Fig. 8. High-fidelity printing of stable structures was enabled by informed design of granular hydrogels.

(A) Granular hydrogels were extruded into square-shaped structures using direct ink writing. (B) Experimental (P < 0.001) and predicted extrusion pressures of granular hydrogels of varying building block stiffnesses represented as means ± SEM (n = 3). (C) Normalized yield stress values of granular hydrogels based on oscillatory rheology (gray), contact model (red), and experimental printing pressures (blue). (D) Schematic of jammed granular hydrogel extrusion process, showing the dependency of printing behavior on the decreased pore space due to contact deformations. (E) Extrusion process using a conical nozzle. (i) Representative printing of microgel packings (Ø = 55 μm) into multilayer structures via a conical nozzle (0.41 mm inner diameter). (ii) Representative image of jammed microgels before loading into extrusion cartridges. (iii) Printed square structures of granular hydrogels composed of stiff (E = 165 kPa, Ø = 55 μm) and (iv) soft (E = 20 kPa, Ø = 55 μm) microgels. Scale bars, 4 mm. (F) Bright-field and fluorescence microscopy images of extruded filaments of (i) stiff (E = 165 kPa, Ø = 55 μm) and (ii) soft (E = 20 kPa, Ø = 55 μm) jammed microgels suspended in fluorescein isothiocyanate–dextran–loaded PBS. Scale bars, 100 μm.