Shaping Synthetic Multicellular and Complex Multimaterial Tissues via Embedded Extrusion Volumetric Printing of Microgels

In living tissues, cells express their functions following complex signals from their surrounding microenvironment. Capturing both hierarchical architectures at the micro- and macroscale, and anisotropic cell patterning remains a major challenge in bioprinting, and therefore a bottleneck towards creating physiologically relevant models. Addressing this limitation, we introduced a novel technique, termed Embedded Extrusion-Volumetric Printing (EmVP), converging extrusion-bioprinting and layer-less, ultra-fast volumetric bioprinting, allowing to spatially pattern multiple inks/cell types. Light-responsive microgels were developed as permissive microenvironment for cell homing and self-organization, and as bioresins ({micro}Resins) for light-based bioprinting. Tuning the mechanical and optical properties of these gelatin-based microparticles enables their use as support bath for suspended extrusion printing, in which features containing high cell densities can be easily introduced. {micro}Resins can then be sculpted within seconds with tomographic light projections into centimetre-scale, granular hydrogel-based, convoluted constructs. Interstitial microvoids within microgels enhanced differentiation of multiple stem/progenitor cells (vascular, mesenchymal, neural), otherwise not possible with conventional bulk hydrogels. As proof-of-concept, EmVP was applied to create complex synthetic biology-inspired intercellular communication models, where adipocyte differentiation is regulated by optogenetic-engineered pancreatic cells. Overall, EmVP offers new avenues for producing regenerative grafts with enhanced functionality, and for developing engineered living systems and (metabolic) disease models.