Preparation of insoluble fibroin films without methanol treatment

Insoluble fibroin films were prepared without methanol treatment. A 15 wt % fibroin solution was obtained through concentration, and then, the insoluble film was achieved by the adjustment of the drying temperature and rate. These films were examined through Fourier transform infrared-attenuated total reflection, X-ray diffraction, and scanning electron microscopy to determine the structure of the silk fibroin. The physical and mechanical properties were investigated to discover the feasibility of using these films as biomedical materials. When fibroin films were dried above 60°C, abundant β-sheet crystals existed in the fibroin films, and many globule-containing micelles aggregated and interacted with each other, which resulted in excellent mechanical properties of the regenerated fibroin films in the wet state. Interestingly, the amide III band of the random coil structure in the fibroin films dried at 70 and 80°C was shifted to a lower frequency, 1228 cm ^-1, which meant that a partly orientated structure formed. This may have also affected the mechanical properties of the fibroin films. The tensile strength and breaking elongation of the films dried at 70°C were 29.8 MPa and 59.6%, which is distinctly superior to fibroin films treated with methanol. If the drying temperature was raised to 60°C, the stability of the films in water was also excellent.