Fresh 3D Printing of Double Crosslinked Hyaluronic Acid/Pectin Hydrogels

3D printing has emerged as a first-line approach for the fabrication of complex structures. In the biomedical field, extrusion-based is the most popular printing technique. However, a limited range of biocompatible printable inks is available for this technique because, typically, low-viscosity inks are not printable, or the resulting constructs are unable to self-support. In this work, use of the Freeform Reversible Embedding of Suspended Hydrogels (FRESH) extrusion-based technique to fabricate self-supported 3D constructs from low-viscosity polysaccharide inks composed of methacrylated hyaluronic acid (HA(GM)) and methacrylated pectin (PEC(GM)) is aimed. The use of a support bath of gelatin slurry to sustain the extruded filaments during both printing and post curing allows reaching a shape fidelity so far unreported for low-viscosity polysaccharide inks. Moreover, the methacrylate groups of HA(GM) and PEC(GM) lead to double crosslinked hydrogels, where the calcium ions added to the gelatin slurry promote the ionotropic gelation of PEC(GM), while the methacrylate groups of both PEC(GM) and HA(GM) promote their photocrosslinking after UV irradiation. The resulting 3D constructs exhibit elastic modulus in the range of 0.5-2.3 kPa, which is suitable for the 3D printing of constructs for soft tissue repair or substitution.