Temperature-Induced Aggregation Kinetics in Aqueous Solutions of a Temperature-Sensitive Amphiphilic Block Copolymer

Effect of PCL end-groups on the self-assembly process of Pluronic in aqueous media

Understanding self-assembly of amphiphilic copolymers in aqueous solution is an important issue in many areas, e.g., in order to tailor-make carriers for drugs and genes. We have synthesized modified versions of the copolymer of type PEO-PPO-PEO (Pluronic, F127), with short (PCL(5)) or long (PCL(11)) PCL blocks at both ends. Turbidity, dynamic light scattering (DLS), small angle neutron scattering (SANS), and rheology measurements were carried out on dilute aqueous solutions of these polymers to investigate their self-assembly behavior. The DLS results clearly show that both micellization and inter-micellization can be controlled by polymer concentration, temperature, and length of the PCL block. The interplay between unimers, micelles, and clusters of micelles could be monitored and the size and size distribution of the species were determined. The SANS data could be portrayed by a spherical core-shell model at all considered conditions of temperature and concentration for F127 and PCL(5) apart from F127 at the lowest temperature measured. The SANS data for PCL(11) were described by a spherical core-shell model at low temperatures, whereas at elevated temperatures asymmetric sub-structures appeared and a cylindrical core-shell model was employed in the analysis of the data. The appearance of pronounced correlation peaks at elevated temperatures signalizes marked intermicellar interactions. The shear viscosity data revealed a minor shear thinning effect, suggesting that the interchain structures are rather stable and not easily disrupted. The work shows that PCL-modification of Pluronic has a large influence on the self-assembly process and on the final structure of the assemblies.

PEG coated vesicles from mixtures of Pluronic P123 and l-α-phosphatidylcholine: structure, rheology and curcumin encapsulation

PEG coated vesicles are important vehicles for the passive targeting of anticancer drugs. With a view to prepare PEG decorated vesicles using co-assembly of block copolymers and lipids, here we investigated the microstructure of aggregates formed in mixtures comprising lipids (l-α-phosphatidylcholine) and block copolymers (Pluronic P123), in the polymer rich regime. DLS and SANS studies show that the structure of the aggregates can be tuned from micelles to rod-like micelles or vesicles by changing the lipid to polymer composition. Rheological studies on gels formed by mixtures of polymer and lipid suggest incorporation of the lipid into the polymer matrix. The encapsulation efficiencies of polymer incorporated liposomes for curcumin and doxorubicin hydrochloride (DOX) are evaluated at different drug to carrier ratios. The pH dependent sustained release of both the drugs from the PEGylated liposomes suggests their application in the development of cost effective formulations for anticancer drug delivery.

Influence of additives on thermoresponsive polymers in aqueous media: a case study of poly(N-isopropylacrylamide)

Thermoresponsive polymers (TRPs) in different solvent media have been studied over a long period and are important from both scientific and technical points of view.

Polymer coated liposomes for use in the oral cavity - a study of the in vitro toxicity, effect on cell permeability and interaction with mucin

In this study we investigated the in vitro toxicity, impact on cell permeability and mucoadhesive potential of polymer-coated liposomes intended for use in the oral cavity. A TR146 cell line was used as a model. The overall aim was to end up with a selection of safe polymer coated liposomes with promising mucoadhesive properties for drug delivery to the oral cavity. The following polymers were tested: chitosan, low-methoxylated pectin (LM-pectin), high-methoxylated pectin (HM-pectin), amidated pectin (AM-pectin), Eudragit, poly(N-isopropylacrylamide-co-methacrylic acid) (p(NIPAAM-co-MAA)), hydrophobically modified hydroxyethyl cellulose (HM-HEC), and hydrophobically modified ethyl hydroxyethyl cellulose (HM-EHEC). With chitosan as an exception, all the systems exhibited no significant effect on cell viability and permeability at the considered concentrations. Additionally, all the formulations showed to a varying degree an interaction with mucin (BSM type I-S); the positively charged formulations exhibited the strongest interaction, while the negatively and neutrally charged formulations displayed a moderate or low interaction. The ability to interact with mucin makes all the liposomal formulations promising for oromucosal administration. Although the chitosan-coated liposomes affected the cell viability, this formulation also influenced the cell permeability, which makes it an interesting candidate for systemic drug delivery from the oral cavity.

Thermogelling properties of triblock copolymers in the presence of hydrophilic Fe3O4 nanoparticles and surfactants

We investigate the supramolecular structure formed by thermogelation of a triblock polymer in the presence of nanoparticles and surfactant using rheometry and small-angle X-ray scattering (SAXS). The triblock copolymer, nanoparticle, and surfactant used in this study are poly(oxyethylene-oxypropylene-oxyethylene), Pluronic F108, Fe(3)O(4) nanoparticles, and sodium dodecyl surfactant, respectively. Addition of 1-5 wt % of Fe(3)O(4) nanoparticle, of average particle size ~10 nm, in a weak template of F108 (15 wt %) shows a decrease in the onset of gelation temperature and dramatic alteration in the viscoelastic moduli. The nanocomposite samples show a linear viscoelastic regime up to 5% strain. The SAXS measurement shows that the intermicellar spacing of the supramolecular structure of pure F108 is ~16.5 nm, and the supramolecular structure is destroyed when nanoparticles and surfactants are incorporated in it. Further, the addition of anionic surfactant to nanocomposites leads to a dramatic reduction in the viscoelastic properties due to strong electrostatic barrier imparted by the surfactant headgroup that prevents the formation of hexagonally ordered micelles. Our results show that the thermogelation is due to the clustering of nanoparticles into a fractal network rather than a close-packed F108 micelles, in agreement with the recent findings in Pluronic F127-laponite systems.