title: Silk Fibroin Degradation Related to Rheological and Mechanical Properties.
abstract: 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.
authors.affiliation: Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, MA, 02155, USA.
authors.forename: Benjamin P
authors.initials: BP
authors.lastname: Partlow
authors.affiliation: Department of Physics Institute for Soft Matter Synthesis and Metrology, Georgetown University, 506 Reiss Science Building 37th and O Streets, N. W., Washington, D.C., 20057, USA.
authors.forename: A Pasha
authors.initials: AP
authors.lastname: Tabatabai
authors.affiliation: Department of Mechanical Engineering, Tufts University, 200 College Ave., Medford, MA, 02155, USA.
authors.forename: Gary G
authors.initials: GG
authors.lastname: Leisk
authors.affiliation: Department of Physics and Astronomy, Tufts University, 574 Boston Ave., Medford, MA, 02155, USA.
authors.forename: Peggy
authors.initials: P
authors.lastname: Cebe
authors.affiliation: Department of Physics Institute for Soft Matter Synthesis and Metrology, Georgetown University, 506 Reiss Science Building 37th and O Streets, N. W., Washington, D.C., 20057, USA.
authors.forename: Daniel L
authors.initials: DL
authors.lastname: Blair
authors.affiliation: Department of Biomedical Engineering, Tufts University, 4 Colby St., Medford, MA, 02155, USA.
authors.forename: David L
authors.initials: DL
authors.lastname: Kaplan
mesh_terms: D000818:Animals; D012831:Bombyx / Q000737:chemistry; D005349:Fibroins / Q000737:chemistry* / Q000627:therapeutic use; D017433:Protein Structure, Secondary; D059748:Proteolysis; D012212:Rheology; D047011:Silk / Q000737:chemistry* / Q000627:therapeutic use; D012996:Solutions / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared; D014783:Viscosity; D014961:X-Ray Diffraction
chemical_list: D047011:Silk; D012996:Solutions; D005349:Fibroins
keywords: biomaterials; biopolymers; degradation; molecular weight; silk fibroin