4. 3D Bioprinting of Shear-Thinning Self-assembly Bioink

When applying a new material as a bioink in microextrusion bioprinting, numerous considerations need to be addressed. As stated in Chap. 3, one of the primary considerations is printability, which normally encompasses the material’s ability to (i) be injected from a printhead (ii) undergo rapid gelation upon deposition, and (iii) exhibit suitable mechanical properties that would support the printed structure. Given this, we seek to explore hydrogel formulation that could meet these criteria. Specifically, in this chapter, we will apply a shear-thinning and rapidly self-healing guest–host hydrogel based on hyaluronic acid (HA) to microextrusion 3DP. Adamantane (Ad, guest) and β-cyclodextrin (CD, host) moieties are separately coupled to HA, to create two hydrogel precursors that form a supramolecular assembly upon mixing [1]. It is hypothesized that such formulation would allow for smooth extrusion and temporary stabilization post-extrusion because of the shear-thinning and self-healing properties, respectively. To enhance the structural integrity of the supramolecularly crosslinked hydrogel, we also introduce photo-crosslinkable groups onto the macromers. We then investigate how each type of crosslinking (guest–host, photo-crosslinking, and their combination) affects the printability of multilayer scaffolds. Post-crosslinking methods are also explored concerning structural integrity and stability over time. Printed structures can be further functionalized to support cell culture. Similar dual-crosslinking mechanisms based on supramolecular and covalent bonding may enable the development of 3D printable hydrogel bioinks from materials that cannot otherwise be printed.