Gradient Multinozzle 3D Printing

Abstract Direct ink writing is compatible with an expansive materials palette. While enabling diverse applications, this materials versatility brings significant bottlenecks in ink formulation, often requiring the mixing, printing, and testing of dozens to hundreds of ink compositions over the course of a project. To accelerate ink-space exploration, we introduce gradient embedded multinozzle (GEM) printheads that combine the high-throughput parallelized printing of multinozzles with combinatorial ink mixing. These printheads allow simultaneous mixing of two-, three-, and four-input inks which are distributed to printer nozzles to create complex 3D structures with graded compositions of inks. Using a two-way GEM printhead, we vali-date cell compatibility by printing scaffolds containing various concentrations of fibroblasts and observing non-linear compaction behaviours. We next test a three-way GEM multinozzle to print ten compositions of di- and multi-functionalized poly(ethylene-glycol) diacrylate hydrogel tri-leaflet valves, optimizing for stiffness, swelling ratio, and toughness. Our GEM multinozzles are compatible with open-source printers and either pressure- or volume-driven extrusion systems and promise to accelerate iterative ink design and testing. Competing Interest Statement M.A.S.-S. owns stock in Formlabs, manufacturer of the Form3B+ and its resin used in this research. L.R., A.S., K.M., and M.A.S.-S. are co-founders of Upbeat Biosciences, a cardiovascular cell and tissue engineering company. Footnotes Updates to SI equations (section 3.2 and 3.3), which led to revisions on Figure 2i and j. Corrected analysis on figure 2c, which led to recalculation on figure 2d