Embedded printing of hydrogels and watery suspensions of cells in patterned granular baths.

Bioprinting within support media has emerged as the superior alternative to conventional extrusion printing. Not only because it allows for more freedom over the shapes that can be printed, but also because it allows for the printing of inks that would not retain shape fidelity in freeform deposition such as watery liquids. Apart from functioning as mechanical support during embedded printing, hydrogel microparticle support media can provide the unique advantage of offering distinct chemotactic cues to cells printed in the baths by varying the composition of the hydrogel microparticles. There is great potential in compartmentalized granular baths consisting of different hydrogel particle materials in the field of tissue engineering, as these allow for the local inclusion of properties or cues to guide tissue development. In this work, we present a method to create compartmentalized embedding baths by printing multiple granular hydrogel materials that are widely used in tissue engineering. After adapting the volume fraction (φp) of the particles in the bath, we print within them using both inks composed of hydrogel or of cells and other particles suspended in watery liquid. Our process consists of three steps: First the hydrogel microparticles are packed at a φp that allows them to be extruded while being reversibly jammed, facilitating the localized deposition of the granular media to form a compartmentalized bath. Then, each granular media is deposited in succession to create a packed suspension compartment, and by adding liquid post deposition, φp is reduced to allow for embedded printing. Finally, we demonstrate the printing of multiple inks within the compartmentalized embedding bath, and highlight the distinct differences between using inks composed of hydrogels or inks composed of particles suspended in watery liquid. This approach combines the advantages of embedded printing through the use of granular media with the added ability to pattern multiple bioactive granular materials to locally affect the behaviour of cells printed within the bath. We expect that this workflow will allow researchers to create spatially compartmentalized, customized bioactive embedding baths, that allow for the embedded printing of inks composed of hydrogels, cells and other particles adapted to their need.