Synthesis of easily-processable collagen bio-inks using ionic liquid for 3D bioprinted liver tissue models with branched vascular networks

Bioprinting has been a flouring way to fabricate complex tissue and organ mimics via precisely depositing printable cell-laden biomaterials.However,there is a limited number of biomaterials that fulfill the mechanical property of printing while meeting the responsive environment desired for the cells.Despite excellent cell compatibility and bioactivity,collagen suffers from difficulties in processing and printability which inhibited its utilization in three-dimensional(3D)bioprinting.Herein,we address this limitation by using ionic liquid as the solvent in the modification process,enabling collagens modified with quantified norbornene for chemical crosslink and extrusion-based 3D printing.With improved solubility and rheological properties,norbornene-functionalized collagen(Col-Nor)exhibited better shape fidelity in extrusion-based 3D printing compared with the one before modification.Photo-crosslinked Col-Nor hydrogel provided structural support and promoted the adhesion,proliferation,and differentiation of various types of cells,which afforded a centimeter-scale liver tissue model.This highly generalizable methodology expands printable,versatile,and tunable hydrogels developed from the natural extracellular matrix,allowing the biofabrication of 3D liver tissue model with branched vascular networks.