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Processing Silk Fibroin (SF) with electrospinning (ES) offers a very attractive opportunity for producing a variety of 2D and 3D matrices with great potential for tissue regeneration and repair due to the superior biocompatibility and mechanical properties of SF. Different combinations of ES parameters were explored to investigate the best experimental set‐up related to the dimension and uniformity of the fibers in the electrospun silk fibroin (ES‐SF) mats. Using SEM it was found that the ES‐SF mats contain uniform fibers with a diameter in the nanometric range obtained by electrospinning a 7.5 % w/v SF solution in formic acid, with an electric field of 2.4 kV/cm and a spinneret‐collector distance of 10 cm. FT‐IR and DSC analyses were performed to investigate the structure of the ES‐SF mats before and after immersion in methanol for different times (5, 10, and 15 min). The methanol treatment was able to promote the crystallization of SF by conformational transition of random coil and other poorly ordered conformations (turns and bends) to the β‐sheet structure. The degree of crystallinity was enhanced as shown by the trend of both the FT‐IR crystallinity index and the melting/decomposition peak temperature (from DSC). To study the cytocompatibility of ES‐SF mats, tests with L929 murine fibroblasts were carried out. Samples were seeded with the cells and incubated for 1, 3, and 7 days at 37 °C. At each time point, SEM investigations and Alamar blue tests were performed. The SEM images showed cell adhesion and proliferation just after 1 day and cell confluence at 7 days. Alamar blue test demonstrated that there were very low differences between cell viability on ES‐SF mats and the tissue culture plastic control.

Silk fabrics were treated with chlorosulphonic acid in pyridine for different times. The amount of sulfur bound to silk increased during the first 2 h of reaction and then reached a plateau. The amino acidic pattern of sulfated silk remained essentially unchanged for short reaction times (< or =2 h). Longer reaction times resulted in drastic changes in the concentration of Asp, Glu, and Tyr. Surface morphology and texture of silk fabrics changed upon sulfation. Warp and weft yarns became progressively thinner, and deposits of foreign material appeared on the fiber surface. Changes were more evident at longer reaction times (> or =2 h). Spectroscopic analyses performed by FT-IR and FT-Raman showed the appearance of new bands attributable to various vibrations of sulfated groups. The IR bands at 1049 and 1014 cm-1, due to organic sulfate salts, were particularly intense. Bands assigned to alkyl sulfates and sulfonamides appeared in the 1300-1180 cm-1 range. Organic covalent sulfates displayed a weak but distinct IR band at 1385 cm-1. Both IR and Raman spectra revealed that silk fibroin mainly bound sulfates through the hydroxyl groups of Ser and Tyr, while involvement of amines could not be proved. Changes observed in the amide I and II range indicated an increase of the degree of molecular disorder of sulfated silk. Accordingly, the I850/I830 intensity ratio between the two Tyr bands at 850-830 cm-1 increased from 1.41 to 1.52, indicating a more exposed state of Tyr residues in sulfated silk. TGA, DSC, and TG analyses showed that sulfated silk attained a higher thermal stability. A thermal transition attributable to sulfated silk fibroin fractions appeared at about 260 degrees C in the DSC thermograms.