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First published online October 18, 2006
Journal of Experimental Biology 209, 4355-4362 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02516
Ex vivo rheology of spider silk
1 Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering,
MIT
2 Harvard-MIT Division of Health Sciences and Technology, Cambridge, MA
02139, USA
3 PMMH-ESPCI, CNRS UMR 7636, 75231 Paris Cedex 05, France
4 Institut für Technische und Makromolekulare Chemie, 20146 Hamburg,
Germany
5 Departement Chemische Ingenieurstechnieken, Katholieke Universiteit
Leuven, 2001 Heverlee, België
* Author for correspondence (e-mail: kojic{at}mit.edu)
Accepted 25 August 2006
We investigate the rheological properties of microliter quantities of the
spinning material extracted ex vivo from the major ampullate gland of
a Nephila clavipes spider using two new micro-rheometric devices. A
sliding plate micro-rheometer is employed to measure the steady-state shear
viscosity of 
1 µl samples of silk dope from individual biological
specimens. The steady shear viscosity of the spinning solution is found to be
highly shear-thinning, with a power-law index consistent with values expected
for liquid crystalline solutions. Calculations show that the viscosity of the
fluid decreases 10-fold as it flows through the narrow spinning canals of the
spider. By contrast, measurements in a microcapillary extensional rheometer
show that the transient extensional viscosity (i.e. the viscoelastic
resistance to stretching) of the spinning fluid increases more than 100-fold
during the spinning process. Quantifying the properties of native spinning
solutions provides new guidance for adjusting the spinning processes of
synthetic or genetically engineered silks to match those of the spider.
Key words: silk rheology, Nephila clavipes, micro-rheometry, extensional viscosity
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