Silk Fibroin Degradation Related to Rheological and Mechanical Properties

• Published in: Macromolecular bioscience Vol. 16; no. 5; pp. 666 - 675
• Main Authors: Partlow, Benjamin P., Tabatabai, A. Pasha, Leisk, Gary G., Cebe, Peggy, Blair, Daniel L., Kaplan, David L.
• Format: Journal Article
• Language: English
• Published: Germany Blackwell Publishing Ltd 01.05.2016; Wiley Subscription Services, Inc
• Subjects: Animals; biomaterials; biopolymers; Bombyx - chemistry; degradation; Fibroins - chemistry; Fibroins - therapeutic use; Fourier transforms; Molecular weight; Protein Structure, Secondary; Proteolysis; Rheology; Silk - chemistry; Silk - therapeutic use; silk fibroin; Solutions - chemistry; Spectroscopy, Fourier Transform Infrared; Viscosity; X-Ray Diffraction; degradation; molecular weight; biomaterials; biopolymers; silk fibroin
• ISSN: 1616-5187; 1616-5195
• DOI: 10.1002/mabi.201500370

Regenerated silk fibroin has been proposed as a material substrate for biomedical, optical, and electronic applications. Preparation of the silk fibroin solution requires extraction (degumming) to remove contaminants, but results in the degradation of the fibroin protein. Here, a mechanism of fibroin degradation is proposed and the molecular weight and polydispersity is characterized as a function of extraction time. Rheological analysis reveals significant changes in the viscosity of samples while mechanical characterization of cast and drawn films shows increased moduli, extensibility, and strength upon drawing. Fifteen minutes extraction time results in degraded fibroin that generates the strongest films. Structural analysis by wide angle X‐ray scattering (WAXS) and Fourier transform infrared spectroscopy (FTIR) indicates molecular alignment in the drawn films and shows that the drawing process converts amorphous films into the crystalline, β‐sheet, secondary structure. Most interesting, by using selected extraction times, films with near‐native crystallinity, alignment, and molecular weight can be achieved; yet maximal mechanical properties for the films from regenerated silk fibroin solutions are found with solutions subjected to some degree of degradation. These results suggest that the regenerated solutions and the film casting and drawing processes introduce more complexity than native spinning processes. Silk fibroin is a promising natural bio­material that is useful for numerous applications. However, a full understanding of how processing affects the final material characteristics is required to effectively engineer devices and scaffolds. The degree of degradation, due to processing, is shown to have a strong influence on both solution and solid state properties.