Bending–Spinning Produces Silkworm and Spider Silk with Enhanced Mechanical Properties

Natural silk-spinning behavior endows freshly secreted (FS) silk with a bending angle. This phenomenon is universal among silkworms and spiders but remains unexplained. In this study, the angle of freshly secreted silkworm (FS-S) silk was revealed to be 70.23°–87.93° and that of freshly secreted spider major ampullate (FS-MA) silk to be 0°–50°. Furthermore, the mechanical properties of FS-S silk and FS-MA silk changed after bending, first increasing and then decreasing as the bending angle was increased (0°–360°). The angle corresponding to FS-S silk with the best mechanical properties is 67.5°–90°, and for FS-MA silk, it is 45°. Structural analysis showed that the β-sheet, crystallinity, and crystal size increased with bending angle and the orientation decreased with bending angle. Regular change of microstructure explains the trend for the mechanical property change with bending angle. These findings suggest that bending–spinning produces silkworm and spider silk with enhanced mechanical properties.