A microfabricated spinneret is described that is capable of spinning meters of fibers from solutions containing as little as 10 mg of purified protein. Using the spinneret, regenerated Bombyx mori fibers were made using various processing parameters. A log-linear relationship was found between the maximum stress sustained by the regenerated fibers and their diameters. Solid state 13 C NMR was used to determine the effects of spinneret diameter and postspinning draw ratio on the secondary structure of the alanine residues in the silk protein. The relationship between the secondary structure of the alanine residues and the maximum stress of the silks was also examined. The results suggest that a relatively high fraction of the alanine residues in the silks must be in the -sheet conformation (>65%) in order to produce the highest stress fibers. However, the fraction of alanine residues in the -sheet conformation does not uniquely determine the maximum stress of a fiber; it is suggested that orientation of these -sheets is also an important parameter.

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