Voltage-responsive reversible self-assembly and controlled drug release of ferrocene-containing polymeric superamphiphiles

Abstract

A new type of voltage-responsive comb-like superamphiphilic block polymer PEG₁₁₃-b-PAA₃₀/FTMA was prepared by the electrostatic interactions of an ionic ferrocenyl surfactant (FTMA) and an oppositely charged double-hydrophilic block polyelectrolyte poly-(ethylene glycol)-b-poly(acrylic acid) (PEG₁₁₃-b-PAA₃₀) in aqueous solution. An in situ electrochemical redox system was designed to research its electrochemical activity in aqueous solution. The polymeric superamphiphile PEG₁₁₃-b-PAA₃₀/FTMA could reversibly aggregate to form spherical micelles of 20–30 nm diameter in aqueous solution, and also disaggregate into irregular fragments by an electrochemical redox reaction when its concentration is in the range of the critical aggregation concentration (cac_red) of the reduction state to its cac_ox of the oxidation state. Interestingly, above cac_ox, the superamphiphile can aggregate into spherical micelles of 20–30 nm diameter, which can be transformed into larger spherical micelles of 40–120 nm diameter after electrochemical oxidation, and reversibly recover initial sizes after electrochemical reduction. Moreover, this reversible self-assembly process can be electrochemically controlled just by changing its electrochemical redox extent without adding any other chemical reagent. Further, rhodamine 6G (R6G)-loaded polymeric superamphiphile aggregates have been successfully used for the voltage-controlled release of loaded molecules based on their voltage-responsive self-assembly, and the release rate of R6G could be mediated by changing electrochemical redox potentials and the concentrations of polymeric superamphiphiles. Our observations witness a new strategy to construct a voltage-responsive reversible self-assembly system.