Processing Influence on Molecular Assembling and Structural Conformations in Silk Fibroin: Elucidation by Solid-State NMR

This study is devoted to the deep evaluation of processing-induced protein conformation changes by using silk fibroin fibers and their cast films stabilized by different methods as a model. The control of the hierarchical assembling of silk fibroin is the key for finely tuning the biological functions and physical-chemical properties of the final materials for applications in biomedical fields. However, previous methods usually only focused on the change of beta-sheet crystallinity in silk materials, which can not explain a lot of their specific prosperities generated from different processing methods. By using complementary solid-state NMR, together with FTIR and DSC techniques, we for the first time established the correlations between processing conditions and silk fibroin molecular configurations, and experimentally assess the presence and quantify the percentage of the asymmetric 3-fold helical conformation (Silk III) in silk materials, together with their well-known Silk I-like helix/coil dominated and Silk II beta-sheet dominated configurations. This work provides a roadmap for researchers to quantify the percentage of different silk structures by solid NMR, and further understand how silk molecular conformations (Silk I-like, II, III) can impact the properties and functions of different silk materials, that are broadly used today for different biomedical applications.