Studies on Micellar Behavior of PEO-PBO or PEO-PBO-PEO Copolymers, or Surface Active Amphiphilic Ionic Liquids in Aqueous Media and Exploration of the Micellar Solutions for Solubilization of Dexamethasone and its Delayed Release

摘要

The aggregation behavior of a di- and tri-block copolymers of type PEO-PBO, PEO-PBO-PEO, surface-active ionic liquid (SAIL) of type 4-dodecyl-4-methylmorpholinium chloride [C(12)mmor][Cl], and 1-dodecyl-1-methylpyrrolidinium chloride [C(12)mpyrr][Cl]) in water as well as in 10 mM of a poorly water soluble dexamethasone (dex) aqueous solution was studied by determining the critical micelle concentrations using drug solubilization, surface tension, and isothermal titration calorimetry (ITC) methods. ITC measurements were also made on solutions prepared by mixing the micellar aqueous solutions of copolymers and simple aqueous solutions of SAIL across the mole fractions at three different temperatures (298.15, 308.15, and 318.15 K). The thermodynamic parameters, namely Gibbs free energy (G(m)), enthalpy (H-m), and entropy (S-m), of micellization were calculated, and it was observed that the negative G(m) and positive S-m for the mixture solutions increase with the increase in mole fraction of SAIL. Otherwise, the micellization is reported to be a spontaneous and highly entropy-driven process. The dex-solubilized micellar solutions were mixed with agar to obtain standing gels. The gel samples were dry-cast into thin films, and the release of dex from films by simple dilution was monitored by UV measurements. The drug release data was fitted to several mechanistic models, and it was inferred that the release mechanism for dex from thin films is non-Fickian for mixtures and Fickian in copolymer or SAIL micellar aqueous solutions. The transport of dex is diffusion-controlled with diffusivities of 5.8-12 x 10(-11) m(2) s(-1) for copolymer micelles, 5-11 x 10(-11) m(2) s(-1) for micelles of SAIL, and 3-14 x 10(-11) m(2) s(-1) for the mixed micelles of copolymer and SAIL in aqueous media.