Comparative Analysis\nof Silk Fibroin Membranes across\nCross-Linking Methods: Processing and Characterization

Silk fibroin (SF)\nextracted from silkworm silk can be transformed\ninto transparent membranes with well-suited physical properties for\nophthalmic applications. There is ample literature on the fabrication\nand characterization of SF-based membranes; however, the use of diverse\nSF extraction protocols and characterization methods or their settings\nmakes it difficult to compare different silk membrane properties across\nstudies. In this work, we fabricated 10 families of SF-based membranes\nby physical cross-linking and one non-cross-linked as a control. We\nevaluated transparency (ranging from 84.5 to 95.3% in the visible\nspectrum), enzyme stability (from 24 h to 200 days in protease XIV),\ndecomposition temperature (280–290 °C), water uptake (40–60%),\nYoung’s modulus (8–30 MPa), roughness (1.6–22.7\nnm), and FTIR spectra for the secondary structure. We found correlation\nbetween water uptake and the Young’s modulus (the lower the\nwater uptake, the higher the Young’s modulus) and a relationship\nbetween membrane stability in protease XIV and the secondary structure\nof the proteins. Higher surface roughness and faster degradation were\nfound in membranes cross-linked with polyethylene glycol, and conversely,\nlower roughness and lower degradation were found in methanol, ethanol,\nor isopropanol crossed-link membranes. This ample compilation of materials\nand their characterization will aid in the selection of a SF-based\nmaterial according to the needs of the application.