The blended films of polyurethane and silk fibroin (PU/SF) were prepared successfully by mixing water polyurethane (WPU) with silk fibroin solution.The structure of the blends was analyzed by means of FTIR spectroscopy

wideangle X-ray diffraction

and scanning electron microscopy.The miscibility and properties of the blends were characterized by ultraviolet-visible-spectroscopy and tensile testing.The blended sheets exhibited smooth surface when the content of silk fibroin was lower than 3 wt%.It suggests that silk fibroin molecules penetrate into the polyurethane and interrupt the intra-hydrogen bonding between the hard and soft segments.A homogeneous distribution of the silk fibroin aggregations in the WPU matrix was observed in the blends when the contents of silk fibroin were higher than 3 wt%.The results indicated that the blended sheets exhibited good miscibility

attributed to intermolecular hydrogen bonding between silk fibroin and polyurethane.The existence of polyurethane and relatively slow dryness process contributed to the crystallization of the silk fibroin.The tensile strength and Youngs modulus increased with an increase of silk fibroin content.The films having 5.6 wt% silk fibroin exhibited a significant increase from 0.56 MPa to 4.60 MPa for tensile strength and from 0.14 MPa to 1.71 MPa for Youngs modulus.They showed high elongation at break in the range from 1065% to 988%.