Silkworm silks, properties

The density of raw silk fibers is about 1.33-1.45 g cm . Raw cocoon silk fibers have good extensibility (25-35%) and reasonably good strength (300-600 MPa). For different silkworms, silk properties also are very different Some silk has strong mechanical properties, and other silk shows good biodegradabihty. The structure of the different types of silk has become a research focus. Recently, the diversity of test instruments is also facilitating the study of silk structure [21, 22]. 

Films or membranes of silkworm silk have been produced by air-drying aqueous solutions prepared from the concentrated salts, followed by dialysis (11,28). The films, which are water soluble, generally contain silk in the silk I conformation with a significant content of random coil. Many different treatments have been used to modify these films to decrease their water solubiUty by converting silk I to silk II in a process found usehil for enzyme entrapment (28). Silk membranes have also been cast from fibroin solutions and characterized for permeation properties. Oxygen and water vapor transmission rates were dependent on the exposure conditions to methanol to faciUtate the conversion to silk II (29). Thin monolayer films have been formed from solubilized silkworm silk using Langmuir techniques to faciUtate stmctural characterization of the protein (30). ResolubiLized silkworm cocoon silk has been spun into fibers (31), as have recombinant silkworm silks (32). 

Although the amino acid sequence as well as the secondary structure of fibroin differs from those of spidroin, the fibers spun from these proteins, that is, silkworm silk and spider silk have comparable mechanical properties. These may be attributed to the structural characteristics, both at the molecular and filament level. The superior mechanical properties of silk-based materials, such as films, coatings, scaffolds, and fibers produced using reconstituted or recombinant silk proteins, are determined by their condensed structures. 

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. 

Perez-Rigueiro, J. Viney, C. Llorca, J. Slices, M. Mechanical properties of single-brin silkworm silk. J. Appl Polym. Sci. 75 1270-1277 (2000). 

Interest in silk-based proteins, particularly those inspired by silkworm and spider silks, is fueled in large part by the extraordinary mechanical properties exhibited by these materials as well as by the continued commercial use of silkworm silks in textiles. Certain forms of spider silks have remarkable combinations of strength and elasticity that could be beneficial for a broad range of applications, from biomedical implants to industrial ropes and cables. We refer to the contribution by Kaplan for more in-depth discussion of the properties and synthesis of silk proteins. 

Spider silks can be expected to be utilized as a new material instead of silkworm silks, since the physicochemical properties of spider silks, such as heat-resistance,UV-resistance, mechanical strength,and flexibility are better. 

Electrospun SF-based fibers were prepared from aqueous regenerated silkworm silk Bombyx mon)/PEO solutions to be used as scaffolds for tissue engineering (Jin et al. 2004). PEO supplied good mechanical properties to the electrospun fibers. An MeOH posttreatment induced an amorphous to silk p-sheet conformational transition. The electrospun silk membrane was washed with water to remove PEO in order to improve the cell adhesion and proliferation. These silk fibrous membranes were nonimmunogenic, biocompatible, and capable of supporting bone marrow stromal cell (BMSC) attachment. In another work, electrospun wool keratin/silk fibroin (WK/SF) blend nanofibers exhibited higher Cu + adsorption capacity than SF nanofibrous membrane (Ki et al. 2007). 

Silk is a natural protein fiber excreted by the moth larva Boinhvx mori. better known as the common silkworm. Silk is a fine continuous monofilament fiber of high luster and strength and is highly valued as a prestige fiber. Because of its high cost, it finds very limited use in textiles. A minor amount of wild tussah silk is produced for specialty items. Attempts have been made to commercialize silk from spiders over the years, but all ventures have met with failure. Domestic and wild silks are essentially uncrosslinked and relatively simple in amino acid composition compared to the keratin fibers. The properties for silk listed here are for silk formed by Bombvx mori moth larvae. 

Silk materials are envisaged for various biomedical, cosmetic, and technical applications. These applications have been mainly based on silkworm silk [59, 103, 104]. Since spider and insect silks have several features in common, the established applications for silkworm silks are also conceivable for spider silk, bearing in mind that spider silk might provide additional outstanding properties. 

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