Protein-Engineered, Dynamic Hydrogel Bioinks for 3D Bioprinting

3D bioprinting has emerged as a promising tool for spatially patterning cells to fabricate models of human tissue. To date, most bioinks have been formulated with a focus on printability, while often overlooking the cell-interactive properties of the material. Here, we present a protein-engineered bioink material designed to have viscoelastic mechanical behavior, similar to living tissue. This viscoelastic bioink is composed of an engineered protein and a recombinant polysaccharide that are crosslinked through dynamic covalent bonds, a reversible bond type that allows for cellular remodeling over time. Viscoelastic materials are challenging to use as inks, as one must tune the kinetics of the dynamic crosslinks to allow for both extrudability and long-term stability of the printed structure. We overcome this challenge through the temporary use of small molecule catalysts and competitors that modulate the crosslinking kinetics and degree of network formation. These inks are used to print a model of breast cancer cell invasion, where the inclusion of dynamic crosslinks was required to allow cell invasion. Altogether, we demonstrate the power of protein-engineered, dynamic bioinks to recapitulate the native cellular microenvironment.