Influence of ethanol post-treatments on the properties of silk protein materials

The use of silk proteins sericin (SS) and fibroin (SF) has been increased for biomedical applications. In order to improve their behavior inside of biological environment, silk biomaterials must be treated after their manufacturing by means of diverse methods. These include ethanol post-treatments to increase their crystallinity, mechanical properties and water stability. In this study, the effect of ethanol post-treatments on the properties of silk protein materials was evaluated. Defective cocoons and silk fibrous waste (SW) were used to obtain silk sericin sponges (S-SS) and silk fibroin films (F-SF), respectively. Two ethanol treatments were evaluated in SS and SF: immersion (I) and solvent vapor annealing (SVA). Morphological modifications induced by ethanol post-treatments were studied by scanning electron microscopy (SEM). Conformational structure of the samples was analyzed by attenuated total reflectance-Fourier-transform infrared spectroscopy (ATR-FTIR), and the thermal properties were evaluated by differential scanning calorimetry (DSC) measurements. SEM images revealed that ethanol process induces changes in treated F-SF and S-SS, the material surfaces are more roughness, and these effects were more pronounced in samples treated by I than that subjected to SVA. As a result of the ethanol treatments, the ATR-FTIR and DSC results showed an increment in relative content of 13-sheet structures in both silk protein materials. The results suggest that ethanol post-treatments induce conformational transitions and morphological modifications in S-SS and F-SF that should be considered to select the post-treatment conditions according to the biomedical application requirements.