3D Bioprinting of carbohydrazide-modified gelatin into microparticle-suspended oxidized alginate for fabrication of complex-shaped tissue constructs.

Extrusion-based bioprinting of hydrogels in a granular secondary gel enables the fabrication of cell-laden three-dimensional (3D) constructs in an anatomically accurate manner, which is challenging using conventional extrusion-based bioprinting processes. In this study, carbohydrazide-modified gelatin (Gel-CDH) was synthesized and deposited into a new multi-functional support bath consisting of gelatin microparticles suspended in oxidized alginate (OAlg) solution. During extrusion, Gel-CDH and OAlg were rapidly crosslinked due to the Schiff's base formation between aldehyde groups of OAlg and amino groups of Gel-CDH, which has not been demonstrated in the domain of 3D bioprinting before. Rheological results indicated that hydrogels with lower OAlg to Gel-CDH ratios possessed superior mechanical rigidity. Different 3D geometrically-intricate constructs were successfully created upon the determination of optimal bioprinting parameters. Human mesenchymal stem cells (hMSCs) and human umbilical vein endothelial cells (HUVECs) were also bioprinted at physiologically-relevant cell densities. The presented study has offered a novel strategy for bioprinting of natural polymer-based hydrogels into 3D complex-shaped biomimetic constructs, which eliminated the need for cytotoxic supplements as external crosslinkers or additional crosslinking processes; therefore, expanding the availability of bioinks.