Structural considerations for physical hydrogels based on polymer-nanoparticle interactions

Designing supramolecular hydrogels for complex translational applications requires the ability to engineer viscoelasticity and flow behaviour at the bulk scale as well as the network structure at the nano and micro scales. Here we examine supramolecular hydrogels formed by polymer-nanoparticle interactions between hydrophobically-modified biopolymers and polymeric nanoparticles. Crosslinking in these systems is driven by dynamic and multivalent interactions between the biopolymers and the nanoparticles. We demonstrate control over viscoelasticity and microstructure by altering the hydrophobicity of pendant groups along the polymer backbone. Increasing the pendant group hydrophobicity creates larger polymer corona heights and, once a critical interparticle distance is spanned, induces a jammed microstructure that reinforces bridging based crosslinking. These studies suggest that design considerations for polymer-nanoparticle hydrogels are analogous to those of jammed soft glasses and provide an engineering handle to tune microstructure and viscoelasticity through chemical modifications to the polymer backbone. These materials are expected to be useful for applications that require injection, spraying, and control over cargo release kinetics.