3D-Printed Anisotropic Nanofiber Composites with Gradual Mechanical Properties

3D printing of bio-based nanomaterials into complex structures with design flexibility, structural anisotropy, and long-term stability is a key issue for biomedical applications. Herein, 3D-printed and ionically crosslinked structures with anisotropic, water-proof, and tunable mechanical properties are fabricated using a polysaccharide ink composed of nanocellulose, alginate, and CaCO3 nanoparticles. The excellent shear thinning properties of the ink, combined with double or even triple extrusion, allow printing of complex structures (tubes, buckets, ears, and boat models) with high shape fidelity even after crosslinking. The anisotropically printed and crosslinked structures can be mechanically tuned by controlling the fiber orientation via the printing path, the amount of crosslinker, the type of acid used for crosslinking (weak to strong), and the storage medium. This allows for tailored flexibility and a tensile modulus of the materials in wet state ranging from 1 to 30 MPa. Application of hydrostatic pressure of 160-600 mmHg for 24 h with a physiological fluid to a tubular structure, a model for the cardiovascular system, shows no leakage or rupture in the tube. The great design freedom offered by 3D printing and spatially controlled structural anisotropy enable the production of tailored materials for soft robotics or biomedical applications.