The behavior of aged regenerated Bombyx mori silk fibroin solutions studied by 1H NMR and rheology

As part of a project to utilize the regenerated silk fibroin (RSF) membranes as a supporting matrix for the attachment and growth of corneal stem/progenitor cells in the development of tissue engineered constructs for the surgical restoration of the ocular surface, the behavior of the aged RSF solutions has been investigated. The solutions were produced from domesticated silkworm (Bombyx mori) cocoons according to a protocol involving successive dissolution steps, filtration and dialysis. The solutions were kept at 4 °C in a refrigerator for a certain period of time until near the gelation time. The changes in molecular conformation were studied by solution-state 1H NMR, while the flow of the solutions was characterized by rheological method. Upon ageing turbidity developed in solutions and the viscosity continuously decreased prior to a drastic increased near the gelation time. The 1H resonances of aged solutions showed a consistent downfield shift as compared to the 1H resonances of the fresh solution. Shear thinning with anomalous short recovery within a certain range of low shear rates occurred in both fresh and aged solutions. While the solutions behave as pseudo-plastic materials, the chain conformation in aged solutions adopted all secondary configurations with β-strand being predominant.