Preparation and characterization of silk fibroin as a biomaterial with potential for drug delivery

BACKGROUND: Degummed silk fibroin from Bombyx mori (silkworm) has potential carrier capabilities for drug delivery in humans; however, the processing methods have yet to be comparatively analyzed to determine the differential effects on the silk protein properties, including crystalline structure and activity. METHODS: In this study, we treated degummed silk with four kinds of calcium-alcohol solutions, and performed secondary structure measurements and enzyme activity test to distinguish the differences between the regenerated fibroins and degummed silk fibroin. RESULTS: Gel electrophoresis analysis revealed that Ca(NO(3))(2)-methanol, Ca(NO(3))(2)-ethanol, or CaCl(2)-methanol treatments produced more lower molecular weights of silk fibroin than CaCl(2)-ethanol. X-ray diffraction and Fourier-transform infrared spectroscopy showed that CaCl(2)-ethanol produced a crystalline structure with more silk I (α-form, type II β-turn), while the other treatments produced more silk II (β-form, anti-parallel β-pleated sheet). Solid-State (13)C cross polarization and magic angle spinning-nuclear magnetic resonance measurements suggested that regenerated fibroins from CaCl(2)-ethanol were nearly identical to degummed silk fibroin, while the other treatments produced fibroins with significantly different chemical shifts. Finally, enzyme activity test indicated that silk fibroins from CaCl(2)-ethanol had higher activity when linked to a known chemotherapeutic drug, L-asparaginase, than the fibroins from other treatments. CONCLUSIONS: Collectively, these results suggest that the CaCl(2)-ethanol processing method produces silk fibroin with biomaterial properties that are appropriate for drug delivery.