Sirina Putthanarat

Investigation of the nanofibrillar morphology in silk fibers by small angle X-ray scattering and atomic force microscopy

Small angle X-ray scattering (SAXS) and atomic force microscopy (AFM) measurements have been shown to be consistent with the presence of nanofibrils in the cocoon silk of Bombyx mori and the dragline silk of Nephila clavipes. The transverse dimensions and correlation lengths range from >> 59 to 220 nm and in the axial direction from >> 80 to 230 nm. Also, the two-dimensional Fourier transforms of the height profiles of AFM topographic images of interior surfaces of B. mori follow a power law approximately the same as that for the Porod region of the SAXS data. In this manner, the AFM can be used to help remove ambiguity about the scatterers responsible for SAXS patterns.

Effect of processing temperature on the morphology of silk membranes

A concise literature survey concerning the processing and uses of silk membranes is presented in this note together with initial observations of new morphological data for the effect of processing temperature on morphology. Liquid silk from the middle section of the Middle Division of the silk gland of Bombyx mori was cast onto glass plates at 20, 40, 50, 60 and 80 °C. Silk from the anterior and posterior sections was cast at 20 °C. Samples cast at 20 °C exhibit particles, grains, nanofibrils and an irregular morphology. Each exhibits approximately the same dimensions for all the samples. Samples cast above 20 °C do not exhibit the irregular morphology. Samples cast above 50 °C exhibit larger grains and larger, more densely packed nanofibrils. All these changes might result from conversion of the amorphous structure to the β-pleated structure (Silk II). The nanofibrils appear to be self-assembled bio-nanofibrils. Membranes of regenerated fibroin treated with aqueous methanol solution exhibit grains and apparent nanofibrils. Opportunities for further work are pointed out.

Aspects of the Morphology of the Silk of Bombyx Mori

Abstract 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 sma...