Ex vivo rheology of spider silk
N. Kojic (1,2), J. Bico (1), C. Clasen (3) & G.H. McKinley (1)
(1) Hatsopoulos Microfluids Laboratory, Department of Mechanical Engineering, MIT, Cambridge, Massachusetts 02139, USA.
(2) Harvard-MIT Division of Health Sciences and Technology,Cambridge, Massachusetts 02139, USA.
(3) Institut für Technishe und Macromolekulare Chemie, 20146 Hamburg, Germany. (3)
The spinning process developed by spiders over millions of years provides a great example of a natural microfluidic system and remains a considerable source of questions1-3. In order to probe the rheological properties of minute amounts of the spinning material extracted ex vivo from the major ampullate gland of a Nephila clavipes spiderwe have developed two new micro-rheometric devices4-6. The present study shows that the spinning liquid is a complex viscoelastic fluid. Its shear viscosity (resistance to flow) decreases ten-fold as it is pushed through the narrow spinning canals of the spider, whereas its extensional viscosity (resistance to stretching) increases more than one hundred-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.