Dynamic Coordination Chemistry Enables Free Directional Printing of Biopolymer Hydrogel

Three-dimensional (3D) printing is a promising technology to develop customized biomaterials in regenerative medicine. However, for the majority of printable biomaterials (bioinks) there is always a compromise between excellent printability of fluids and good mechanical properties of solids. Three-dimensional printing of soft materials based on the transition from a fluid to gel state is challenging because of the difficulties to control such transition as well as to maintain uniform conditions three-dimensionally. To solve these challenges, a facile chemical strategy for the development of a novel hydrogel bioink with shear-thinning and self-healing properties based on dynamic metal ligand coordination bonds is presented. The noncovalent cross-linking allows easy extrusion of the bioink from a reservoir without changing of its bulk mechanical properties. The soft hydrogel can avoid deformation and collapse using omnidirectional embedding of the printable hydrogel into a support gel bath sharing the same cross-linking chemistry. After combination with photoinitiated covalent cross-linking, it enables manufacturing of hydrogel structures with complex shapes and precise location of chemically attached ligands. Living cells can be entrapped in the new printable hydrogel and survive the following in situ photo cross -linking. The presented printable hydrogel material expands the existing tool-box of bioinks for generation of in vitro 3D tissue-like structures and direct in vivo 3D printing.