The post-processing temperature or humidity can importantly control the secondary structure and characteristics of silk fibroin films.

Temperature and humidity (TH) are highly important factors that can control the secondary structure and characterization of silk fibroin (SF) biomaterials. In this study, the water stability, secondary structure, mechanical properties, surface morphology, and degradation of silk fibroin films (SFFs) with post-processing in different TH were investigated. Fourier transform infrared indicated that the SFF secondary structure did not change under low-relative humidity (RH) despite temperatures up to 180°C, while it transformed at 40°C with 100% RH in 10 min. A film with a higher tensile strength (42.1 ± 8.2 MPa) could be obtained after post-processing at 90°C/100% RH for 10 min. While a film with higher ductility (elongation at break: 198.8 ± 31.8%) was generated after post-processing at 40°C/100% RH for 10 min. Scanning electron microscope showed that the film presented a network structure of nanoparticles in series under certain TH post-treatment. Enzymatic hydrolysis proved that the SFFs containing a higher content of silk II structure degraded more slowly. Therefore, TH post-treatment is a relatively mild way to change the secondary structure and properties of SFFs, which can be widely used in loading drugs and maintaining the activity of drugs in SF biomaterials.

Degraded Sericin Significantly Regulates Blood Glucose Levels and Improves Impaired Liver Function in T2D Rats by Reducing Oxidative Stress.

Sericin could be degraded well into low-molecular-weight sericin (SS) through a novel and environmentally friendly recycling process using an ultrasonically degumming method in Ca(OH)2 aqueous solution. The oral administration of the SS has an evidently hypoglycemic effect on STZ-induced T2D rats. At oral doses of 2.5 and 5% SS for four weeks, the fasting blood glucose decreased by over 60% compared with that in the untreated model group. Oral glucose tolerance and insulin tolerance were ameliorated by the peptide treatment. The serum insulin level was reduced by approximately 35%, the insulin resistance index was reduced by more than 66%. The 8-hydroxy-2 deoxyguanosine level showed a large reduction of 20%, and the total antioxidant activities significantly increased. Hematoxylin-eosin staining and fluorescent immunostaining sections showed that liver and pancreas damage was partly recovered in T2D rats. In summary, oral SS demonstrated evidently hypoglycemic effects mainly related to reducing oxidative stress in the damaged liver and pancreas of T2D rats. Therefore, these results have suggested that the degraded sericin has a potential use in SS-based healthy functional food or hypoglycemic drugs as a waste recovered from sericulture resources.