3D-printed ultra-stretchable silk fibroin-based biocompatible hydrogels

Flexible hydrogels are extensively being explored for potential applications in biomedical devices and flexible electronics. Long-term stability and excellent flexibility are two critical criteria for hydrogel-based devices. In this study, a ternary blend ink was formulated specifically for three-dimensional (3D) printing of stretchable hydrogels comprising silk fibroin, polyvinyl alcohol, and methylcellulose. The ink composition was tuned to ensure favorable rheological properties for 3D printing. The printed hydrogels were subjected to methanol treatment to achieve the desired flexibility. The developed silk hydrogels exhibited superior mechanical properties: elongation at break (459 ± 5 %), breaking strength (137 ± 6 kPa), elastic modulus (37 ± 3 kPa), toughness (334 ± 7 kJ/m3), and hysteresis (1.1 ± 0.4 kJ/m2). Additionally, the hydrogel exhibited anti-fatigue and shape recovery abilities. The in vitro degradation study demonstrated the long-term stability of the hydrogel. Furthermore, the in vivo biocompatibility was evaluated by subcutaneous implantation of the printed construct in a rodent model. The histological analysis of the tissue morphology and assessment of blood parameters showed no hallmarks of adverse immune reaction or toxicity caused by the implanted construct. Overall, the developed silk-based ternary blend ink can serve as a potential material platform for 3D printing hydrogel-based implantable devices.