Incorporation of nanoparticles in silk fibroin solution: Toward water‐stable silk fibroin films possessing silk I structure

Abstract Water‐stable silk fibroin (SF) films are normally prepared by transforming the secondary structure of SF, from amorphous silk I (random coils) to silk II (β‐sheet), via physical or chemical means. Although mechanically strong, these films are generally brittle. Herein, we prepared water‐stable flexible SF films possessing silk I rather than silk II structure. Films were prepared by casting SF solution possessing SF nanoparticles induced by two different methods: (1) pre‐prepared SF nanoparticles by ethanol were added into SF solution; (2) nanoparticles were induced in SF solution via autoclaving. These films were compared with each other and with water‐annealed and methonol‐annealed films for their secondary structure and physical properties. The as‐prepared films were primarily composed of silk I structure, as validated by x‐ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy. However, the water‐annealed and methanol‐annealed films exhibited silk II structure. The films prepared by induction of nanoparticles were water‐stable, transparent, mechanically strong (tensile strength as high as 5.14 ± 1.43 MPa), exhibited tunable degradation and sustained drug release properties. As for mechanical properties, these films displayed 4 times and 12 times improved mechanical ductility as compared with water‐annealed and methanol‐annealed films, respectively. Moreover, these films exhibited fast enzymatic degradation as compared with their counterparts with silk II structure. These films hold great promise as a biomaterial for tissue engineering applications especially where flexibility and fast degradation of scaffold are important.