Fig. 4.

(A) Schematic of the 3D bioprinting system: the temperature controller on the syringe regulated the viscosity of GelMA/gelatin bioinks; the cooling system under the receiving platform temporarily thermo-cross-linked gelatin in the bioinks; and the UV light permanently photo-crosslinked GelMA in the bioinks. (B) Two-step cross-linking of GelMA/gelatin bioinks. Reprinted with permission from Ref. [132]. Copyright 2018, ACS. (C) Schematic illustrating the setup for generating hollow GelMA/Gel microfibers by microfluidic coaxial biofabrication for cannular tissue engineering. Reprinted with permission from Ref. [50]. Copyright 2019, ACS. (D) Photograph of an Organovo bioprinter. Schematic of the coaxial needle where the bioink is delivered from the core and the ionic crosslinking CaCl₂ solution is sheathed on the side. Schematic diagrams showing the two-step crosslinking process, where the alginate component is first physically crosslinked by the CaCl₂ followed by chemical crosslinking of the GelMA component using UV illumination. Reprinted with permission from Ref. [49]. Copyright 2016, Elsevier.