Modulating the 3D-printability with nanocellulose hydrogels

3-dimensional (3D) printability with hydrogels can be engineered from first principles by modelling their viscoelastic and interfacial behaviour. Printability is defined as the ability of a gel to maintain shape during and after unsupported extrusion. We hypothesized that the quality and resolution of 3D gel printing can be predicted and optimized from the material viscoelastic response in the shear relaxation test. Hydrogels with varying ratios of cellulose nanofibrils (CNF) and cellulose nanocrystals (CNC) ionically crosslinked with CaCl 2 were characterized by rheology, and printing quality was tested using a filament sag test. A predictive model based on Euler-Bernoulli's beam-bending theory was developed to estimate the maximum span length that limits sag below a desired threshold using the linear viscoelastic relaxation modulus. The model accurately predicted the maximum span length required to limit filament sag across different hydrogel compositions and experiments confirmed close agreement between theoretical predictions and measured deflections. By reformulating sag into dimensionless parameters, the framework removes dependence on specific geometry and hydrogel composition which enables generalization to any soft colloidal gels. This study establishes a quantitative platform for engineering, from first colloidal, interfacial, and continuum mechanics principles, the 3D-printability of hydrogels beyond nanocellulose systems. • A filament sag test directly quantified hydrogel print fidelity. • Euler–Bernoulli's beam bending equation predicted sag from viscoelastic modulus. • Dimensionless sag ratios generalized printability across gel types. • CNC/CNF blends with CaCl 2 improved stiffness and yield stress. • Framework enables predictive design of 3D-printable colloidal hydrogels.