Loaded silk fibroin aerogel production by supercritical gel drying process for nanomedicine applications

Silk fibroin (SF) is a protein that can be used in biomedical field thanks to its biocompatibility, biodegradability and mechanical properties. SF is generally produced in form of aerogel by freeze drying; but, during this process, the delicate nanostructure of the gel can be destroyed, due to the surface tension action on the polymer matrix. The polymer organization at nanoscale (i.e., nanostructure) is preferably required for cells cultivation to ensure their adhesion, differentiation and migration inside the artificial support (i.e., scaffold). In this study, SF aerogels at 10 and 15 % w/w were produced by Supercritical gel drying, potentially useful for nanomedicine applications. SF aerogels were loaded with Ascorbic acid (AA) at 5 % w/w with respect the protein; it was selected since it should favor cell growth and, for example in case of bone tissue engineering applications, for osteoblast differentiation. The obtained aerogels were characterized by scanning electron microscopy and porosity analyses. Moreover, release tests by a spectrophotometer UV/Vis to measure AA release kinetics from SF aerogels and mechanical tests to determine the Young modulus of the produced SF aerogels were also performed. Supercritical assisted process allowed to preserve SF aerogel morphology at nanoscale, thanks to the near zero surface tension of the supercritical mixture (CO2 + organic solvent) at the selected operative conditions (i.e., 200 bar and 35 °C). Moreover, AA release rate can be controlled as well as mechanical properties of the produced aerogels, depending on SF concentration in the starting gel.