Aspects of the morphology of the silk of Bombyx mori

Atomic force microscopy was used to examine the exterior surface of as-spun cocoon silk, raw silk, and degummed silk as well as the interior surface of peeled degummed silk of Bombyx mori. The images yielded a broad variety of features with a wide range of dimensions. They are qualitatively similar to those of the dragline silk of Nephila clavipes. Examination of the surface roughness, the surface profiles, and the Fourier transforms of the profiles showed the surface of the degummed silk to be quantitatively similar to the silk of N. clavipes. The average roughness is 4 nm. The average dimensions of the features are approximately 100 to 150 ( > 2000 in peeled samples) nm axially and 50 to 300 nm laterally. They appear to emerge from and to enter the surface, to vary in width, and to twist about one another in an irregular manner. In the peeled degummed silk they extend more regularly for long distances in approximately the axial direction. In some cases they appear to be, oriented at different small angles with respect to the fiber axis in different layers. Taken together with other data, they suggest the presence of large fibrillar structures. The same suggestion also applies to similar structures in N. clavipes.