Fabrication of Protein Films from Genetically Engineered Silk-Elastin-Like Proteins by Controlled Cross-Linking

Protein films are an important class of materials for applications in biomedicine and biotechnology. The rational design of protein polymer sequence and selection of customized cross-linking offers unique opportunities to engineer desirable functionalities into these materials. Here we report the fabrication of a series of films with tunable physiochemical properties from genetically engineered silk-elastin-like proteins (SELPs). The SELPs were recombinantly biosynthesized with different ratios of silk-to-elastin blocks and periodic cysteine residues incorporated in the elastin blocks. A disulfide cross-linking method was developed for the preparation of the SELP films under mild oxidative conditions with a low concentration of hydrogen peroxide, in comparison with the physical cross-linking method used with the organic solvent methanol. Film properties were characterized for solubility, water absorption, hydrophilicity, surface roughness, and cyto-compatibility. The results indicated that customized cross-linking supported the fabrication of films from the SELP proteins with tunable features, including smooth, water stable film materials with cyto-compatibility. Interestingly, hydrogen peroxide oxidation was a preferred cross-linking method for the cysteine-containing SELPs with a low ratio of the silk-to-elastin blocks, whereas methanol treatment was suitable for fabricating films from the SELPs with a high ratio of silk-to-elastin blocks into stable films with rougher surfaces. We anticipate that an appropriate combination of polymer design and cross-linking might be a useful strategy for the preparation of protein films for diverse applications.