In Situ Cross-Linkable Gelatin-CMC Hydrogels Designed for Rapid Engineering of Perfusable Vasculatures

Hydrogels that can be rapidly cross-linked under physiological conditions are beneficial for the engineering of vascularized 3-dimensional (3D) tissues and organs, in particular when cells are embedded at a high cell density or tissues are fabricated using bottom-up processes, including bioprinting and micromolding. Here, we prepared a gelatin-carboxymethylcellulose (CMC) hydrogel that cross-linked rapidly (<30 s) by mixing hydrazide-modified gelatin (gelatin-ADH) and aldehyde-modified CMC (CMC-CHO). Vascular endothelial cells encapsulated in the gelatin-CMC hydrogels were viable and sprouted readily, indicating that the hydrogels and their cross-linking reactions were cytocompatible and provided a suitable microenvironment for angiogenesis. Sprouting length of the vascular endothelial cells was modulated by altering the stiffness of the hydrogels and varying the concentrations of the two hydrogel components. Furthermore, we used an electrochemical reaction to detach cells from a gold electrode surface. In this approach, cells that were seeded on a gold surface via the oligopeptide layer, detached rapidly along with the electrochemical desorption of the layer and transferred to the hydrogel. Owing to the rapid gelation of the hydrogels and rapid electrochemical detachment of cells, cell transfer was completed within 10 min (including 30 s of gelation and 5 min of potential application). Rapid cell transfer was observed not only on a flat surface but also on different shapes, such as cylindrical needles. Vascular endothelial cells were transferred from needles onto the hydrogel to fabricate endothelial cell-enveloped microchannels. In subsequent perfusion culture, the transferred endothelial cells migrated and formed luminal structures in the hydrogel. This in situ cross-linkable hydrogel may be useful for the rapid fabrication of perfusable vascular networks to engineer vascularized and cell-dense 3D tissues and organs.