Structural characterisation of B. mori silk fibroin fibres grafted with methacrylamide and their stability towards alkaline hydrolysis

B. mori silk fibroin fibres grafted with methacrylamide (MAA) were characterized by Raman and IR spectroscopy before and after alkaline hydrolysis. Upon grafting, the fibres underwent conformational rearrangements towards a more unordered state, while at weight gains higher than 60% they lost also the orientation. Upon hydrolysis, silk fibroin resulted enriched in β-sheet conformation, due to the preferential removal of the unordered domains, more prone to the alkaline attack. As a result of the interactions with the silk fibroin, the polymer increased its stability towards alkaline hydrolysis; in the presence of the fibres, the complete solubilization of the polymer is avoided. The A731/A1004 Raman ratio proved to be a suitable parameter to evaluate the composition of the grafted samples; its value linearly increases with weight gain (R2 = 0.998). Vibrational spectroscopy resulted a valid technique to investigate the mechanism and the effects of the hydrolytic attack, both fundamental for the designing of new-generation silk-based materials.