Silk fibroin (SF) films were prepared using a casting method and the change of secondary structure and crystal structure owing to treatment with ethanol–water mixtures of different concentrations was investigated by Fourier transform infrared spectroscopy and X‐ray diffraction. The results were used to reveal the influence of structure of SF matrix on the release kinetics of drug compounds incorporated. It was found that the content of silk II structure, constituted by β‐sheet, first increased and then decreased with increasing ethanol concentration ranging from 50 to 90%, reaching a maximum around 70–80%. The release kinetics of Rhodamine B, a model compound for small molecule drugs, was described by Peppas equation. The results indicated that Rhodamine B released from SF films via Fickian diffusion mechanism and the diffusional exponent n increased with increasing β‐sheet content in the matrix. The experimental data had a good linear fit, suggesting that the silk II crystal could be used as a natural regulator for drug release from SF material. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

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Circular dichroism, intrinsic fluorescence of protein and exogenous fluorescence probe of 8-anilino-1-naphthalenesulfonic acid hemimagnesium salt (ANS) was used to investigate the mechanism of conformational change of silk fibroin (SF) in aqueous alcohol including methanol and ethanol. The conformational transition of SF from random coil to β-sheet was found to be of a close relationship with the microstructure of the solvent. The alcohol-water mixture at low concentration had little effect on the solvation of the peptide unit, as the inherent water structure was conserved. At high alcohol concentration, the transition from the tetrahedral-like water structure to the chain-like alcohol structure in the mixtures induced a β-sheet conformation of SF, as a result of the formation of intramolecular hydrogen bond between the peptide units in order to eliminate the thermodynamic unfavorite from the contact to the solvent molecules. Meanwhile, the aggregating of hydrophobic side chains was decreased by the alcohol via the destruction of hydrogen bond network of water by alcohol and the binding of alcohol to hydrophobic group.