Colloidal Heterostructures Enable Interfacial Transport of Immiscible Molecules in Printable Organohydrogels

Surfactant-stabilized colloidal emulsions ensure simultaneous transport of immiscible molecules in hydrogels, but the release of small molecules is restricted by solubility in the continuous phase, or by uncontrolled transport pathways that cause overly slow or rapid release. This study shows that the molecular transport of multiple components through heterostructured organohydrogels can be tuned by adjusting their microstructural tortuosity through temperature and shear. The precursors are thermoresponsive nanoemulsions that contain hydrophilic methylene blue and lipophilic coumarin-6. Heating or shearing the precursors induces self-assembly of oil-rich phase into distinct microstructures through which the release kinetics of both molecules are independently tunable. Mechanistically, lipophilic molecules hop between oil droplets, while hydrophilic molecules traverse water-rich domains unless the hydrogel mesh size becomes too confined, at which point they undergo accelerated transport at the oil-water interface. Fluorescent imaging reveals that moderately hydrophilic molecules localize at the charged oil-water boundary, providing evidence for interfacial migration consistent with the acceleration in hydrophilic solute transport. The organohydrogels can be synthesized with bespoke form factors and diffusion coefficients that vary with processing parameters. Because the nanoemulsion precursor is compatible with continuous manufacturing methods, it can lead to scalable gels that possess powerful delivery properties without complex modification or formulation steps.