An investigation into silk fibroin conformation in composite materials intended for drug delivery

Regenerated silk fibroin (SF) is a promising biomaterial to design drug delivery systems. To guarantee satisfactory prolonged release of loaded drugs, the native β-sheet conformation of SF is generally induced by a final curing which can determine instability of the loaded drug. This work aimed to investigate the influence on SF conformation of the addition of hydrophilic polymers, namely poloxamer 188 (PEO), a range of poly(ethylenglycol) (PEG)and poly(vinyl pyrrolidone) (PVP) and drying conditions, namely spray-drying or evaporation at 60 °C. DSC data on spray-dried products indicated that SF in composite materials was in the random coil conformation. ATR-FTIR spectroscopy with Fourier self-deconvolution of the amide I band revealed that SF in spray dried products was partially organized in the β-sheet structure only in presence of PEG4000. Both DSC and ATR-FTIR spectra registered on composite materials obtained by the slowest evaporation method indicated that all hydrophilic polymers favoured the β-sheet conformation. This feature was attributed to the formation of H-bonds with the tyrosine residues of the semicrystalline region in SF. In conclusion, this approach to prepare of SF/hydrophilic polymer composites at slow evaporation rate leads to water insoluble materials which could be used in the development of drug delivery systems.