Spider silk fibre extrusion: combined wide- and small-angle X-ray microdiffraction experiments.
The major and minor ampullate silks from live Nephila senegalensis (Tetragnathidae) and the major ampullate silk from Euprostenops spp. (Pisauridae) spiders were investigated in situ by X-ray diffraction during forced silking. Wide- (WAXS) and small-angle (SAXS) scattering patterns were obtained at the same time. WAXS data show that the thread at the exit of the spigots already contains beta-sheet poly(alanine) crystallites. SAXS data suggest the presence of microfibrils with an axial repeating period of approximately 8 nm for both Nephila and Euprostenops. Minor ampullate (MI) Nephila silk, however, does not show this axial repeat which is probably due to a higher amount of crystal forming poly(alanine). A microfibrillar morphology, connected by a network of random polymer chains, can explain the presence of highly oriented crystallites, an oriented halo and a diffuse background in the WAXS patterns. At high reeling speeds, bound water is co-extruded with the fibre. It can be squeezed out of the fibre by friction at a needle. Under natural conditions it is the spider's tarsal claws which might serve to squeeze out the water to improve the mechanical properties of the thread during dragline production.
Riekel
C
C
European Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble Cedex, France. riekel@esrf.fr
Vollrath
F
F
D000818:Animals; D019476:Insect Proteins / Q000737:chemistry*; D047011:Silk; D013045:Species Specificity; D013112:Spiders; D014961:X-Ray Diffraction / Q000295:instrumentation* / Q000379:methods*
D019476:Insect Proteins; D047011:Silk