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Bioprinting in granular support hydrogels - characterizing the role of particle morphology and packing density

Embedded bioprinting into support hydrogels enables controlled extrusion of low viscosity bioinks into complex 3D structures with high-resolution features. Granular hydrogels, formed through packing of hydrogel microparticles, are increasingly employed as support materials due to their shear-thinning and self-healing properties that are essential for the embedded bioprinting process. Despite the widespread use of granular support hydrogels for embedded bioprinting, their general design criteria such as the optimal particle morphology, size, and packing density have not been established. Here, we developed granular support hydrogels with varied particle morphologies and packing densities, to explore how these parameters can influence rheological behaviour and the embedded bioprinting process. Interestingly, lower viscosity support hydrogels with a higher yield point, formulated from particles with irregular morphologies that increased particle-particle interactions, were found to improve print quality outcomes. In particular, we observed these formulations improved extrusion consistency during complex print paths and reduced disruption of adjacent filaments during successive print paths. These results improve our understanding of particle-particle interactions in granular support hydrogels during embedded bioprinting, and can be used to inform the design of future support hydrogel compositions.