Native B. mori silk is composed of silk fibroin protein coated by sericin proteins. Sericins are adhesive proteins that account for 25-30% of the total silkworm cocoon by weight. The silk fibroin consists of a light chain (Mw approximately 26 kDa) and a heavy chain (Mw approximately 390 kDa) linked by a disulfide bond9. Silk fibroin is a block copolymer rich in hydrophobic β-sheet forming blocks linked by small hydrophilic linker segments or spacers. The crystalline regions are primarily composed of glycine-X repeats, where X is alanine, serine, threonine, or valine. Within these domains lie subdomains rich in glycine, alanine, serine, and tyrosine9. The result is a hydrophobic protein that self-assembles to form strong and resilient materials. The dominance of the β-sheet-forming regimes 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®11. 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 MPa12. Therefore, silk fibroin is an excellent candidate polymer for biomedical applications.