Sericin improves alginate-gelatin hydrogels’ mechanical properties, porosity, durability and viability of fibroblast in cardiac spheroids

Biofabrication of cardiac patches is a challenging strategy proposed as an alternative to transplantation for end-stage heart failure patients. The optimization of the bioink used for this aim can be limited by costs, properties and biocompatibility of its building blocks. Lately, sericin has emerged within a wide range of natural proteins thanks to its bioadhesive and biocompatibility potential. In this study, we assessed for the first time the effects of adding silk sericin on alginate-gelatin hydrogels, proposed for cardiac applications. To this aim, we first biofabricated sericin-containing hydrogels with increasing protein concentrations. Thus, we characterized hydrogels’ mechanical behaviour, porosity and structure through rheology, Brillouin microspectroscopy and SEM. Then, we bioprinted the formulated hydrogels and evaluated their effects on human cardiac spheroids (CSs) in vitro. Our mechanical characterisation demonstrated that adding sericin significantly enhanced the elasticity and the viscosity of alginate-gelatin hydrogels. Sericin also modified hydrogels’ swelling behaviour and their pore size, increasing by 20%, 62%, and 92% in Ser1%, Ser2% and Ser3%, respectively. Although Ser1% did not exhibit significant effects on CSs, Ser2% and Ser3% enhanced cardiac cell viability for up to 14 days compared to the sericin-free hydrogel by acting on the fibroblast population. Sericin-based bioinks showed better printability and durability with +33% and +28% intact patches after 28 days of culture at 37°C compared to alginate-gelatin. Altogether our results validated the use of sericin as a promising component for the optimization of bioink intended for cardiac applications.