Block Polyelectrolyte Additives That Modulate the Viscoelasticity and Enhance the Printability of Gelatin Inks at Physiological Temperatures

We demonstrate the utility of block polyelectrolyte (bPE) additives to enhance
viscosity and resolve challenges with the three-dimensional (3D) printability of extrusion-based
biopolymer inks. The addition of oppositely charged bPEs to 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 3D networks) formed by the oppositely charged bPEs, 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 postextrusion flow characteristics for 3D printing,
including prominent yielding behavior, strong shear thinning, and rapid recovery upon flow
cessation. Moreover, the bPE self-assemblies also contribute to the robustness of the photo-cross-
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linked hydrogels; photo-cross-linked GelMA/bPE hydrogels are shown to exhibit higher shear
strength than photo-cross-linked GelMA hydrogels. Last, the assessment of the printability of GelMA/bPE inks indicates excellent
printing performance, including minimal swelling postextrusion, satisfactory retention of the filament shape upon deposition, and
satisfactory shape fidelity of the various printed constructs. We envision this study to serve as a practical guide for the printing of
bespoke extrusion inks where bPEs are used as scaffolds and viscosity enhancers that can be emulated in a range of photocurable
precursors.