We demonstrate the utility of block polyelectrolyte (bPE) additives to enhance viscosity and resolve longstanding challenges with the three-dimensional printability of extrusion-based biopolymer inks. The addition of oppositely charged bPEs into solutions of photocurable gelatin methacryloyl (GelMA) results in complexation-driven self- assembly of the bPEs, leading to GelMA/bPE inks that are printable at physiological temperatures, representing stark improvements over GelMA inks that suffer from low viscosity at 37 °C leading to low printability and poor structural stability. The hierarchical microstructure of the self-assemblies (either jammed micelles or three-dimensional networks) formed by the oppositely charged bPEs, as confirmed by small angle X-ray scattering, is attributed to the enhancements in the shear strength and printability of the GelMA/bPE inks. Varying bPE concentration in the inks is shown to enable tunability of the rheological properties to meet the criteria of pre- and post-extrusion flow characteristics for 3D bioprinting, including prominent yield stress behavior, strong shear thinning, and rapid recovery upon flow cessation. Moreover, the bPE self-assemblies also contribute to the robustness of the photocrosslinked hydrogels – photocrosslinked GelMA/bPE hydrogels are shown to exhibit higher shear strength than photocrosslinked GelMA hydrogels. We envision this study to serve as a practical guide for the bioprinting of bespoke extrusion inks where bPE are used as scaffolds and viscosity enhancers that can be emulated in a range of biopolymers and photocurable precursors.
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