Silk fibroin has a unique and useful combination of properties, including good biocompatibility and excellent mechanical performance. These features provided early clues to the utility of regenerated silk fibroin as a scaffold/matrix for tissue engineering. The silk fibroin scaffolds used for tissue engineering should degrade at a rate that matches the tissue growth rate. The relationship between secondary structure and biodegradation behavior of silk fibroin scaffolds was investigated in this study. Scaffolds with different secondary structure were prepared by controlling the freezing temperature and by treatment with carbodiimide or ethanol. The quantitative proportions of each secondary structure were obtained by Fourier transform infrared spectroscopy (FTIR), and each sample was then degraded in vitro with collagenase IA for 18 days. The results show that a high content of β-sheet structure leads to a low degradation rate. The random coil region in the silk fibroin material is degraded, whereas the crystal region remains stable and the amount of β-sheet structure increases during incubation. The results demonstrate that it is possible to control the degradation rate of a silk fibroin scaffold by controlling the content of β-sheet structure. 1. Introduction Silk fibroin is a natural protein produced by the domestic silkworm Bombyx mori, which is composed of a heavy-chain (H-chain, 350？kDa), light-chain (L-chain, 25？kDa), and an accessory protein (30？kDa). The amino acid composition of silk fibroin from Bombyx mori consists primarily of glycine, alanine, and serine [1, 2]. The three simple amino acids form the crystalline regions of silk fibroin, while the amino acids with bulky and polar side chains form the amorphous regions [3]. The silk polymorphs include silk I, silk II, and an air/water assembled interfacial silk III [1, 4]. The molecular conformation of silk II is antiparallel β-sheet structure. Silk fibroin has been used for centuries in production of textiles and clinical sutures [5]. Silk fibroin materials can support the attachment, proliferation, and differentiation of primary cells and cell lines [6–8] and is easily prepared as films [9], porous scaffolds [10], gels [11], and mats [12]. The impressive cytocompatibility and malleability of SF materials make silk a popular starting material for tissue engineering scaffolds used in skin, bone, blood vessel, ligament, and nerve tissue regeneration [13–15]. An ideal tissue engineering scaffold is nonimmunogenic and nontoxic but is biocompatible and supports cell adhesion, proliferation, and
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