Cellulose nanocrystal/collagen hydrogels reinforced by anisotropic structure: Shear viscoelasticity and related strengthening mechanism

To meet the requirements of applications, the viscoelasticity of hydrogels is usually improved by some ways, such as incorporating nanoparticles , designing network nanostructure and regulating cross-linking density. However, it is rare to improve the viscoelasticity by designing pore microstructure for hydrogels. In this work, cellulose nanocrystal (CNC)/collagen hydrogels with different pore structures (ordered tubular pores and disordered interconnected pores) and CNC concentrations (2.5–15 wt%) were prepared. The hydrogen bonding interaction between CNCs and collagen was confirmed by FTIR. The effects of pore structure and CNC concentration on the shear viscoelasticity of hydrogels were investigated, including creep, stress relaxation, frequency and strain response. The anisotropic structure and CNCs affected the creep and stress relaxation of the hydrogels, and enhanced the stiffness and dissipated energy, which demonstrated their reinforcing effect. The anisotropic structure with horizontally tubular array not only constrained collagen network rearrangement, but enhanced the elastic properties and torsion resistance of the hydrogels under torsional oscillation compared to the disordered porous structure. The mechanism for the multi-complexation between CNCs, collagen network and pore structure was proposed to understand the relationship between component, structure and hydrogel properties.