3D bioprinting of dual-crosslinked nanocellulose hydrogels for tissue engineering applications

Abstract

Hydrogels based on cellulose nanofibrils (CNFs) have been widely used as scaffolds for biomedical applications, however, the poor mechanical properties of CNFs hydrogels limit their use as ink for 3D bioprinting in order to generate scaffolds for tissue engineering applications. In this study, a dual crosslinkable hydrogel ink composed of poly(ethylene glycol) (PEG) star polymer and 2,2,6,6-Tetramethyl-1-piperidinyloxy (TEMPO)-oxidized nanocellulose fibers (CNFs) is presented. As the resulting hydrogel was of low structural integrity, at first crosslinking of CNF was introduced by Ca2+. Strong physical interaction between CNFs and Ca2+ cation allowed easy regulation of the viscosity of the inks for extrusion printing raising the solution viscosity by more than 1.5 times depending on the amount of Ca2+ added. The resulting hydrogel had high structural integrity and was further stabilized in a second step by photo crosslinking of PEG under visible light. In only a few seconds, hydrogels with Young’s modulus between ~10-30 kPa were obtained just by altering the CNFs and Ca2+ content. 3D printed hydrogels supported fibroblasts with excellent cell viability and proliferation. The dual crosslinkable hydrogel ink herein developed is versatile, easy to prepare, and suitable for 3D printing of bioscaffolds with highly tailored viscoelastic and mechanical properties applicable in a wide range of regenerative medicine.