Viscoelasticity of Fibrous Hydrogels Driven by Dynamic Intrafibrillar Imine Cross-Linking

Viscoelasticity of biological fibrous networks impacts cell fates and may reflect pathological conditions in vivo. Imine-cross-linked fibrous hydrogels can serve as effective in vitro models for studying viscoelastic properties of biological tissues; however, the specific role of intrafibrillar dynamic covalent bonds in governing hydrogel elasticity and stress relaxation remains unexplored. Here, for fibrous hydrogels derived from cellulose nanocrystals and polyethylene glycol, we systematically varied the content of intrafibrillar imine cross-links to explore their impact on hydrogels' elastic response, stress relaxation, and fibrous structure. We showed that higher imine group contents resulted in greater elastic moduli and higher degrees of stress relaxation in fibrous hydrogels. The fibrous structure did not significantly change with varying imine group contents, which enabled the decoupling of changes in hydrogel morphology and viscoelastic properties. This work provides the capability of designing fibrous hydrogels with controlled viscoelasticity and exploring their roles in bioengineering.