,000
  N
• Can hold about 16,000 N before breaking, which is
  about 27X its weight
• K constant 18.55 /- 0.02 N/m pre-expansion
• K constant 21.98 /- 0.01 N/m post-expansion

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Conclusions

• Combined properties of both beta sheets and
  rubber band connections
• Model was
• less elastic than rubber band
• Elastic to a degree, but inelastic after certain
  point
• Could hold more than rubber band, but less than
  beta sheet after expansion (and less per mass
  than both)
• Became less elastic as weight was added
• Broke at the weakest connection

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Limitations, Errors, Discrepancies

• Limited to parts given readily available, could
  not have stronger than rubber band
• Only could attach so many bands to plastic balls
• Ratio should be much higher than 2.51
• Had to tie rubber bands on, not strong connection
• Break at weakest link, emphasis on chaos
  detracted from distributed support

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Facts
A web with pencil thin strands of spider silk can
halt a Boeing 747 Spider silk stretch over 30
without snapping Silk strands thinner than your
hair are 5 times stronger than steel wire of the
same diameter Spider silk genes have been spliced
into cells from the udders of goats and has
worked well enough for scientists to produce high
quality silk
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