Injectable Gelatin Microgel-Based Composite Ink for 3D Bioprinting in Air

Injectable hydrogels have attracted much attention in tissue engineering and regenerative medicine for their capability to replace implantation surgeries with a minimally invasive injection procedure and ability to fill irregular defects. The proposed composite ink is a gelatin microgel-based yield-stress and shear-thinning composite material that is injectable and solidifies quickly after injection at room temperature, which can be utilized for the creation of three-dimensional parts in air directly. The gelatin composite ink consists of a microgel solid phase (gelled gelatin microgels) and a cross-linkable solution phase (gelatin solution-based acellular or cellular suspension). The gelatin composite ink can be injected or printed directly in air and solidifies as physical cross-linking to hold printed structures at room temperature. The fabricated part further undergoes a chemical cross-linking process when immersed in a transglutaminase solution to enzymatically gel the gelatin solution, making a physiologically stable construct as needed. Lattice, tube-shaped, cup-shaped, and human anatomical (ear and nose) structures are printed to demonstrate the feasibility of the proposed composite ink for printing applications. The morphology and metabolic activity of cells cultured in the gelatin composite ink are further analyzed to confirm the suitability of the proposed composite ink to provide a beneficial physiological environment for bioprinting needs.