Solubilization of parabens in aqueous Pluronic solutions: investigating the micellar growth and interaction as a function of paraben composition

Structural Behavior of Amphiphilic Triblock Copolymer P104/Water System

A detailed study of the different structural transitions of the triblock copolymer PEO₂₇-PPO₆₁-PEO₂₇ (P104) in water, in the dilute and semi-dilute regions, is addressed here as a function of temperature and P104 concentration (C_P104) by mean of complimentary methods: viscosimetry, densimetry, dynamic light scattering, turbidimetry, polarized microscopy, and rheometry. The hydration profile was calculated through density and sound velocity measurements. It was possible to identify the regions where monomers exist, spherical micelle formation, elongated cylindrical micelles formation, clouding points, and liquid crystalline behavior. We report a partial phase diagram including information for P104 concentrations from 1 × 10^-4 to 90 wt.% and temperatures from 20 to 75 °C that will be helpful for further interaction studies with hydrophobic molecules or active principles for drug delivery.

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.

Hydrophilic-hydrophilic mixed micellar system: effect on solubilization of drug

Mixed micellar systems have been tried with the aim of achieving higher solubility of drugs compared to single micellar systems. Hydrophobic-hydrophilic mixed micellar systems have been used for the above purpose for the drug ciprofloxacin in the past. In the present study, a hydrophilic-hydrophilic binary micellar system comprising of pluronic copolymers pluronic F127 and pluronic L64 has been studied for its effect on solubilization of the drug Ciprofloxacin. The solutions of the two individual pluronic and their mixed micellar system with drugs were subjected to characterizations viz. UV-spectrophotometry, fluorimetry, FT-IR, dynamic light scattering (DLS), rheology, and partition coefficient. The mixed pluronic–drug system displayed greater solubility of the drug compared with the neat pluronic-drug systems in most of the characterizations. New C–OH bond formation was evidenced by FT-IR spectra due to drug micelle interaction. The values of free energy changes of micellization were found to be −25 kJ mol−1 for pluronic F127, −74.5kJmol−1 for L-64, and −170.4 kJ mol−1 for the mixed pluronic. This is suggestive of spontaneous and stronger binding of drug ciprofloxacin with mixed pluronic in comparison with that in single micellar systems.

Graphic abstract

Small molecule-mediated self-assembly behaviors of Pluronic block copolymers in aqueous solution: impact of hydrogen bonding on the morphological transition of Pluronic micelles

The influence of hydrogen bonding on the self-assembly behaviors of Pluronic P123 micelles is experimentally and theoretically investigated by introducing three small molecules, i.e. propyl benzoate (PB), propyl paraben (PP) and propyl gallate (PG) into the aqueous solution. It is discovered that the number of phenolic hydroxyl groups and concentration of the tested small molecules exhibit a profound impact on the micellar morphology. Although all the small molecules increase the size and polydispersity of Pluronic micelles in a concentration-dependent manner, the micellar morphologies induced by them vary considerably as demonstrated by DLS and cryo-TEM measurement. PB, without phenolic hydroxyl, cannot bring about the morphological change of P123 micelles, while PP induces a series of morphological transitions from spheres to long worm-like micelles and then to unilamellar vesicles by increasing the PP content. Upon increasing the number of phenolic hydroxyls in small molecules, i.e. PG, the fusion of the intermicellar core takes place, resulting in the formation of large micelles and micellar clusters. A qualitative study by NMR reveals that the different locations of small molecules within the micelles are attributed to the balance of hydrogen bonding and hydrophobic interaction between small molecules and copolymers. In addition, molecular dynamics simulations (MDS) are performed to further confirm the experimental results and provide quantitative information on intermolecular interaction strength. It is supposed that the mechanism of micellar morphological transition mediated by small molecules is ascribed to the hydrogen bonding interactions with varying strengths between the PEO blocks and their phenolic hydroxyls, which governs their locations in micelles, affecting the free energies from different regions of micelles, and consequently leads to the varying micellar morphologies. This study deepens our understanding of the role of hydrgen bonding in the self-assembly behaviors of Pluronic micelles and provides an alternative strategy for manipulating the nanostructure of Pluronic micelles.

