Silk Fibroin Purification and Characterization

The silk fibroin (SF) used in this work was extracted from Bombyx mori silk cocoons kindly provided by Instituto Murciano de investigación y Desarrollo Agrario y Alimentario (Murcia, Spain). The SF was purified as reported elsewhere [47 (link)]. In brief, cocoons were shredded in a mill and filter through a 1 mm stainless still mesh and later boiled for 2 h in a 0.2 N Na₂CO₃ solution to remove sericin, waxes and other impurities. Following this, the SF was collected in a 0.1 mm pore size strainer and washed thoroughly with warm water to remove any unbounded sericin. Finally, the SF was air-dried in a fume hood until constant weight was achieved. NAR was purchased from Sigma-Aldrich (Madrid, Spain) and was used as received. Purified water from a Millipore Direct-Q1 ultrapure water system (18.2 MΩ·cm at 25 °C; Billerica, MA, USA) was used throughout the experimentation.