title: Tensile Reinforcement of Silk Films by the Addition of Telechelic-Type Polyalanine.
abstract: An appropriate modification technique for silk materials is needed to effectively improve their physical properties for specific applications. A telechelic-type polyalanine (T-polyA) was synthesized by papain-catalyzed polymerization as a novel reinforcing agent for silk materials. A silk fibroin obtained from Bombyx mori was homogeneously doped with T-polyA, and casting a solution of silk fibroin and T-polyA in 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) resulted in a robust and transparent film. Tensile deformation studies of the silk composite film containing T-polyA with prestretching revealed that the tensile strength and toughness were enhanced relative to those of a silk-only film. To determine the capability of T-polyA to reinforce the tensile property of silk films, the secondary structure in the silk composite film was characterized by wide-angle X-ray diffraction (WAXD) analysis. Antiparallel β-sheet structures of T-polyA and GAGAGS motifs of silk fibroin formed independently in the prestretched composite film. In addition, measuring the tensile deformation and performing WAXD analysis simultaneously demonstrated that the β-sheet structures of both T-polyA and the silk fibroin were aligned along the stretching direction and that T-polyA had no significant effect on the final morphology of the silk crystal domains. The silk film was toughened by the addition of T-polyA because of the generation of the T-polyA β-sheet in the amorphous region of the composite film. This work provides novel insight into the design and development of tough silk materials with controlled and aligned β-sheet structures.
authors.affiliation: Enzyme Research Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Kousuke
authors.initials: K
authors.lastname: Tsuchiya
authors.affiliation: Japan Synchrotron Radiation Research Institute, 1-1-1, Kouto, Sayo-cho, Sayo-gun, Hyogo 679-5198, Japan.
authors.forename: Hiroyasu
authors.initials: H
authors.lastname: Masunaga
authors.affiliation: Enzyme Research Team, Biomass Engineering Research Division, RIKEN Center for Sustainable Resource Science , 2-1 Hirosawa, Wako, Saitama 351-0198, Japan.
authors.forename: Keiji
authors.identifier: 0000-0003-2199-7420
authors.initials: K
authors.lastname: Numata
mesh_terms: D000818:Animals; D012831:Bombyx; D005349:Fibroins / Q000737:chemistry*; D010455:Peptides / Q000737:chemistry*; D020005:Propanols / Q000737:chemistry; D017433:Protein Structure, Secondary; D013718:Tensile Strength; D014961:X-Ray Diffraction; D006845:Hydrocarbons, Fluorinated
chemical_list: D005349:Fibroins; D010455:Peptides; D020005:Propanols; C019529:polyalanine; C001337:hexafluoroisopropanol; D006845:Hydrocarbons, Fluorinated