Mechanical testing of spider silk

Bo Madsen

Materials Research DivisionRisø National Laboratory for Sustainable Energy

Technical University of DenmarkDenmark

COST Action FP0802 – Workshop on single fiber testing and modeling – Stockholm, Sweden, 4-5 Nov 2009

Typical properties of spider silk (Nephila edulis, major ampullate silk):Diameter: 3 μmInitial modulus: 8 GPaYield stress: 150 MPaBreaking stress: 1200 MPa Breaking strain: 0.40Breaking energy: 200 MJ/m3

Fixation of spider

Experimental procedure for tensile testing of spider silk

Sampling of silk from spider

Experimental procedure for tensile testing of spider silk

Sampling of silk from take-up spool

Experimental procedure for tensile testing of spider silk

Mounting of silk on tensile testing instrument

Experimental procedure for tensile testing of spider silk

Measurement of load-elongation behaviour of silk

Control of motor

LabView programson computer

Recording of data

Experimental procedure for tensile testing of spider silk

Data sampling panel

Motor setting panel

Instrument calibration panel

Data analysis panel

Measurement of load-elongation behaviour of silk

Experimental procedure for tensile testing of spider silk

Measurement of silk diameter

5 μm

Experimental procedure for tensile testing of spider silk

Video showing the experimental procedure

Experimental procedure for tensile testing of spider silk

Assessment of experimental procedure

Effect of glue type

Effect of stretching of silk thread

Assessment of experimental procedure

Diameter variation and roundness of silk

o Normal silk thread• Twisted silk thread

Assessment of experimental procedure

Variation in mechanical properties

Assessment of experimental procedure

Results

Difference in mechanical properties of silk from different spider species

1: Pisauridae2: Cyrtophora citricola3: Latrodectus mactans

4: Nephila edulis5: Araneus diadematus

Results

Effect of reeling speed

0.01 0.1 1 10 100 1000

Reeling speed (mm/s)

For “normal” reeling speedsbetween 0.01 and 20 mm/s:

-Thread diameter is decreased

- Breaking stress is increased

- Breaking strain is decreased

- Breaking energy is unchanged

Results

Effect of CO2 anesthesia

Silking time (s)

--- Control, no CO2

• CO2 between 120-210 so CO2 between 120-540 s

Results

Effect of CO2 anesthesia

Results

Effect of CO2 anesthesia

A: Before CO2 exposure

B: “Thinning” response

C: “Fibrillation” response after short time of CO2 exposure

D: “Fibrillation” response after long time of CO2 exposure

E: Example of sudden change in diameter

5 μm

5 μm

Current research on spider silk

Oxford Silk Group: http://users.ox.ac.uk/~abrg/spider_site/

References

• Madsen B. (1999). Mechanical properties of spider silk. Master thesis. Department of Zoology, University of Aarhus, Denmark.

• Madsen B., Shao Z.Z. and Vollrath F. (1999). Variability in themechanical properties of spider silks on three levels: interspecific, intraspecific and intraindividual. International Journal of Biological Macromolecules. 24: 301-306.

• Madsen B. and Vollrath F. (2000). Mechanics and morphology of silk drawn from anaesthetized spiders. Naturwissenschaften 87: 148-153.

• Riekel C., Madsen B., Knight D. and Vollrath F. (2000). X-ray diffraction on spider silk during controlled extrusion under a synchroton radiation X-ray beam. Biomacromolecules 1: 622-626.

• Vollrath F., Madsen B. and Shao Z.Z. (2001). The effect of spinning conditions on the mechanics of a spider’s dragline silk. The Royal Society, Proceedings in Biology. 268: 2339-2346.