Spinning process, spiders

From the viewpoint of zootaxa, the silkworm and the spider belong to insect and arachnid of arthropod, respectively. Their silk proteins (fibroin for silkworm silk and spidroin for spider major ampullate silk) do not have any genetic heritage in common and their amino acids sequence compositions are different too. However, the silkworm and spider employ a similar spinning process to produce silk. Furthermore, the silkworm silk and the major ampullate silk have a number of similar structural characteristics, both at the level of the secondary protein structure and the condensed silk morphology. Therefore, for the sake of convenience, they are discussed together in some parts of this text. 

As to fibers, it was reported that the inferior mechanical properties of silk from cocoons compared to spider silk result from the silkworm spinning process. If silkworm silk is processed at a constant pulling speed rather than constant force pulling, it possesses excellent properties, approaching the spider dragline silk (Shao and Vollrath, 2002). This suggests that the silkworm silk has the potential to produce better fibers, and the regenerated fibroin, which is easy to harvest, has the possibility to be fabricated into a reconstituted super-fiber. 

Nevertheless, silk spinning remains a very complex process. Spiders and silkworms not only have a set of well-developed spinning glands but also have a set of well-defined and controlled chemical boundary conditions. Besides the composition of the spinning dope, the spinning techniques and the combination of chemical parameters (pH and metallic ions) must be considered and optimized. 

In man-made fibres, any stretching will irreversibly alter the crystallinity and there is no control of the lateral size of polymer crystals. Semicrystalline polymer networks typically consist of platelet type crystals whose width exceeds their thickness by several order of magnitudes because only the thickness is controlled by the chain folding [61]. In contrast to synthetic fibres, spider silk does not need any mechanical treatment by external forces the constituents self-assemble directly during the spinning-process. These examples clearly demonstrate the need for more detailed control of the mesoscopic structures for further development of man-made materials. 

Spinning process [17,18], as well as on tuned dopants in the polymer feedstock [19]. Several factors may contribute to the toughness of a spider silk fibre ... 

In the fibers produced from lyotropic spinning dopes, there still appear to be limitations on the ultimate physical properties due to higher-order morphological defects (the periodic director-orientation distortions alluded to earlier) [115]. In this context, much experimental and theoretical work remains to be done to delineate those parameters that control disclination textures and director patterns created by complex shear fields encountered in processing LCPs. As is typically the case, there are natural systems wherein these difficulties appear to have been optimally minimized spiders spin nearly defect-free fibers from a mesomorphic form of silk [116]. Consequently, efforts to analyze the spinning process - the spinner draw-down geometry and its associated shear field - used by arachnids are under way. 

The major textiles before the 1920s were wool (animal hair), cotton (a seed pod), and silk (a protein used for making cocoons). The silk spider also had a clever device in its abdomen for expelling a gel in a sac through a spinneret where reactions with air made a solid fiber with a uniform cross section. DuPont took this idea in spinning hydrolyzed cellulose into rayon fibers and scaling-the process up far beyond the needs of spiders. 

Silkworms and spiders have developed a set of complicated but efficient spinning systems. They can produce silks with different properties under mild, ambient conditions in an aqueous solution. Considering the supreme properties, they really employ an efficient procedure with minimum energy consumption. Only the conformation transitions happen and no active enzymes work in the solidifying process. As a result, there is a great deal of interest in understanding the precise details of how silk forms from silk proteins - whether in vivo or in artificial circumstances (Fahnestock and Steinbuchel, 2003 Vollrath and Knight, 2001). 

With the exception of silk, which the silkworm or spider extrudes as a continuous filament, natural fibers are of finite length. For textile use, these need to be cleaned and then spun into threads or yams. Synthetic fibers, on the other hand, are continuous filaments produced from a solution or melt. The term spinning is used to describe the formation of synthetic fibers, but in this sense it has no relation to the process for combining fibers into threads. 

Nexia is already working with the US army to develop bulletproof vests and surgical suture material from spider silk. The team produced soluble recombinant spider silk proteins with molecular masses of 60-140 kDa (Lazaris ef al., 2002). They were able to wet spin the silk monofilaments derived from a concentrated aqueous solution of soluble recombinant spider silk protein under conditions of low shear and coagulation. The spun fibers were water-insoluble with diameters ranging from 10 to 40 pm and exhibited toughness and modulus values comparable to those of native dragline silks but had lower tenacity. They anticipate that the manufacturing processes for these products would be more environmental friendly than the production of conventional plastics. 

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