Preparation of thermoresponsive & enzymatically crosslinkable gelatin-gellan gum bioink: A protein-polysaccharide hydrogel for 3D bioprinting of complex soft tissues.

Developing superior bioinks present several challenges in achieving ideal properties such as biocompatibility, viscosity, degradation rates & mechanical properties which are required to make functional tissue constructs. Various attempts have been made to prepare excellent bioink compositions that are suitable to address the above challenges. Herein, a versatile combination of gelatin (GL) - gellan gum (GG) bioink was successfully formulated & the bioink 7.5GL/2GG was found to be ideal for printing complex and highly intricate structures with excellent shape fidelity. Two different crosslinkers namely transglutaminase (TG) and calcium chloride (CaCl) were utilized for crosslinking. The rheological properties of GL/GG bioink indicated that TG and dual (TG + CaCl) crosslinked constructs had storage modulus equivalent to the that of native skin. Direct and indirect cytotoxicity assays revealed that the developed constructs were cytocompatible as well as hemocompatible. The 3D bioprinted GL/GG constructs crosslinked with only TG showed better cell viability, proliferation, cell spreading and wound healing efficiency in vitro compared to dual crosslinked constructs. In conclusion, TG crosslinking of 7.5GL/2GG bioink was ideal for bioprinting of skin tissue constructs for regenerative medicine applications. By altering the concentrations & printing conditions, this bioink may be tuned for other soft tissue engineering applications.