Spider silk fibre extrusion: combined wide- and small-angle X-ray microdiffraction experiments

The major and minor ampullate silks from live Nephila senegalensis (Tetragn athidae) and the major ampullate silk from Euprostenops spp. (Pisauridae) s piders 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 al ready contains P-sheet poly(alanine) crystallites. SAXS data suggest the pr esence of microfibrils with an axial repeating period of approximately 8 nm for both Nephila and Euprostenops. Minor ampullate (MI) Nephila silk, howe ver, does not show this axial repeat which is probably due to a higher amou nt 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 WAX S patterns. At high reeling speeds, bound water is co-extruded with the fib re. It can be squeezed out of the fibre by friction at a needle. Under natu ral 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 dr agline production. (C) 2001 Published by Elsevier Science B.V.