Polymersome formation induced by encapsulation of water-insoluble molecules within ABC triblock terpolymers

We found a morphological transition from spherical micelles to polymersomes induced by encapsulation of hydrophobic guest molecules.

The effect of cisplatin on the nanoscale structure of aqueous PEO-PPO-PEO micelles of varying hydrophilicity observed using SAXS

Aqueous solutions of polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) copolymers form micelles and cubic lattices as their temperature is raised. The presence of added solutes within the dispersions can also affect the kinetics of structure formation. Here, we investigate the structures formed in the amphiphiles P104, P105, and F108 solutions at 31% mass per v both neat and co-formulated with the drug cisplatin (0.02% to 0.1% mass per v) using small-angle X-ray scattering. P104 formed BCC colloidal crystals while P105 and F108 formed FCC structures. Cisplatin had a minor influence of the formation and stability of the crystals during these thermal excursions. The largest interaction between the amphiphiles and cisplatin was P104 where there was a 2% reduction in the BCC lattice parameter of P104 as cisplatin loading rose to 0.1% at 28 °C. The F108 unit cell swelled ∼2% upon cisplatin loading of 0.1%. A progressive evolution and breakdown of these structures was noted as the temperature rose from 10 °C to 35 °C. For the different amphiphiles, crystal thermal expansion coefficients of ∼1 × 10-2 °C-1 were determined in neat and loaded amphiphiles with cisplatin and all the crystals swelled with increasing temperature.

Engineered nanomaterials growth control by monomers and micelles: From surfactants to surface active polymers

In pseudo-micellar phase, the crystal growth is primarily achieved by the surface activity of the monomers in the presence of micelles. To ensure the maximum potential of surface activity of monomers in morphology control, a micellar phase is required. This account specifically focuses on the crystal growth control by the surface active monomers of conventional surfactants and that of water soluble polymers. It also distinguishes the mechanisms involved in the shape control driven by the micellar phase of micelle forming polymers, their role as nanoreactors, micellar stability, and micellar transitions from the monomeric phase. The fundamental basis of the crystal growth control by the surface active agents holds the key of using other non-convectional surface active species like proteins, carbohydrates, and bioactive polymers to achieve morphology control bionanomaterials for their specific biological applications.

Unravelling the Excellent Chemical Stability and Bioavailability of Solvent Responsive Curcumin-Loaded 2-Ethyl-2-oxazoline-grad-2-(4-dodecyloxyphenyl)-2-oxazoline Copolymer Nanoparticles for Drug Delivery

A new gradient copolymer has been synthesized by the living cationic ring-opening polymerization of hydrophilic 2-ethyl-2-oxazoline with lipophilic 2-(4-dodecyloxyphenyl)-2-oxazoline (EtOx-grad-DPOx). The prepared copolymer is capable of assembling in water to yield polymeric nanoparticles that are successfully loaded with an anticancer agent, curcumin. Self-assembly of the copolymer was found to be tuned by the polarity as well as the hydrogen bonding ability of solvents. Solvent took distinctive role in the preparation of unloaded and curcumin-loaded nanoparticles. The stability of the nanoparticles was increased by curcumin loading promoted by curcumin-polymer interactions. Further, the chemical stability of curcumin in water is largely enhanced inside the polymeric nanoparticles. Curcumin-loaded (EtOx-grad-DPOx) copolymer nanoparticles showed excellent stability in the biological medium, low cytotoxicity, and concentration dependent uptake by U87 MG and HeLa cells, which indicate the possibility of their efficient application in drug delivery.

Length vs. stiffness: which plays a dominant role in the cellular uptake of fructose-based rod-like micelles by breast cancer cells in 2D and 3D cell culture models?

Internalization of rod-like micelles by breast cancer cells is significantly affected by the stiffness of nano-rods.

