Dynamic diffusion experiments were performed on aqueous polymeric micelles mixed with malachite green (0.05% mass v −1), erythrosin (0.1% mass v −1), and cisplatin (0.1% mass v −1) to gauge release from sequestered structures using ultraviolet-visible spectroscopy. The additives were formulated with 20% mass v −1 aqueous solutions of polyethylene oxide-polypropylene oxide-polyethylene oxide, PEO-PPO-PEO (F127). Each additive was tested neat at room temperature, neat at 40 C, and formulated with F127 at room temperature, and 40 C. After constructing calibration curves, the dynamic release for each ternary additive and corresponding diffusion coefficients were calculated. Results show that F127 retards permeation at room temperature. In general, the neat additives at 40 C showed the highest permeability for both malachite green and erythrosin. Malachite green released almost 90% of the dye by 60 min of permeation. When formulated with F127 at 40 C, sizeable release was still noted, but with an induction period of 10-30 min to register release. The behavior with cisplatin was more complicated as the first 5 h of permeation resulted in a burst delivery with cisplatin (6% total release with cisplatin-F127-RT compared to 4% total release cisplatin-RT) but with overall lower release. The higher fluence at elevated temperature is attributed to reducing the blocking effect of the amphiphiles on the walls of the dialysis tubing as they are directed to form colloidal gels. There is also likely a correlation between higher temperature and higher overall permeability if the membrane pores also expand with temperature. Keywords Surfactant Á Cisplatin Á Diffusion Á Drug delivery Á Malachite green chloride Á Erythrosin B dye

Aqueous solutions of polyoxyethylene–polyoxypropylene–polyoxyethylene (PEO–PPO–PEO) triblock copolymers (commercially available as Pluronic surfactants) micellize and structurally arrange into cubic quasicrystalline lattices as their temperature is raised. This structural evolution is seen macroscopically as a gelation, and the presence of these ordered phases can be controlled through both polymer concentration and temperature. The presence of added solutes within the dispersions can also affect the onset and kinetics of structure formation. Here we investigate the structures formed in Pluronic F127 solutions ranging from 20 to 30% with two pharmaceutical additives [methylparaben (MP) and dexamethasone (DX)] using small-angle X-ray scattering (SAXS). We observe both the progressive evolution and breakdown of these structures as the temperature is increased from 0 to 80 °C. Additionally, we conducted time-resolved SAXS measurements to elucidate the kinetics of the structural evolution. On the basis of the evolution of scattering peaks as the samples were being heated, we suggest that added MP changes the nucleation behavior of fcc phases within the sample from a heterogeneous process to a more homogeneous distribution of nucleated species. MP and DX also stabilize the micelle lattices, allowing them to persevere at higher temperatures. We observed the unusual result that the presence of DX caused the primary peaks of the structure factor to be suppressed, while preserving the higher order peaks. The primary peaks reappeared at the highest temperatures tested.

In situ photorheology experiments were conducted to investigate the kinetics of UV-triggered photogelation of aqueous Laponite nanoparticle dispersions formulated with less than 10 wt% of a triblock copolymer (Pluronic F127) and diphenyliodonium-2-carboxylate monohydrate, a photoacid generator (PAG). We show that gelation kinetics depend strongly on solution composition and intensity of UV light used during in situ photorheology experiments. A decrease in gelation rate was observed with increasing Pluronic F127 concentrations while higher PAG and Laponite concentrations result in higher gelation rates. Changing the intensity of UV light from 100 mW cm À2 to 150 mW cm À2 at a constant composition reduced the exposure time required prior to onset of gelation by half. Finally, the effect of Laponite and PAG on the micellization of F127 was probed using differential scanning calorimetry (DSC). The results show that the presence of Laponite particles and PAG suppresses the enthalpic endotherm associated with micelle formation in solutions containing up to 7.2 wt% Pluronic F127. Using these results, we present a detailed mechanism for the photogelation phenomenon as well as the parameters surrounding intelligent design and formulation of these systems.