An IPN Bioink and Cross-Linking Process for Enhanced Mechanical Properties and Dynamic Control of Cell Spreading in 3D Bioprinting

Most hydrogel-based 3D bioprinting results in mechanically soft and weak constructs that are not suitable for practical tissue engineering applications. Conventional approaches to increase the stiffness of hydrogels lead to entrapment of encapsulated cells and suboptimal biological responses. In this paper, we report on a bioprinting process that provides dynamic control over stiffness and strength of the printed cell–hydrogel constructs, which promote cell spreading. The biomaterial ink consists of gelatin, gelatin methacryloyl (GelMA), and alginate, with each component independently cross-linked by enzymatic, photo-, and ionic cross-linking, respectively, to form interpenetrating networks (IPNs). The formation of IPNs significantly improved the mechanical properties and chemical stability of the printed structures. Temporal control of each cross-linking mechanism significantly increased cell spreading, avoiding cell entrapment in the stiff 3D hydrogel environment, while improving the mechanical properties of the constructs. This bioink and cross-linking process is expected to become a useful tool for producing mechanically robust engineered tissues.