Mechanical properties spider silk

Hayash C.I., Shipley N., and Lewis R., Hypotheses that correlate the sequence, structure, and mechanical properties of spider silk proteins, Int. J. Biol. Macromol., 24, 271, 1999. 

Raw silk was dissolved in hexafluoro-iso-propanol (HFIP) [17, 33]. A typical working concentration for spinning was 2.5% (w/v) silk fibroin in HFIP. The spinning solution was pressed through a small needle (0 80-250 pm) into a precipitation bath (methanol for Bombyx mori silk proteins and acetone for Nephila clavipes silk proteins) and the silk solution immediately precipitated as a fiber. The best performing fibers approached the maximum strength measured for native fibers of Bombyx mori, but did not achieve the mechanical properties of natural spider silk. 

Porter, D., Vollrath, F., and Shao, J. Z. (2005). Predicting the mechanical properties of spider silk as a model nanostructured polymer. Eur. Phys. J. E 16, 199-206. 

Shao, Z., Hu, X. W., Frische, S., and Vollrath, F. (1999). Heterogeneous morphology of Nephila edulis spider silk and its significance for mechanical properties. Polymer 40, 4709-4711. 

In Nature, there are many examples of protein and peptide molecular self-assembly. Of the genetically engineered fibrous proteins, collagen, spider silks, and elastin have received attention due to their mechanical and biological properties which can be used for biomaterials and tissue engineering. 

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. 

The attractive properties of silk fibers as a natural, sustainable product have inspired researchers to look for options to fabricate such fibers without the use of worms or spiders. Furthermore, these natural polymers, silk proteins (both fibroin and spidroin), allow for adjustable mechanical properties, thermal resistance (Drummy et al., 2005 Motta et al., 2002), as well as biomedical compatibility (Vepari and Kaplan, 2007). 

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. 

Liu, Y., Shao, Z.Z., and Vollrath, F. "Relationships between supercontraction and mechanical properties of spider silk". Nat. Mater. 4(12), 901-905 (2005b). 

The next example of the mechanical properties of a standard polypeptide structure is that of silk, which is composed of extended (1 sheets. The stress-strain curve for drag silk of the spider (Figure 6.3) shows an ultimate tensile strength (UTS) of about 800MPa, a modulus of about 7.0 GPa, and a strain at failure of about 30%.The value of the UTS and modulus appears to be higher than that of collagen as we show in Chapter 7 after correction for orientation effects and other complications the values for collagen are... 

The key components in all sophisticated biological materials are the macromolecules that the cells produce and subsequently incorporate into the material. These include proteins, glycoproteins, proteoglycans, lipid assemblies and polysaccharides. Many biological materials are composed almost entirely of these assembled macromolecules. Common examples are the cuticles of many insects, the skin and tendons of vertebrates or the silk of spider webs. A very widespread adaptation is to stiffen the material by the introduction of a mineral phase. Common mineralized biological materials include the shells of mollusks, the carapaces of crustaceans, and the bones and teeth of vertebrates. Many of them are composite materials and are known to possess remarkable mechanical properties, especially when taking into account that they form at ambient temperatures and pressures, and that their mineral components are often commonplace materials with rather poor natural mechanical properties... 

The cocoon silk of the silk worm is an excellent textile material and the commercial activity in this realm attests to that. Its mechanical properties, however, are rather modest. This has been attributed to the fact that superior mechanical characteristics are not required in the cocoon. On the other hand, in spider s orb-web silk, the spider needs a fiber that can absorb the impact of the falling insect prey. Hence, the need for superior mechanical characteristics. 

Dragline spider silk has aroused considerable interest due to its excellent mechanical properties, for example stability, elasticity and low weight. A. Bram and co-workers (ESRF) have succeeded in recording X-ray diffraction patterns from a single spider dragline of less than 10 pm diameter(Figure 3(b)). These results allow the elastic properties of the fibres to be linked to the molecular architecture of the polymer chains. 

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