Enabling 3D printability and vascular morphogenesis with double network dynamic hydrogels

Hydrogels are crucial biomaterial candidates for tissue engineering and biofabrication applications. The matrix dynamics of hydrogels have recently been demonstrated to contribute to vascular morphogenesis, which is significant for tissue vascularization. However, such dynamic hydrogels are usually mechanically non-stable during culture due to bonding dissociation and cell-mediated degradation, which hinder their usage in advanced biofabricaiton technologies, such as 3D bioprinting. Here, we introduce a double-network dynamic hydrogel (DNDH) bioink strategy to integrate the structural printability, stability, and induction of vascular morphogenesis. Specifically, we synthesize a gelatin-based bioink that is composed of a hydrazone crosslinked dynamic hydrogel network and a methacrylate crosslinked non-dynamic hydrogel network. We demonstrate that our optimized DNDH formulation can be 3D printed into customized structures while retaining structural stability for weeks. Moreover, the DNDH exhibits matrix dynamics with a much shorter stress relaxation time than the non-dynamic counterpart, which is demonstrated to trigger vascular morphogenesis through cell-matrix interactions in a stiffness-independent way. The inclusion of biochemical cues in the matrix and co-culture with supporting cells further enhances the formation of vascular networks and confirms the advantages of DNDH over its non-dynamic counterpart. The in vivo studies further confirm the importance of matrix dynamics in vascularization promotion. Our work provides a generalizable and easy-to-use approach to introduce matrix dynamics to bioinks, which could expand the capability of dynamic hydrogels in biofabrication scenarios.