Silk composition

Cupilure was also detected on silk from the related and sympatric species Cupiennius getazi and Cupiennius coccineus (M. D. Papke, S. Schulz and H. Tichy, unpublished data). Barth and Schmitt (1991) have shown that the three Cupiennius spp. can discriminate between hetero- and conspecific silk, but vibrational cues are more important in discrimination than silk composition. The ability to discriminate conspecific silk may originate from its mechanical or physical characteristics, rather... 

Kirker-Head, C., Karageorgiou, V., Hofmann, S., Fajardo, R., Betz, O., Merkle, H.P., Hilbe, M., von Rechenberg, B., McCool, J., Abrahamsen, L., Nazarian, A., Cory, E., Curtis, M., Kaplan, D., and Meinel, L. "BMP-silk composite matrices heal critically sized femoral defects". Bone 41(2), 247-255 (2007). 

Robson, R.M. Silk composition, structure and properties. In Fiber Chemistry Handbook of Science and Technology, Lewin, M., Pearce, E. Eds., Marcel Dekker, New York, Vol. IV (1985). 

Another interesting silk composite, the sticky capture silks of Nephila and Araneus, are complex, albeit microscopic, mechanical windlass systems that make good use of the physics of biological micro-engineering (Fig. 8.3). In the windlass silk (which operates in the wet state) the elasticity is given by a combination of surface tension of the aqueous coat and recoil of the plasticised silk fibre [12-14] while adhesion is bestowed by a separate glycoprotein complex [12, 15]. 

Kirker-Head, C. et al. 2007. BMP-silk composite matrices heal critically sized femoral defects. Bone, 41, 247-55. 

Crystallinity. Generally, spider dragline and silkworm cocoon silks are considered semicrystalline materials having amorphous flexible chains reinforced by strong stiff crystals (3). The orb web fibers are composite materials (qv) in the sense that they are composed of crystalline regions immersed in less crystalline regions, which have estimates of 30—50% crystallinity (3,16). Eadier studies by x-ray diffraction analysis indicated 62—65% crystallinity in cocoon silk fibroin from the silkworm, 50—63% in wild-type silkworm cocoons, and lesser amounts in spider silk (17). 

Figure 14.9 Spicier fibers are composite materials formed by large silk fibroin polypeptide chains with repetitive sequences that form p sheets. Some regions of the chains participate in forming 100-nm crystals, while other regions are part of a less-ordered mesh-work in which the crystals are embedded. The diagram shows a model of the current concepts of how these fibers are built up, which probably will be modified and extended as new knowledge is gained. (Adapted from F. Vollrath, Sci. Am. p. 54-58, March 1992 and A.H. Simmons, Science 271 84-87, 1996. Photograph courtesy of Science Photo Library.)...

Charlotte s Web Revisited Helix-Sheet Composites in Spider Dragline Silk... 

Short fiber reinforcement of TPEs has recently opened up a new era in the field of polymer technology. Vajrasthira et al. [22] studied the fiber-matrix interactions in short aramid fiber-reinforced thermoplastic polyurethane (TPU) composites. Campbell and Goettler [23] reported the reinforcement of TPE matrix by Santoweb fibers, whereas Akhtar et al. [24] reported the reinforcement of a TPE matrix by short silk fiber. The reinforcement of thermoplastic co-polyester and TPU by short aramid fiber was reported by Watson and Prances [25]. Roy and coworkers [26-28] studied the rheological, hysteresis, mechanical, and dynamic mechanical behavior of short carbon fiber-filled styrene-isoprene-styrene (SIS) block copolymers and TPEs derived from NR and high-density polyethylene (HOPE) blends. 

Fig. 6. Structural stability of major ampullate silk protein in constrained Nephila edulis. The graph shows a time series of circular dichroism spectra of major ampullate (MA) protein at 1% w/v in distilled water. The spiders prior to dissection were prevented from spinning, but fed and watered for at least 2 weeks. With time, the secondary structure of silk protein is becoming more and more disordered. The arrow indicates increasing time (days). Note that the amino acid composition of the silk protein was similar to that of a native N. edulis spider. Interestingly, silk protein extracted from the constrained spider did not respond to denaturing conditions (detergents, alcohols, pH, and salts Dicko et al, 2004a, 2005).

In summary, the physiological control of silk protein conversion shows an ingenious balance of activating and inhibiting mechanisms that are dependent on composition and sequence arrangement (Krejchi et al., 1994). Denaturing effects observed in silks appear to be identical to those found in amyloid-forming proteins, and they principally alter the competitive outcome of the hydration of nonpolar and polar residues (Anfinsen, 1973 Dill, 1990 Dobson and Karplus, 1999 Kauzmann, 1959). The key differences to amyloids may lie in the hierarchical level of the structures (Muthukumar et al., 1997) involved in the assembly of silks compared to amyloids. 

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