Spider Dragline Silk Applicationsin Polymer Science

Hieu T. NhanApril 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 sharedamino acid motifs have been found

– (1) GPGGX/GPGQQ

– (2) GGX

– (3) poly-Ala/poly-Gly-Ala

– (4) ‘spacer’ sequence which do not conform totypical amino acid sequences of spider silks

Sequencing

•GPGGX/GPGQQ

– Suggested conformation: β-spiral

– Spring-like structure gives the elastic properties

– Only ampullate and flagelliform silks contain thissequence

•poly-Ala

• Suggested conformation: Linked β-sheet

• Presumed to be the crystalline areas which bindprotein molecules together, providing tensilestrength

•poly-Gly-Ala

• Suggested conformation: Linked β-sheet

• Lower binding energy, therefore lower tensilestrength than poly-Ala

Sequencing

Sequencing

Mechanical Properties

Mechanical Properties

The material is elastic and onlybreaks at between 2 - 4 times itslength. In the pictures a strand ofa social spider, stegodyphussarasinorum, is shown as normalsize, stretched 5 times and 20times its original length.

Mechanical Properties

Polycarbonate

•Why PC?

• 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:

(1) Increase strength

(2) Increase the extensibility

Polycarbonate

Polycarbonate

•Which do we choose?

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 optimallike PC.

• Mass production on a mechanical level has notbeen 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?

References

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, CelluloseEsters, 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: FromFibroin 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 BiologicalMacromolecules, 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 03March 2004, Available

References

11) Fedic, Robert, Michal Zurovec, Frantisek Sehnal, Correlation between Fibroin Amino Acid Sequence andPhysical 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 SilkProtein Gene, 25 February 2000, Science, Vol. 287, pp. 1477-1479

13) Stupp, Samuel I., Paul V. Braun, Molecular Manipulation of Microstructures: Biomaterials, Ceramics, andSemiconductors, 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 SolubleRecombinant 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: Foldingand 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.

Sequencing

•GGX

– Suggested conformation: Helical

– Could serve as link between crystalline β-sheetregions and less rigid protein structures

•‘Spacer’ Sequence

•Suggested conformation: Unknown

•Could serve as alternative structure for pre-drawn, liquidform

Mechanical Properties