EXPLOITING THE VERSATILITY OF CHOLESTEROL IN NANOPARTICLES FORMULATION

The biocompatibility of polymers, lipids and surfactants used to formulate is crucial for the safe and sustainable development of nanocarriers (nanoparticles, liposomes, micelles, and other nanocarriers). In this study, Cholesterol (Chol), a typical biocompatible component of liposomal systems, was formulated in Chol-based solid nanoparticles (NPs) stabilized by the action of surfactant and without the help of any other formulative component. Parameters as type (Solutol HS 15, cholic acid sodium salt, poly vinyl alcohol and Pluronic-F68), concentration (0.2; 0.5 and 1% w/v) of surfactant and working temperature (r.t. and 45°C) were optimized and all samples characterized in terms of size, zeta potential, composition, thermal behavior and structure. Results demonstrated that only Pluronic-F68 (0.5% w/v) favors the organization of Chol chains in structured NPs with mean diameter less than 400nm. Moreover, we demonstrated the pivotal role of working temperature on surfactant aggregation state/architecture/stability of Chol-based nanoparticles. At room temperature, Pluronic-F68 exists in solution as individual coils. In this condition, nanoprecipitation of Chol formed the less stable NPs with a 14±3% (w/w) of Pluronic-F68 prevalently on surface (NP-Chol/0.5). On the contrary, working near the critical micelle temperature (CMT) of surfactant (45°C), Chol precipitates with Pluronic-F68 (9±5% w/w) in a compact stable matricial structure (NP-Chol/0.5-45). In vitro studies highlight the low toxicity and the affinity of NP-Chol/0.5-45 for neuronal cells suggesting their potential applicability in pathologies with a demonstrated alteration of neuronal plasticity and synaptic communication (i.e. Huntington's disease).

Macromolecular Brushes as Stabilizers of Hydrophobic Solute Nanoparticles

Macromolecular brushes bearing poly(ethylene glycol) and poly(d,l-lactide) side chains were used to stabilize hydrophobic solute nanoparticles formed by a rapid change in solvent quality. Unlike linear diblock copolymers with the same hydrophilic and hydrophobic block chemistries, the brush copolymer enabled the formation of ellipsoidal β-carotene nanoparticles, which in cosolvent mixtures developed into rod-like structures, resulting from a combination of Ostwald ripening and particle aggregation. The stabilizing ability of the copolymer was highly dependent on the mobility of the hydrophobic component, influenced by its molecular weight. As shown here, asymmetric amphiphilic macromolecular brushes of this type may be used as hydrophobic drug stabilizers and potentially assist the shape control of nonspherical aggregate morphologies.

Chemosensitization of doxorubicin in multidrug-resistant cells by unimolecular micelles via increased cellular accumulation and apoptosis

OBJECTIVES

Unimolecular micelles were prepared by modification of polyamidoamine (PAMAM) dendrimers using Pluronic F127 (PF127), which is expected to reverse multidrug resistance (MDR). And the reversal mechanisms have been studied.

METHODS

Characterization of the products was carried on. MTT assay was used to evaluate the cytotoxicity of the DOX-loaded conjugates. Cellular uptake study was measured by confocal laser scanning microscope and flow cytometry. Apoptosis assay was identified by Annexin V-FITC/PI apoptosis assay and Hoechst 33 342 staining.

KEY FINDINGS

Improved cytotoxicity of DOX-loaded conjugates in MCF-7/ADR cells (as much as 33-fold according to the IC50 values) was observed in contrast with that of free DOX. The DOX-loaded conjugates induced a much quicker and 100% uptake in MCF-7/ADR cells, and more than fivefold accumulation of DOX-loaded conjugates was observed compared with free DOX. Apoptosis assay showed that DOX-loaded conjugates decreased the cell viability from 81.87 ± 5.94% to 54.83 ± 3.63% (DOX concentration 2 μg/ml). At 48 h, more accumulation and distribution in the nuclei were observed after treatment with DOX-loaded conjugates.

