The Spinning Mechanism Of Spider Silk

Spider silk has attracted a great number of researchers' attention because of it's high strength , high elasticity and high break energy from 70's, and until 20th 90's the research climax came. At present, artificial spidroin produced by genetic engineering has got first fruits and recombinant spider silk with good mechanical properties has been made, but there is still some difference in mechanical properties between the artificial spider silk and the nature one. The mechanical properties not only correlate with it's amino acid compositions and sequences, but also depend on the molecular structures and morphologies. It is necessary to explore the change of microstructures in the spinning process of spider silk, and study the relationship between spinning condition, spinning method and properties to know how a spider spins it's silk, which also provide some theory bases for producing artificial spider silk.Araneus Ventrcosus spiders are collected as our study object that widely distribute in China. To realize the molecular compositions and bio-spinning mechanisms of spidroin in spider major ampullate, the molecular weight and amino acid compositions of spidrion solution were measured and compared with that of dragline silk. The molecular conformations and morphologies of spidroin and dragline silk in different spinning phases were determined by circular dichroism (CD) spectroscopy and laser Raman spectroscopy. To understand how the spinning speed and method influence structures and properties of spider dragline silk, the molecular conformations and microstructures of dragline silk fibers obtained at several rolling speeds and secreted by a falling spider were investigated by laser Raman spectrum and atomic force microscopy (AFM). The mechanical properties of these silk fibers were also measured. To explore the control capability of spider on the spinning process and it's influence on the mechanical properties of dragline silk, spiders were anaesthetized and the mechanical properties of dragline silk reeled from an being anaesthetized spider were measured. We also studied the relationship between spinning tension, humidity and the mechanical properties of dragline silk. The results showed thatspidroin in spider major ampullate had two molecular weights, 200KDa and 300KDa and were mainly composed of Alanine, Glycine and Glutamine. The structure of spider spidroin changed during flowing through the major ampullate because of the shear stress, flow elongation, change of duct diameter etc., some of the a -helix and random coil molecules turned into B -sheet ones. After the dragline silk leaving the spinneret, the fibers had more highly oriented molecules with B-sheet conformations. Spinning speed and method both affected the structures and properties of spider dragline silk. The break strength of dragline silk had a maximum in the rolling speed range of 10mm/s to 20mm/s. At that point, there was also the highest intensity corresponding with B-sheet conformation and the molecular orientation was the best The break strain and surface toughness of dragline silk had decrease trends. AFM images showed the surface roughness of dragline silk varied with the spinning speed. The break strength, break strain and toughness of dragline silk obtained from a falling spider were bigger than that of silk reeled at the similar speed. The former had much more B-sheet molecules with higher orientation and AFM results showed that their microstructures were different. The environment condition during spinning such as anaesthetization, humidity and spinning tension could change the mechanical properties of dragline silk.