Spider Dragline Silk Applications in Polymer Science - Duke University

Spider Dragline Silk Applications
in Polymer Science
Hieu T. Nhan
April 12, 2004
Duke University

Outline
•Spiders and Spider Silk
•Polymers (Polycarbonate)
•Applications

Introduction
•Spider silk evolution—400 million years
–Tough stuff!
–Entire genetic makeup unknown.
–Bulk production?

Spider Anatomy

Spider Anatomy

Silk Composition
•All proteins are made of amino acids
–Spider silk is composed primarily of the
three simplest forms of amino acids:
(1) Glycine
(2) Alanine
(3) Serine

Silk Composition

Silk Composition

Silk Composition
•α-helices primarily combined with other materials
– Provides only some of the needed properties
•β-sheets constitute the majority of silk proteins
– Provides most of the needed properties

Sequencing
•Various silk proteins studied and four types of shared
amino acid motifs have been found
– (1) GPGGX/GPGQQ
– (2) GGX
– (3) poly-Ala/poly-Gly-Ala
– (4) ‘spacer’ sequence which do not conform to
typical amino acid sequences of spider silks

•GPGGX/GPGQQ
Sequencing
– Suggested conformation: β-spiral
– Spring-like structure gives the elastic properties
– Only ampullate and flagelliform silks contain this
sequence

•poly-Ala
• Suggested conformation: Linked β-sheet
• Presumed to be the crystalline areas which bind
protein molecules together, providing tensile
strength
•poly-Gly-Ala
Sequencing
• Suggested conformation: Linked β-sheet
• Lower binding energy, therefore lower tensile
strength than poly-Ala

Sequencing

Mechanical Properties

Mechanical Properties

Mechanical Properties
The material is elastic and only
breaks at between 2 - 4 times its
length. In the pictures a strand of
a social spider, stegodyphus
sarasinorum, is shown as normal
size, stretched 5 times and 20
times its original length.

•Why PC?
Polycarbonate
• Polycarbonate is tough.
• Has great optical properties.
• Used in the area of safety (helmets, glasses, etc.)
• Military uses

•Goal: Increase toughness
– Two ways to do it:
Polycarbonate
(1) Increase strength
(2) Increase the extensibility

•Which do we choose?
Polycarbonate
Property Spider Silk Polycarbonate
Ultimate Tensile Strength 1.1 GPa 72 GPa
Elongation at yield ~27% ~6%

Fabrication
•Why not just reproduce spider silk?
• Entire genetic makeup of silk is complicated.
• Optical properties of pure spider silk not optimal
like PC.
• Mass production on a mechanical level has not
been done.
• Nexia, US Army, and……goats?

Fabrication
•Methods already used in PC to increase toughness
– Increasing molecular weight
– Addition of ‘other’ polymers
Similar idea to Acrylonitrile/butidiene/styrene
(ABS) co-polymer system

Synthesis Proposal
•Addition of known basic amino acid chains to PC
• Choose GPGGX sequence (adds elasticity)
• Synthetic chemistry

Summary
•Evolution of spider silk occurred over 400 million years
•A lot has been learned, but a lot left unknown
•Synthesis of silk --> mammalian epithelial cells
•Use knowledge to alter other polymeric systems

Questions
?

Reference
s
1) Alberts, Bray, Dennis Bray, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter,
Essential Cell Biology, An Introduction to Molecular Biology of the Cell, 1997, Garland Publishing, Inc.,
pp. 140-148
2) Bottenbruch, Ludwig, Engineering Thermoplastics—Polycarbonates, Polyacetals, Polyesters, Cellulose
Esters, 1996, Hanser/Gardner Publications, Inc., Cincinatti
3) Christopher, William F., Daniel W. Fox, Polycarbonates, 1962, Reinhold Publishing Corporation, New York
4) Clark, Catherine L., Spiderwebs and Silk—Tracing Evolution from Molecules to Genes to Phenotypes, 2003,
Oxford University Press
5) Foelix, Rainer F., Biology of Spiders, 1996, Oxford University Press, pp. 110-149
6) Gosline, J.M., P.A. Guerette, C.S. Ortlepp, K.N. Savage, The Mechanical Design of Spider Silk: From
Fibroin Sequence to Mechanical Function, 16 November 1999, Journal of Experimental Biology, 202, 325-
3303
7) Hayashi, Cheryl Y., Nichola H. Shipley, Randolph V. Lewis, Hypotheses That Correlate the Sequence,
Structure, and Mechanical Properties of Spider Silk Proteins, 1999, International Journal of Biological
Macromolecules, 24, pp. 271-275
8) Hinman, Michael B. Justin A. Jones, Randolph V. Lewis, Synthetic Spider Silk: A Modular Fiber,
September 2000, Tibtech, Vol. 18, pp. 374-379
9) Nieuwenhuys, Ed, Spider Silk, http://www.xs4all.nl/~ednieuw/Spiders/Info/spindraad.htm, Accessed 03
March 2004, Available

Reference
s
11) Fedic, Robert, Michal Zurovec, Frantisek Sehnal, Correlation between Fibroin Amino Acid Sequence and
Physical Silk Properties, 12 September 2003, Vol. 278, No. 37, pp 35255-35264
12) Hayashi, Cheryl Y., Randolph V. Lewis, Molecular Architecture and Evolution of a Modular Spider Silk
Protein Gene, 25 February 2000, Science, Vol. 287, pp. 1477-1479
13) Stupp, Samuel I., Paul V. Braun, Molecular Manipulation of Microstructures: Biomaterials, Ceramics, and
Semiconductors, 29 August 1997, Science, Vol. 277, pp. 1242-1248
14) Lazaris, Anthoula, Steven Arcidiacono, Yue Huang, Jiang-Feng Zhou, Francois Duguay, Nathalie Chretien,
Elizabeth A. Walsh, Jason W. Soares, Costas N. Karatzas, Spider Silk Fibers Spun from Soluble
Recombinant Silk Produced in Mammalian Cells, 18 January 2002, Science, Vol. 295, pp. 472-476
15) van Beek, J.D., S. Hess, F. Vollrath, B.H. Meier, The Molecular Structure of Spider Dragline Silk: Folding
and Orientation of the Protein Backbone
16) Witt, Peter N., Charles F. Reed, David B. Peakall, A Spider’s Web—Problems in Regulatory Biology, 1968,
Springer Verlag New York Inc.

•GGX
Sequencing
– Suggested conformation: Helical
– Could serve as link between crystalline β-sheet
regions and less rigid protein structures
•‘Spacer’ Sequence
•Suggested conformation: Unknown
•Could serve as alternative structure for pre-drawn, liquid
form

Mechanical Properties