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This paper describes a method of molecular self-assembly by using two interacting streams for the production of bioinspired and biocompatible fibers. A first stream of an aqueous solution (dope) of polymer molecules (fibroins) is extruded from a capillary. The end of the capillary is surrounded by a focusing fluid which is miscible with the dope solution. The interaction between the dope solution and the surrounding focusing fluid, which can be an environmentally friendly solvent like ethanol or a water-based solution, leads to hydrodynamic stretching of the dope and allows molecular diffusion processes between the fluids to be established. Polymer molecules within the solution at stretched regions of the jet interact and self-assemble, forming a fiber which could be wound onto a mandrel. This work provides an exhaustive description of the geometrical and hydrodynamic conditions required to achieve the optimum interaction which triggers the formation of fibers. A simplified theoretical model that accounts for the influence of the main parameters of the process on the fibers is also given and experimentally validated. [ABSTRACT FROM AUTHOR]

As spun silkworm ( Bombyx mori ) silk fibers were compared in terms of their tensile behavior and microstructure with fibers subjected to different degumming treatments. Fibers were initially retrieved by forced silking directly from the worms and, either characterized in the as spun condition, or subjected to one of the following treatments: immersion in water, conventional degumming or degumming under longitudinally constrained conditions. Microstructure was assessed by X-ray diffraction and Raman spectroscopy. In addition, polyacrylamide gel electrophoresis was used to determine the influence of degumming on silk at a molecular level. Our study not only shows that degumming represents a major contribution to the accepted idea of silkworm silk as a highly variable material, but also provides new insights in the relationship between microstructure and tensile behavior in these fibers. In particular, it is shown that the arrangement of the hydrogen bond network in fibers subjected to different treatments plays a critical role in determining the mechanical behavior of silkworm silk. [ABSTRACT FROM AUTHOR]

Regenerated silk fibroin solutions from Bombyx mori were tested for electrospinning. Simple and reproducible tensile tests were performed on threads of aligned fibers to obtain information about their mechanical performance at the fiber level. The binary solvent formic acid/chloroform (10:1, v/v) rendered unbeaded thinner fibers with increased extensibility before failure when compared with pure formic acid. A remarkable improvement in strength was induced by immersing length-restricted fibers into ethanol for 5 min. Conformational changes of the protein chains were studied by solid-state NMR. [ABSTRACT FROM AUTHOR]