Current reports show that various researchers are investigating methods for the formation of silk fibroin films from the Bombyx mori silk worm. In this study, we investigated four factors involved in insoluble fibroin film formation. These factors were glycerol concentration, dr ying conditions including temperature and humidity, and pH. Addition of under 0.05 v/v% glycerol to the fibroin solution led to soluble films, whereas glycerol concentrations of up to 0.10 v/v% produced insoluble films.

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... At temperatures and humidity of up to 30 and 70% RH, respectively, the film was insoluble. In terms of the effect of pH on insoluble fibroin films, at pH <11 the fibroin film did not dissolve. At fibroin concentrations of 2~10 mg/mL the films did not dissolve, and the requirement for insoluble film formation was >2 mg/mL fibroin. From these results, the factors involved in insoluble fibroin film formation are a glycerol concentration of 0.10 v/v%, drying conditions of up to 30 and up to 70% RH, pH < 11 and a fibroin concentration of >2.0 mg/mL.