Physico-chemical properties assessment of silk fibroin during its processing and aging

Silk fibroin is a protein extracted from silkworm cocoons used since ancient times for the production of textiles and for centuries in medicine as medical sutures due to its characteristics of stability, biocompatibility and biodegradability. Currently researches are focused on the use of fibroin as a biomaterial for regenerative medicine, such as films, hydrogels, membranes, as well as in drug delivery systems. Silk fibroin aging and degradation resulted from several complex combinations of degradation forces such as light, temperature, humidity and exposure of microorganisms. Recent research has focused on the evaluation of the influence of these factors on fibroin through artificial aging procedures. However, the assessment of deterioration characteristics during the natural aging of the silkworm cocoons is extremely important due its current usage. In this work, silkworm cocoons produced in the years 2009 and 2013 were investigated, in order to analyze the influence of the shelf life on the properties of silkworm cocoons and on the materials obtained during fibroin extraction from the cocoons. The steps of degumming, stretching and milling of fibroin fibers were analyzed through TGA, XRD and FTIR characterization techniques. The results show that, despite the aging, the fibroin fibers have a high thermal stability and amorphous structure. Regarding its composition, the fibers show mainly silk II (β-sheet) and silk I (α-helix) structures. These results contribute to the knowledge of how aging influence the physico-chemical characteristics of silk fibroin during processing conditions.