Recombinant Silk-Elastinlike Protein Polymer Displays Elasticity Comparable to Elastin

We evaluated the mechanical properties of the genetically engineered, recombinant silk-elastinlike protein copolymer, SELP-47K. In tensile stress-strain analysis, methanol-treated non-cross-linked SELP-47K films exceeded die properties of native aortic elastin, attaining an ultimate tensile strength of 2.5 +/- 0.4 MPa, an elastic modulus of 1.7 +/- 0.4 MPa, an extensibility of 190 +/- 60%, and a resilience of 86 +/- 4% after 10 cycles of mechanical preconditioning. Stress-relaxation and creep analysis showed that films substantially maintained their elastic properties under sustained deformation. Chemical cross-linking of SELP-47K films doubled the elastic modulus and ultimate tensile strength and enhanced the extensibility and resilience. The underlying conformational and microstructural features of the films were examined. Raman spectroscopy revealed that the silklike blocks of SELP-47K existed in antiparallel beta-sheet crystals in the films, likely responsible for the robust physical cross-links. Scanning electron microscopy (SEM) revealed that the various processing treatments and the mechanical deformation of the films induced changes in their surface microstructure consistent with the coagulation and alignment of polymer chains. These results demonstrate that films with excellent elasticity, comparable to native aortic elastin, are obtainable from SELP-47K, a protein copolymer combining both silk- and elastin-derived sequences in a single polymer chain.