(682g) Polymer Nanoparticle Hydrogels: Physical Hydrogels with Extreme Extensibility

Supramolecular hydrogels are appealing for biological applications such as drug delivery, 3D printing bio-inks, cell therapies and bioadhesives. Polymer nanoparticle (PNP) hydrogels are one class of injectable yield stress fluids that been shown to be effective in biomedical translational studies requiring non-invasive injections, biocompatibility and slow degradation. These hydrogels are composed of core-shell polymeric nanoparticles and dodecyl-modified cellulose polymers. The dodecyl-modified polymers interact with the hydrophobic nanoparticle cores yielding a robust network with shear-thinning and self-healing properties. These completely physically crosslinked materials exhibit functional yield stress values and gel-like properties across most frequencies. Herein, we have modified the outer shell of the nanoparticles with different polymers, including polyethylene-glycol and various acrylamide polymers, and observe great changes in mechanical properties of the resulting PNP hydrogels, suggesting variations in supramolecular PNP interactions. We employ traditional shear bulk rheometry and filament stretching extensional rheometry to understand structure-property relations. Different nanoparticle formulations in PNP hydrogels exhibit different strain rate dependence in extension. Nanoparticles with an outer corona of poly(N-isopropylacrylamide) in the PNP hydrogel exhibit extensional properties past 2000% Hencky strain. We find that the physical on and off rates of the dynamic interactions can be non-dimensionalized and elucidate mechanism behind extreme extensibility. These extensional physical hydrogels show great promise in applications requiring bioadhesion and provide insight in designing and understanding new hydrogel materials.