Direct ink writing of a bio-based ink made of low concentration cellulose nanofiber crosslinked with poly (ethylene glycol) via hydroxyl-yne click chemistry.

Achieving both low solid content and printability for cellulose nanofiber inks remains challenging. In this study, mild hydroxyl-yne click chemistry was used to chemically crosslink dipropiolate ester of polyethylene glycol (DA-PEG) with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) oxidized cellulose nanofibers (TOCN), forming TOCN-PEG (TP) inks. This crosslinking network allowed for effective viscosity control, with TP ink viscosity increasing by 128.5 % upon PEG addition. As a result, direct ink writing (DIW) 3D printing of TOCN was feasible at low concentrations (1.0-2.0 wt%). The printed TP hydrogel scaffolds exhibited high mechanical strength, bearing loads over 500 times their weight, and fluorescence due to conjugated double bonds and carbonyl groups. Additionally, cell viability rates exceeded 96 % at 24 h and 93 % at 48 h, indicating non-cytotoxicity (viability >80 %). Thus, the easily customizable TP inks prepared via hydroxyl-yne click chemistry hold promise for various applications, especially in 3D-printed bio-cellular scaffolds.