(50e) Exploiting Amphiphile Interactions with Polyelectrolyte/Multivalent Ion Coacervates in Long-Term Sustained Release

Recent years have seen a growing interest in complex coacervates – i.e., solute-rich, insoluble aqueous liquids that form through complexation of polyelectrolytes with oppositely charged polymers, proteins, surfactants or multivalent ions. These complex fluids can range from Newtonian liquids to stiff/gel-like putties, and find use in diverse applications such as encapsulation and release, wet adhesion, sensing, and inorganic materials synthesis. In the last few years, our group has shown that putty-like coacervates prepared via self-assembly of poly(allylamine hydrochloride) (PAH) with strongly binding, pyrophosphate (PPi) or tripolyphosphate (TPP) anions can form densely crosslinked ionic networks that, due to their small hydrodynamic mesh size, sustain release of small hydrophilic molecules over months. Building on this work, here we show how interactions of these coacervate-based sustained release systems with anionic amphiphiles can enhance their performance. Specifically, when used to deliver weakly amphiphilic anionic molecules (e.g., ibuprofen), PAH/TPP coacervates produce a remarkable combination of extremely high payload contents (where the payload comprises up to 30% of the coacervate weight) with a highly sustained, multiple-month release. When added to PAH solutions, weak anionic amphiphiles form colloidal complexes with the PAH. Upon the addition of TPP to these colloidal PAH/amphiphile dispersions, however, the stronger PAH/TPP binding displaces the amphiphile from the PAH chains to form macroscopic PAH/TPP coacervates. Because the amphiphilic payload is concentrated near the PAH chains (due to the initial PAH/amphiphile binding), this encapsulation method generates extremely high payload contents, while preserving the coacervate’s multiple-month release functionality. Incorporating strong anionic amphiphiles (such as sodium dodecyl sulfate or sodium dodecyl benzene sulfate), on the other hand, disrupts the ionic PAH/TPP crosslinks. This disruption can: (1) accelerate molecular diffusion, and (2) enhance payload partitioning into the coacervates. The faster diffusion evidently reflects an increase in network pore size, while the enhanced payload partitioning likely stems from changes in coacervate hydrophobicity. Thus, while weak anionic amphiphiles are excellent payloads for PAH/TPP coacervates (which can be released in high doses over many months), strong anionic amphiphiles can be utilized to tailor PAH/TPP coacervate payload uptake and permeability to their various potential applications, such as drug delivery, disinfection technologies and separations.