title: Structure and properties of biomedical films prepared from aqueous and acidic silk fibroin solutions.
abstract: Silk fibroin films are promising materials for a range of biomedical applications. To understand the effects of casting solvents on film properties, we used water (W), formic acid (FA), and trifluoroacetic acid (TFA) as solvents. We characterized molecular weight, secondary structure, mechanical properties, and degradation behavior of cast films. Significant degradation of fibroin was observed for TFA-based film compared to W and TA-based films when analyzed by SDS-PAGE. Fibroin degradation resulted in a significant reduction in tensile strength and modulus of TFA-based films. Compared to water, TFA-based films demonstrated lower water solubility (19.6% vs. 62.5% in 12 h) despite having only a marginal increase in their β-sheet content (26.9% vs. 23.7%). On the other hand, FA-based films with 34.3% β-sheet were virtually water insoluble. Following solubility treatment, β-sheet content in FA-based films increased to 50.9%. On exposure to protease XIV, water-annealed FA-based films lost 74% mass in 22 days compared to only 30% mass loss by ethanol annealed FA films. This study demonstrated that a small variation in the β-sheet percentage and random coil conformations resulted in a significant change in the rates of enzymatic degradation without alteration to their tensile properties. The film surface roughness changed with the extent of enzymatic hydrolysis.
authors.affiliation: Institute for Technology Research and Innovation, Deakin University, Geelong, Victoria, Australia.
authors.forename: Rangam
authors.initials: R
authors.lastname: Rajkhowa
authors.forename: Brett
authors.initials: B
authors.lastname: Levin
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Redmond
authors.forename: Lu Hua
authors.initials: LH
authors.lastname: Li
authors.forename: Lijing
authors.initials: L
authors.lastname: Wang
authors.forename: Jagat R
authors.initials: JR
authors.lastname: Kanwar
authors.forename: Marcus D
authors.initials: MD
authors.lastname: Atlas
authors.forename: Xungai
authors.initials: X
authors.lastname: Wang
mesh_terms: D000143:Acids / Q000737:chemistry; D001672:Biocompatible Materials / Q000138:chemical synthesis* / Q000737:chemistry*; D004591:Electrophoresis, Polyacrylamide Gel; D005349:Fibroins / Q000737:chemistry*; D008422:Materials Testing; D018625:Microscopy, Atomic Force; D011402:Pronase / Q000494:pharmacology; D011487:Protein Conformation; D012995:Solubility; D012996:Solutions; D012997:Solvents; D013718:Tensile Strength / Q000187:drug effects
chemical_list: D000143:Acids; D001672:Biocompatible Materials; D012996:Solutions; D012997:Solvents; D005349:Fibroins; D011402:Pronase