Mechanical cues of an interpenetrating polysaccharide matrix regulate self-assembly of collagen fibers.

Collagen molecules self-assemble into supramolecular fibers within a molecularly crowded, polysaccharide-rich extracellular matrix (ECM) that has fluid-like, viscoelastic properties. Here, we determine that the viscoelasticity of alginate networks regulates the assembly of type I collagen fibers. The viscoelasticity and shear moduli of the alginate network were tuned by the polymer weight percentage and degree of cooperative ionic and covalent norbornene-tetrazine cross-linking. Stepwise shear strain applied to covalently cross-linked hydrogels generated higher stress than in ionic hydrogels. Hydrogels with reduced viscoelasticity also showed reduced water permeability. Second-harmonic generation confocal imaging revealed that decreasing viscoelasticity significantly suppressed collagen fiber self-assembly. Simulations demonstrated mechanical coupling between the hydrogel network and the aggregate size of collagen molecules, which was consistent with experimental results showing impaired rate and magnitude of self-assembly in covalently cross-linked networks. These results provide a framework for understanding how ECM mechanical properties can influence the assembly and organization of fibrillar macromolecules.