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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

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Ex vivo rheology of spider silk

N. Kojic^1,2,*, J. Bico^1,3, C. Clasen^4,5 and G. H. McKinley¹

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

View larger version (76K): [in a new window]   Fig. 1. (a) Adult female Nephila Clavipes (golden-orb) spider provided by the Miami Metrozoo, Florida. (b) (A) Dissected major ampullate (MA) gland of the spider. The 1 µl blob (B) protruding through a rupture of the gland wall near the spinning canal (C) was used for the rheology experiments.

View larger version (26K): [in a new window]   Fig. 2. (a) Schematic diagram of the flexure-based micro-rheometer. The fluid sample is sheared between two interferometrically aligned flat plates (A). The compound flexure system (B) is actuated by an `inchworm' motor (C) and provides a planar (Couette) shear flow. The shear stress is deduced from the corresponding deflection of the top fixture as detected by an inductive sensor (D). (b) Shear viscosity of the native silk dope. Diamonds (and shaded red area) correspond to Nephila clavipes spider; open circles (and blue shaded area) are from Bombyx mori silkworm. The solid lines (blue for silkworm and red for spider) represent the Carreau-Yasuda fit from Eqn 2 to experimental data (markers). Reproducibility was confirmed by testing specimens from two other spiders and silkworms whose abdomens were similar in size. The variation in the data is represented by the shaded band.

View larger version (25K): [in a new window]   Fig. 3. (a) Radius R of necking thread formed from the ex vivo-obtained Nephila dope (measured at thread midpoint, see inset in b) in blue markers. The solid red line represents the model fit using the processability parameter of P=2.715x10-2. (b) The transient extensional rheology of ex vivo spider dope. The extensional viscosity is shown as a function of the total strain in the material. Here, R0 is the initial radius of the thread measured at the midpoint between the plates with a laser micrometer. The decrease of the midpoint radius R was monitored over time (see a). The extensional viscosity was then deduced from Eqn 1 and is represented by the markers. The solid line is an analytical fit of these values. For low strains, we obtain the limit e30=11 400 Pa.s as expected for a Newtonian liquid. Inset, a silk thread of diameter 40 µm formed by separating the plates to a distance of 5 mm and allowing the thread to neck under the action of capillarity and viscoelastic stresses (scale bar, 1 mm).