Silk fibroin-based inks for in situ 3D printing using a double crosslinking process

The shortage of tissues and organs for transplantation is an urgent clinical concern. <i>In situ</i> 3D printing is an advanced 3D printing technique aimed at printing the new tissue or organ directly in the patient. The ink for this process is central to the outcomes, and must meet specific requirements such as rapid gelation, shape integrity, stability over time, and adhesion to surrounding healthy tissues. Among natural materials, silk fibroin exhibits fascinating properties that have made it widely studied in tissue engineering and regenerative medicine. However, further improvements in silk fibroin inks are needed to match the requirements for <i>in situ</i> 3D printing. In the present study, silk fibroin-based inks were developed for <i>in situ</i> applications by exploiting covalent crosslinking process consisting of a pre-photo-crosslinking prior to printing and <i>in situ</i> enzymatic crosslinking. Two different silk fibroin molecular weights were characterized and the synergistic effect of the covalent bonds with shear forces enhanced the shift in silk secondary structure toward β-sheets, thus, rapid stabilization. These hydrogels exhibited good mechanical properties, stability over time, and resistance to enzymatic degradation over 14 days, with no significant changes over time in their secondary structure and swelling behavior. Additionally, adhesion to tissues <i>in vitro</i> was demonstrated.