Silk concentration

Silk concentration plays a major role in fiber diameter. No fibers were formed at less than 5% silk concentration for any electric field and spinning distances. Figures. 22 and 23 show the morphology of fibers obtained at the electric fields of 3 and 4 kV/cm, respectively, at silk/formic acid concentrations of 5, 8, 10, 12, 15, and 19.5% with a constant tip-to-collection plate distance of 7 cm. 

Increase in the regenerated silk concentration in the formic acid increases the solution viscosity. At low concentrations beads are form instead of fibers and at high concentrations the formation of continuous fibers are prohibited because of inability to maintain the flow of the solution at the tip of the needle resulting in the formation of larger fibers. Continuous... 

Sukigara et al. [78] designed a factorial experiment by using two factors (electric field and concentration). For a quadratic model, experimentsmust be performed for at least three levels of each factor. These levels are best chosen equally spaced. The two factors (silk concentration and electric field) and three levels resulted in nine possible combinations of factor settings. A schematic of the experimental design is shown in Figure 28(A) and (B). 

Sukigara [115] studied the effect of electrospirming parameters (electric field, tip-to-collector distance and concentration) on the morphology and fiber diameter of regenerated silk from Bombyx mori using response surface methodology and concluded that the silk concentration was the most important parameter in producing uniform cylindrical fibers less than 100 run in diameter. 

One procedure makes use of a box on whose silk screen bottom powdered desiccant has been placed, usually lithium chloride. The box is positioned 1-2 mm above the surface, and the rate of gain in weight is measured for the film-free and the film-covered surface. The rate of water uptake is reported as u = m/fA, or in g/sec cm. This is taken to be proportional to - Cd)/R, where Ch, and Cd are the concentrations of water vapor in equilibrium with water and with the desiccant, respectively, and R is the diffusional resistance across the gap between the surface and the screen. Qualitatively, R can be regarded as actually being the sum of a series of resistances corresponding to the various diffusion gradients present ... 

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). 

Concentrated, aqueous solutions of ZnCla dissolve starch, cellulose (and therefore cannot be filtered through paper ), and silk. Commercially ZnCla is one of the important compounds of zinc. It has applications in textile processing and, because when fused it readily dissolves other oxides, it is used in a number of metallurgical fluxes as well as in the manufacture of magnesia cements in dental fillings. Cadmium halides are used in the preparation of electroplating baths and in the production of pigments. 

There are many additives in shampoos and conditioners that appear to be there mainly for marketing purposes. Honey, various herb extracts, and other compounds might add to the fragrance, but they are unlikely to have any other effects in the small concentrations used. Amino acids can act as conditioners, but the source of the amino acid is not important. Silk amino acids are essentially no different from soy amino acids. 

Benzyl salicylate (10.176) at an applied concentration of 2% o.w.f. is reported [420] to have given good protection from fading to two anthraquinone acid dyes on silk. 

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. 

The spinning of silk monofilaments from a concentrated aqueous solution (>20% protein) of recombinant spider silk protein might be the best way to generate stress-... 

Spider silk proteins from plants remain soluble at high temperatures, allowing them to be enriched by boiling [26]. In order to enrich the spider silk-ELP fusion protein, we therefore exposed tobacco leaf extracts to heat treatment at 95°C for 60 min and then cleared the supernatant by centrifugation. In further steps, the reversible precipitation behavior of ELP fusion proteins was exploited to develop a suitable purification strategy. For the selective precipitation of SOl-lOOxELP, NaCl was added at a final concentration of 2 M and the temperature was increased to 60 °C. In this man-... 

Bombyx Cocoon mori Heavy, light chains fibroins and P25 (6-6-1) (GAGAGS)5 15 / -sheet (GX)5 i5 / -turns/helices GAAS spacer Gly (43), Ala (30), Ser (12), SSC (85), PC (23) Low-concentration H-fibroin disorder/PPII / fi-tum type II silkl) High -concentration helical / -Sheet (silk II) 40-50 10-20... 

A possible mechanism for such tight control is illustrated in Fig. 5. Clearly, increasing the protein concentration has a dramatic impact on the secondary structures of silk proteins in solution. The low concentration silk protein solution at 1% w/v is dominated by disordered structures or equally possible a polyproline II type structure (Sreerama and Woody, 2003). 

Fig. 5. The effect of protein-protein interactions on Nephila edulis major ampullate circular dichroism spectra in solution. A change in secondary structure with increasing concentration is observed. At low concentration (minimal protein-protein interactions) silk proteins appear partially unfolded in solution. At higher concentration (higher protein-protein interactions) silk proteins refold into a helix-like structure, most likely a molten-like globule (from Dicko et al., 2004c). This final molten structure would facilitate local chain rearrangement while preserving the global structure for protein storage and transport. (Copyright 2004 American Chemical Society.)...

Dicko, C., Knight, D., Kenney, J. M., and Vollrath, F. (2004b). Secondary structures and conformational changes in flagelliform, cylindrical, major, and minor ampullate silk proteins. Temperature and concentration effects. Biomacromolecules 5, 2105-2115. 

Hydrogen cyanide has recently been recognized in significant concentrations in some fires, as a combustion product of wool, silk, and many synthetic polymers it may play a role in toxicity and deaths ftom smoke inhalation." ... 

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