Micellar structural transitions and therapeutic properties in tea tree oil solubilized pluronic P123 solution

Structural and therapeutic properties of salicylic acid-solubilized Pluronic solutions and hydrogels

Salicylic acid (SA) finds extensive applications in the treatment of rheumatic and skin diseases because of its analgesic, anti-inflammatory and exfoliating properties. As it is lipophilic in nature, there is a need for appropriate delivery systems to harness these properties for different applications. Herein, we examined the suitability of Pluronic P123/F127 micellar systems as delivery media by investigating the structural, flow and antimicrobial properties of P123/F127-SA solutions and hydrogels using DLS, SANS, rheological and zone inhibition measurement techniques. SA modulates the aggregation characteristics of these surfactant systems and brings about spherical-to-worm-like micelle-to-vesicular structural transitions in the hydrophobic Pluronic P123 system, a spherical-to-worm-like micellar transition in the mixed P123/F127 system and an onset of inter-micellar attraction in the hydrophilic Pluronic F127 system. SA-solubilized systems of both hydrophobic and hydrophilic Pluronics inhibit the growth of Gram-positive and Gram-negative bacteria with comparable MIC values. This suggests that the interaction of SA molecules with the bacterial cell membrane remains unobstructed upon encapsulation in Pluronic micelles. F127 hydrogel-based SA formulations with rheological properties suitable for topical applications and up to 15% SA loading were prepared. These will be useful SA ointments as F127 is an FDA-approved excipient for topical drug delivery applications. The results indicate that Pluronics remain effective as delivery agents for SA and exhibit interesting structural polymorphism upon its solubilization.

Unusual Growth and Hydration Characteristics of Oil Solubilized Micelles in Aqueous Pluronic Systems

Lipophile induced modulations of self-assembly characteristics in aqueous Pluronic systems merit attention because of wide-ranging uses of Pluronics as solubilizing agents of lipophilic substances. In this paper, we report unusual evolutions of structural and hydration properties in lavender essential oil (LO) solubilized Pluronic P85 aqueous micellar systems as a function of micellar volume fraction and temperature. Our DLS, SANS, and viscometry studies show that the spherical-to-wormlike micellar structural transition observed in 1% P85 solutions upon solubilization of LO quite unexpectedly gets suppressed with increased P85 concentration to ≥5%. Detailed SANS studies reveal that the core sizes of the oil solubilized micelles cannot attain the threshold value required for the onset of structural transition at higher copolymer concentrations due to their progressive shrinking with an increase in P85 concentration. Oil solubilized P85 solutions show two cloud points and very interestingly exhibit micellar growth upon cooling to their lower cloud points. Steady state fluorescence studies explain this based on increasing dehydration of micellar corona with a decrease in temperature, very much opposite to what is observed in pure aqueous Pluronic systems. The results give new insight into viscous flow properties and low temperature storage possibilities of oil solubilized aqueous Pluronic systems.

Self-assembly of Tween 80 micelles as nanocargos for oregano and trans-cinnamaldehyde plant-derived compounds

The self-assembly of Tween 80 (T80) micelles loaded with plant-based oregano essential oil (OR) and trans-cinnamaldehyde (TCA) was studied. The effect of different factors, including the surfactant to oil ratio, the presence of sodium chloride, thermal treatment, and dilution on their formation and physicochemical stability was evaluated. The creation of nano-cargos was confirmed by TEM. The self-associated structures had z-average droplet diameters of 92 to 337 nm without any energy input. Whereas addition of 10% (w/v) NaCl prevented the formation of oregano essential oil nano-assemblies of T80, swollen micelles containing TCA were successfully produced. Moreover, the OR or TCA loaded-micelles had only a slight droplet size variation upon thermal treatment. Ultimately, their antibacterial activity analysis against some food pathogens revealed that the encapsulation of OR and TCA within micelles crucially improved their antibacterial activity. These straightforward and cost-effective designed systems can be applicable in different products, including foods and agrochemicals.

Alginate-poloxamer beads for clotrimazole delivery: Molecular interactions, mechanical properties, and anticandidal activity

Calcium alginate (CA) beads loaded with clotrimazole (CZ) were modified by adding poloxamer (PLX) in this study. Blends of PLX188 or PLX407 into sodium alginate (SA) dispersions caused a decrease in the SA zeta potential and led to viscosity synergism. SA with carboxyl and hydroxyl groups can interact with the hydroxyl groups of PLX via hydrogen bonding. A stronger interaction of SA with PLX407 was found when compared to the interaction between SA and PLX188. The PLX-CA beads gave a higher CZ entrapment efficiency than the CA beads. The highest PLX content used created an amorphous form of CZ in the beads because of the CZ solubilization by the PLX micelles. The addition of 0.5 or 1% w/v PLX can strengthen the CZ-loaded CA beads. Furthermore, the PLX-CA beads display a lower water uptake than the CA beads. PLX micellization can enhance CZ release and enhance the efficacy of CZ against Candida albicans. This study indicates that the molecular interaction of SA with PLX and the PLX micellization of CZ can improve the characteristics of CZ-loaded CA beads, which offer good potential for use as drug delivery systems or drug reservoirs in tablets for oral candidiasis.

Micellization of Pluronic P123 in Water/Ethanol/Turpentine Oil Mixed Solvents: Hybrid Particle-Field Molecular Dynamic Simulation

The hybrid particle–field molecular dynamics simulation method (MD-SCF) was applied to study the self-assembly of Pluronic PEO₂₀-PPO₇₀-PEO₂₀ (P123) in water/ethanol/turpentine oil- mixed solvents. In particular, the micellization process of P123 at low concentration (less than 20%) in water/ethanol/turpentine oil-mixed solvents was investigated. The aggregation number, radius of gyration, and radial density profiles were calculated and compared with experimental data to characterize the structures of the micelles self-assembled from P123 in the mixed solvent. This study confirms that the larger-sized micelles are formed in the presence of ethanol, in addition to the turpentine oil-swollen micelles. Furthermore, the spherical micelles and vesicles were both observed in the self-assembly of P123 in the water/ethanol/turpentine oil-mixed solvent. The results of this work aid the understanding of the influence of ethanol and oil on P123 micellization, which will help with the design of effective copolymer-based formulations.

Structural Characterization of Pluronic Micelles Swollen with Perfume Molecules

The insertion in nonionic polymer micelles (Pluronics F127) of seven essential oils and some of the pure compounds that compose them was investigated by complementary differential scanning calorimetry, small-angle X-ray, and neutron scattering (SAXS and SANS). The study revealed various insertion and swelling behaviors for the different oil molecules, an evidence of different interaction mechanisms involved between oils and Pluronic monomers. Thermodynamically, the addition of oil increased the micellization enthalpy due to an enhanced release of water molecules, leading subsequently to a decrease of the critical micellar temperature (CMT). Structurally, with oil, SANS revealed the presence of large aggregates at lower temperature than the CMT for which their size is maximal. Above the CMT, the size decreased and the equilibrium was reached a few degrees after the temperature corresponding to the maximum of the endothermic peak. At 37 °C, the detailed combined SANS and SAXS analysis demonstrated a partial phase separation between the oil and the poly(propylene oxide) core. The hydrophilic stabilizing poly(ethylene oxide) shell remains unchanged.