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.