Regenerated Bombyx silk solutions studied with rheometry and FTIR

Several different solvent systems are commonly used to dissolve Bombyx mori silk fibroin to prepare regenerated silk membranes and fibers though diffe rences in the behavior of these solvents have not been fully investigated. Here we compare the effects of four of these on the rheology of silk fibroi n solutions and on protein secondary structure as revealed by FTIR spectros copy of cast membranes. The results demonstrated that Ca(NO3)(2)-MeOH-H2O a nd LiBr-EtOH-H2O had the strongest solvation on the silk fibroin chains, wh ich showed an almost constant viscosity (Newtonian behavior) over most of t he shear rate range (0.1-500 s(-1)). In contrast, the 9.5 M aqueous LiBr ap peared to have the weakest solvation with similar effects on the silk fibro in molecules to pure water as indicated by rheological behavior. It was als o found that the silk fibroin membranes prepared using all four solvent sys tem showed mainly random coil conformation with a small proportion of P-she et by FTIR spectroscopy. We discuss the implications of these findings for the preparation of regenerated silk for different applications. (C) 2001 Pu blished by Elsevier Science Ltd.