Silk-based hydrogels for 3D bioprinting with fibroin and sericin

Silk-based hydrogels have emerged as a promising class of biomaterials in the field of 3D bioprinting. These 3D structures have desirable biocompatibility, versatility, and tunable mechanical properties. In addition, high water content and fibrous-like features of silk hydrogels, similar to natural tissues, enables them to mimic the extracellular matrix and provide a suitable environment for cells. Silk is primarily composed of two types of proteins: silk fibroin (SF) and silk sericin (SS). SF facilitates the formation of βsheets, providing mechanical robustness, while SS enhances cell adhesion and proliferation when used as an organic matrix or medium additive for cell growth, due to its abundant random coil structures. Thus, both proteins offer benefits toward cell-laden bioinks. In the current study, a synergistic approach was pursued that combines the unique attributes of both silk proteins to advance the development of 3D printed structures. Gelatin and glycerol were added to the SS and SF formulations to improve printability. Enzymatic crosslinking post-printing using horseradish peroxidase/hydrogen peroxide (HRP/H2O2) was conducted to stabilize the constructs. In this approach, a SS-based bioink with encapsulated human dermal fibroblasts (HDFs) was developed. Additionally, SF-based ink was incorporated into the 3D printing process to provide structural support and additional adhesion points for the cells. The 3D bioprinted structures positively impacted cell viability and proliferative capacity of HDFs in culture to highlight the potential of silk-based biomaterials as bioinks for tissue engineering.