2890
Biomacromolecules 2010, 11, 2890–2895
Enhancing the Toughness of Regenerated Silk Fibroin Film through Uniaxial Extension Jianwei Yin,† Erqiang Chen,‡ David Porter,§ and Zhengzhong Shao*,† Key Laboratory of Molecular Engineering of Polymers of Ministry of Education, Advanced Materials Laboratory, Department of Macromolecular Science, Fudan University, Shanghai 200433, China, Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of the Ministry of Education, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China, and Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, United Kingdom Received June 11, 2010; Revised Manuscript Received August 13, 2010
Films of regenerated silk fibroin (RSF) are usually brittle and weak, which prevents its wide application as a structural material. To improve the mechanical properties of RSF film, uniaxial extension under swollen conditions was employed to introduce preferred orientation of molecular chains of silk fibroin. Such a prestretching treatment resulted in the strain at break, ultimate stress, Young’s modulus, and energy to break along the predrawn direction of the RSF film increasing from approximate 5%, 90 MPa, 2.7 GPa, and 2.1 kJ/kg to 35%, 169 MPa, 3.5 GPa, and 38.9 kJ/kg, respectively, which is an attractive combination of strength and toughness. The mechanism of these property enhancements was investigated using techniques such as small-angle X-ray scattering, wide-angle X-ray diffraction, atomic force microscopy, and dynamic mechanical analysis.
1. Introduction In recent years, spider silk and silkworm silk have aroused considerable interest for their outstanding mechanical properties.1–3 At the same time, the primary structural component of the silk (silk fibroin) is potentially useful in biomedical fields because of its excellent biocompatibility and biodegradability.4–8 Although the regenerated silk fibroin (RSF) produced by dissolving natural silk hardly changes its composition of amino acids, whether or not the molecular chain of the silk protein is degraded, mechanical properties of films cast from such RSF solutions are much weaker than those of natural silk, which prevents its wider application.9–11 Researchers have tried to improve the mechanical properties of RSF films by blending with various synthetic and natural polymers, but unfortunately, the results were not satisfactory.10–12 Recently, Kaplan and his coworkers have obtained the RSF film with relatively good properties by spin-coating and layer-by-layer strategy, yet the film was still brittle, and its thickness was