CONCLUSIONS

PF127-PAMAM conjugates showed superiority in the treatment of MCF-7/ADR, which implied the potential vehicles of anticancer drugs for the reversal of MDR.

TBP induced double cloud point in aqueous EO13PO30EO13 solutions: investigating the evolution of associated micellar characteristics as a function of temperature

TBP solubilized Pluronic L64 solutions exhibit inter-micellar attraction driven micellar cluster formation upon cooling, which is unique in non-ionic micellar systems.

Colloidal micelles of block copolymers as nanoreactors, templates for gold nanoparticles, and vehicles for biomedical applications

Target drug delivery methodology is becoming increasingly important to overcome the shortcomings of conventional drug delivery absorption method. It improves the action time with uniform distribution and poses minimum side effects, but is usually difficult to design to achieve the desire results. Economically favorable, environment friendly, multifunctional, and easy to design, hybrid nanomaterials have demonstrated their enormous potential as target drug delivery vehicles. A combination of both micelles and nanoparticles makes them fine target delivery vehicles in a variety of biological applications where precision is primarily required to achieve the desired results as in the case of cytotoxicity of cancer cells, chemotherapy, and computed tomography guided radiation therapy.

Interaction, solubilization and location of p-hydroxybenzoic acid and its sodium salt in micelles of moderately hydrophilic PEO-PPO-PEO triblock copolymers

Micelles of ABA type triblock copolymers (where A is polyethylene oxide PEO and B is polypropylene oxide PPO) viz. Pluronic® P103, P104 and P105 (each containing almost the same PPO mol wt. ~ 3250 g/mol and 30, 40 and 50 wt.% of PEO, respectively) in the presence of p -hydroxybenzoic acid (PHBA) and its sodium salt (Na-PHBA) were examined by viscosity, dynamic light scattering (DLS), small angle neutron scattering (SANS) and NMR. Spherical polymeric micelles (apparent hydrodynamic diameter ~ 20 nm) in water at 30 °C grow in the presence of PHBA and transform into prolate-ellipsoidal shape with an increased aggregation number. The micellar transition was favored at higher PHBA concentration, temperature and for copolymers with more hydrophobicity. The PHBA salt, however, increased cloud point and showed only a marginal decrease in aggregation number even at much higher concentrations. The location of PHBA in micelle was elucidated by nuclear Overhauser enhancement spectroscopy (NOESY).

Drug-induced morphology switch in drug delivery systems based on poly(2-oxazoline)s

Defined aggregates of polymers such as polymeric micelles are of great importance in the development of pharmaceutical formulations. The amount of drug that can be formulated by a drug delivery system is an important issue, and most drug delivery systems suffer from their relatively low drug-loading capacity. However, as the loading capacities increase, i.e., promoted by good drug-polymer interactions, the drug may affect the morphology and stability of the micellar system. We investigated this effect in a prominent system with very high capacity for hydrophobic drugs and found extraordinary stability as well as a profound morphology change upon incorporation of paclitaxel into micelles of amphiphilic ABA poly(2-oxazoline) triblock copolymers. The hydrophilic blocks A comprised poly(2-methyl-2-oxazoline), while the middle blocks B were either just barely hydrophobic poly(2-n-butyl-2-oxazoline) or highly hydrophobic poly(2-n-nonyl-2-oxazoline). The aggregation behavior of both polymers and their formulations with varying paclitaxel contents were investigated by means of dynamic light scattering, atomic force microscopy, (cryogenic) transmission electron microscopy, and small-angle neutron scattering. While without drug, wormlike micelles were present, after incorporation of small amounts of drugs only spherical morphologies remained. Furthermore, the much more hydrophobic poly(2-n-nonyl-2-oxazoline)-containing triblock copolymer exhibited only half the capacity for paclitaxel than the poly(2-n-butyl-2-oxazoline)-containing copolymer along with a lower stability. In the latter, contents of paclitaxel of 8 wt % or higher resulted in a raspberry-like micellar core.