2.1. Preparation of silk fibroin solution
Cocoons of B. mori silkworm were supplied by Bratac
(São Paulo, Brazil). The cocoons were degummed three
times by soaking in 1 g/L of Na2CO3 solution at 85 C for
30 min to remove the sericin of the cocoons, and then rinsing
in distilled water to remove Na2CO3 residues. The SF
fibers were dried and dissolved in a ternary solvent of
CaCl2:CH3CH2OH:H2O, in a molar ratio of 1:2:8, at 85 C
until total dissolution, to a SF salt solution of 10% (w/v).
The SF salt solution was then dialyzed (cellulose membrane,
Viscofan 22 EU – 20 USA) against distilled water
for 3 days, at 8 C, with water changes every 24 h [27].
The final concentration of the SF aqueous solution was
4% (w/v), which was determined by weighing the remaining
solid after drying.