Tough all-polysaccharide hydrogels with uniaxially/planarly oriented structure.

Considering that the poor mechanical performances of polysaccharide hydrogels always limit their practical applications, herein, we design and fabricate tough all-polysaccharide hydrogels by incorporating uniaxially/planarly oriented tunicate cellulose nanocrystals in physically cross-linked alginate networks. Firstly, alginate chains were loosely cross-linked by surface quaternized tunicate cellulose nanocrystals (Q-TCNCs) and Ca through electrostatic interaction. Secondly, the loosely cross-linked hydrogel was pre-stretched and immersed into CaCl solution, obtaining uniaxially oriented hydrogel, whose tensile strength was 31.6 MPa along the pre-stretching direction. After biaxial stretching, the orientation of TCNCs in hydrogel networks converted from dominantly uniaxially oriented structure to planarly oriented structure. The tensile strength, elastic modulus, and toughness of the planarly oriented hydrogels were about 6.6-, 44- and 3.3-folds of those of isotropic Q-TCNC/alginate hydrogel. This work provided a facile and efficient strategy for developing tough hydrogels with uniaxially/planarly oriented structure from biodegradable polymers.