within the fibroin structure impart the protein-based materials with high mechanical strength and toughness. The toughness of silk fibers is greater than the best synthetic materials, including Kevlar. In terms of strength, silkworm silk is superior to commonly used polymeric degradable biomaterials such as collagen and poly(L-lactic acid)(PLA). The ultimate tensile strength (UTS) of B. mori silk fibers is 740 MPa. In contrast, collagen has a UTS of 0.9-7.4 MPa and PLA 28-50 MPa. Therefore, silk fibroin is an excellent candidate polymer for biomedical applications.